sensitivity analysis of soil site response modelling in ... · ii sensitivity analysis of soil site...

Sensitivity Analysis of Soil Site Response

Modelling in Seismic Microzonation for

Lalitpur, Nepal

Umut DESTEGÜL March 2004

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal II

Sensitivity Analysis of Soil Site Response Modelling in Seismic

Microzonation for Lalitpur, Nepal

By

Umut DESTEGÜL Thesis submitted to the International Institute for Geo-information Science and Earth Observation in partial fulfilment of the requirements for the degree of Master of Science in Earth Resources and Envi-ronmental Geosciences. NATURAL HAZARD STUDIES Degree Assessment Board Prof . Dr. F. D. (Freek ) van der Meer Chairman Prof. Dr. S. B. (Salomon Bernard) Kroonenberg External Examiner, Delft University Dr. C. J. (Cees) van Westen First Supervisor Ir. S. (Siefko) Slob Second Supervisor Dr. P. M. (Paul) van Dijk Internal Examiner

INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION

ENSCHEDE, THE NETHERLANDS

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal III

Disclaimer This document describes work undertaken as part of a programme of study at the International Institute for Geo-information Science and Earth Observation. All views and opinions expressed therein remain the sole responsibility of the author, and do not necessarily represent those of the institute.

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal II

Acknowledgement

First of all, I would like to express my gratitude to Netherlands organization for international coopera-tion in higher education (Nuffic) that I had the opportunity to study in ITC, and experience a lot more, during this 18 months period. It is pity that Turkey is no longer in the list, thus I believe many other colleagues could have benefited from this unique opportunity. Secondly, I would like to express my gratitude to my first supervisor; Mr. Westen for his guidance and support in all phases of my thesis. His continuous detailed reviews and suggestions on my challenging works, made it possible to come to an end. And, I would like to thank my second supervisor Mr. Slob. From the early beginning of the thesis, he has been very kind to spare time and contribute to very fruit-ful discussions on the research topic. I would like to thank to Mr. De Mann, for keeping an eye on me and my work during the fieldwork and afterwards. His guidance is very appreciated. And also, my respectful gratitude goes to Mr. Brus-sels, Mr. Ellis, Mr. Boerboom for not leaving me alone with the important meetings in Nepal. And to my fieldwork companions, first to jumping team; Jimmy and Tung, and second to Senani, Tung, Maz-harul, and Jeewan. And my respectful thanks also goes to Mr. Ranamagar, who has opened his library and files without hesitation in Kathmandu. And to NSET and ICIMOD staff who have been very kind to host us in many situations, especially to Mr. Dhakal who has assisted me in the field. I am very grateful to my student advisor, Mr. Voskuil for being there when I needed, with a great sup-port in any subject. The endless care and support of Mrs. Kingma, led me easily through many obsta-cles. And, with Mr. Damen they all made me feel that I am not that far from home. Also, I would like to express my gratitude to Mr. Van Dijk, for his contributions and support on many topics from the very beginning of my study in ITC. Thanks to Mr. Rossiter for his reassurances on my work and for his special conversations. And to Mr. Sporry, Mr. Alkema, Mr. Ordonez, Mr. Avouac, Mr. Stein, Mr. Woldai for their valuable discussions and contributions. I am very grateful to my cluster friends, Maria, Marlina, Maulida, Syarif, Pablo, Piya that they have been great supporters in many cases. And, I would like to thank to Amani for being my family when I am away from them. Particularly, I would like to thank to Ana for being my company in hardship and fun. And, to my compatriot, Derya. And most importantly, I would like to express my deepest gratitude to my parents, for their endless support and love. Lastly, to my spirit companion; Ozdem, for being so patient and encouraging partner for all these time.

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal III

Abstract

For a proper design of earthquake-resistant structures and facilities a good estimation of the ground

amplification level during the expected earthquake is required. The level of shaking is mostly de-

scribed in terms of peak ground acceleration and amplification, and visualised by response spectra. In

order to determine the ground response using a one-dimensional numerical approach, several input

parameters are required for each site. These include: soil profile and bedrock level; shear strength

and other geotechnical properties of the subsurface and the “design earthquake”. In most cases, many

of these input parameters are very poorly known. This study describes, through a sensitivity analysis,

which of these input parameters are the most important to know and with which accuracy in order to

arrive at a proper estimation of the expected amplifications. This study included also the development

of a method to create a seismic microzonation map on the basis of a simplified geological subsurface

GIS model. The results of this microzonation study were compared with actual borehole data and the

reliability of this simplified model was determined.

Key words: Soil site effects, sensitivity analysis, seismic microzonation, shear wave velocity, Kath-mandu Valley

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal IV

Table of Contents Page

Acknowledgement............................................................................................................................... ii Abstract .............................................................................................................................................. iii

Table of Contents ............................................................................................................... iv List of Figures .................................................................................................................... vi List of Tables...................................................................................................................... ix List of Abbreviations............................................................................................................x

1. Introduction ....................................................................................................................................1 1.1. Scope of the study ....................................................................................................................1 1.2. Problem Statement ...................................................................................................................4 1.3. Research Objectives .................................................................................................................5 1.4. Research Methodology.............................................................................................................5

1.4.1. Input data..........................................................................................................................6 1.4.2. Data collection................................................................................................................11 1.4.3. Data organization ...........................................................................................................13 1.4.4. Structure of the Thesis....................................................................................................14

2. Literature Review.........................................................................................................................16 2.1. Overview Of Methods For Seismic Hazard Assessment........................................................17

2.1.1. Seismic Hazard Assessment ...........................................................................................17 2.1.2. Seismic Microzoning......................................................................................................22 2.1.3. Ground Response Modelling; Soil Site Effects..............................................................24 Experimental Methods ...................................................................................................................24 Numerical Analysis ........................................................................................................................30 Advanced methods .........................................................................................................................32 Empirical and semi-empirical methods ..........................................................................................33 2.1.4. Sensitivity Analysis........................................................................................................34

2.2. Conclusıons ............................................................................................................................36 3. Shake2000 .....................................................................................................................................38

3.1. Introduction ............................................................................................................................38 3.2. Background ............................................................................................................................38 3.3. Program Structure...................................................................................................................41

4. Study Area ....................................................................................................................................49 4.1. Location..................................................................................................................................49 4.2. Geology ..................................................................................................................................50 4.3. Seismicity ...............................................................................................................................54

5. Seismic Response Analysis For Lalitpur, Nepal ........................................................................56 5.1. Ground Response Modelling Methodology ...........................................................................56

5.1.1 Methodology 1: Modelling based on available borehole data........................................57 5.1.2 Methodology 2: Generating acceleration maps ..............................................................74

6. Sensitivity Analysis.......................................................................................................................85 6.1. Methodology ..........................................................................................................................85 6.2. Sensitivity to changes in Shear Wave Velocity......................................................................86 6.3. Sensitivity to Input Motions ...................................................................................................90

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal V

6.4. Sensitivity for Unit Weight ....................................................................................................93 6.5. Sensitivity for soil thickness...................................................................................................95 6.6. Conclusions on the Sensitivity Analysis ................................................................................97

7. Discussion, conclusions and recommendations..........................................................................99 7.1. Discussions and Recommendations .......................................................................................99 7.2. General Conclusions.............................................................................................................103

References ........................................................................................................................105 Appendix A: Input Strong Ground Motion (3 Scenario)..................................................109 Appendix B: Soil Profile Information On Calculations Done In Shake2000...................112 Appendix C: Generalized Soil Profile Frequency Values ................................................119

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal VI

List of Figures Figure 1-1 The risk management cycle showing the sequence of assessment, response and education

which is essential for successful disaster reduction (Smith 2001). ..................................................1 Figure 1-2 The seismic hazard map of Asia depicting peak ground acceleration (PGA), given in units

of m/s2, with a 10% chance of exceedance in 50 years. The site classification is Rock. (Zhang, Yang et al. 1992-1999).....................................................................................................................3

Figure 1-3 Flowchart of the methodology used in the research. ..............................................................7 Figure 1-4 A representation of the crosshole tomography method. Left borehole consists of the

transmission signals and the right one has the geophones, which receives the signals transmitted from the other borehole. .................................................................................................................10

Figure 1-5 The borehole names and locations that are used in the analysis...........................................14 Figure 1-6 Figure showing the contacts, data collected and metadata relation diagram. .......................15 Figure 2-1The four steps of probabilistic seismic hazard analysis (Kramer 1996). ...............................18 Figure 2-2 A probabilistic seismic hazard map showing U.S. for the peak acceleration (%g) with %10

probability of exceedance in 50 years (USGS 2003). ....................................................................19 Figure 2-3 The illustration of the single degree of freedom systems. ....................................................20 Figure 2-4 The deterministic seismic hazard assessment diagram in steps (Kramer 1996). ..................21 Figure 2-5 Diagram showing the topographic and soil site effects. Seismic waves travel through the

settlements passing the Rock site and soil site. For both the soil site and the Rock hill top there is generally a referring topographic effect such as hill top, ridge and basin effects. .........................22

Figure 2-6 Two simple topographic irregularities. (a) a triangular wedge (b) approximation of real surface at rough and crest by wedges (Faccioli, 1991) ..................................................................23

Figure 2-7 The microtremors are placed to an alluvial site, a Rock site and at the top of a hill. The recordings are received and processed. Then, the amplification spectrum is plotted. The differences between the sites are explained using the ratios and comparisons of the H/V components. This method refers to Standard Spectral Ratio of site effect estimations (Duval, 1994) ..............................................................................................................................................26

Figure 2-8 Figure showing the representative situation for Poisson’s ratio on material. (Lakes 2004).27 Figure 2-9 Transfer functions for (a) Standard spectral ratio (e) H/V ratio for S wave part of the

earthquake records (f) Nakamura’s technique (H/V ratio of ambient vibrations). Dashed line represent 95% confidence limits of the mean ((Lacave, Bard et al. 2002).....................................28

Figure 2-10 The incident wave and its reflected and refracted components in two media. (Transverse waves are S-waves and longitudinal waves are the P-waves). .......................................................29

Figure 2-11 Subsurface geology could be referred as one-dimensional, two-dimensional or three-dimensional (Smith 2001). .............................................................................................................32

Figure 2-12 Diagram showing the continuum and the nodal points (Kramer, 1996).............................33 Figure 2-13 The diagram for the Empirical Green’s function method (Bour 1994) ..............................34 Figure 3-1 An intensity map done by rapid instrumental technique. (Wald, 1999) ...............................39 Figure 3-2: Diagram showing the relationships between Shake software..............................................40 Figure 3-3 The main menu of Shake2000 software. ..............................................................................42 Figure 3-4 The window for choosing and filling in the options for Shake2000. ...................................43 Figure 3-5 The first option from the earthquake response analysis for the dynamic material properties.

........................................................................................................................................................44 Figure 3-6 The window where the soil profile is implemented..............................................................44

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal VII

Figure 3-7 The display of results for the analysis in table format..........................................................46 Figure 4-1 Small map showing Asia, the rectangle indicates Nepal. Also, Lalitpur is indicated in Nepal

map. ................................................................................................................................................49 Figure 4-2 Study area; Lalitpur. North of Lalitpur is Kathmandu City..................................................50 Figure 4-3 From south to north it can be seen, main frontal fault system, main boundary trust and the

main central trust boundaries. The Indus Suture Zone starts from the border of north side (Avouac, Bollinger et al. 2001). .....................................................................................................51

Figure 4-4 Geology map of the Kathmandu Valley and the Lalitpur city..............................................53 Figure 4-5 Taken from Bilham et al (2001) this figure shows the seismic gap regions and the potential

magnitudes for the Himalayan region. It can be seen that Kathmandu has a potential slip of 4 m for certain and even more is possible. ............................................................................................54

Figure 4-6 Map showing, seismic data for the years between 04/01/1995 and 10/12/1999, geodetic measurements and major geological structures with (MFT, MBT, MCT) (Cattin and Avouac 2000). .............................................................................................................................................56

Figure 5-2 Flowchart of the method 1....................................................................................................61 Figure 5-3 The deep boreholes correspondent PGA values for the shear wave velocity set 1 (A:

minimum Vs values) and 2 (B: maximum Vs values)....................................................................66 Figure 5-4 The response spectrum curves for three critical boreholes and correspondent points for the

earthquake scenarios (For PR 16 LA M=6.2). ...............................................................................69 Figure 5-5 The response spectrum curves for three critical boreholes and correspondent points for the

earthquake scenarios (M=8, R=48km for B23).............................................................................70 Figure 5-6 The response spectrum curves for three critical boreholes and correspondent points for the

earthquake scenarios (M=8, R=48km for B25)..............................................................................71 Figure 5-7 The stratigraphic section of P37 borehole log. .....................................................................72 Figure 5-8 The Figure is showing the actual borehole (ID: P37) and the point read from the

generalized soil profile. A and C belongs to the actual borehole. The A and B are the response spectra for the chosen scenario earthquake (Los Angeles M: 6.2; D: 15 km)................................73

Figure 5-9 The Figure is showing the actual borehole (ID: P37) and the point read from the generalized soil profile. A and C belongs to the actual borehole, the others C and D are from the generalized profile. The C and D are the amplification spectrums for chosen scenario earthquake (Los Angeles M: 6.2; D: 15 km). ...................................................................................................74

Figure 5-10 Flowchart of the method 2..................................................................................................75 Figure 5-11 The dynamic material properties and their relation to the shear strain, which are used for

the four-layer soil profile. (a and b) ...............................................................................................77 Figure 5-12 The illustration of the generalized subsurface geology of the Kathmandu Valley.............78 Figure 5-13 The intensity maps visualized from JICA report. (JICA, 2001) The intensities are for the

scenario earthquakes named (from left through right) respectively; Mid Nepal, Kathmandu Valley Local and North Bagmati. ..............................................................................................................79

Figure 5-14 The second methodology’s inputs and outputs. The first part represents the calculations with Shake 2000. The second part was done in ILWIS using 60 points derived from the 500 m pixel sized thickness map. ..............................................................................................................82

Figure 5-15 Graph showing the resonance maps corresponding to frequencies; 1, 2, 3 and 5 Hz and the MMI map for the worst scenario earthquake and soil thickness map. ...........................................83

Figure 5-16 The natural frequency maps for 500, 800 and 1500 m/s shear wave velocities. ................84

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal VIII

Figure 6-1 Methodology of the sensitivity analysis. In the analysis shear wave velocity unit weight and thickness had been also variables. The program was run for the selected range of values for the variables and the output PGA values are plotted against the variable values. ...............................86

Figure 6-2 Calculated PGA values for different shear wave velocities. The blue dotted curve is the original curve obtained by plotting the two data sets against each other. The pink line is the trend line obtained from this original curve. ...........................................................................................87

Figure 6-3 The PGA values obtained after the running of Shake2000 for the shear wave velocity sample set. ......................................................................................................................................88

Figure 6-4 Graph showing the initial analysis for PGA values obtained for different shear wave velocities in two-layer model. Series 1 is Sand and series 2 is Clay. The x-axis shows Vs values; y-axis shows the PGA (g) values. ..................................................................................................89

Figure 6-5: Graph showing the PGA values that are obtained for the 3 different earthquakes (Scenario 1, 2, and 3) from the methodology 1 / Model 2. The black arrow shows the range of PGA’s that could be in the site. Amax is the maximum acceleration recorded in time domain of the earthquake. .....................................................................................................................................91

Figure 6-6: A and C graphs show the response spectra of two boreholes (B25 and B23) for the first scenario earthquake (M=8; R=48km). B and D show the response spectra for the same boreholes but with the third scenario earthquake (M=6.7; D=6.4 km). Please note that the y-axis range is differing in each graph. ..................................................................................................................93

Figure 6-7: The correlation between PGA values and the unit weights (Two layer model). .................94 Figure 6-8: Unit weight and PGA relations for a two-layer soil profile (Sand and Clay)......................95 Figure 6-9 The relation between PGA values and depth difference in a two-layer model. Sand was

used for the two-layer model. The Rock layer shear wave velocity was 9842 f/s. ........................96 Figure 6-10 Two-layer model for the analysis of thickness and PGA values sensitivity results. ..........97 Figure 7-1 The response spectrum showing the linear and non-linear approach results; SHAKE is

linear and MARES is the non-linear. Compare the maximum and the difference between the two.......................................................................................................................................................103

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal IX

List of Tables Table 1-1 Investigation list in groups of different methods, from surface and by drilling. .....................8 Table 1-2 The names and abbreviations of the organizations contacted in the fieldwork. ....................12 Table 1-3 The borehole names and locations that are used in the analysis (Wald, 1999)......................13 Table 3-1 The conversion formulas used in the calculations for Shake2000. ........................................42 Table 4-1 Important high magnitude earthquakes happened in the Himalayan region..........................55 Table 5-1 Actual Deep and shallow boreholes.......................................................................................58 Table 5-2 The borehole points and their corresponding thickness’ read from the generalized profilee.

........................................................................................................................................................58 Table 5-3 Assumed shear wave velocity values for different soil types. ...............................................59 Table 5-4 Strong ground motion obtained from the PEER Strong Motion database (Silva 2000). .......63 Table 5-5 The selected 3 scenario earthquakes form the Shake2000 strong motion database...............64 Table 5-6 Generalized soil profile values that are used in the soil site analysis. ...................................65 Table 5-7 The chosen points (they correspond to actual boreholes) from the generalized 4 layer profile.

........................................................................................................................................................68 Table 5-8 Four-layer generalized soil profiles attributes that are used in the response calculation in

Shake2000. .....................................................................................................................................75 Table 5-9 Dynamic material properties are shown for the four-layer generalized model. .....................76 Table 5-10 The relations between the fundamental frequencies and the storey numbers of the buildings

from three different sources (Vidal and Yamanaka 1998; INGEOMINAS 1999; Day 2001). ......80 Table 5-11 The fundamental frequencies for Lalitpur and their storey numbers. ..................................80 Table 6-1 The comparison table for the PGA ranges of the consequent scenario earthquakes..............91

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal X

List of Abbreviations PGA : Peak Ground Acceleration SA : Spectral Acceleration SDOF : Single Degree of Freedom System Vs : Shear Wave Velocity UW : Unit Weight RS : Response Spectrum H/V : Horizontal and Vertical component ratio of seismograms SPT : Standard Penetration Test JICA : Japan International Cooperation Agency

Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal 1

1. Introduction

1.1. Scope of the study

Natural disasters such as earthquakes, floods, tornados and drought are unavoidable, but we can miti-gate their effects by disaster prevention systems. Earthquakes are the most destructive of the various geological hazards. During the twentieth century, well over 1,000 fatal earthquakes were recorded with a cumulative loss of life estimated at 1.5-2.0 million people (Pomonis 1993). In order to reduce the casualty numbers, we have to know more about the hazard status and find out how to decrease the effects. On the whole, this can be done using risk management. Risk management has three main phases; pre-disaster, during disaster and post-disaster. The pre-disaster phase involves the hazard, vul-nerability and risk assessments. Here the hazard and the effects on the community are defined. During disaster emergency actions are taken. In case of earthquakes, which have a very short time to take ac-tion, closing down the electricity, gases etc. are examples of during disaster actions. Post-disaster deals with relief, rehabilitation, reconstruction of buildings and implementation of the knowledge to the regulations. Hazard assessment, can also be analysed in another cycle where it focuses on risk man-agement with relation to education of the community and world (Smith 2001). Looking at the diagram (Figure 1-1), it can be seen that this research takes in the preliminary phases of risk management. A good understanding of the hazard will help the risk management work more efficiently. But there are cases where the disaster reduction measures have been taken very well but do not have a well-defined hazard classification, such as Kathmandu.

Figure 1-1 The risk management cycle showing the sequence of assessment, response and education which is essential for successful disaster reduction (Smith 2001).


As the population grows the risk gets higher in many earthquake prone areas, especially in developing countries. Over 90 % of disaster related deaths occur among the two-thirds of the world’s population who live in the less developed countries and about three quarters of all the economic damage is con-fined to the more developed countries (Smith 2001). Thus Asia, suffers greatly from natural disasters because of its large population, many of whom live in poverty and are concentrated in dense clusters in tectonically active zones or near low-lying coasts subject to cyclones and floods. Additionally, most earthquakes killing more than 100,000 people have occurred along the Himalayas, the Middle East and the Alps to the western Mediterranean and North Africa (Smith 2001). Casualty and the occurrence rate make Nepal one of the most vulnerable areas in the world. Above all, being a developing country, it is one of the places that need special attention regarding the disaster issues. Many developing countries lack in funding for the studies that are needed for risk analysis and further studies. Many big organizations such as European Commission (EC) and United Nations (UN) have projects ongoing in the area. Although the special attention needed is given, there is still need for new researches and implementations. One of the current research projects at ITC also focuses on risk management, and is entitled “Strength-ening Local Authorities in Risk Management”. In this project Kathmandu and its surrounding regions are chosen as case study areas. This research falls into the seismic hazard assessment section and also will be an input for further analysis such as, building and population vulnerability estimation. As mentioned before risk management starts with the characterization of the hazard, which is seismic hazard analysis. For seismic hazard analysis and mapping a popular approach is to create zones. Seis-mic zoning can be distinguished into two: macro and microzoning. Seismic macrozoning consists of dividing the national territory into several areas indicating progressive levels of expected seismic in-tensity for different return periods. These zones can be described in terms of peak acceleration values or any other strong ground motion parameter (Giardini 1999). Macrozoning, different then microzon-ing focuses on small scales and includes probability. As seen below (Figure 1-2), the scale of the maps helps just to give an overall idea of the earthquake prone regions. For defining earthquake source zones regional tectonics are used but they do not take into account the regional geology. Earthquake catalogues are important in this assessment since they point out the tectonically active regions.


Figure 1-2 The seismic hazard map of Asia depicting peak ground acceleration (PGA), given in units of m/s2, with a 10% chance of exceedance in 50 years. The site classification is Rock. (Zhang, Yang et al.

1992-1999)

Seismic hazard microzoning is used for more detailed zoning, outlining the parameters with a finer spatial resolution and providing a description of the hazard parameter with higher accuracy and preci-sion (Mayer-Rosa and Jimenez 2000). Microzoning consists of recording in detail all seismological, geological and hydrogeological parameters that may be needed in planning and implementing a given project area at an appropriate scale for physical planners, urban designers, engineers and architects, or any other qualified user. For example civil engineers and urban planners use fragility curves that define the building type and number of storeys versus the peak ground acceleration values. Peak ground acceleration values come from response modelling studies as an output data. Conclusively, these values create a link among the disciplines. Problems that increase the risk are mainly based on lack of attention to where and how settlements are built (UNDRO 1991). An unsuitable type of building with an unsuitable number of storeys would result in serious damage and might collapse during the expected earthquake. As a matter of fact, the decision for the location and the type of the settlements are an important factor to take into account. According to the location decision, it is important to know the local soil and topographic conditions. The effect of local site conditions on the amplification of ground motions has long been recognized (Seed 1982). Depending on the subsurface characteristics, seismic waves might undergo amplification


and create more severe strong ground motions at the surface. Many earthquake prone cities are settled over very susceptible areas with young deposits such as Mexico City (Seed, Romo et al. 1987), Loma Prieta (Rodriguez-Marek and Bray 1999) and Kathmandu/Nepal. Having a high potential for earth-quakes and a susceptible local site environment, the situation in Kathmandu might turn a hazard into a disaster in the future. In microzoning the seismic hazard is assessed by means of expected response of the seismic waves for a given (scenario) earthquake for a specific area. Since the local soil site has significant effects on the seismic waves, “Ground Response” is one of the most important sections in microzoning. Addition-ally, the subsurface and surface conditions in Kathmandu valley also are favourable for the occurrence of secondary hazards such as landslides, liquefaction, and fires. Ground response studies could be handled in different dimensions: one, two or three-dimensional. One-dimensional ground response analyses are based on the assumption that the ground surface and all material boundaries below the ground surface are horizontal and extend infinitely in all lateral di-rections (Kramer 1996). The methods of one-dimensional ground response analysis are useful for level or gently sloping sites with parallel material boundaries. The subsurface geology of Kathmandu Valley is also assumed to be suitable for one-dimensional ground response analysis, as Kathmandu valley is underlain by a thick deposit of alluvial and lacustrine deposits. In addition, the assumption that the valley or another topographical feature could be one-dimensional is a major simplification. For one-dimensional calculations of the ground response, SHAKE software is used widely since 1971(Ordonez 2002). Using SHAKE, the research problem then tends to focus on sensitivity analysis of the seismic response modelling for Kathmandu city, which will try to define and simplify the in-formation needed and evaluate it within the concept of microzonation analysis. The main reason to focus on sensitivity analysis is to try to get more information for the valley, where there is lacking in data.

1.2. Problem Statement

In general terms, a seismic response analysis needs detailed geotechnical data, geology information, thickness of the subsurface geology profiles and a specific earthquake accelerogram file. More details on the required data will be explained in the coming section. Many countries, which are vulnerable to earthquakes, are lacking in data for seismic response studies. Estimating the soil site response for strong ground motion is costly. In order to quantify the expected ground motion, we have to determine the manner in which the seismic signal is propagating through the surface. Propagation is particularly affected by the local geology and the geotechnical ground con-ditions. Borehole data, geotechnical, geological and geophysical parameters should be determined. Such an investigation is not always easy to obtain hence you will need people with sufficient knowl-edge, tools, and laboratories which is not always the case for many developing countries. In Kathmandu the available data is not sufficient .To deal with this gap, numerical analysis could be used additionally to the existing data. For seismic response analysis the readily available data was used and then sensitivity analysis was applied. The aim of sensitivity analysis is to estimate the rate of change in the output of a model with respect to changes in model inputs (Isukapalli 1999). A priority order for the input parameters will be produced from the sensitivity assessment.


1.3. Research Objectives

Sensitivity analysis of ground response in SHAKE will provide in general, the priority of importance of the input parameters and the estimation of output response values (acceleration, velocity etc.). To do that, several analyses will be applied for the available data in different combinations. Such an ap-proach will try to give a generalized answer for the input data lacking and to improve the understand-ing of the information content of geophysical data. The general research objectives can be explained as follows:

• To estimate the strong ground motions for soil site responses with the available data for Kathmandu valley.

• To assess the sensitivity of the parameters that can be used to determine a microzona-tion study in Kathmandu valley.

1.4. Research Methodology

For seismic response modeling in the topic of seismic micro hazard assessment, the information needed in general is as follows;

• Detailed geotechnical data (Shear wave velocity, unit weight, shear modulus and damping and modulus reduction curve information)

• Detailed geology data available near the site. (Borehole log information with defined material and formations)

• Digital seismic accelerograms (From a real earthquake or a synthetic one) • Depth to bedrock level • Ground water level

In order to predict the seismic response it requires a lot of work in many disciplines. The equipment and the knowledge are rarely found in many third world countries. It can be seen that the first thresh-old is to find out how much data is available in the region (Figure 1-3). If the information obtained from the consultancy offices, agencies and governmental offices is abun-dant, then the sensitivity analysis will be more accurate and site-depended. If not, then the existing literature information is assessed in the analysis. The topics that have been investigated from the litera-ture are geotechnical data (shear wave velocity, depth etc.), characteristic earthquake of the region and subsurface geology studies. The main hypothesis in the assessment of sensitivity is that there is a clear relation between the various parameters. Overall, the first analysis will be looking at specific parameters (E.g. shear wave velocity, unit weight) while keeping the input motion constant. The second analysis uses the constant parameter as a generalized profile, which can be chosen from the existing boreholes in the Lalitpur municipality; Kathmandu study area. And test the range of re-sponses related to the input motions chosen.


The results of the analysis then are converted into a range of accelerations that can be expected in the sites. These accelerations can be used to derive the response spectrum for the various parts of the study area. Then, it is possible to assess the values where the building frequency and the accelerations corre-spond. The resonance happens where the natural frequency of the buildings and the frequency created on the soil site. Accordingly, the predicted high damage sites can be defined from the areas with the same frequency with the buildings. From the peak ground acceleration value, it is also possible to cal-culate the seismic intensities using specific formulas. General methodology steps are as follows in the Figure 1-3, A. Literature survey B. Data acquisition C. Data processing D. Data Analysis

1.4.1. Input data

Under ideal conditions, a complete ground response study should involve the rupture source modelling (length, width and displacement of a rupture for a fault), the seismic wave behaviour to the top of the bedrock; (attenuation of the seismic waves in the bedrock site), the soil site wave propagation behav-iour; (amplification of the seismic waves in the soil site) and the site specific strong ground motion records (Kramer 1996).Generally, the rupture source modelling and the seismic wave behaviour to the top of the bedrock specifically for a site are hard to obtain. Soil site wave propagation and site specific or similar site’s strong ground motion could be used to study the ground response. To understand the soil site wave propagation behaviour, empirical or numerical methods can be used. One of the numerical methods deals with 1D response of soil columns where Shake2000 could be used. To apply this method the site should be horizontally layered. Input data that Shake2000 requires are; soil site geotechnical properties, depth and strong ground motion for the site. Then, the software can run properly and give results for ground response.Nevertheless Shake2000 also needs detailed in-formation. One of the unknown parameters is often the shear wave velocity of the various sediments in the site and the way how this value changes with depth. There are expensive geophysical tools to in-vestigate shear wave velocity, but the time and budget constraints of this research did not allow the geophysical investigations. In general, these investigations are hard to carry out in the framework of an MSc study. Additionally, in Kathmandu this information was not readily available at the moment of the fieldwork. So readily available data from boreholes and literature are used. To improve these as-sumptions a sensitivity analysis applied for the outcomes.


A) Literature Review

B) Data Acquisition(Field Survey)

1. Finding out the similar earthquakes that can happen in the valley.

2. Defining scenario earthquakes. Accelerogram & seismogram record collection.

3. Collection of borehole geotechnical parameter from boreholes.

4. Collection shear wave velocity data.

Creation of the access database file for the data collected from the consultancy offices, municipalities etc.

Field datasufficiency

check.

C) Data Processing:Generalization of shear wave velocity and subsurface geology profiles using the field data and the existing ones.

Methodology

D) Data Analysing(SHAKE analysis)

1st analysis for constant input motion and varying geotechnical parameters (Vs, unit weight etc)

2nd analysis for constant geotechnical parameters (generalized profile for a specific area: Lalitpur) and varying input motions.

Output of analysis; range of acceleration values and their response spectrum.

Generation of seismic intensities.

C) Data Processing: Generalization of shear wave velocity andprofiles of subsurface geology usingthe existing data.

Figure 1-3 Flowchart of the methodology used in the research.


Here, the geophysical investigations that can be used to obtain the input parameters will be discussed with short descriptions. In Table 1-1, given investigations techniques refer not only shear wave veloc-ity but also to the other parameters (depth to bedrock, material thickness and types etc.)

Investigations from surface. Investigations using drilling methods.

Seismic Methods Deep/Shallow Drilling

Electrical Surveys Crosshole Tomography

Georadar Technique.

Array Technique

Spectral Analysis of Surface Waves

Table 1-1 Investigation list in groups of different methods, from surface and by drilling.

The soil site wave propagation analysis could be done using one of the following geophysical tools:

• Seismic methods Travelling from the source, a seismic wave reaches a point/surface and it creates the ground to move and oscillate. This can be measured in digital or analogue seismometers. This wave’s propagation can be analysed and, shear and primary wave velocities can be calculated using a seismometer. Using these reflection and refraction seismic methods seismometers: superficial deposit surveys, site investi-gation for engineering projects, boundaries, material types and elastic moduli can be measured or de-rived. Refraction seismology is a powerful and relatively cheap method for finding the depths to approxi-mately horizontal seismic interfaces on all scales from site investigations to continental studies (Musset and Khan 2000). It also yields the seismic velocities of the Rocks between interfaces, which is important for ground response analysis. This method is also used and improved in microtremor stud-ies, down hole shear wave velocity logs and P-wave refraction method. These methods result in shear wave velocity versus depth, after a couple of wave transformations (Louie, R. et al. 2003). Reflection seismology is often used to determine fine details of the shallow structures, usually over small area. The resolution obtainable with reflection seismology makes it the main method used by oil exploration companies to map subsurface sedimentary structures. Oil companies’ investigations are generally sources for other purposes such as: the deep drillings for oil in Kathmandu are used to obtain knowledge for deep lithology.

• Electrical surveys In seismology electrical surveys could be done by using ground self-potential, resistivity surveys, ground and airborne electro-magnetic surveys and induced polarization surveys. These surveys result in anomaly maps and profiles, position of ore-bodies and most important of all for this research: the depths to Rock layers. Additionally, Sand and Gravel deposits could be investigated.

• Georadar

Georadar is a portable digital subsurface sounding radar. They are designed for solving a broad range of geotechnical, geological, environmental, engineering and other tasks such as bedrock depth deter-mination, water table determination, anomalies or heterogeneities in the material, stratigraphic pro-files, material layering etc. wherever non-destructive operational environmental monitoring is needed (Christos, 2002).


• Array method using ambient vibrations.

The array method aims to lower the costs and the difficulties to undertake a local site effect using the borehole techniques and active seismic study within a city. The array technique represents a cheap and fast method to measure shear wave velocities of the surficial sediments and the underlying bedrock (Kind, Fah et al. 2003). The array technique for measuring shear wave velocities is based on a theory developed by J. Capon 1969. It can be used in horizontally layered structures, like Kathmandu valley.

• Spectral analysis of surface waves (SASW) method SASW is practical because surface waves are easy to generate. It is therefore suitable in areas of high seismic background noise (such as industrial and built-up areas), which a technique like seismic re-fraction cannot be used. SASW can be used to map bedrock topography, low/velocity/density zones, shear wave velocities and site stiffness (Gmax). Also the bottom of lakes and the information about overburden stratigraphy can be gathered.

• Deep or shallow drilling with geotechnical information or lithological information Comparing to the other surface measurements (Refraction, Reflection seismology etc.), this method relates the physical quantities more specifically. The general parameters that can be obtained from drilling are: lithology, microfossils, permeability, porosity and fluids (Musset and Khan 2000). These measures can then be used to determine unit weight, shear modulus and shear wave velocity. Drilling costs are generally high and the number of drillings needed is generally hard to obtain. Additionally, drillings for building purposes are common but they are shallow. Deep drillings are often for oil inves-tigations and does not contain geotechnical properties of soil but has lithology information.

• Crosshole Tomography

Seismic signals are generated in one borehole and are recorded by a string of geophones in a second borehole (Figure 1-4). By mathematical processing of all the recorded data, a detailed velocity cross-section is obtained between the boreholes, which directly relates to materials quality. Fracture net-works can also be followed, as they will slow down the velocity of seismic signals (Paul, 1998). The objective of the crosshole method is the 2D or 3D detail exploration between drillings. A great advantage of crosshole tomography is also a higher resolution of underground structures in greater depths. P- and S-wave tomographic measurements are conducted to determine the structure, the elastic properties and the stress state of the Rock. Every tool mentioned in the list has its own difficulties to implement. In general terms, time, money and people with sufficient knowledge are needed to execute them. Under these circumstances, the fieldwork was focused on collecting readily available data. The general input parameters for SHAKE2000 are;

• Geotechnical properties and depth information of the subsurface materials • Earthquake acceleration signal measured in Rock in a nearby site.


Figure 1-4 A representation of the crosshole tomography method. Left borehole consists of the transmis-sion signals and the right one has the geophones, which receives the signals transmitted from the other

borehole.

Material properties should contain shear wave velocity or shear modulus, damping ratio, unit weight and thickness. Water table depth is also another parameter that is needed to implement. Unit Weight Unit Weight parameter is the weight of a unit volume of soil is referred to as its unit weight. The units of unit weight will be force per unit volume, whereas the units of density are mass per unit volume. Unit weights can be calculated as follows;

• Dry Unit weight γd =ρd g kN/m3

• Bulk Unit weight γ =ρ g kN/m3

• Saturated Unit Weight γsat =ρsat g kN/m3 • Unit weight of water γw =ρw g kN/m3

• Submerged unit weight γ =γsat - γw kN/m3

The gravitational acceleration “g” is generally taken as; 9.81 m/s2. Above calculations are in scientific international units but for SHAKE2000 for unit weight pounds cubic feet is used. Shear Modulus

Modulus of rigidity or shear modulus can be explained using elastic properties of materials. The quan-tity µ, sometimes also called the rigidity, that is experimentally observed to relate stress and strain ac-cording to Hooke's law (Weisstein, 1999 ),

[Stress]= µ[Strain] It can also be explained as, a measure of the resistance of the body to shearing strains. Stress can be describes as, a force per unit area provided either by gravity or by the flow of viscous fluid. And strain can be described as, the dimensionless parameter describing deformation. It can be thought of as the movement of one corner of a cubic box from its initial position under a stress. In simple words, it is the relative change in shape and/or volume of a body.The concept of the formulas shown here are related with Elasticity in Mechanics, here the basics are given but the broader explana-tion is out of this research therefore it will not be explained in detail. This parameter is used if shear wave velocity of the material is not known in SHAKE2000 and should have a unit of kilo pounds per feet.


Shear wave velocity Just like the other waves (P, Love and Rayleigh etc.) shear wave velocities are also measured in the same way. An energy source (hammer, explosives etc.) is used to generate elastic waves in the ground. The signals are then collected and displayed on a seismograph. The advantage of this parameter on the other wave types is that it gives more information on the material type characteristics. And they de-pend on the shear strength of the material, which is the strength that supports buildings and piles and keeps a ripping tooth from the cutting Rock (Geomatrix, 2003). The information on the shear wave velocities with density information and P-wave velocity also yields to the elastic constants, which is related to the magnitude of strain response to the applied stress. The units of the results are generally in meters per second or feet per second. Thickness The soil profile from the boreholes should have every layer’s thickness. The borehole logs usually have the soil boundaries obtained from the soil types and this can be measured, referring to thickness. The unit of thickness should be in feet for SHAKE2000 calculations. Damping ratio Damping properties of soils are also used for each soil type and layer in the soil profile of SHAKE2000. In real life, energy is lost by friction, heat generation, air resistance or other physical mechanisms. Damping acts as a force opposing vibration and decreases the amplitudes of the free vi-brations (US Army Corps of Engineers, 2001). The damping ratio is calculated by:

ξ = c / 2√ k m “ξ “ is the damping ratio coefficient, “c” is the viscous damping coefficient, “k” gives the stiffness and ”m” is the mass. The “2√ k m “ gives the critical damping coefficient. The reason for using systems with variable damping information is to incorporate non-linear soil behaviour (Ordonez, 2002). It is expressed in decimals. The earthquake input signal ideally should be available from a recent earthquake that happened in a nearby site. This requires the availability of a network of accelerometers. Unfortunately for Kath-mandu there is no such network in operation. As an alternative an input signal could be chosen from the vast database that is already in the software or on the Internet and implemented using an ASCII coded accelerogram file.

1.4.2. Data collection

From 8th of September till 3rd of October 2003 data was collected in many private and governmental offices in Kathmandu and its surrounding places. The main partners were NSET (National Society for Earthquake Technology) and ICIMOD (International Center for Integrated Mountain Development) Since there were very few deep drillings with geotechnical information available for the Kathmandu area (Piya, 2004), most emphasis was given to on finding shallow boreholes with geotechnical infor-mation and deep boreholes with lithological descriptions. Additionally, the accelerogram files and suggestions on similar 1934 (M=8.4) earthquake information. Similar earthquake information would help to choose a correct input signal for the analysis. The organizations that were visited for the collec-tion of borehole data are listed in Table 1-2.


Abbreviations Name

KMC DMC Kathmandu Metropolitan City Disaster Management Center

MLSC Municipality of Lalitpur sub-metropolitan city

Governmental offices

MK Municipality of Kathmandu

DMG Department of mines and geol-ogy (Remote Sensing Labora-tory and National Seismology Centre) Purbachar University

University

IOE, TU Institute of Engineering- Trib-huvan University

DWIDP Department of Water Induced Disaster

JICA Japan International Coopera-tion Agency

ICIMOD International Center For Inte-grated Mountain Development

Organizations

NSET National Society for Earth-quake Technology

Nissaku Co -

Nippon Koei -

Geotech -

Silt -

East Drilling -

Private Consultancies

Tech -

Table 1-2 The names and abbreviations of the organizations contacted in the fieldwork.

From the various organisations the following types of information were collected:

• Borehole descriptions (from different consultancies and agencies- 6 shallow with geotechnical information and 11 deep drillings with lithology information)(Table 1-3)(Figure 1-5)

• Digital GIS maps (geology, lineaments etc) • Reports (JICA study and reports that are related to Kathmandu valley geology, characteristics

of soil etc) • Articles


• Hard copy maps of the engineering geology of Kathmandu valley, seismic hazard and macro-seismic epicentral maps

• Meetings for discussion on SPT-n value correction and SHAKE software. • Reports from Himalayan region for defining similar earthquakes for the region

Deep Boreholes Shallow Boreholes

Borehole ID Location Borehole ID

Location

B1 Harisidhi C - 40 UNDP Building Pulchok, Lalitpur

B 24 Shanta Bhawan C-296 Kantipur Television network P.Ltd Pul-chok, Lalitpur

B 25 Surendra Bhawan C-291 Lalitpur Bisalbazar, Communication Com-plex Pulchok, Lalitpur

B 23 Patan C - 288 Jawalakhel AG 68 Patan Hospital SPT - 6 Lele

BHD 3 B & B Hospital Guarkhu SPT - 39 Dhobighat DMG 13 Balkumari, Lalitpur

P 37 Interknit industries

P 29 Hotel Himalaya

PR 16 Nursing Campus, Sanepa

SPT 25 Khumaltar

Table 1-3 The borehole names and locations that are used in the analysis (Wald, 1999)

1.4.3. Data organization

Many people are working on the Valley’s hazard issues not only on seismic but also floods and land-slides etc. The data collected in Kathmandu resulted in 90 individual pieces of information obtained from 72 different contacts. For both the data and the organisations it was decided to store the metadata using Microsoft Access, in a database. Contacts database has columns titled: information topic, first name, surname, company name, title, home address, home and work phone, email, fax number and mobile phone number. The contact also had a unique identification number. For the data collected each item has a metadata word file describing the source and the type of data information. The database of the metadata has unique identifiers and the related contacts identifiers and the name of the data collected. In Access software it is easy to make queries for example if you are interested in only the emails and the items collected, you can easily create the query using a wizard.


Figure 1-5 The borehole names and locations that are used in the analysis

The metadata included the name of data, ID number in the database, theme, abstract, keywords, type of data etc. The numbers of the word files represents the ID number for the data in the data collected database, which can be also linked to the contact ID (Figure 1-6). The database files can be found in the annexes section of the thesis.

1.4.4. Structure of the Thesis

The structure of the thesis in short explanations is as follows: 1. Chapter one gives a general context of the study including the introduction, problem statement, and research objectives. 2. Chapter two presents the literature review on the topics from seismic microzoning to sensitivity analysis. 3. Chapter three gives an overview of the software used; Shake2000. 4. Chapter four presents the study area including geology and seismicity. 5. Chapter five gives the results of the seismic response analysis.

#Y #Y#Y

#Y

#Y#Y

#Y#Y

#Y#Y

#Y

#Y#Y

#Y#

B_25B_24

#

PR_16#

P_29#

C_40#

C_296#AG_68

SPT_6#B_23

#

BHD_3

#

P_37

#SPT_25

#DMG_13

#

SPT_39

3000 0 3000 6000 Meters

N

EW

S

Boundary of Lalitpur#Y Borehole ID's

Legend

Borehole Locations in LalitpurSub-metropolitan city.


6. Chapter six the assessment of the result of the sensitivity analysis, the response spectrum and seis-mic intensity map. 7. Chapter seven will be presenting the results of the study and the discussions about them.

Figure 1-6 Figure showing the contacts, data collected and metadata relation diagram.


2. Literature Review

Sensitivity analysis can be applied to many disciplines from politics to physics. In geological hazard studies this also can be done for the input parameters for seismic response models, which is selected for this study. If it is deducted from the wider concepts of the seismic hazard assessment, the main branches include:

• Seismic Hazard Assessment • Seismic Microzonation • Ground Response Modelling • Sensitivity Analysis

To give a summary of the literature review of these topics, the terms and concepts that are going to be dealt in the review should be clarified. Although, in this research the focus is on sensitivity analysis, it is also based on a broader concept of Seismic hazard assessment. Seismic hazard assessment involves the quantitative evaluation of ground shaking hazards (primary hazard; earthquakes damage to the site and secondary hazards such as: fires, landslides and liquefaction etc) at a specific location. The analysis can be taken in two ways; determin-istically and probabilistically. The deterministic approach uses an accepted earthquake scenario, whereas the probabilistic approach quantifies the rate (or probability) of exceeding various ground-motion levels at a site, given all possible earthquakes (Field 2001). This research follows a deterministic approach and will be based on earthquake scenarios. In seismic microzonation studies, seismological, geological, hydrogeological, topographical and geotechnical data are necessary to implement the analysis. Microzonation studies provide important information on the parameters that may be needed in planning and implementing a project done by physical planners, urban designers, engineers, architects etc. Apart from compiling input data, estimation of the ground response takes place, which is one of the most important sections in microzonation. Second, estimation of the ground response will be applied in the research focusing on the soil site ef-fects. To model ground response, two main effects should be considered, soil site and topography ef-fects. Soil site effects are much more commonly investigated, then the topographical effects. The main reason for that is usually, the urbanization takes place where soft soils develop, such as coastal plains and river valleys. On the other hand, topographic effects are also very important for urban areas, since settlements are generally on basins where there is a great amount of amplification due to topography. Above all, topographic amplification is very complex and needs 3D analysis in order to have better accuracy where, soil site effects could be investigated using 1D models. Since more population and more risk involved on the soil site, the estimation of these effects was more popular for the scientific community. So far the destructive earthquakes like Mexico 1985, Kobe 1995 and Turkey 1999 took


place where the ground responses were amplified because of the soil site properties. Soil site proper-ties define the seismic wave behaviour under the site. The waves can be affected in such a way that when they reach the surface, they create more shaking. Macroseismic observations have demonstrated very clearly that the damaging effects associated with such soft deposits may lead to local intensity increments as large as 2, in extreme cases even 3 degrees on the MM (Modified Mercalli) or MSK/EMS (Medvedev, Sponheuer and Karnik ; 1964 scale) scale (Irikura 1983; Lacave, Bard et al. 2002). For the investigations of the soil site effects, the methods used are empirical, theoretical or semi-empirical. For this research, widely used software (SHAKE2000) is applied and one-dimensional (horizontally layered) responses of soil layers are calculated using numerical methods. Finally, SHAKE2000 needs specific geotechnical inputs such as; input signal (scenario earthquake) shear wave velocity and soil thickness. The overall research problem is focused on analysing the sensi-tivity of these input parameters. For that, one of the parameters is kept constant and others vary in real-istic values. Not so many sensitivity analyses have taken place for the general input parameters for ground response modelling so far in literature. Though, there is a great demand from engineers and planners to be able to conduct earthquake resistant buildings for high-risk areas. The outcome of the sensitivity analysis and the research provides range of values for the input parameters and their proper-ties. The general terminology and the overall research concept have been introduced above. In the coming sections the various components will be treated more in detail. Different views and newly ad-vised ideas will be presented in a short summary.

2.1. Overview Of Methods For Seismic Hazard Assessment

2.1.1. Seismic Hazard Assessment

Seismic hazard analyses involve the quantitative estimation of ground shaking hazards at a particular site (Kramer 1996). On the other hand in the Global Seismic Hazard Assessment Program (1992-1999), seismic hazard analyses were defined as “the assessment of seismic hazard measures our under-standing of the recurrence of earthquakes in seismogenic sources” (Giardini 1999). Here, the probabil-ity of earthquakes was mentioned to be involved in the overall assessment. Occasionally, the division between the deterministic and the probabilistic studies still continues to take place in studies. Seismic hazard assessment could be deterministic or probabilistic; the two ways could also be used for one study. The decision is more depends on the approach and available data for the region. Initially, for the probabilistic approach (PSHA) first formed by Cornell (1968), the following proce-dures are applied. First, the delineation of earthquake source regions in terms of their boundaries, level of activity and upper intensity threshold are applied (Step 1 in the Figure 2-1). Second part is the de-termination of the macroseismic intensity changes with distance, magnitude, focal length and ground conditions (Step 2-3; Particularly in the direction from the source region to the site) Third, applica-tions of a theoretical model to the calculation of the seismic hazard at the site under study (Step 4) (Schenk 1996).


Figure 2-1The four steps of probabilistic seismic hazard analysis (Kramer 1996).

Probabilistic hazard assessment maps are generally called “peak acceleration (%g) with %10 probabil-ity of exceedance in 50 years “ (Figure 2-2). In simple words, the name refers to the chance of an earthquake to happen (probability percentage (2, 10 etc.)) in 50 years. Cornell (1968) added that even well defined single numbers such as the “expected lifetime maximum “ or “ 50-year” intensity are in-sufficient to give the engineer an understanding of how quickly the risk decreases as the ground mo-tion intensity increase. This also still raises the questions for the convenient parameter, to use for the maps and visualization of the strong ground motion analysis.


Figure 2-2 A probabilistic seismic hazard map showing U.S. for the peak acceleration (%g) with %10 probability of exceedance in 50 years (USGS 2003).

One of the recent discussions related to the probabilistic approach was on the selection of the proper ground motion parameter in calculations and representation of the maps. As can be seen form the Fig-ure 2 the title of the map is a bit complex in style. For representations of the maps the ground motion parameters are obtained in acceleration, velocity and displacement. The first practices were mostly in favour of acceleration values. Then, velocity values were suggested for use as well. Regarding to these discussions, E.H. Field (2001) suggested using the response spectral acceleration, which is another parameter that can be derived from acceleration values. Traditionally, peak ground acceleration (PGA) has been used to quantify ground motion in probabilis-tic seismic hazard assessment. It is used in liquefaction analyses and to define building codes. PGA has been an important parameter since the earthquake and civil engineers were using this value for creating the building codes. On the other hand, it is suggested that Response Spectral Acceleration (SA), should be used. SA gives the maximum acceleration experienced by a damped, single-degree-of-freedom oscillator (a crude representation of building response) (Field 2001).


When computing the seismic response on a structure, it would be better to start simplifying them to a single degree of freedom system (Figure 2-3). The SDOF oscillator may be regarded as the simplest model of a building that is separated from the basement.

Figure 2-3 The illustration of the single degree of freedom systems.

In Figure 2-3, the rigid mass M represents the building and the linear spring k represents the separation bearing. Damping may be accounted for by a viscous damping coefficient; dashpot c. Coming back to the discussions on the appropriate parameter, they still going on but for many approaches peak accel-eration values are the popular ones. The second approach of the seismic hazard assessment, a basic “Deterministic Seismic Hazard Analy-sis (DSHA)” is a relatively simple process that is useful especially where tectonic features are rea-sonably active and well defined. The focus is generally on determining the Maximum Credible Earth-quake (MCE) motion at the site. The steps in the process are as follows:

1. Identify nearby seismic source zones - these can be specific faults or distributed sources (Step 1 in Figure 2-4) 2. Identify distance to site for each source (nearby distributed sources are a problem) (Step 2) 3. Determine magnitude and other characteristics (ie. fault length, recurrence interval) for each source (Step 3) 4. Establish response parameter of interest for each source as a function of magnitude, dis-tance, soil conditions, etc., using the average of several ground motion attenuation relation-ships (Step 3) 5. Tabulate values from each source and use the largest value (Step 4) (Mahin and Rogers 1999)


Figure 2-4 The deterministic seismic hazard assessment diagram in steps (Kramer 1996).

In general discussion on deterministic seismic hazard assessment, the criticism on Maximum Credible Earthquake (MCE) was on the determination was basically depended on the expert, which may and would lead to a subjective result in most of the cases. Then, another term has been raised, which is “Safety Evaluation Earthquake” (SEE). This term differs from a MCE that might be considered for the area, in that it takes into account the types of structures which are vulnerable to the various earthquake hazards in the area, as well as the risk that is acceptable to the community in the light of other social considerations (Bolt 1994). The discussions of seismic hazard assessment are also focused on the selection between the ap-proaches (deterministic and probabilistic). For example Panza et al. (2003) have outlined that “the probabilistic approach, unavoidably based on rough assumptions and models (e.g. recurrence and at-tenuation laws), can be misleading as it cannot take into account, with satisfactory accuracy, some of the most important aspects which characterize the critical motion for base-isolated and standard struc-tures (E.g. rupture process, directivity and site effects are not involved in probabilistic approach) (Decanini, Mollsioli et al.; Panza, Romanelli et al. 2003). This is evidenced by the comparison of re-cent recordings with the values predicted by the probabilistic methods. We prefer a scenario-based, deterministic approach in view of the limited seismological data, of the local irregularity of the occur-rence of strong earthquakes, and of the multiscale seismicity model..” The authors of this paper are in favour of deterministic approach and highlight the important aspects that are missing in the probabilis-tic approach such as rupture process (rupture front (The instantaneous boundary between the slipping and locked parts of a fault during an earthquake) direction and velocity; and site effects which have great influence on the shaking (soil site type or topography type)). When we compare the two approaches, both of them have their advantages and disadvantages. Many adaptations have been published to reduce their disadvantages. For deterministic approaches one of the recurrent criticisms was that they make use of a controlling earthquake (usually the maximum to have occurred within a given time and space domain) instead of frequency of earthquake occurrence. Oro-


zova and Suhadolc (1999) proposed a method to overcome this criticism and at the same time maintain the advantages of the deterministic approach, which are clear and realistic estimation of engineering parameters needed in the calculation of Seismic Risk. They have used a deterministic method for seis-mic hazard assessment where they have replaced the fixed controlling scenario earthquake with earth-quake frequency.

2.1.2. Seismic Microzoning

After having looked at the broader concept of Seismic Hazard Analysis, this part focuses on more de-tailed studies, which are carried out for microzonation. Since the method for this research falls under the microzonation type, the general approaches of microzonation will be treated and illustrated by ex-amples and several discussion topics will be pointed out. A microzonation study should include the two effects that have the greatest influence on the seismic wave behaviour, which are site and topographic amplification. Topographic amplification can be ob-served in instrumental studies on the ground motion amplitudes and frequency content. Some of the studies can be found in Geli et al (1988) and Faccioli (1991). Examples of topographic structures that can have considerable effects on the damage are hill tops and ridge crests which have a increasing ef-fect on the one hand side of valleys and bases of hills on the other hand which have a de-amplification effect (Lacave, Bard et al. 2002) (Figure 2-5).

Figure 2-5 Diagram showing the topographic and soil site effects. Seismic waves travel through the set-tlements passing the Rock site and soil site. For both the soil site and the Rock hill top there is generally a

referring topographic effect such as hill top, ridge and basin effects.

However, the number of instrumental studies about topographic effects is too low to derive any statis-tical relations from the existing data. That is also one of the reasons that site effects are chosen for this research. Lalitpur city is in Kathmandu Valley, it forms a basin surrounded by the hilly terrain, where the so-called basin effects should be considered. The shape of a basin is curvature and filled with soft sediments, which can trap some of the body waves and transform to surface waves. Surface waves can


create stronger shaking and make longer the duration of the shaking. The simple irregularities (Figure 2-6; a, triangular wedge) can be solved using idealized problems (Aki, 1988)

Figure 2-6 Two simple topographic irregularities. (a) a triangular wedge (b) approximation of real surface at rough and crest by wedges (Faccioli, 1991)

There are two examples shown below with different approaches of seismic microzonation. The first one uses many geotechnical analysis results to create a zonation map. The method is more conven-tional then the second one. Second one, additional to the several geotechnical information gathered, they give ranking to each set of information in a geographical information system. A good example of seismic microzonation studies is presented by Topal et. al. (2003) who studied the microzonation for Yenişehir settlement in Turkey. They have performed detailed geological, hydro-geological and geotechnical studies for the assessment of the foundation conditions of the present and future settlement areas of Yenişehir. The geotechnical evaluation included trial pitting, drilling, in situ testing and laboratory testing. Borehole logs, index properties of soils, standard penetration test results and ground water level measurements were used for activity and liquefaction assessments of the foun-dation material. The study gave some advice on the conditions of the soil. They did not expect any landslide or flood problems; on the other hand, the northern sector was characterized by Clayey soils with high expansion. According to the article, in this area shallow foundations should be avoided and buildings with basement floors should be preferred. And in the southern sector, medium to loose satu-rated Sand lenses and layers are common within the Clayey foundation. Thus, this part of the area was susceptible to liquefaction under dynamic loading conditions. Considering the earthquake potential of the area (high), the design stage must include geotechnical investigations for detailed assessment of the foundation conditions (Topal, Doyuran et al. 2003). In 1997 Noack et.al., published a microzonation study for Basel city in Switzerland. The study was based on detailed knowledge of the geological and geotechnical conditions, measurement and interpre-tation of ambient noise data and numerical modelling of expected ground motion. Differing from the above-mentioned study they used a detailed rating scheme using geographical information systems, which accounts for the effects of local geological and geotechnical conditions on the amplification of ground motion. Seven characteristics parameter were mapped and rated on a 25*25 m grid within the area of the district of Basel-Stadt. The resulting qualitative microzonation map of the center of the town is discussed and compared to the historically reported damage of the 1356 earthquake. The re-sulting map was also a practical tool for recognizing areas where amplification effects have to be ex-


pected. It was also envisaged to apply measurements of shear-wave velocities, numerical simulations and calibration to future strong-motion recordings (Noack, 1997)

2.1.3. Ground Response Modelling; Soil Site Effects

The nature of local site effects can be illustrated in many ways by simple theoretical ground response analyses, by measurements of actual surface and subsurface motions at the same site and by measure-ments of ground surface motions from sites with different subsurface conditions. There are several techniques, which can be experimental, numerical, advanced, semi-empirical and empirical (Field, 1993 ;Lermo, 1993; Aki, 1991; Schnabel, 1972; ). In general terms, empirical methods use the seismic records on the local site where the amplification and frequency could be determined directly. But on the other hand the theoretical methods require detailed analysis of the geotechnical information related to the subsurface of the region (Zaslavsky 2001).

Experimental Methods Experimental methods try to clarify the response on the surface using the outcomes of the seismic re-cords. The methods use the spectral ratios between the two components (Horizontal and Vertical) of the seismic record. The most common used methods are,

• Standard spectral ratio (SSR) • H/V noise ratio; (Nogishi-Nakamura technique) • H/V spectral ratio of weak motion (HVSR); (Lacave, Bard et al. 2002)

The Standard Spectral Ratio method was widely used through out the world from the year Borcherdt has introduced it, in 1970. Though it is still widely used the latter method proposed by Nakamura in 1989 (Nakamura 1989) took also big attention. The method of Nakamura uses the two components (horizontal and vertical) of background noise at a site and computes the site-specific resonant fre-quency from these components. In other words it measures the ratio of earthquake shaking at uncon-solidated sedimentary sites with respect to a nearby bedrock reference site. Seismographs are installed in the field and left to record ambient vibrations. Ambient vibrations can also be called microseisms, microtremors or ambient noise they refer to continuous ground motion constituting background noise for any seismic experiment. They could involve traffic, machinery noises and/or seismic tremors. The method gives the frequency dependent site response amplitude or amplification, relative to the Rock site (Figure 2-7) The Standard Spectral Ratio technique uses the comparison of the ground surface motions recorded at several sites in the same region. These sites should have the same earthquake source and path effects. It is assumed that the source, path and site effects on ground motions are separable. Source effect: re-fers to the effect of the earthquake source on seismic motions. And, path effect: refers to the effect of the propagation path on seismic ground motions. From this technique the importance of the site effects also can be observed well. Similar effects have been observed in many other earthquakes. Such as Mexico 1985 earthquake (Stone, Yokel et al. 1987) and the Loma Prieta 1989 (Seed, S.E. et al. 1990) earthquake. SSR technique uses two conditions: first the reference site should be free of any site effect regarding to the source radiation and travel path meaning, when the reference site is on an unweath-ered, horizontal bedrock. Secondly, it should also be close to the examined station. Jensen (2000)


agreed on the method’s functionality but added that it is expensive and cumbersome since it requires an impractical amount of time to acquire enough data to zone the area in Australia, which is character-ized by infrequent earthquakes. The SSR method has also been attempted by recording microtremor noise, rather than actual earthquakes, simultaneously on hard Rock and sediments and then taking the spectral ratio of the recorded components. As a conclusion the noise level was so much greater at the sediment site that the special ratios could not be used to determine the resonance period for this study. Another example for the use of SSR method is, Triantafyllidis et. al. (1999). They have used the tech-niques SSR (Standard Spectral Ratio) and HVSR (H/V spectral ratio of weak motion) in Thessaloniki (Greece). The technique of SSR was applied to a reference station located on Rock, while the HVSR technique was applied to earthquake records as well as on noise records. . The results from all methods were compared in terms of resonant frequencies and amplification levels. At the end, the obtained mean spectral amplifications were compared with those derived from experimental data, the two sets are found to be consistent at most of the stations (Petros Triantafyllidis 1999; Triantafyllidis, Panagiotis M. Hatzidimitriou et al. 1999). Second technique; H/V noise ratio was introduced in the early seventies by several Japanese scien-tists but is often referred to as the Nogishi-Nakamura technique (Nogoshi and Igarashi 1971; Nakamura 1989; Y. 1989). This is the ratio between the Fourier spectra of the horizontal and vertical components of ambient vibrations. To clarify the Fourier Spectra, these terms should be explained. The seismic records could be accepted as periodic functions. And any periodic function can be ex-pressed using the Fourier analysis, which means the sum of a series of simple harmonic terms of dif-ferent frequency, amplitude and phase. And, simple harmonic motion can be characterized by sinusoi-dal motion at constant frequency. Using the Fourier series a periodic function X (t) can be written as,

∞ X ( t) = c 0 + ∑ c n sin (ωn t + φn )

n = 1 In the formula; c n is the Amplitude and φn is the phase angle. Fourier amplitude spectrum is plotted using the ωn versus c n . For Fourier phase spectrum ωn versus φn should be plotted. The technique proposes to use only one recording station in the methodology, and assumes that site response could be estimated from the horizontal (H) to vertical (V) ratio of microtremors, also refers to the name H/V ratio. This technique estimates the site response using the division between the horizon-tal component noise spectra by vertical component noise spectra.


Figure 2-7 The microtremors are placed to an alluvial site, a Rock site and at the top of a hill. The re-cordings are received and processed. Then, the amplification spectrum is plotted. The differences between

the sites are explained using the ratios and comparisons of the H/V components. This method refers to Standard Spectral Ratio of site effect estimations (Duval, 1994)

Various sets of experimental data confirmed that these ratios are much more stable than the raw noise spectra. Above all, Lacave and Bard added that several theoretical investigations supported these ob-servations (Lacave, Bard et al. 2002). They showed that synthetic strong motion records obtained with randomly distributed near surface sources lead to horizontal-vertical ratios sharply peaked around the fundamental S-wave frequency, whenever the surface layers exhibit a sharp difference with the under-lying stiffer formations. Meaning that the formations with high differing properties; unit weights, shear wave velocities etc have been estimated successfully from the H/V ratios. On the other hand the studies formerly mentioned also concluded; the amplitude of this peak is not well correlated with the S wave amplification at the site’s resonant frequency. But more sensitive to Poisson’s ratio near the sur-face, which is the ratio of the transverse strain to the longitudinal extension strain (n). Tensile defor-mation (its ability to support a load without breaking; the material can be stretch) is considered posi-tive and compressive deformation is considered negative. The definition of Poisson's ratio contains a minus sign so that normal materials have a positive ratio (Figure 2-8).


n = - etrans / elongitudinal

Strain (e) is defined in elementary form as the change in length divided by the original length. And is given by the formula;

e = DL/L.

Figure 2-8 Figure showing the representative situation for Poisson’s ratio on material. (Lakes 2004)

In order to apply this technique, one should be aware of its limitations in different situations. In prac-tice, the H/V ratios from ambient vibrations are sometimes “non-informative” so that no clear interpre-tation is possible. In Figure 2-9, transfer functions are shown which is a mathematical representation of the relation between the input and output of a linear time-fixed system. It is mainly used in signal processing. The comparison between the graphs show that they provide the fundamental resonant frequency but fails to give information on the higher frequencies (Lacave, Bard et al. 2002).


Figure 2-9 Transfer functions for (a) Standard spectral ratio (e) H/V ratio for S wave part of the earth-quake records (f) Nakamura’s technique (H/V ratio of ambient vibrations). Dashed line represent 95%

confidence limits of the mean ((Lacave, Bard et al. 2002).

Since the reliability of this technique is under investigation, there have been several approaches to test it. One of these studies is the project held for European Commission by the Swiss Seismological Ser-vice, Institute of Geophysics (Fäh, 2001). The objective of the project was to investigate the reliability of the two techniques developed in Japan using ambient noise recordings; the very simple H/V tech-nique and the more advanced array technique. The array technique uses the noise recordings on small aperture arrays. The analysis is thorough spatial correlation to measure the phase velocities of surface waves and invert the surface velocity structure. From this information then it is possible to compute the site response theoretically (Fäh, Kind et al. 2001). The project is still ongoing but supports the idea of that the technique needs assessment and also has many advantages. On this topic detailed experimental studies are ongoing but several conclusions appear which shows that many other observations should be held in order to assess the reliability of this technique. But since it is one of the most inexpensive methods it is still convenient to estimate fundamental frequen-cies of soft deposits in many cases. Additionally, there are some strong supporters of the technique such as Zaslavsky et al (2001), who had worked on the seismic microzoning of Israel using the Naka-mura technique, where they focused on 3 steps:

• Detailed mapping of site response functions using microtremor recordings • Use of geological information and borehole data with empirically obtained response functions

to derive subsurface models for different sites across the study area • Estimating the seismic hazard in terms of uniform hazard site specific acceleration Spectra.

Another supporting example is that from Louie et al (2003) from the Seismological Laboratory of Uni-versity Nevada, who tried to compare the microtremor refraction and borehole logging refraction methods. They have obtained similar average velocities and spectra between the velocity models esti-mated with refraction methods and borehole logging. But also concluded that the adding of geological information to models suggests velocities from only the upper 100 meters are not adequate for estimat-ing spectra (Louie, R. et al. 2003). The third technique; H/V spectral ratio (HVSR) of weak motion is another simple technique that consists in taking the spectral ratio between the horizontal and the vertical components of the shear wave part of weak earthquake recordings. Lermo and Chavez-Garcia (Lermo and Chavez-Garcia 1993) applied the method in Mexico. These recordings exhibit very encouraging similarities between the classical spectral ratios and these HVSR, with good fit in both, the frequencies and amplitudes of the fundamental resonant peaks.


Several other studies have looked to this technique and end up with good results, such as the HVSR shape showed good experimental stability, also well correlation with surface geology. But also, the absolute level of HVSR depends on the type of incident waves. Incident wave term is used in Snell’s law that refers to the waves refraction and reflection in optics. Optics properties could also be used when the seismic wave passes between two media. The formula given is represents the relation be-tween the waves; the normal one and the reflected or refracted one.

Figure 2-10 The incident wave and its reflected and refracted components in two media. (Transverse waves are S-waves and longitudinal waves are the P-waves).

The angles α and β in the figure are used in the formula. The theory assumes that the seismic wave comes to the boundary of the two different mediums and changes its direction with different angles and this can be related to its speed given in the formula. Furthermore it should be pointed out that this technique has been applied and checked for soft soil sites only and might not be valid for other kinds of site effects (Lacave, Bard et al. 2002). The experimental methods explained in short summaries in this section provide important information for the fundamental resonance frequency on the site. The peak amplification factor decreases with the natural frequency of soils, the greatest amplification factor will occur approximately at the lowest natural frequency which is also known as the fundamental frequency and is given by (Kramer, 1996);


ω n ≅ Vs / H ( π /2 + n π) In general, several recording stations are needed to pick up the ambient noises near the study area (ex-cept Nakamura) and if possible microtremors; real earthquake recordings are needed for these analysis. These studies would be appropriate where the recordings or the instruments for recording the signals are available. In case of this research, time, budget and data constraints did not allow to implement these experimental studies in the site. But, these investigations would be appropriate for future since they would provide double-check for the shear wave velocities and the fundamental resonance fre-quency. As, the two parameters are very related to the building codes, the results will improve the ac-curacy of the building codes being used for that time.

Numerical Analysis If the geotechnical characteristics of a site are known then, the site effects can be estimated using nu-merical analysis. Sufficient density of boreholes and sufficient geotechnical information will allow the application of numerical analysis for numerically based zoning. The numerical methods of site effects could be distinguished as follows,

• One dimensional response of soil columns • Advanced methods

Since the one-dimensional response of soil columns is the main method used in this research it will be treated in more detail. Here the new approaches and arguments according the literature will be dis-cussed. For one-dimensional response analysis the soil and bedrock surface are assumed to be extending hori-zontally and infinitely. The method simply uses, the geotechnical parameters of soils in linear or non-linear behaviour using specific calculations to estimate the ground response for a specific input mo-tion. In linear systems the structure damage is proportional to the ground shaking, which means the level of shaking assigns the level of damage. On the other hand, non-linear systems behave different at each level of shaking. The reason of the damage results from the changes in the structure while the shaking increases. In linear approaches the nonlinearity could also be implemented using the soils properties such as damping and rigidity. With this kind of calculations the input parameters are based on velocity of shear wave, unit weight, thickness and damping. These parameters could be obtained using direct in situ measurements or from drillings and subsequent laboratory measurements or from known relations between the parameters such as using SPT-N (Standard Penetration Test, N values) values for the shear moduli calculation. Shake2000 software is one of the most common programs that are used for these calculations (see chapter 3). And for the non-linear models CyberQuake program can be used (CyberQuake 1998). However, this analysis requires a quantitative knowledge of actual non-linear material behaviour, which can be ob-tained by sophisticated laboratory tests. As can be concluded, the approach requires deep understand-ing of analytical models and the numerical methods. If the approach is not handled with care, the result could be unreliable in both cases linear or non-linear. In one dimensional ground response analysis, the linear and non-linear approaches are compared in literature. Although equivalent linear approach provides reasonable results for many practical prob-lems and is widely used, it remains an approximation of the reality. Here, the mathematical aspects of


the two approaches are not going to be presented but some of the terms could be explained related to the approaches. An alternative approach is to analyse the actual non-linear response of a soil deposit using direct numerical integration in the time domain, which falls under the non-linear approach title. In linear approach transfer functions are used to compute the response of single degree of freedom sys-tems. Simply, mentioned before a transfer function is a function that relates one parameter to another. And single degree of freedom system is a discrete system whose position can be described completely by a single variable (Figure 2-3). The mathematical analyses of the two approaches differ so the results obtained also differ. There has been some results obtained on the comparison of the approaches (Joyner and Chen 1975; Martin and Seed 1978; Dikmen and Ghaboussi 1984). In general the results can be listed as follows;

1. Artificial high amplifications may occur due to a strong component of the input motion that corresponds with the natural frequency of a linear soil deposit.

2. The use of an effective shear strain in an equivalent linear analysis can lead to an over sof-tened and over-damped system.

3. Equivalent linear analyses can be much more efficient than non-linear analyses. 4. Non-linear methods can be formulated in terms of effective stresses to allow modelling of the

generation, redistribution and eventual dissipation of excess pore pressure during and after earthquake shaking. Equivalent linear methods do not have this capability.

5. Non-linear methods require a reliable stress-strain or constitutive model. 6. Differences between the results of equivalent linear and non-linear analyses depend on the de-

gree of nonlinearity in the actual soil response. In conclusion both of the approaches could be used successfully for one dimensional ground response analysis. Neither can be considered mathematically exact or precise, yet their accuracy is not consis-tent with the variability in soil conditions, uncertainty in soil properties and scatter in the experimental data upon which many of their input parameters are based (Kramer 1996). The dependency to the in-put parameters and their variability highlights this study’s importance. It is very essential that we know about the parameters variability as mentioned in the previous paragraph. Many analysis are held depending on many assumptions, where at some levels this will lead to less accurate outcomes. After discussing the two approaches, one of the examples that use the non-linear approach is done by Slob and Hack (2002). They had suggested using the GIS and SHAKE combined in an iterative way for microzonation for Armenia, Colombia. They have proposed using an automating the repetition of response calculation through the execution of a computer program that forms the interface between the gridded semi-3D ground model from the GIS and the seismic response calculation program SHAKE. Also, they used the geological conditions after the classification into areas of different hazard level is done, contradictory to the traditional way, which generally uses the geological conditions at first hand. Conclusively the case study area showed correlation between the spatial variations of the spectral ac-celeration for different frequencies and the observations after the earthquake happened (Slob, Hack et al. 2002). Another study that used SHAKE (91) and one-dimensional ground response was done by Rodriguez-Marek and Bray (1999), they have used this software and analysis in order to understand the behaviour of soil deposits. They have suggested a methodology for development of the proposed empirically


based site-dependent amplification factors. For the classification scheme of the site, they have used SHAKE91 and checked the responses. And, observed that an increase in depth shifts the fundamental period, where amplification is most significant, toward higher values. Also added that, the signifi-cantly higher response at longer periods for deep soil deposits is an important expected result that should be accommodated in a seismic site response evaluation (Rodriguez-Marek and and Bray 1999). Overall, it can be concluded that one dimensional soil column analysis is a practical method and widely used in many studies and the applications have varieties in soil site effect analysis.

Advanced methods Advanced methods refer to the different models that have been proposed to investigate several of the various aspects of site effects. These aspects usually involve complex phenomena. Various types of incident wave fields, such as near field (comparable or shorter than the wavelength concerned.), far field (It is used to refer a distance to a seismic source longer than the wavelength concerned), body waves, surface waves should be considered. The structure geometry may be 1D, 2D or 3D (Figure 2-11). Or, the mechanical behaviour of materials may have a very wide range like, viscoelasticity (Vis-coelastic materials are those for which the relationship between stress and strain depends on time), non-linear behaviour, water-saturated media and liquid domains.

Figure 2-11 Subsurface geology could be referred as one-dimensional, two-dimensional or three-dimensional (Smith 2001).

Lacave et. al (2002) have distinguished these complex conditions into four.

1. Analytical methods 2. Ray methods 3. Boundary based techniques 4. Domain based techniques

Above mentioned methods need heavy computational processes, on the other hand their flexibility and versatility have leaded the way to the understanding of the site effects. In one-dimensional response analysis the soil structure is essentially horizontal. However the condi-tions of other structures should also be taken into account. Sloping or irregular ground surfaces, the


presence of heavy structures or stiff, embedded structures or walls or tunnels all require two-dimensional even three-dimensional analysis. For this kind of problem analysis, the common approach is to make the analysis using dynamic finite-elements (This method assumes that a continuum as an composition of discrete elements whose boundaries are defined by nodal points, and uses the response of the continuum can be described by the response of the nodal points; Figure 2-12) An example for a required three-dimensional analysis could be an earth dam in a narrow canyon, a site where the subsur-face geology differs too much in 3D or a site where the soil response is influenced by response of other structures (Kramer 1996).

Figure 2-12 Diagram showing the continuum and the nodal points (Kramer, 1996)

Konno et. al. (1999) tested the analytical methods used for California using empirical modelling. They have used two dense 3D strong motion arrays and operated in California to directly measure the re-sponse of stiff quaternary soil to earthquake shaking. They have recommended that the site response measurements from these arrays along with detailed geotechnical and geophysical site investigations would provide important calibration and confirmation of site response modelling techniques used for seismic siting criteria development (Konno, Kato et al. 1999). Lacave et. al. (2002) have pointed out some of the concerns related to site effects evaluations. They have highlighted that the numerical models were a posterior computation, basically the analyser knew what to look and find. They have also found the compiling the sufficient input parameters, which de-pend on geotechnical and geophysical investigations to be expensive. Adding, “This issue may some-times be overcome through parametric studies, but this is useful only when the results do not exhibit too much sensitivity (which is rarely the case)”. Here we can see that they have already proposed to overcome the situation by parametric studies such as this one. But they also argued the sensitiveness of the results. The result of this research might give some answers to this opinion.

Empirical and semi-empirical methods Seismic waves of all types are progressively damped as they travel because of the inelastic properties (stiffness etc) of the Rocks and soils (Bolt 2001). The amplitude of seismic waves changes for two main reasons; first, the wave front usually spreads out as it travels away from the source and, because the energy in it has to be shared over a greater area, the amplitude decreases. Second, it happens when some of the wave energy is absorbed (Musset and Khan 2000). Many empirical attenuation laws have been derived on the basis of available strong ground motion recordings. They all relate to the magni-tude, distance and ground motion parameter; they also might consider the site parameter in a simple manner such as Rock or non-Rock. The reason for this is detailed information on strong ground mo-tion recording sites are generally missing. But a very important development in this area has been in Japan. They have installed 1000 sites with 20 m deep boreholes for obtaining P and S waves after the destructive earthquake Kobe. The network is called K-Net. (K-Net 2002)


Another type of empirical methods uses Green’s function, which originally comes from seismology studies. In seismology, Green’s functions are mathematical representations of how the earth’s geologic structure affects seismic waves generated by small earthquakes (Figure 2-13). Artificial ground mo-tions can be developed in a number of different ways. And generation of artificial motions using Green’s functions is one of them. Since the subsurface geology is in most cases not well known, though the aim is to figure out it in detail using these functions one should choose a simple geology structure. Green’s functions are similar to actual recordings of micro earthquakes. As such, these re-cordings can be used instead of mathematical forms to more accurately represent the seismic waves that could be expected at any given point on or in the earth, even when we don’t know the subsurface structure. The significant differentiation from the general methods which only look at parameters ob-tained at a single moment in time, is that it incorporates the whole time history, rather than simply at one point in time (Hutchings 1999).

Figure 2-13 The diagram for the Empirical Green’s function method (Bour 1994)

The Empirical Green’s Function method also has two types of approaches in literature. The basic dif-ference between the two is summing up of the EGF. First one sums up with kinematic models (Irikura 1983; Irikura 1986; Hutchings 1994; Irikura and K. Kamae 1994) . The second approach uses essen-tially statistical tools that allow to sum up the EGF’s in a way that the relevant earthquake scaling laws will be presented (Lacave, Bard et al. 2002).

2.1.4. Sensitivity Analysis

One of the main objectives for this research is to assess the sensitivity of the parameters that can be used to determine a microzonation study in Kathmandu Valley, Lalitpur. In simple words, sensitivity analysis measures the impact on analysis outcomes of changing one or more key input values about which there is uncertainty. Principally, a pessimistic, expected and optimistic value could be chosen to be the uncertain variables. Then, an analysis could be performed with each variable at a time while the


other parameters are kept constant. As a result, the outcomes would be interpreted related to the cho-sen values. All indirect inference of parameters and system states in the Earth Sciences is subject to uncertainty (Symes, Stark et al. 2002). Uncertainty is associated with incomplete or imperfect knowledge and in-herent to a physical process or property (Steward 2002). The complexity of the Earth system imposes limitations: many features of the subsurface have an ag-gregate effect on the data and estimation of these subresolution aspects of models is subject to great ambiguity. Many approaches have been proposed to quantify this uncertainty, including linear sensi-tivity analysis, Bayesian PDF estimation, minimax, construction of solutions that are extreme in some sense and many others. Such studies are meant to provoke much needed progress towards better un-derstanding of the information content of geophysical data (Symes, Stark et al. 2002) . Above all, the sensitivity and uncertainty analyses should address parameter selection and ranges, not the selection of scenarios. On the other hand this research’s aim is also to touch on the scenarios cre-ated using the input motion and parameters in Shake2000. Because the case study done in this research can also be analysed using the values sensitivity. The results could also address the scenario or meth-odology’s quality, which is used for the site. In site response the uncertainty could be found in the non-linear properties of velocity of shear wave in spatial varieties and measurement errors and for shear modulus and depth parameters in non-linear properties and sample disturbance. To deal with such problems one can use the conventional sensitivity/uncertainty analysis methods. Conventional methods for sensitivity and uncertainty propagation can be broadly classified into four categories (Isukapalli 1999). Form the list; “Sensitivity Testing” is applied in this study.

• Sensitivity testing • Analytical methods • Sampling based methods • Computer algebra methods

The general methodology is to figure out the important parameters in a model, making multiple runs for specific values chosen and fitting a polynomial least square analysis to the result curve. This fitted response surface is then used as a replacement or proxy for the computer model and all inferences re-lated to sensitivity/uncertainty analysis for the original model are derived from this fitted model. Regarding to the sensitivity analysis and Shake2000 software, there were no literature reachable at the moment. But there are some other analysis done which are related to the approach and here will be summarized. Helton, (Helton 1993) studied the applicability of response surface methods in performance assess-ment of radioactive waste disposal. It has also been used in conjunction with soil erosion modelling, with vegetative plant growth modelling and with structural reliability problems. Rebez and Slejko did an example of sensitivity analysis on the seismic hazard estimates for Italy in 2000. They have chosen the parameters to be important. Adding that, these choices are subjective and undoubtedly condition the final results. The choices were;

• The definition of maximum magnitudes for the seismogenic zones


• The definition of variable soft boundaries of the seismogenic zones • The choice of the seismicity rates as an input • The PGA attenuation relation chosen.

The scope of this work was to analyse the sensitivity of the hazard estimates when different choices are considered for the above-mentioned input parameters. These data were used to perform several tests. The conclusions were; the major differences were caused by the introduction of soft boundaries for the seismogenic zones and by the cautious corrections of the seismicity rates coming from the completeness analysis. Secondly, the influence of the attenuation relation seems relevant only in spe-cific areas such as southern Italy, where high magnitude earthquakes with a very long return period occur (Rebez and Slejko 2000). There are other studies, which focuses on the input parameter assessments for seismic hazard. In Swit-zerland, (Sellami, F. Bay et al.) have been assessing the input parameter selection and ranges. The out-come of this study will also address the estimation of uncertainties for the region. In site effects input parameters assessments of Rodriguez-Marek and Bray (1999) they have found that both analytical studies and observation of previous earthquakes indicated depth is indeed an important parameter affecting seismic site response (Rodriguez-Marek and and Bray 1999) Sensitivity studies (Field and Jacob 1993) also draw attention to the need for multiple redundant geotechnical measurements (which increases the actual cost of numerical estimations) (Lacave, Bard et al. 2002).

2.2. Conclusıons

This literature review was done in the early stages of the study, the list of reference has been broadened while the study continued. The concept of seismic hazard assessment, microzonation and ground response analysis is very wide and has been on the focus of scientific community for long years. The aim for this review was to bring the latest ones as possible. More detailed research can be and should be done in order to have a better review in all the topics. One of the difficulties faced was the absence of sensitivity analysis as it is and the sensitivity analysis done for the response analysis. There were not sufficient works done or reached for the help of this study in the response analysis. On the other hand the review supported the approach that is used for this study. For example, the experimental methods were not proper enough to apply in the chosen study area, because of the time, budget and data constraints. The second option which is the numerical analysis was not really proper since the geotechnical parameters were not known very well in the site. Though, many boreholes were obtained for the Kathmandu Valley, from this database only 14 boreholes (even 10 since 4 of them are very close points to each other) were in Lalitpur. And from this list only 2 of them had a couple of geotechnical information needed. So this was also not applicable. That is also another reason why the focus was moved to sensitivity analysis. But the main reason here is to try solving the data lacking problem using some statistical analysis and compare them with simplified reality. This review also helped for future studies that could be related to this one. For instance, the advanced methods in numerical analysis and the combination of the empirical and numerical methods could also highlight new approaches to deal with the data lacking problem. And it is also possible to use the other statistical methods mentioned (analytical methods, sampling based methods and computer algebra methods) in order to understand better the behaviour and range of values for the input parameters.


3. Shake2000

3.1. Introduction

Local site effects influence the intensity of shaking, and they have been a popular research area for many earthquake engineers, seismologists and other scientists. The reason is also it plays an important role in earthquake resistant design of buildings. The basics of this analysis depend on the wave propa-gation theory. In a nutshell the theory comes from seismology, which studies the ability of seismic waves -vibrations of Rocks- to propagate through the Earth. Generally, seismic waves do not travel in straight lines but are deflected, by refraction or reflection, by the layers they encounter, before they return to the surface of the Earth and this allows the internal structure to be determined (Musset and Khan 2000). Using wave propagation theory combined with material properties and seismic input motion the ex-pected ground movement could be determined. This is done using quantitative inputs into complex mathematical calculations. One of the earliest and most successful attempts was in the early seventies when Schabel and Lysmer (1972) published, “A computer program for conducting equivalent linear seismic response analyses for horizontally layered soil deposits” called SHAKE. This software was based on Kanai (1951), Roesset and Whitman (1969), and Tsai and Housner (1970), SHAKE assumes that the recurrent and circular soil behaviour can be simulated using an equivalent linear model (e.g. (Kramer 1996)). From then, many upgrades and derived programs have been released. In general the upgrades were focused on the user friendliness of the software; the fundamental part; the core algo-rithm was left untouched. The program is still in use widely all over the world and the upgrades are still continuing in the same way.

3.2. Background

The software that is used in this research is called SHAKE2000, which is a software package that inte-grates ShakEdit and SHAKE. Computer programs such as WESHAKE (Wallace, 1999), ProShake (Edu Pro Civil Systems, 2002) and ShakEdit are examples of the trend towards the development of the next generation of user-friendly, geotechnical earthquake engineering software. ProShake, was developed from EduShake, is a public domain program developed to help engineering students under-stand the mechanics of seismic ground response. Differing from the ProShake, EduShake can only be used with the seven ground motions that are included in the software itself. The development of EduShake evolved through several stages and was eventually beta tested by graduate students, re-searchers and practicing engineers. After a few modifications in response to the comments of beta test-ers, EduShake was made public domain. Shortly thereafter, the restrictions of EduShake were re-moved and a few additional features added to produce ProShake. And, ProShake featured a windows graphical user interface that both simplifies and speeds the analysis and interpretation of seismic ground response (Edu Pro Civil Systems, 2002 ).


In addition to the above-mentioned software, in 1998, the computer program EERA was developed starting from the same basic concepts as SHAKE. EERA stands for “Equivalent linear Earthquake Re-sponse Analysis”. EERA implements the well-known concepts of equivalent linear earthquake site response analysis taking advantages of FORTRAN 90 and spreadsheet program Excel. In 2001, the implementation principles used for EERA were applied to NERA, a nonlinear site response analysis program based on the material model developed by Iwan (1967) and Mroz (1967). NERA stands for “Non-linear Earthquake Response Analysis” and takes full advantages of FORTRAN90 and Excel. Concepts similar to those in NERA have been used by Joyner and Chen (1975) and Lee and Finn (1978). The French Geology Survey BRGM developed another software called CyberQuake, in 1998. The software was meant for Earthquake engineers and researchers. It uses the 1D geometry; multi lay-ered soil profiles with no lateral heterogeneity. Differing from the other software it has the choices like rigid or deformable Rock, totally drained condition for layers above the water level and totally or par-tially drained conditions for saturated layers underneath the water level. The future developments in ground response analysis software seems to be improving the abilities of input and output of the basic theory and making it more user friendly. One of the recent developments regarding to this issue is that the Shake maps are produced online on the internet (Wald, 1999). Fol-lowing moderate and large earthquakes, this rapid -response ground motions maps are generated automatically (Figure 3-1). So there is a great focus and use of these analysis and will be improving itself onwards.

Figure 3-1 An intensity map done by rapid instrumental technique. (Wald, 1999)

Therefore, integrating an analysis program with a user-friendly interface facilitates and greatly en-hances the interpretation of the dynamic behaviour of a particular site. The integration of SHAKE and ShakEdit into an affordable, quality computer program is the next logical upgrade of the SHAKE com-puter program (Ordonez 2002). ShakEdit was originally developed as a 16-bit, windows 3.1 applica-


tion that provided a graphical interface for SHAKE. It was originally conceived as an aid to the user in the creation of the input file and to the user in the creation of the input file and the graphical display of the program’s numeric output. In 1999, ShakEdit was upgraded to ShakEdit32 which is a 32 bit shell (Kahmann 2002). SHAKE was developed in 1991 by the University of California Berkeley, H. Bol-ton Seed, John Lysmer and Per B. Schnabel (Figure 3-2). This program computes the response in a system of homogenous, viscoelastic layers of infinite horizontal extent subjected to vertically travel-ling shear waves.

SHAKE

SHAKE 2000

SHAKEDITEDUSHAKE

PROSHAKE

Figure 3-2: Diagram showing the relationships between Shake software.

SHAKE2000 is a Windows based, user-friendly computer program. The main objective in the devel-opment was to add new features to transform SHAKE into an analysis tool for seismic analysis of soil deposits and earth structures. Apart form a learning tool for students, this version also serves to practi-tioners of geotechnical earthquake engineering as a tool to provide a first approximation of the dy-namic response of a site. Depending upon the prediction of the site response, the practitioner judges whether more sophisticated dynamic modelling is needed such as two or three-dimensional modelling. The solution of a particular problem requires use of realistic ground motions, modelling site dynamics and the interpretation and prediction of soil behaviour subject to dynamic loading. To help the engi-neer in the solution of this problem, SHAKE2000 was developed as a computer program that the prac-ticing engineer could employ to address geotechnical aspects of earthquake engineering of a project site. It includes the following (Ordonez, 2002):

• Numerous attenuation relationships • Design Spectra • Permanent Slope displacement calculation • Cyclic stress ratio (using Seed & Idriss ’71 or equivalent uniform shear stress) • Cyclic resistance ratio estimation • Settlement induced by earthquake shaking • PGA’s from the latitude and longitudes • Ground motion database (2500+) and motion file conversion utility • Response Spectra • Print out in report style


As mentioned by Ordonez (2002), the graphical display of the results is the most important feature when compared to the earlier versions. For the future improvements, the working group is working on the inclusion of liquefaction analysis using Cone Penetration data and shear wave velocity, the evaluation induced ground deformation and on a feature that will facilitate the creation of output reports.

3.3. Program Structure

Before running SHAKE2000, required input parameters should be collected. These parameters in principle can be obtained from borehole loggings and several other geophysical investigations such as seismic reflection method or electric surveys. In order to run the program you need minimum input parameters as follows,

• Soil type • Thickness of the layer • Unit weight of the material • Shear modulus value of the material • Shear wave velocity of the material • Earthquake acceleration file

Between velocity of shear wave and shear modulus there is compatibility. So, if you do not have one you can use the other. But both of them are generally difficult to obtain. For example, you can calcu-late using special equations for Gmax (Shear Modulus) with SPT N (Standard Penetration Test) val-ues. Some of these equations are also found in Shake2000 software the ones that could be easily used are:

Gmax = 325 (N60) * 0.68 Gmax = 65 * N

Here, SPT test determines the relative densities of noncohesive soils, Sands, or Silts; N value refers to the number of blows used in the test. This value could be corrected and then, it is called N60 . Depending on the value type that the borehole record has one can use one of the above formulas. For the other input parameters, thickness and the soil type are of course essential to know. And, the soil type can be defined more accurately using the option “dynamic soil properties”. This option uses standard damping and modulus equations already in the program that you can select from a list. Another important information for the required input values is that they have to be converted to feet, feet per second, kips cubic foot and kips square foot. This conversion is needed if you are using inter-national system of units (SI) (Table 3-1). The program uses the generally used units in U.S. and/or U.K. for calculations.

Parameter International System of Units (SI) Shake2000 Units

Thickness 1 meter 3.28083 feet


Shear Wave Velocity 1 meter/second 3.28083 feet/second

Unit Weight 1 KN/m3 (Kilo Newton per meter cube)

0.0063 kcf (Kips (kilo pounds) cubic foot)

Shear Modulus 1 Mpa (Mega Pascal) 20.88511 ksf (kilopound per square feet)

Table 3-1 The conversion formulas used in the calculations for Shake2000.

For the above-adopted formulas, Factors for conversion to the Metric System (SI) of Units article was used (Meritt, 1995). The Figure 3-8 represents a summarized methodology that is used to calculate the earthquake response in SHAKE2000. Here, it can be seen that the general steps are creating the file using several options then running the SHAKE, and then processing it. In the end displaying results, creating graphs and implementing the graphs to the report takes place. In the main menu you can create, edit a file or you can process an output file, which has been already calculated (Figure 3-3). If you are creating a new file you go to the earthquake response analysis menu, which includes all the 10 options that could be used in an analysis (Figure 3-4). These 10 op-tions are used to create the input information file before running the Shake.

Figure 3-3 The main menu of Shake2000 software.


In the first option the dynamic soil properties are implemented to the materials within the profile you have (Figure 3-5). This includes the damping and modulus ratios for the specific type of material. For example if you have 4 materials (For example; Sand, Clay, Gravel and Rock) you create 4 damping and 4 shear modulus ratios. This is done by choosing the best option from the list of the curves. The list includes the widely used and recognized references such as, for damping of a soil: “Damping Soil with PI (Plasticity Index) =15 used from Vucetic & Dobry 1/1991” can be chosen. It is not that easy to choose the dynamic soil properties from the list, once you don’t have sufficient knowledge on the geo-technical properties of the materials. But it is possible to use medium values since there are choices of for instance 3 types with different values. So the middle or 2nd value will be generally proper for most of the soil conditions.

Figure 3-4 The window for choosing and filling in the options for Shake2000.


Figure 3-5 The first option from the earthquake response analysis for the dynamic material properties.

The second option creates the soil profile using material types and layers (Figure 3-6). Here, you put into operation the input values of thickness; unit weight, damping and velocity of shear wave/ shear modulus for each layer. If there the shear wave velocity values are not available, instead there are some geotechnical information (such as SPT-N values), then it is possible to use some of the equations which are in the software.

Figure 3-6 The window where the soil profile is implemented.


The third option lets you to choose the proper input motion for the study area. The list of accelero-grams includes over 2500 real and simulated records from all over the world. You can also use other strong ground motion files. To do this you need to convert the input strong ground motion file into a file that SHAKE2000 can use. There is a converter to deal with this problem. But so far it can be seen that the list of earthquakes is generally sufficient to work for the analysis. The fourth option assigns the object motion to the sub-layers, which is generally the Rock material beneath the soil site. The input signal could be assigned to the Rock or other sublayers that the soil profile have. The fifth option is to define the number of iterations and strain ratio. The iterations are for obtaining an error of less than 5-10 % in the calculations. As proposed in the help menu of the software normally 3-5 iterations are sufficient (Ordonez, 2002) and strain ratio depends on your mag-nitude of input motion. Strain ratio is given by the formula:

Strain Ratio = (Magnitude of the input motion-1) /10

The sixth option computes the acceleration at specified sub-layers. Since the top layer (surface) is the important layer for microzonation studies, the results for intermediate layers are not computed for this study but if needed the acceleration values can also be calculated for each individual layer contact. The seventh option calculates the time histories for shear stresses or strains at the top of the specified sub-layer. Each layer undergoes some stress and strain depending on its properties and the input mo-tion signal properties. This could also be plotted against the time that depends on the input signal dura-tion. Option eight calculates the response spectrum for different damping chosen (5, 10 and 20). This graph could be plotted in frequency or period. Option nine is for amplification spectrum you can as-sign different sub-layers and outcrop or within the soil options are also available to work. The last op-tion computes the Fourier Spectrum. In simple words Fourier spectrum any periodic function that meets certain conditions can be expressed as the sum of the sinusoids of different amplitude, fre-quency and phase (Kramer, 1996). The Fourier spectra show the frequency content of a motion very clearly. After filling in the options we are interested in, we can run SHAKE. This takes a couple of seconds. After that we can use the display option, to see the analysis (Figure 3-7). One of the significant advan-tages of SHAKE2000 is that the user has a large variety of selections for displaying results. After cre-ating the graph you can execute these into your report.


Figure 3-7 The display of results for the analysis in table format.

Above, a very general and simplified methodology of SHAKE2000 was mentioned in a short sum-mary. However, it could be seen that the program has many options and one has to be very careful with all, in detail in order not to make any mistakes, because one of the drawback of the software is that it does not allocate the error you have done.


SHAKE 2000 METHODOLOGY

MAIN MENU

OPTIONS

1. Dynamic Soil Properties 2. Soil Profile 3. Input (Object) Motion4. Assignment of Object

Motion to a specific Sublayer

5. Number of iterations & Strain Ratio

6. Computation of Acceleration at Specified Sublayers

7. Computation of Shear Stress or Strain Time History

8. Response Spectrum 9. Amplification Spectrum 10. Fourier Spectrum

Create, Edit andProcess files

Plot Options

Other Analysis(Attenuation

Relationships, Newmark Method etc.)

SHAKE

Process

Display

Analysis

Plot Options

Report

EARTHQUAKE RESPONSE ANALYSIS

Figure 3-8 SHAKE 2000 methodology (summarized).


4. Study Area

4.1. Location

Nepal is surrounded by China on the North, India on the south and west, Bhutan and Bangladesh on the east (Figure 4-1). It has a landlocked and strategic location between China and India. Although it contains eight of world's 10 highest peaks, including Mount Everest; the world's tallest, which is on the border with China, it also has flat river areas- so called Terai. Terai lies to the south having an alti-tude of 70 m above sea level. Economy is depended on tourism and textile. Almost half of the popula-tion is living below the poverty line and is one of the least developed countries in the world. Its total area is 140,800 and % 20.27 of the area is arable.

Figure 4-1 Small map showing Asia, the rectangle indicates Nepal. Also, Lalitpur is indicated in Nepal map.

Kathmandu is the capital of the country and has the highest population of 1,093,414 (2001). It is sur-rounded by high hills and forms a valley, including Lalitpur, Bhaktapur and Patan cities. Kathmandu is almost in the middle of the country and has an elevation around 1400 m surrounded by some 2100 m mountains and peaks reaching up to 2765 m.


Lalitpur is on the south of Kathmandu city; the Bagmati River separates them. The border is almost unseen, and the separation is more on governmental issues (Figure 4-2). While Kathmandu is the met-ropolitan city, Lalitpur is a sub-metropolitan city with smaller population of approximately 336.677. The coordinates of the study area are 27o32’58. 51’’/ 6o 21’02. 15’’ NW and 27o 30’41. 00’’/ 6o 23’52. 75’’ SE with an area of 15 square kilometres. The reason for choosing Lalitpur sub-metropolitan city is it was chosen for the SLARIM projects case study area and also it fulfilled the data-lacking problem better than Kathmandu. Not only data insufficiency but also it also maintained the required organiza-tional support in the region.

Figure 4-2 Study area; Lalitpur. North of Lalitpur is Kathmandu City.

4.2. Geology

Nepal has one of the most remarkable geological formations throughout the world; it emerges from the Himalayan Mountain Range to the flat river; Ganga Plain. The Himalayas were formed by a collision between the Indian and Tibetan plate that started about 50 million years ago. Having the some of the highest peaks of the world it can be derived that the region is tectonically very active. The coming to-gether of two lithospheric plates and forming of the mountains has a speed of 2 cm/year in the region. Not only collisions of the continent appear in Nepal, but also subduction takes place between the In-dian subcontinent and Eurasia forming convergent boundaries. Subduction happens where; dense oce-anic crusts are pushed under the continental plates, which are lighter in density. The major fault systems are parallel to the Himalayan arc formed by the collision and subduction. In-dia, Nepal and Bangladesh are the countries that are associated with the Himalayan Frontal Arc with high seismic activity. The fault systems in the Himalayan arc are divided into four major systems:

• Himalayan Frontal Fault System (HFF) • Main Boundary Thrust Fault System (MBT)


• Main Central Thrust Fault System (MCT) • Indus Suture Zone (ISZ)

The movement of these major active fault systems and the branches of them creates the earthquakes in the region.Shown in Figure 4-3, till the boundary of MBT, the region is called Sub-Himalayas. From that boundary to MCT Lesser-Himalayas and from the MCT boundary to the small fault is called Higher-Himalayas and the last part to the north is called Trans-Himalayas. The boundary between the Higher-Himalayas and the Trans –Himalayas also gives the boundary of the Indian Plate and the Eura-sian Plate.

Figure 4-3 From south to north it can be seen, main frontal fault system, main boundary trust and the main central trust boundaries. The Indus Suture Zone starts from the border of north side (Avouac,

Bollinger et al. 2001).

Nepal topography could be divided into three regions; Himalayan Mountain Range, Mahabharat range in the middle and the plain area Terai. Terai has the 17% of the land and it’s altitude changes from 100 to couple of hundred meters. This lowland has fertile soils and therefore it is used for agriculture and is well known for its national parks in this region. Mahabharat range covers the 65% of the land. The altitude of this region changes from 500 to 3000 meters. And the Himalayan range has the 8 of the highest peaks of the world; which are Mt. Everest (8848m), Kanchanjunga (8586m), Lhotse (8516m), Cho Oyu (8201m) and Dhaulagiri (8167m), Mt. Makalu (8463m), Manaslu (8163m) and Annapurna I (8091m). Kathmandu valley lies in the middle of Nepal and is in the south of the higher Himalayan range and has the Mahabharat Lekh range on its south. It is an intramontane basin that was formed during Qua-ternary period. The uplift of the Mahabharat Lekh range is believed to cause the lake formation in the basin. The southward drainage has stopped because of this uplift and formed very thick reaching up to ~545 m river and lake sediments. The lake had been dried and drained out from a gorge that is cut by the Bagmati River. The sediments of the Kathmandu valley have a wide variety in category. The northern part of the valley consists of riverbed layered deposits of Clay, Silt, Sand and Gravel. South-ern part has mostly Clay and Silt with coarse sediment layers (Yadav, Singh et al. 1994). The unconsolidated sediments of the valley consists of fine-grained lake deposits of late Tertiary to


solidated sediments of the valley consists of fine-grained lake deposits of late Tertiary to Quaternary (5 million years ago or younger). Kathmandu valley forms a syncline in the Lesser Himalayas. On the north range of this syncline lies the Gneisses of the Shivapuri Lekh and on the south the granitic Rocks of the Mahabharat Range (Stöcklin 1986). In the Valley there are small anticlines and synclines bordered by faults running EW direction (Dill, Kharel et al. 2001). In general the valley has recent Quaternary deposits, but it also in-cludes the formations Tistung, Sopyang and Chandragiri defined by Bajracharya, 2003. On the north of Valley, Rocks are defined as Gneiss. The west boundary includes the Tistung, Chitlang and Ghan-apokhara. To the east Tistung and Chandragiri takes place on the boundaries of the recent deposits and the hills surrounded (Figure 4-4). Tistung Formation has; dull green grey coloured phyllites, pink pur-plish thin bed Sandstone with Sandy limestones ripple marks, Clay cracks, worm tracks are abundant. And, pebbly beds near base can be seen. Chandragiri Formation has; light fine-grained crystalline limestones, partly siliceous thick- to massively bedded white quartzites in upper parts. Chitlang For-mation has; Dark slates with white quartzites at the base and impure limestones. Ghanapokhara Forma-tion is defined as, black grey shales with black limestones thin calcareous slate, grey dolomitic lime-stones, black carbonaceous slates with thin calcareous Sandstone beds and grey to black dolomitic limestone (Bajracharya 2003). Though the surrounding of the Valley is defined in detail and the inside in general, Lalitpur area has been defined using river terrace levels in the JICA’s report on earthquake disaster assessment and da-tabase system in 2002. They have defined 1, 2 and 3 types of terrace deposits, talus deposits and recent river deposits (Figure 4-4). Also from the work done by the ICIMOD and R. Bajracharya 2003, the area was defined as alluvium; boulders, Gravels, Sands and Clays from Quaternary period. In general the boreholes in the study area shows that the main thick sediment type as Clay. On the north side of the area, thick Clays and Gravely Sand can be found. Northwest side has less thick Clay deposits with some Sandy Gravel at the base. Central part consists of Silt and thick Clays with boulder and Gravels at the base. Southeast part has mainly Sandy Clay and Sandy Silt with some Sand close to surface but there is a sudden change in the stratigraphy laterally when we compare this borehole with its neighbouring one, which consists of mainly Clay and Silty Sand. East section has thick Clay deposits over the Sands. In the study of National Building Code Development Project 5 main and active faults have been iden-tified (Yadav, Singh et al. 1994). Pleistocene to Holocene period aged sediments was moved by these faults. Three of them had been named, which are Thankot, Basoigaon, and Bungamati. One of the other two faults is a normal fault. It is found on the flood plain of the Bagmati River in the Pharping area. The other runs through the northern foothills of the Kirtipur- Chobhar Ridge, which is as close as 5 km to Kathmandu city. This is also estimated a normal fault. Thankot fault is a normal fault that strikes N-NW and truncates the toe of the alluvial fan on the slopes of the Chandragiri Range. The length of it is 8 km. Basigaon fault is probably the conjugate of the Thankot fault. It has a length of 3 km and it has a similar strike. Bungamati fault is close to Lalitpur about 5 km and has an estimated length of 26 km. It has a strike of N-NE form the channel of the Bagmati River to the village of Suna-kothi.


10 0 10 20 Kilometers

N

EW

S

Geology Map of Kathmandu Valley.(Department of Mines and Geology)

Geopoly.shpChandragiri formationChitlang formationGodavari LimestoneKulekhani FormationMarkhu FormationRecent river depositSheopuri FormationSopyang formationTalus depositTerrace I depositTerrace II depositTerrace III depositTerrace IV depositTerrace V depositTistung Formation

Terrace II deposit

Terrace III deposit

Terrace I deposit

Recent river deposit

Talus deposit

Terrace IV deposit

3 0 3 Kilometers

N

EW

S

Study Area, Lalitpur Geology Map

Geology LegendChandragiri formationChitlang formationGodavari LimestoneKulekhani FormationMarkhu FormationRecent river depositSheopuri FormationSopyang formationTalus depositTerrace I depositTerrace II depositTerrace III depositTerrace IV depositTerrace V depositTistung Formation

Lalitpur Boundary

Figure 4-4 Geology map of the Kathmandu Valley and the Lalitpur city.

There are other faults within the region but they are outside of Kathmandu about 20- 50 km. There are three of them with estimated potential magnitude level. First one is Kalphu Khola Fault to the north-west of the Valley is interpreted that it could generate a maximum Richter’s magnitude of 6.9. Second fault, Kulikhani is also estimated to generate the same magnitude. Third one, which lies about 35km SE of Kathmandu, could generate 7.1 Richter’s magnitude. Any of these faults movement will create effects to the Valley’s cities.


4.3. Seismicity

Nepal is within the seismic zone from Java-Myanmar-Himalayas-Iran and Turkey, where many de-structive earthquakes happens. The earthquakes that occurred in the Himalayan region are the biggest intra-continental earthquakes of the 20th century including the Kangra-India 1905, Bihar-Nepal 1934 and Assam-India 1950. These earthquakes had magnitudes around 8.5. So far, the seismological stud-ies showed that the big gap in the seismicity refers to Western and Central Nepal (Karanth 2002). This situation makes seismic hazard in Kathmandu valley, which is central Nepal and the western part of the country in high risk for the future earthquakes (Figure 4-5).

Figure 4-5 Taken from Bilham et al (2001) this figure shows the seismic gap regions and the potential magnitudes for the Himalayan region. It can be seen that Kathmandu has a potential slip of 4 m for cer-

tain and even more is possible.

In Figure 4-5, the years that represent the orange circular areas are referring to the high magnitude earthquakes happened in the Himalayan arc region. Below a table is given for their magnitude and time information (Table 4-1).

Year Location Magnitude (Ms)

1803 Kumaon 8?

1833 Kathmandu 7.7

1885 Kashmir 7

1905 Kangra 7.8

1934 Bihar/Nepal 8.4

1947 Assam 7.7


1950 Arunchal Pradesh 8.5

Table 4-1 Important high magnitude earthquakes happened in the Himalayan region.

Kathmandu valley has experienced many destructive earthquakes within history, such as 1833 with a magnitude of 7.5, 1934 with magnitude 8.4 and 1988 with 6.8 (Figure 4-6). One of the earliest infor-mation obtained for the valley is in 1255 in a report of the earthquake, it is said that 1/3 of the King-dom of Nepal was perished. Additionally in 1408, 1681 and 1810 earthquakes had been reported with a Modified Intensity values ranging around IX and X (Yadav, Singh et al. 1994). It can be seen that the effects of these earthquakes had been devastating. The earthquake of 1934 had given a lot of dam-age to the Kathmandu valley and the Terai region though it was located in the city Chainpur in the east. It has been estimated that around 1.100.000 houses were damaged in this earthquake. Also, Yadav, Singh et al has mentioned that (1994) in the valley Bhaktapur had suffered more damage than the other cities in the Valley (Yadav, Singh et al. 1994). 1934 earthquake had been very damaging to the Kathmandu Valley though it was 240 km away. The valley experienced intensities of IX-X on the Modified Mercalli scale. About 8500 casualties were reported and 80.000 houses were damaged. The Valley itself had the 4300 people dead and 12500 houses were damaged out of these numbers (Yadav, Singh et al. 1994). Also the 1988, Udayapur earthquake (Magnitude: 6.6) that was again located relatively far from the Valley (1665 km) had been felt in the Valley. A few buildings were damaged and several people were injured. These cases had proved that Kathmandu Valley had unfavourable characteristics for the earthquake hazard. In September 2002, Pandey et al produced the seismic hazard map of Nepal. They have collected around 5000 local earthquakes in the microseismic database. The study had collected all the earth-quakes greater than 2 between 1994 and 2002. In Figure 4-6 can also be seen the clustering of the mi-croseismic epicentral distribution is mainly parallel to the Himalayan Frontal Arc. This region was divided into eastern and western for their study. The computation between the local magnitude (Ml) (or undefined magnitude Mo) and the moment magnitude (Mw) was done by using the Ambrassey, 2000 formula. Using the formula given;

Log (Mo) = 19.08 +Ms Mw = (2/3) log (Mo) – 10.73

The reason to convert local magnitude to the moment one is, that it is a better measure of the true size of an earthquake and is recommended to be used with the attenuation relationships (Erdik, Biro et al. 1999). The magnitude-frequency relation for the earthquakes is given by the formula:

Log N = constant – b Ms

N, is the number of earthquakes with magnitudes equal to M or greater than M. M is “Ms” in the for-mula (surface wave magnitude). This formula represents that there is a close relationship between sur-face wave magnitude and N. B in the formula represents relatively small and large earthquakes meas-ure. If b has a high value then small earthquakes are more frequent in the area. And if the value is small then the large earthquakes are more frequent in the area. For this formula the b values are calcu-lated as 1.7 ± 0.2 for a given magnitude of 5 by the study of Pandey et al. They have also calculated the rate of activity for this earthquake, which is approximately equal to one event per year.


Figure 4-6 Map showing, seismic data for the years between 04/01/1995 and 10/12/1999, geodetic meas-urements and major geological structures with (MFT, MBT, MCT) (Cattin and Avouac 2000).

5. Seismic Response Analysis For Lalitpur, Nepal

5.1. Ground Response Modelling Methodology

This chapter describes the input data, procedures and methods used for the ground response analysis applied in the Lalitpur study area. Ground response analysis could be done in several ways depending


on the availability of the data in the site. If there is a dense network of boreholes in the site, then it is possible to create 1D information and this could be used in the analysis of Shake2000 or other pro-grams. It is also possible to obtain geotechnical information through geophysical investigation meth-ods (such as, seismic and electrical methods), and these provide 2D cross-sections with geotechnical information (layer thickness, shear wave velocity etc). Another method to do a ground response analy-sis/modelling is to use a generalized 2,5 or 3D subsurface model. Though, there were some boreholes in the region (17), the number was not sufficient to model the area using interpolation techniques. And geophysical investigations were not available from the fieldwork or the literature. On the other hand, the 2,5 D subsurface geology was available to use (Piya, 2004). Conclusively, this subsurface geology model was used to do the modelling. The PGA, MMI and resonance maps are produced using this sub-surface geology model and running them in Shake2000. To understand the reliability of the models, the boreholes were also used to make a crosscheck. The results are discussed in this chapter. Ground response modelling has been carried out using two methodologies. The first methodology fo-cused on the use of the actual borehole information in the soil response modelling, whereas the second methodology uses the results from the generalized soil profiles and the GIS based layer models devel-oped by Piya (2004). In the first methodology two models are used with 3 different earthquake scenar-ios. The second methodology used the generalized soil profile for the Lalitpur region and resulted in different maps (PGA, MMI and Resonance etc.) for the worst earthquake scenario.

5.1.1 Methodology 1: Modelling based on available borehole data

Methodology 1 uses two models (see Figure 5-2), which are explained below. Model 1: Using actual borehole data The borehole database for Kathmandu valley generated by Piya (2004) contains 17 boreholes for the Lalitpur area. Table 5.1 shows the deep and shallow boreholes with their depths and Figure 5-1 shows their locations. Table 5-2 gives the points and their thickness values from the generalized profile. Three boreholes (Borehole ID: C291, B1 and C288) were initially included in the analysis but no proper results could be obtained because the ground motion caused shear strains greater than the shear strain used to define the material properties in the analysis. Several analyses were done in order to overcome this situation but they did not work. On the other hand B1 was corrected for the shear strains using other reduction modulus values and working well, but this result came too late to implement it in the analysis (Ordonez, personal communication). 14 Boreholes included; thickness values for each layer with stratigraphic information (Table 5-1). Four of them (C 296, SPT 6; SPT 39 and SPT 25) were only a few meters deep. On the other hand, they (C296 and SPT 6) were the ones with much more geotechnical information than the others. Basically the geotechnical information in the borehole logs consisted of SPT-N values, void ratio, or unit weight (dry, saturated) etc. From borehole SPT-6, the SPT-N values and from borehole C296, SPT N-corrected values were used. SPT (Standard Pene-tration Test) is a soil sampling method called Standard Penetration Test, which is a commonly standardised site investigation test method to determine the relative densities of noncohesive soils, such as Sands, or Silts. The procedure is as follows: At the bottom of a borehole a cylindrical sampler is driven with standardised dimensions (ASTM 2004). To determine the number of blows a drive hammer (A short tube like device designed to be forced, without rotation) is used. The blow count, which is the N value, is obtained by the total blows required from a hammer, over the interval 150 to 450 mm per 0.3 m. The numbers of blows are counted where it requires the hammer to move from 150


m. The numbers of blows are counted where it requires the hammer to move from 150 to 450 mm and it is repeated every 0.3 meters. In liquefaction analysis and foundation design the N-value is used as a basis. It is possible to improve the N-values using a correction formula:

N’= 15 + ½(N+15)

Where: N = N value and N’ = corrected N value. If the test is done in very fine Sand or Silty Sand be-low the water table the measured N value, if greater than 15 (derived from laboratory tests), should be corrected (Craig 1987). This formula was applied to C296 borehole using the existing N-values.

Shallow Boreholes

Deep Boreholes

ID code Depth (m) ID code Depth (m)

C 40 12 B 23 304.19

C 296 2.45 B 25 136.12

SPT 6 1.45 DMG 13 298

SPT 39 6.5 BHD 3 195

PR 16 48 P 29 174

SPT 25 4.45 P 37 350

B 24 60 AG 68 189

Table 5-1 Actual Deep and shallow boreholes.

Point ID

Thickness of the post-lake deposits (m)

Thickness of the lake depos-its (m)

Thickness of the pre- lake deposits (m)

Total Thickness (m)

B24 & B25 (Point No:8) 3 62 7 72

SPT39 & PR16 (14) 3 91 79 173

BHD 3 (44) 2 133 80 215

SPT6 & AG68 (24) 16 85 126 227

C 40 (10) 14 118 106 238

C 296 (16) 9 50 184 243

B 23 (43) 30 141 95 266

P 29 (2) 1 173 149 323

DMG 13 (29) 1 161 246 408

SPT25 & P37 (58) 43 36 419 498

Table 5-2 The borehole points and their corresponding thickness’ read from the generalized profilee.


For each borehole an excel sheet was prepared. These sheets involved the conversion from SI units to the units that Shake2000 uses (See Appendix), the interpreted shear wave velocity, unit weight, thick-ness and soil types. In the table shown below (Table 5-3), only the unit weight and two sets of shear wave velocities are involved. Damping was selected as 5% for the whole analysis. In general damping ratio is accepted as 5, 10 or 20 percent (Kramer 1996). It is assumed that 5 percent will be sufficient for the analysis. And thickness varies in every layer.

Unit Weight Shear wave velocity (minimum value used)

Shear wave velocity (maximum values used)

Soil Type

KN/m3 Kcf M/s F/s M/s F/s

Soil 15 0.10 250 820 250 820

Clay 16 0.10 300 984 600 1968

Silt 17 0.11 450 1476 800 2625

Sand 18 0.11 600 1969 1200 3937

Gravel 20 0.12 1700 5577 1700 5577

Boulders 21 0.13 1500 4921 2000 6562

Rock 22 0.14 3000 9842 3000 9842

Table 5-3 Assumed shear wave velocity values for different soil types.

According to discussions held with experts on the range of shear wave velocities and the unit weight values, the first set of shear wave values was produced. The unit weight values were kept constant for both of the sets. The unit weight values could have been analysed in more detail using the water table information, by using dry unit weight above and saturated unit weight below the water table. But, this would also change the assumptions balance between the parameters. For instance it would be better if we could estimate the shear wave velocities and its value changes with depth. But if this is done, then the other inputs like unit weight should also be more accurately estimated through the assigning of values.


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GROUND RESPONSE MODELLING

METHOD 1METHOD 1

Model 1

Input Parameters

•Soil type, unit weight and shear wave velocity are defined by generalization from literature.

•Two different sets of shear wave velocity are used for the region.

•Damping is chosen %5 for all soil types.

Input Motion

6.4 km (epicentral)

6.7SAC Steel Northridge 1994

17.5 km (epicentral)

7.1Los Angeles Simulated

48 km (hypocentral distance)

8Mae Center RR 2B Synthetic

DistanceMagnitudeName of the earthquake

Model 2

Input Parameters

14 boreholes with defined depth and

soil type information.

•Model 1 Outputs

•Peak Ground Acceleration Values

•Response Spectrum

•Amplification Spectrum

•14 points with the same coordinates

thickness read from the generalized map.

4 layer simplifiedsoil profile.

Borehole defined soil profiles.

•Model 2 Outputs

•Peak Ground Acceleration Values

•Response Spectrum

•Amplification Spectrum

Comparison of the two models outputs.

Figure 5-2 Flowchart of the method 1.


For the other input parameter, strong motion record, which is necessary to run Shake2000, three earth-quake scenarios were chosen. In order to estimate the ground response in a region, the best would be having actual records from the area. But the single set of available acceleration records obtained from Kathmandu Valley was not sufficient to use. To overcome this, Shake2000 software’s database could be used. Since Shake2000 has 2500 scenario earthquakes in the software, it should be possible to choose an earthquake that represents the regional characteristics. Selection procedure generally de-pends on the magnitude and distance parameters, though it is advised to use data from similar tectonic setting, fault properties and attenuation charactreristics. Because of the unavailability of such input motions, the approach was to use the existing database in Shake2000. These scenarios are based on discussions with Nepalese geologists, seismologists and other scientists who worked in this region (Avouac, personal communication). From the Department of Mines and Geology (DMG), the accelera-tion records for a real earthquake were also obtained. There were two stations that recorded one in DMG and one in the Rock outcrop called Kakani. The response spectra were also obtained in paper format but they are lacking one direction (Z; vertical component is missing). The earthquake’s proper-ties (magnitude, distance and location etc.) were also not certain; enough information could not be gathered from the scientists of the national seismological centre. The file of the accelerograph can be found in the appendices in digital. But, these records did not have sufficient data in order to imple-ment them into the software. For example they did not specify the acceleration units or direction of the components (North, South or Z (Vertical)), which are essential to run the program. Though, assuming a couple of inputs, they were tried to implement and convert to the specific file input for Shake2000 but it also didn’t work. As a conclusion, all of the three used earthquake scenarios are chosen from the software’s own data-base (Table 5-5). One of these, corresponding to the Bihar-Nepal 1934 earthquake, with a magnitude of M=8 and a 10 km epicentral distance, was proposed, which can be considered as the worst scenario for the Valley. A more plausible scenario was considered to be the same magnitude but with a 50 km distance. As a result, MAE with a Magnitude of 8 and distance of 48 km was chosen for thewrost sce-nario. Another one was with a magnitude of 7, at some 10-15 km using this information internet and the software’s database was investigated. The second scenario is LA with 7.1 magnitude and 17.5 km. The third one is the Northridge 6.7 magnitude and 6.4 km distance. Table 5-4 shows the initially used strong ground motions that were obtained from online strong ground motion database; PEER. The study for this project was supported in part by the Pacific Earth-quake Engineering Research (PEER) Center through the Earthquake Engineering Research Centres Program of the National Science Foundation. The PEER Strong Motion Database contains 1557 re-cords from 143 earthquakes from high seismicity areas, processed by Dr. Walt Silva of Pacific Engi-neering using publicly available data from federal, state, and private contributors of strong motion data (Silva 2000). With these databases having the ASCII (American Standard Code for information inter-change; a seven bit code representing a character set of modern written English) format have been im-plemented successfully to Shake2000. One of the good opportunities of this software is the option that allows you to input the strong ground motion file from other sources. To use the files, one has to use the converter option within the software, which makes it readable for Shake2000.

Earthquake Name (Strong Ground Motion File Name)

Magnitude Distance Time


Loma Prieta M=6.9 28.2 km (distance closest to fault rupture)

1989/10/18 00:05

Kocaeli, Turkey 1999/08/17 M=7.4 197.6 km (Hypocentral) 1999/08/17

Kobe M=6.9 157.2 km (distance closest to fault rupture)

1995/01/16 20:46

Coalinga Thrust Fault Ms=6.5 25.5 km 1983/05/02 23:42

Table 5-4 Strong ground motion obtained from the PEER Strong Motion database (Silva 2000).

Other sources of strong ground motion files are also analysed but reaching the data was hard or the catalogue did not cover the area related to the study area. Some of the databases that were investigated are:

• ANSS (Advanced National Seismic System) (ANSS 1990) • (http://quake.geo.berkeley.edu/anss/cnss-detail.html#description) • IRIS SeismoQuery (Incorporated Research Institutions for Seismology)

(http://www.iris.washington.edu/SeismiQuery/index.html)(IRIS 2003) • MCEER (Multidisciplinary Center for Earthquake Engineering Research) (MCEER 2004)

(http://mceer.buffalo.edu/links/agrams.asp#top) • CISN (California Integrated Seismic Network) (CISN/Trinet 2004)

(http://docinet3.consrv.ca.gov/csmip/cisn-edc/default.htm) • NGDC (National Geophysical Data Center) (NGDC 2002)

(http://www.ngdc.noaa.gov/seg/hazard/strong.html) In the ANSS database the earthquake catalogue was covering China, India, Pakistan, Bhutan and Ne-pal. The database was from 1964 to 2002; it gave an idea for the general magnitudes for that region which ranges from 6.1 to 7.5. From IRIS database it was not possible to obtain data, because you needed to know exactly the network, station id, and channel number in order to make a query. They did not have data for Nepal or India but some 10 stations from China. MCEER has a web site to guide for other sources of databases. CISN is a combined database for engineering purposes, such as the strong motion that could be felt on a building. This information is more for earthquake resistant design issues. NGDC maintain an earthquake strong motion archive of over 15,000 digitised and processed accelerograph records. This web site is produced by NOAA (National Oceanic and Atmospheric Ad-ministration)(NGDC 2002). Another source of earthquakes was also obtained, the Uttarkashi and Chamoli from the northern India. In 29 March 1999 - Chamoli (Uttaranchal), India, a Mw 6.6 with the epicentral distance 9.8 km has happened. And Uttarkashi had Mw: 6.8 with a 10.5 km on 21st October 1991. The strong ground mo-tions obtained could not be converted in order to use them in the software: Shake2000. As mentioned before, it was possible to input the PEER strong motion files into Shake2000; this has been done for the Loma Prieta and Kocaeli earthquakes and used for the first trials in the analysis. But for the Kathmandu Valley the proposed worst scenarios were not compatible with the PEER list ob-tained from the web sites. So the earthquake database that is within the software was queried in order to find a similar characteristics earthquake. The input motions within the database are more than 2500. The three earthquakes selected are shown in Table 5-5. The first two are synthetically generated files


and the third one is from real records. Synthetically (theoretically) generated files are based on a series of mathematical assumptions. All of the considered three scenarios have the epicentre very close to the location of the city.

Name of the earthquake Magnitude Distance Mae Center RR 2B Synthetic 8 48 km (hypocentral distance)

Los Angeles Simulated 7.1 17.5 km (epicentral)

SAC Steel Northridge 1994 6.7 6.4 km (epicentral)

Table 5-5 The selected 3 scenario earthquakes form the Shake2000 strong motion database.

These assumptions are basically related to source parameters, such as slip, rupture velocity and slip velocity function. Using these parameters and the particular geometry with elastic or inelastic earth results in theoretical amplitudes versus time of arrival times for the seismic waves. The travel time curves could be defined from the seismograms recorded from an earthquake. These curves show the time and the signal characteristics. Using this information and special formulas the magnitude and the location of the earthquake can be calculated. In principle this procedure is inverted in the generation of synthetic seismograms. The seismogram records of the three selected earthquakes can be found in the appendix of the thesis. After acquiring the input parameters for 14 boreholes, the process of ground response analysis was done in Shake 2000. The information for the 14 boreholes was implemented into the database of Shake2000. The first approach for the boreholes was to analyse the PGA’s (Peak Ground Accelera-tion). So the program had been used to run the 1D linear ground response analysis and the result of the analysis were mainly focused on the PGA values. The response spectrum and other analysis were also done for the selected boreholes from the database. This will be discussed in later parts of this thesis. Model 2: Selection of generalized profile data With the same procedure of model 1, also model 2 was calculated. The basic difference between the models is the input of 14 points instead of the actual boreholes. These 14 points were having the same coordinates of the actual boreholes in the city of Lalitpur, but the soil profile used the generalized pro-file generated by Piya, (2004). Since the simplified soil profile had 4 layers, these points also had the same 4 layers. Unit weight, and shear wave velocity have been interpreted using the former assumptions. The only variable in this case was the thickness for each layer. The thickness of the 4-layer model was read us-ing the maps of Piya, (2004) using the ILWIS table calculation programme. The maps provided the thickness of the pre-lake deposits, the lake deposits and the materials overlaying the lake sediments. Here, the soil part is basically divided into three types: top, bottom and lake. From the bedrock till the surface the soil types are: Rock, Gravel, Clay and Sand/Silt. Using the information in the Table 5-6, the input values were integrated into Shake2000. Damping was kept at 5% just like in the former analysis. The shear wave velocities are again used in two sets as in Table 5-3. The input motions are also the same three earthquakes, as chosen before.


Layer Thickness (exam-

ple values) Unit Weight

Shear wave Velocity

(Feet) Meters (Kcf) KN/m3 (Fps) M/s

Damping (decimal)

Recent alluvial: 1 82 24.9 0.11 17.5 1476 450 0.05

Lake deposits: 2 360 109.7 0.1 16 1968 600 0.05

Pre-lake deposits: 3 580 176.7 0.13 20 5577 1700 0.05

Bedrock: 4 - 0.14 22 9842 3000 0.05

Table 5-6 Generalized soil profile values that are used in the soil site analysis.

Comparison of the two models (Model 1 & 2) Results of the Peak Ground Acceleration Values The results of the analysis provided information on the sensitivity of the following four aspects:

1. Shear wave velocity (Set 1 and 2: minimum and maximum values) 2. Earthquakes (3 Scenarios) 3. Thickness (Deep and Shallow boreholes, generalized soil thickness) 4. Soil Profile (Many layers versus 4 layers)

All these aspects are assessed and compared using the output Peak Ground Acceleration values. It was more convenient to use PGA outcome then the others (response spectrum and amplification spectrum graphs) since it gives a single value. Such as response spectrum, amplification graph is also hard to compare once you have many data and time constraints. All these four aspects can be divided into smaller sections and compared between each other. But the general research question that should be answered from these graphs is the difference in resulting acceleration between the actual and the gen-eralized soil profiles. This could be answered by plotting the PGA values of the actual boreholes and the corresponding points read from the generalized soil profile. Such a graph, including the other pa-rameters such as shear wave velocity and earthquake scenarios, would be relatively complex so that it has been divided into smaller charts (Figure 5-3). In Figure 5-3, the first earthquake scenario has smaller PGA values then the other two. This is a little contrary to what one would expect, since the magnitude is higher than the other two (M=8). But the other two earthquakes occur very close to the Lalitpur area. The second earthquake is 17,5 km and the third one is 6.4 km, which would influence the accelerations more, with the earthquakes that are chosen. (Second scenario; M=7.1 and Third sce-nario; M=6.7)


00.20.40.60.8

11.21.41.6

PGA (g)

B25 BHD3 AG 68 B23 P29 DMG13 P37

Borehole ID

Scenario 1 Scenario 2 Scenario 3

00.20.40.60.8

11.21.41.6

PGA (g)

B25 AG 68 P29 P37

Borehole ID

Series1 Series2 Series3

Figure 5-3 The deep boreholes correspondent PGA values for the shear wave velocity set 1 (A: minimum Vs values) and 2 (B: maximum Vs values).

From Figure 4-3 several things can be concluded for the deep boreholes and their PGA results. First, the two graphs show different PGA for different shear wave velocities (Set 1 and 2). When we com-pare the PGA value range for the two, it is easy to see that the second set which has higher shear wave velocity values than the first set gave higher PGA values for all boreholes. So an increase of shear wave velocity gives a higher Peak Ground Acceleration, which is unexpected. Second, the second sce-nario earthquake has almost always higher PGA values then the other two scenarios. The lowest PGA values are produced from the worst scenario earthquake, which is also unexpected. But this conse-quence is very related to Shake2000 limitations and the use of the synthetic earthquake that has been chosen. This will be further discussed in Chapter 7. The general acceleration differences between the actual boreholes and the generalized soil profile points are basically depend on the:

• Depth of bedrock level

A

B


• Soil thickness. The two mentioned parameters show similarity when the point of view is the shear wave velocity sets. The correlation between the PGA values for actual boreholes and the simplified 4-layer points are ob-served to be good in the deep boreholes/points. The expected good correlation refers to the close range of peak acceleration values for both the actual boreholes and the generalized profile points. For exam-ple, the range of acceleration values with the same shear wave velocity set (1) for P37 borehole/point is from 0.2 to 0.4 g. On the other hand for shallow boreholes/points the difference range could go as high as up to 2.75 g. The probable reason for this is; high values are produced by the shallow bore-holes, which are very close to the surface (Even 1.45 m). The profile then uses the bedrock as close as this value, which is not a realistic case. In reality the area has thick unconsolidated materials reaching up to 500 meters. The shallow borehole does not end at the level of the bedrock. Because, of this the results from the shallow boreholes were excluded from the analysis. The correlation between the PGA values from the deep boreholes correlation and the generalized soil profile points is more de-pendable then for the shallow boreholes. But, this also changes when the shear wave velocity changes. Likewise, for lower values of shear wave velocity the correlation of the actual boreholes and the points are much better then the second set with higher values. So, we expect the actual shear wave velocity values to be more close to the minimum values that were used in the analysis. But this should be tested with many other tests, using several shear wave velocity sets. Overall Results indicate that:

• Depth of bedrock level and soil thickness plays an important role in the correlation of the ac-tual boreholes and the generalized soil profile points.

• Los Angeles simulated earthquake with a magnitude of 7.1 and distance 17.5 km produced the highest acceleration values for both the actual boreholes and the generalized profile points in Lalitpur.

• The extreme values of PGA could be caused by wrong selection of soil depths and shear wave velocities for the soil profiles. Assigning very thick or thin levels to a specific soil type also affects the output values. For instance, very thick Clay sediment would result in high accelera-tion values, but a thin Clay layer would not affect that much within the profile.

• The shallow boreholes should not be used if the layers till bedrock are not known. They create unrealistic values.

• In general, the assumption that higher acceleration values are obtained if the soil thickness in-creases and if the shear wave velocity decreases was not supported by the results.

Results of the Response Spectra Analysis Apart from the PGA value analysis, response spectra curves were also generated for the selected bore-holes. The selection was based on the acceleration responses with lowest, mean and highest values for the 3 scenario earthquakes and two sets of shear wave velocities (minimum and maximum values). For the highest values borehole PR16 was taken, Borehole B25 for the medium values, and B23 for the lowest values. Figures 5-4, 5-5 and 5-6 shows the response spectra of the actual boreholes and the cor-responding generalized profile points. On the left side of the Figures, the response spectra are given for the generalized profiles and on the right side the ones for the actual boreholes. For B25 the shear wave velocity set 1 was used, and for PR16 and B23 the shear wave velocity set 2 was used (Table 5-


7). Though the magnitude is great and the hypocentral distance is very close, a value over 2.35 g is not a reliable value theoretically.

Point ID

Thickness of the post-lake deposits (m)

Thickness of the lake deposits (m)

Thickness of the pre-lake deposits (m)

Total thick-ness of the soil site (m)

B25 (Point ID: 8) 3 62 7 92

PR 16 (Point ID: 14) 3 91 79 202

B23 (Point ID: 43) 30 141 95 318

Table 5-7 The chosen points (they correspond to actual boreholes) from the generalized 4 layer profile.

For borehole PR16 using the scenario earthquake Los Angeles, with Magnitude: 6.2 and distance 15 km the maximum acceleration of the acceleration record is 0.32 g. This earthquake is used because of the results obtained from the sensitivity analysis and the extreme values obtained before. From the up-coming analysis it is found out that the scenario earthquakes should not exceed the acceleration maxi-mum of 0.45 g for the Shake2000 software. For PR 16 the bedrock level from the generalized soil pro-file was also used. The last layer contained the weathered limestone so the bedrock was already shown when the actual borehole profile was used. There was no need to assign a soil layer type for the differ-ence between the given bedrock level (from generalized profile) and the actual log. The various peaks at different frequencies of the response curve match with the height of buildings and may cause resonance if they coincide with the natural frequency of the buildings. So it seems high buildings would suffer much more damage then the low ones in Lalitpur city. Looking at the other curves, for example for point 43 (B23) it suggests reliable values and gives the peak acceleration val-ues 0.6 and 1.5. Here also high buildings are considered to be very susceptible to damage. As the fre-quencies gets low the storey number increases. Again the generalized and the actual borehole response spectra do not fit well. The response spectrum from the actual borehole shows a high peak in the fre-quency of 1 Hertz (related to 10 storey buildings). The last curves in Figure 5.6 are for the borehole with the lowest acceleration values. At first sight, the two curves fit in pattern, but in detail they are not very good linked. The generalized profile shows a high peak for the frequency value of 4.9 Hertz. Here, four storey buildings are more susceptible to the damage. And, the real spectrum shows a peak at frequency of 1 Hertz with an acceleration of 2.4 g creating damage to 10 storey buildings more then the others. On the whole, B23 showed reliable values for both of the curves. B25 showed a bit less reliability for the generalized profile but it’s the actual borehole showed trustable spectrum. General results obtained from the response spectrum curves can be summarized as follows:

• Either generalized profile or real investigations for the same point could differ significantly. • The first two scenario earthquakes did reach high values but the third one did not reach that

much (Northridge). This relation will be discussed in further sections. • The Peak Ground Acceleration values, which depend on the accelerations time history, reflect

more sensible values as compared to the response spectrum. The highest peaks did not reach very extreme values in the acceleration time histories.


PR 16 - Analysis No. 1 - Profile No. 2 - Layer 1Sp

ectr

al A

ccel

erat

ion

(g)

Frequency (Hz)

0

1

2

3

4

0.1 1 10 100

Point 14 (PR16)

Soil Profile No. 1 - Analysis No. 1 - Profile No. 1 - Layer 3

Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.5

1.0

1.5

0.1 1 10 100

PR16 Borehole

Figure 5-4 The response spectrum curves for three critical boreholes and correspondent points for the earthquake scenarios (For PR 16 LA M=6.2).


B 23 - Analysis No. 1 - Profile No. 3 - Layer 1

Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.5

1.0

1.5

2.0

2.5

0.1 1 10 100

Point 43 (B23)

VS SET 2 - Analysis No. 1 - Profile No. 1 - Layer 1

Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.1 1 10 100

B23 Borehole

Figure 5-5 The response spectrum curves for three critical boreholes and correspondent points for the earthquake scenarios (M=8, R=48km for B23).



Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0

1

2

3

4

5

0.1 1 10 100

Point 8 (B25)


Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.5

1.0

1.5

2.0

2.5

0.1 1 10 100

B25 Borehole

Figure 5-6 The response spectrum curves for three critical boreholes and correspondent points for the earthquake scenarios (M=8, R=48km for B25).

For the examples shown above, the bedrock level was considered to be right after the last soil layer in the borehole profile. In this example, the borehole: for P37 the bedrock level was read from the gener-alized profile. P37 has the following stratigraphy and altitudes (in meters)(Figure 5-7). In generalized profile the depth was 419 feet (127.71 m) and the actual borehole was till 370 feet (112.7 m). The dif-ference between the levels was 160.7 feet. This difference was considered to be the Gravely layer till bedrock level of the generalized profile. The calculations for this borehole were done using this layer also. The aim was to see if the two layers match up or not in the response analysis. The earthquake


used is Los Angeles, Magnitude: 6.2 distance 15 km and the maximum acceleration of the acceleration record is 0.32 g like PR16 borehole. Looking at the Figure 5-8 and 5-9, the range of values for both of the graphs response and amplifica-tion spectrum, was close. But, in detail the peaks and frequencies were different. It appears to be they would suggest very different natural frequencies for the same environment. This could be taken as one or other is not giving the reality close enough. Since, borehole log depends on the actual data, it shows the reality. Nevertheless, this example shows that simplifying the subsurface geology will not show the ground response accurate enough.

Figure 5-7 The stratigraphic section of P37 borehole log.


Soil Profile No. 1 - Analysis No. 1 - Profile No. 1 - Layer 1

Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.5

1.0

1.5

2.0

0.1 1 10 100

A

SPT 25 - Analysis No. 1 - Profile No. 1 - Layer 1

Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.5

1.0

1.5

2.0

0.1 1 10 100

B

Figure 5-8 The Figure is showing the actual borehole (ID: P37) and the point read from the generalized soil profile. A and C belongs to the actual borehole. The A and B are the response spectra for the chosen

scenario earthquake (Los Angeles M: 6.2; D: 15 km).


Soil Profile No. 1 - Analysis No. 1 - Profile No. 1

Am

plifi

catio

n R

atio

Frequency (Hz)

0

1

2

3

4

5

6

0 5 10 15 20 25

C

SPT 25 - Analysis No. 1 - Profile No. 1

Am

plifi

catio

n R

atio

Frequency (Hz)

0

2

4

6

8

0 5 10 15 20 25

D

Figure 5-9 The Figure is showing the actual borehole (ID: P37) and the point read from the generalized soil profile. A and C belongs to the actual borehole, the others C and D are from the generalized profile. The C and D are the amplification spectrums for chosen scenario earthquake (Los Angeles M: 6.2; D: 15

km).

5.1.2 Methodology 2: Generating acceleration maps

In the second methodology, a generalized subsurface layer model was used (Piya, 2004). Figure 5-10, shows a flowchart of the followed method. This layer model (consisting of bedrock, pre-lake deposits, lake deposits, and recent sediments) was based on 185 boreholes that are collected from the Kath-mandu Valley, and it gives for each point an idea on the soil types and soil thickness. Shear wave ve-locity and unit weight parameters that are essential in the soil site response analysis should be linked to these layers. The values that are used in the analysis are shown in Table 5-8.


Methodology 2Methodology 2

60 points with generalized thickness data and generalized 4 layer soil profile.

Mae Center RR 2B Synthetic

Magnitude: 8

Hypocentral Distance: 48 km

Input Motion

Output

•PGA Map of the study area.

•Modified Mercalli Intensity Map (using Trifunac and Brandy 1975 formula)

•Map showing the natural frequency of

buildings that would create resonance

with the input motion frequencies.

•Different period maps for selected

shear wave velocities.

GROUND RESPONSE MODELLING

Input Parameters

Figure 5-10 Flowchart of the method 2.

Soil Type Unit weight

KN/m3 kcf

Shear Wave Velocity (1st set) m/s

f/s Shear Wave Velocity

(2nd set) m/s Ft/s

Sandy/Silty 17.5 0.11 550 1804 450 1476

Clay 16 0.10 300 984 600 1968

Gravel 20 0.13 1000 3281 1700 5577

Rock 22 0.14 3000 9842 3000 9842

Table 5-8 Four-layer generalized soil profiles attributes that are used in the response calculation in Shake2000.


The soil profile is divided into four layers. The first layer from the surface is mainly consisting of Sandy and Silty sediments. The second layer consists of Clay sediments, which were formed in the lake that existed in the valley up to 29000 B.P. The third layer mainly consists of Gravel. Lastly, the fourth layer is the bedrock mainly consisting of limestone, Sandstone, Slates and Phyllites. After de-fining the sediment types it is possible to interpret the geotechnical parameters used in the analysis. The unit weight and shear wave values are based on the general values which were derived from dif-ferent information sources (Koloski, Schwarz et al. 1989; Whitlow 1995; Cur 1996) and discussions (S. Slob and R. Hack, personal communication). For damping a percentage of 5 has been accepted as a default value. Every material type had to be also defined using the dynamic material properties (Figure 5-11). For damping of Sand, Clay, Gravel and Rock, there was only one option, which was based on the various studies, mentioned in Table 5-9. For the Gravel layer a choice had to be made between the Gravely soils and Gravel options. Gravely soils found to be more representative for the region. And for the modulus reduction curves, Clay options were depending on the plasticity index of Clays .The plasticity of fine soils has importance in the engineering purposes where it defines the shear strength and compressibility. And, the plastic states of soils are given by the plasticity index. The options in-cluded 0, 10, 20, 40 and above 80. In order to make a sensible assumption Clay 20 was chosen. For Sand, three types were defined Sand 1, 2 and 3 for reduction modulus curve option. Sand 2 was cho-sen. And for Gravel, Gravel average was used. The shear strain and modulus reduction curve/ damping ratio relations can be observed from Figure 5-11. The first graph shows that the shear modulus types are gradually decreasing while the shear strains increases. After 1% of the shear strain, only Clay could continue to decrease till 10 %. Clay can undertake more strains then the other materials in the chosen profile. In the damping curve, while the damping percentage increases the shear strains also increase. For values more then the 1 % shear strain Clay and Sand has shear strains till 10% corre-sponding up to 30% damping ratios. Material Type Modulus Name (Shake 2000) Damping

Sandy/Silty G/Gmax - S2 (SAND CP=1-3 KSC) 3/11 1988 Damping for SAND, February 1971

Clay G/Gmax - C3 (CLAY PI =20-40, Sun et al. 198) Damping for CLAY May 24 - 1972

Gravel G/Gmax - GRAVEL, Average (Seed et al. 1986) Damping for Gravely Soils (Seed et al 1988)

Rock G/Gmax - ROCK (Schnabel 1973) Damping for ROCK (Schnabel 1973)

Table 5-9 Dynamic material properties are shown for the four-layer generalized model.


Shear Modulus Reduction Curves

Sand S2 G/Gmax - S2(SAND CP=1-3 KSC)3/11 1988Clay PI=20 G/Gmax -C3 (CLAY PI =20-40,Sun et al. 198)Gravel Avg. G/Gmax -GRAVEL, Average(Seed et al. 1986)Rock G/Gmax -ROCK (Schnabel 1973)

Mod

ulus

Red

uctio

n (G

/Gm

ax)

Shear Strain (%)

0.0

0.2

0.4

0.6

0.8

1.0

0.00001 0.0001 0.001 0.01 0.1 1 10

Damping Ratio Curves

Sand Damping forSAND, February 1971

Clay Damping forCLAY May 24 - 1972

Gravel Damping forGravelly Soils (Seed etal 1988)Rock Damping forROCK (Schnabel 1973)

Dam

ping

Rat

io (%

)

Shear Strain (%)

0

5

10

15

20

25

30

0.00001 0.0001 0.001 0.01 0.1 1 10

Figure 5-11 The dynamic material properties and their relation to the shear strain, which are used for the four-layer soil profile. (a and b)

The first parameter; thickness was obtained from the thickness maps produced before. Three thickness maps were used which refer to the altitudes of the boundaries between the four layers. For developing

a.

b.


the input data, all spatial calculations have been made in ILWIS. The pixel size has been changed to 500 by 500 m pixels in the Lalitpur area, which gave 60 pixels for Lalitpur site. 60 pixels meant 60 times running Shake2000, so that the denser pixel sizes were not chosen because of the time con-straints. In ILWIS the three thickness maps have been converted to point maps and then all the values for each map were collected in a table. So, each point had three values: thickness of the layer, which is above the lake layer (also called top of the lake), the lake layer thickness and the layer below the lake layer (also called lake bottom) (Figure 5-12). For the thickness of the fourth layer; Rock, it is consid-ered that this layer has an infinite thickness in the analysis of 1D horizontal layer earthquake response analysis. Resulting thickness values were passed to the Excel files that are used to prepare the calcula-tions. As there were now 60 different points for which the Shake2000 had to be used, which took a long time, especially in preparing the input files, only one scenario earthquake has been chosen. The worst scenario was applied in the calculations (M=8, R=48km; Synthetic).

Lake deposits

Top of the lake deposits

Bottom of the lake deposits

Rock Layer

Figure 5-12 The illustration of the generalized subsurface geology of the Kathmandu Valley.

From the analysis results in Shake 2000, 60 PGA values have been produced. From the raster map showing 500 by 500 m pixels, a point map was created in order to make it easier to link the points with the attributes. These PGA values were associated with the points in the map. After converting to raster the PGA map had been densified and resampled. It can be seen from the PGA map produced (Figure 5-13) Along with China, Myanmar, Afghanistan and Taiwan, Nepal has the highest hazard values of PGA in the Asian continent (Giardini 1999). Once, the PGA value is known, it is possible to calculate the MMI (Modified Mercalli Intensity). For this the formula from Trifunac and Brandy (1975) was used:

MMI =1/0.3*(LOG10(PGA*980)-0.014) The relation between Shake 2000 analysis and the ILWIS map creation can be seen in a summarized diagram in Figure 5-14. In the report of JICA (2001) on earthquake loss estimation for Kathmandu Valley, the Mid Nepal earthquake was corresponding to a great magnitude earthquake (Above 8). The Kathmandu Valley Local earthquake is a local earthquake occurring within the Valley. The last scenario earthquake used by JICA (2001) is the so-called North Bagmati Earthquake, which is a middle scale earthquake. These earthquake scenarios have been used by JICA (2001) to create the ground response and the intensity


estimations Figure 5-13. An earthquake occurring in the subduction boundary of Himalayas was calcu-lated to give intensity of 8 for the region. Considering the closeness of the source in this research, the MMI map produced is indeed in good correlation with the JICA’s intensity map. For the Kathmandu Valley local earthquake the high intensity is clustered on the northwest of the region. This clustering could also be recognized in the MMI map of this study. JICA assigned intensity nine for a local sce-nario and this scenario is basically in close relationship with the scenario chosen for Lalitpur site. The scenario of the North Bagmati earthquake also coincides with the intensities of this study since it has shown the intensity seven in general.

Figure 5-13 The intensity maps visualized from JICA report. (JICA, 2001) The intensities are for the sce-nario earthquakes named (from left through right) respectively; Mid Nepal, Kathmandu Valley Local and

North Bagmati.

A further step is to create spectral acceleration maps for different frequencies for resonance zonation. Every calculation in each point has produced a response spectrum. The response spectrum was calcu-lated for the surface so that it can be related to the buildings on the surface. This information is impor-tant since it gives the relation between the buildings and the strong ground motion. First, for the engi-neering purposes, the generally used storey number should be determined. The average number of floors is 3 or 4 in the Lalitpur area (Guragain, personal communication). A series of frequencies matching this average value and other special frequencies were determined. Table 5-10 shows the rela-tions that could be used.

Fundamental Frequency (Hz)

Fundamental Period (sec.)

N (Ingeominas, 1999; Arnold, 1982)

N (Vidal et. al.,1998)

N(Day, 2001)

10 0.1 1 storey 2 1 5 0.2 2 4 2 2 0.5 4 8 5

1-0.5 1.0-0.2 10-20 20-40 10-20


Table 5-10 The relations between the fundamental frequencies and the storey numbers of the buildings from three different sources (Vidal and Yamanaka 1998; INGEOMINAS 1999; Day 2001).

From the relations mentioned in the table Day, 2001 was used. The relation was defined as follows;

F= 10/N Here F is the fundamental frequency and N is the storey number. Using above formula and the deter-mined frequencies for the study area, resonance maps were produced. There are rarely 10 storey build-ings in the study area but it is included for references.

Frequency (Hz) N (Storey num-ber, Day, 2001)

5 2

3 3

2 5

1 10

Table 5-11 The fundamental frequencies for Lalitpur and their storey numbers.

Given the frequencies, the spectral accelerations were read from the response spectra of the points. Then, these values were moved to the ILWIS tables and attribute maps were created from these col-umns. The attribute maps F1, F2, F3 and F5 can be seen in the Figure 5-14. The graphs for frequencies 1, 2, 3 and 5 have high spectral accelerations in the North West side of the area. The high values in the middle could also be seen in the frequency of 3 Hz map. The highest spectral acceleration was ob-tained in the frequency map of 1 Hz with a value of 4.9 g. The high values of the spectral accelerations will be discussed in further sections. For 3Hz-frequency map, there are three clusters of high values. For 2 and 1 Hz it is a bit broader area then shown in the 3 Hz map. Since, in Lalitpur buildings mostly have 3 or 4 storeys, matching this number, the frequencies 3 and 2 Hz could be used to determine the most hazardous places for the new buildings and the ones are already there. It can be interpreted that the north; northeast and south of the site are safer than the other areas in the city for the specific storey buildings. The Figure 5-16 was produced from the existing thickness files for the subsurface geology. The formula used is:

F= Vs /4 * H Where; F is the fundamental soil frequency, Vs is the shear wave velocity and H is the thickness of the soil taken from total thickness map produced by Piya, 2004. This formula also represents the first-mode (resonant) frequency if we replace the shear wave velocity with the arithmetic average of it within the thickness of soil considered. For this we can assume that the generalized profile represents the general setting in the site. Then, the shear wave velocities used can be calculated for the arithmetic average Vs. Then, for the layers the Vs; from the surface to the bedrock respectively is 450, 600 and 1700 m/s. The average makes 916 m/s. If we also consider the average thickness to be 257 m read from the histogram of the total thickness map. Then, the formula gives ~1 (0.89) and corresponds with the 10 storey buildings in the area. The largest spectral amplifications will happen in this range of fre-quencies and the matching building storeys; 10 (Ni, Siddharthan et al. 1997). For now, Lalitpur does not have such high buildings but in the future there will be probably buildings as high as 10 storeys and even higher.


For the representative shear wave velocities, 500, 800 and 1500 m/s were chosen. They slightly repre-sent, the Clay, Sand and Gravel layers of the generalized profile. The Figure 5-15 assesses the relations between frequencies and intensity and thickness. In general, the high spectral acceleration values correspond to the high MMI intensity X. Though, the densest part of the city does not match with the high spectral accelerations, the spot on the 3 frequency map show that this part would have suffered severely also. Looking at the Figure 5-15; if we consider the actual situa-tion which would correspond to the 500 and 800 shear wave velocities since we are certain that the there exists a thick unconsolidated layer beneath the city. Then, form 2 to 5 storey buildings would be in unsafe situation in a worst scenario case like shown. Formerly, it was mentioned that the first mode frequency for the city was ~1 Hertz (10 storey). But, the thickness maps also show that in case of earthquake not only 10 storey buildings, but also 2, 3, 4 and 5 storey buildings would receive the high-est damage. Overall conclusions for this method;

• When we compared the generalized soil profiles response model with the actual boreholes in several ways presented before, the correlation between them was not good enough to use in-stead of each other. For instance it is not advised to use the generalized profile instead of an actual borehole log since they differ in their response spectrum curves, which is essential to re-lay on in order to create an accurate building code for the area for building vulnerability stud-ies.

• The natural resonance maps were generally clustered in the northwest of the city for all the chosen values (1, 2, 3 and 5). The thickness of this place is less then the rest of the city. Gen-erally thick sediments are known for their behaviour of increasing the accelerations comparing to the other geological situations. But this was not clearly shown by the maps produced. It can be interpreted that for the frequencies chosen the thinner part produced higher values.

• For a good result it seems the shear wave velocity is very essential in all cases.


Four-layer Model(Generalized Soil

Profile)

Input MotionSynthetic Earthquakewith M=8 R= 48 km.

PGA (Peak Ground Acceleration) Values (g)

Shake2000

Methodology 2 Input and Output Relations.

Figure 5-14 The second methodology’s inputs and outputs. The first part represents the calculations with Shake 2000. The second part was done in ILWIS using 60 points derived from the 500 m pixel sized thickness map.


Figure 5-15 Graph showing the resonance maps corresponding to frequencies; 1, 2, 3 and 5 Hz and the MMI map for the worst scenario earthquake and soil thickness map.


Figure 5-16 The natural frequency maps for 500, 800 and 1500 m/s shear wave velocities.


6. Sensitivity Analysis

6.1. Methodology

The objective of this study is to assess the sensitivity of the parameters that can be used to determine a microzonation study in Kathmandu Valley. The use of 1D horizontally layered soil profile response analysis, which is broadly used, such as this one requires specific parameters. This analysis could be done using the Shake2000 software, which is also a popular approach. But, to do this ground response analysis, detailed geotechnical (shear wave velocity, unit weight etc.), geometrical (thickness of soils) and seismol-ogical (Input Signal) parameters are needed. It is very often the case that all these data are not available and/or gathered with less accuracy. Most of the time, an expert’s knowledge on the input parameter will be needed to fill the gap of data. Under these circumstances, the objective of this study is to use a sensi-tivity analysis to understand the natural variation of the parameters, additionally; the objective is to assess their effect on the output of the response analysis. Unless expensive investigations (such as seismic and electrical surveys etc.) are carried out, the exact value range of shear wave velocity, soil depth and acceleration values are not well understood or solved in the concept of soil site analysis. These input parameters have close relations among themselves. Shear wave velocity and soil depth are the most important parameters in response analysis and they influence the acceleration values received on the surface. In this research, there were no real values for shear wave velocity available that have been measured in Kathmandu valley itself, unit weights were only available from a limited number of boreholes, as is the soil depth. Also a real earthquake accelerograph record, which is needed to apply the numerical response analysis, was missing for Kathmandu valley, as there is no network of accelerographs. In an attempt to address the parameter selection and range of values for the parameters, a sensitivity analysis is applied. Every type of analysis always includes a certain degree of uncertainty, as the range of input parameters is almost never fully understood. Likewise, both the numeri-cal or experimental seismic microzonation techniques need a critical evaluation of the results, which should preferably be done quantitatively. This could be done using various statistical uncertainty and/or sensitivity techniques. Principally, they are divided into four:

1. Sensitivity testing; 2. Analytical methods (Green’s function, Differential analysis etc.); 3. Sampling based methods (Monte Carlo and Latin hypercube, Fourier Amplitude Sensitivity Test

Response Surface etc.); 4. Computer algebra methods (ADIC, ADIFOR, etc) (Isukapalli 1999)

Sensitivity testing focuses on the set of changes, in the model using one variable and the rest as constant parameters. Analytical methods, reformulate the original method with algebraic equations. Sampling based methods uses the original model with different combinations for one of the input parameters for numerous trials. The last one is the automatic differentiation, which is called computer algebra method. Most of the mentioned techniques involve heavy mathematics and understanding of statistics. On the contrary, the technique applied in this study is relatively easier in the theory part. The sensitivity testing applied in this research is a straightforward technique. This technique does not use the model equations and codes like the other more complex techniques. It establishes a relationship be-


tween the inputs and outputs of the model. And also, it assesses the behaviour of the parameter selected for the analysis. Firstly, a general knowledge on the importance of the input parameters is needed. From the beginning of this study, the shear wave velocity and depth were known for their significance in soil site response. Therefore, the sensitivity analysis was applied for these two factors initially. Secondly, the general ranges of values for these parameters were determined. For example for shear wave velocity the possible range was between 100 and 10.000 feet per second. Then, the software; Shake2000 was run for numerous times using the defined pair values. Finally, the output value to assess the result was the PGA value. This value was chosen because; it is believed that it represents the soil site response better than the peak ground velocity and displacement values. In essence, the resulting table included the shear wave values and their correspondence PGA values. Finally, the values are plotted against each other and a fit-ting polynomial function is derived from it using the least square method. A schematic overview of the method is given in Figure 6-1.

Variable OUTPUT

INPUT PARAMETERS

SHAKE2000

Earthquake

Soil thickness

Unit weight One of the variables

İs chosen for the calculations.

The rest is Kept

constant.

PG

A (g

)

Variable values

Shear wave velocity

Figure 6-1 Methodology of the sensitivity analysis. In the analysis shear wave velocity unit weight and thick-ness had been also variables. The program was run for the selected range of values for the variables and the

output PGA values are plotted against the variable values.

The variable shear wave velocity has also been replaced by thickness and unit weight. Also for these vari-ables, a two layer and a three-layer soil profile model has been applied. Variations in earthquakes input motions could also be assessed using this method. This is done in the first methodology of the soil site response analysis section, which applied 3 earthquakes (see Chapter 4). Therefore, the consequences for different input motions could also be assessed from that analysis, which will be discussed in further sec-tions. Since the change is detected using the software outputs, it can be inferred that this analysis also ad-dresses the sensitivity of the Shake2000 software.

6.2. Sensitivity to changes in Shear Wave Velocity

For the two-layer model, which was tested, the values that are used for shear wave velocity are between 100 and 10.000 and for the three-layer model they are from 100 to 4000 feet per second. The range of values has been reduced for three-layer model since above 4000 fps the PGA values are changing in very small intervals (See Figure 6-2 and 6-3). For the two-layer model, Sand was selected as soil type, soil damping and reduction modulus were chosen to be the Sand-1 and Sand-Damping (See chapter 4). For


the thickness a value of 40 feet was selected and 0 .11 kcf for the unit weight. For Rock, which is the sec-ond layer, the thickness was empty (it is considered to be infinite), and the unit weight was selected to be 0.14 kcf and the shear wave velocity 9842 f/s (3000 m/s). The given values are based on the discussions and the literature. Damping and Reduction modulus were chosen to be “Rock type” for the underlying Rock layer. The properties of Rock did not vary throughout the sensitivity analysis. Damping was kept at % 5 as in all calculations. The input motion chosen was the seismogram record for the 1971 Adak, Alaska earthquake with a M=8 and R=67 km. For the above-mentioned range of values, the calculation was done by running Shake2000 for numerous times. Figure 2 shows the resulting graph, where peak accelerations are plotted against the shear wave velocity values.

00.05

0.10.15

0.20.25

0.30.35

0.4

0 1000 2000 3000 4000 5000 6000

Vs (f/s)

PGA

(g)

Vs (ft/s) Poly. (Vs (ft/s))

Figure 6-2 Calculated PGA values for different shear wave velocities. The blue dotted curve is the original curve obtained by plotting the two data sets against each other. The pink line is the trend line obtained from

this original curve.

The graph in Figure 6-2 shows a dotted blue and a purple curve. The latter one is the direct result of the two parameters relation. The dotted curve gives high accelerations between 700 and 1750 f/s shear wave velocities. The three peaks are at respectively, 700, 1450 and 2200 f/s. The curve could also be related to the fundamental natural frequency of the soil. Given the formula, the thickness for the two layer model is 40 feet:

HV

f s

40 =

For frequency 1, the Vs should be 160 since the below part of the division is 4*40 feet = 160 .The effect that can be seen is the rapid increase of the PGA values close to this value. And, the decrease values are almost falling to the frequencies 1 and 5, but then this pattern is also lost in the higher values. As a result, a two layer soil profile with velocities around 700 and 1750 would result in worse situations than the other shear wave velocities can cause. The purple line curve is a 6-degree polynomial function curve, with an R2, which is 0.8523. The R-squared value represents the correlation between the two curves. If the number is close to 1 or 1 then, it is considered to be highly correlated. But if it is less then, 0.40 then the correlation is not good enough to compare the two lines. The R square is given by:


R2 = 1- SSE

SST SSE= ∑ (Yi-Ỳi )2

SST = (∑Yi2) - (∑Yi )2 / n

Here, the Y (Yi-Ỳi ) is the variable symbol for the 2 data sets used.. And the formula of the 6th degree polynomial is:

Y = -6E-23x6+2E-18x5-3E-14x4 +2E-10x3-6 E-07x2 + 0.0007x - 0.062 The behaviour of the shear wave velocities for two layered soil profile could be interpreted from the above curve and formula. Once you have your shear wave velocity value (x), you can calculate the aver-age acceleration (y) that could result. The main idea here is to estimate close values of acceleration for the two-layered model. On the other hand, these relations are basically for presentation. In order to use them, in a practical way, these relations should be understood better. When this analysis is done for the three-layered model, Figure 6-3 was obtained.

(0,05000)

0,00000

0,05000

0,10000

0,15000

0,20000

0,25000

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Vs fps

PGA

(g)

Sand Clay Poly. (Sand) Poly. (Clay)

PGA values for shear wave velocity sample set.

Figure 6-3 The PGA values obtained after the running of Shake2000 for the shear wave velocity sample set.

The Figure 6-3 shows the two soil types selected, Sand and Clay and their response to the shear wave ve-locity sample set which is from 100 to 4000 f/s. Sand layer is the first layer from the surface and Clay is the second layer, then the Rock layer comes. The PGA values were read for both of the layers in one analysis so that the graph shows the two layer values. Sand is outcropping and Clay is within the profile for all calculations done for the sensitivity analysis. Though both of the layers are shown here, major fo-cus is on the material, which is outcropping. Because, the damage will be created on the buildings by the response of the surficial layer mostly. This range has been chosen since the changes after this value are dramatically small. The values tend to lower down starting from 2500 f/s and continue till 10.000 in the calculations. The lowering of the PGA values reach at the end 0.08 g. The curve in Figure 6-3 suggests a second-degree polynomial trend line with high R-square values (Sand R=0.99; Clay R=0.97). Looking at this statistics it looks like there is almost a linear relation between PGA and shear wave velocities. On the


contrary, this relation should not be like this. In general, low shear wave velocities create higher accelera-tions and higher damage on the surface. To understand and give an explanation to this phenomenon, we can refer to the shear wave velocity limitations.

0,00000

0,00500

0,01000

0,01500

0,02000

0,02500

0,03000

0,03500

0,04000

0,04500

0,05000

0 100 200 300 400 500 600

Series1 Series2

Figure 6-4 Graph showing the initial analysis for PGA values obtained for different shear wave velocities in two-layer model. Series 1 is Sand and series 2 is Clay. The x-axis shows Vs values; y-axis shows the PGA (g)

values.

In Figure 6-4, the expected decrease of the PGA values could be seen for the first preliminary part and only for the Clay layer. One of the aspects that create these high values could depend on the limitations of the shear wave velocity of the specific material. For example, Rock does not have low shear wave veloci-ties like 100 or 300 m/s. Likewise, unconsolidated materials should not have high shear wave velocities close to 1500 m/s and above. It is also effective that the other constant parameters such as damping, re-duction modulus and unit weight are kept constant though the material changes its type while increasing the shear wave velocity. The below formula also creates a link between the rigidity, mass and the shear wave velocity.

____ Vs = √ µ / ρ

In which µ is the elasticity parameter called rigidity (The property of a material to resist applied stress that would tend to distort it.) and ρ is the density of the material. If the general values of the chosen soil type: Sand is known then, the limitation could be defined for the shear wave velocity. The limitation of the shear wave velocity values are also depended on the soil type chosen with the information that follow to the chosen soil type. Such as, once you select Sand as the material, then the unit weight and the dynamic soil properties also reflects these material properties. In turn, this selection would also give some limitations to the calculations done. So for the specific soil profile that was selected for this test it could be inter-preted that the shear wave velocity of 250 f/s is the limit. Higher values of the shear wave velocity in the graph could not be representative in this case. Apart from the above analysis, in the ground response analysis two sets of shear wave velocities were used for the boreholes and the generalized profile in method 1. And, the comparison result of the shear wave velocity analysis using two sets showed that the PGA values are affected very much with the different values of shear wave velocity.


6.3. Sensitivity to Input Motions

The sensitivity analysis could also be applied to input motions, since they are also one of the input pa-rameters for ground response analysis. Input motions have a more direct affect on the output values; PGA’s, if the input motion has a high magnitude then, the PGA will also have high values. But of course apart from this affect, there are other essential things that change the PGA’s such as the source parameters of the focus and the distance to the location etc. In Shake2000, the input parameters could be divided into two types: those related to the soil material properties and those related to the earthquake motion. For the same soil profiles, one can apply several different input motions, which represent different earthquakes. The earthquakes could be from the database of the software or other sources of strong motion records mentioned in Chapter 4. A number of different trials have been done in the beginning of the research but these did not have the same soil profiles. On the other hand, the Methodology 1 (Model 2), explained in Chapter 4, used 3 different earthquakes for the same soil profile. So the sensitivity analysis could also be applied to these results obtained. To present the different earthquakes and the PGA values could be plot-ted against each other (Figure 6-5).


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Amax (g)

PGA

(g)

Scenario 1 Scenario 2 Scenario 3

Scenario Earthquakes and Their PGA Values.

Figure 6-5: Graph showing the PGA values that are obtained for the 3 different earthquakes (Scenario 1, 2, and 3) from the methodology 1 / Model 2. The black arrow shows the range of PGA’s that could be in the

site. Amax is the maximum acceleration recorded in time domain of the earthquake.

Looking at the graph (Figure 6-5); the range of PGA’s for the first scenario earthquake is between 0.17 and 0.70 g. The second scenario has values between 0.32 and 1.59 g, and the last one between 0.29 and 1.07 g. The points in the graph related to different soil profiles that will result in different PGA values given the same input motion. PGA (peak acceleration) is what is experienced by a particle on the ground. And, A max is the maximum acceleration recorded in time domain of the earthquake. The ranges of PGA values are very different from scenario 1 when comparing with the other 2. Almost the range is doubled for the second and third scenario. Looking at the graph it could be concluded that the region will suffer from 0.3 to 0.9 g for sure if there is a major earthquake.

Scenario Earthquake Acceleration max. (The maximum of the input signal) in g.

PGA range In g.

PGA max. In g.

Los Angeles Synthetic 1.19 0.32 - 1.59 1.59

Northridge (SAC Steel) 0.50 0.29 - 1.07 1.07

Mae Center Synthetic (RR 2B)

0.074 0.17 - 0.70 0.70

Table 6-1 The comparison table for the PGA ranges of the consequent scenario earthquakes.

The input motions (either synthetic or actually measured) on Rock could have high acceleration values in their time domain records. The maximum of the record is called the acceleration maximum (Table 6-1). This also characterises the input motion severity. The three earthquakes chosen appeared to have very high values of Amax for the first two earthquakes.. This yielded the high output accelerations on the soil, which were as high as 1.59 g. These values will be discussed in the further sections in the aspect of the analysis limits.


When the response spectra are considered, the spectral accelerations reach high values such as 2g. This is also related to the limitations of the software, which was used, and the analysis chosen. The large variabil-ity of the response spectra is illustrated in Figure 6-6, which shows response spectra for two different boreholes and two different earthquakes. It can be seen that the frequencies and the spectral acceleration relations for borehole B25, are giving different peaks for different frequencies. For example, the second scenario created higher SA (spectral accelerations) values than the first scenario. The first scenario gives the peak acceleration on the frequency of 1 Hz. But the second scenario gives a first peak at 0.7 Hz, and a second peak is at 3 Hz for both of the curves. The second earthquake gives only two major peaks and the rest is more straightforward when we compare with the first curve. If the curves are compared in more detail the SA versus frequency types will differ a lot for the two earthquakes. The same behaviour can also be seen in the response spectra for the other example in Figure 6-6 (B23). The second earthquake has an effect of smoothing the values for SA and also increasing the SA values. The differences are important since the different frequencies refer to different building storey numbers. So in this case the far end of the analysis, in the branch of the vulnerability assessment of the buildings, changes a lot. Conclusively, the outcome of the sensitivity analysis for the earthquake variation shows that it is very important which earthquake to choose in the response analysis.



Sa for 5% dampingSHAKE

Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.5

1.0

1.5

2.0

2.5

0.1 1 10 100


Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.1 1 10 100


Sa for SHAKE

Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.2

0.4

0.6

0.8

0.1 1 10 100


Spec

tral

Acc

eler

atio

n (g

)

Frequency (Hz)

0.0

0.2

0.4

0.6

0.8

1.0

0.1 1 10 100

Figure 6-6: A and C graphs show the response spectra of two boreholes (B25 and B23) for the first scenario earthquake (M=8; R=48km). B and D show the response spectra for the same boreholes but with the third

scenario earthquake (M=6.7; D=6.4 km). Please note that the y-axis range is differing in each graph.

6.4. Sensitivity for Unit Weight

Unit weight is related to the water content of the soil material. The value for the unit weight depends on the material type and its water-holding capacity. The maximum available water-holding capacity occurs in the Silty loam type of soil. So the maximum unit weight value changes would be in this soil type. The difference between a saturated soil and a dry one could differ in 2 or even 3 (in KN/m3) units for the pa-rameter. But, this situation was not taken into consideration for the analysis since it would unbalance the precision with the other input parameters. Additionally, the porosity (the empty space in a material; Abso-lute porosity refers to the total amount of pore space in a reservoir, regardless of whether or not that space is accessible to fluid penetration) and the degree of compaction of the soil are important when it is as-sessed for the amplification relation. Apart from these information Figure 6-7 shows the results of a sensi-tivity analysis for a two-layer model for differing unit weights.

A B

C D


0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16

Unit Weight (Kcf)

PGA

(g)

Unit Weight (Kcf)

Figure 6-7: The correlation between PGA values and the unit weights (Two layer model).

The calculation was done for the general value pair from 15 till 22 (KN/m3 ) for Sand (Sand 1 in the dy-namic soil properties option in the software). A constant thickness of 40 feet and a shear wave velocity of 1640 f/s were used. Damping was 5% as was the case for all calculations. The input motion chosen was the seismogram record for the 1971 Adak, Alaska earthquake with a M=8 and R=67 km. The calculation resulted in a constant PGA value of 0.3 g for all tests. So it can be concluded that unit weight is not a very important factor in the analysis, and that the model is not sensitive to changes in unit weight. However, this relation changes for the two-layer soil profile (Figure 6-8). The calculations for the same pair of values of unit weight (15-22 KN/m3), gave a 2nd degree polynomial function. The calculations were done and recorded for the two layers: Sand and Clay. Sand PGA values resulted with a high R-squared number (0.9961). Clay PGA values also resulted with a good correlation (0.998). The formulas for the Sand and Clay are respectively:

Y = -30.206x2 + 8.298x - 0.3601 Y = -15.809x2 +4.2514x - 0.1503

In the formula x refers to the unit weight value and y is the output PGA value.


y = -30,206x2 + 8,298x - 0,3601

R2 = 0,9961

y = -15,809x2 + 4,2514x - 0,1503

R2 = 0,998

0

0,05

0,1

0,15

0,2

0,25

0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16

Unit Weight (Kcf)

PG

A (g

)


Figure 6-8: Unit weight and PGA relations for a two-layer soil profile (Sand and Clay).

In the two layer model the same properties for Sand were used as in the one-layer model described above (thickness 40 feet and shear wave velocity of 1640 f/s), The input parameters for the Clay layer were ba-sically the same: a thickness of 100 feet and a shear wave velocity of 1840 f/s.. The graph in Figure 6-8 indicates that the Sand layer has higher PGA values than the Clay layer. Also, Sand has a more rapid in-crease for the PGA values. In general it can be concluded that, unit weight variations create only slight changes in PGA values. For instance, the increase from the minimum unit weight value to the maximum affects the PGA values for 0.158 to 0.208 (0.50 g difference for Sand layer).

6.5. Sensitivity for soil thickness

For the sensitivity analysis of the model to variations in the depth to bedrock, a two-layer as well as a three-layer model was used. Sand (Sand 1 in dynamic soil properties) and Clay (Clay PI=0) were used, and damping was again 5 percent. The shear wave velocity of Sand was fixed at 1640 f/s and the thick-ness was the variable. The same earthquake was used for this analysis also (1971 Adak, Alaska earth-quake with a M=8 and R=67 km). The result for the two-layer model (bedrock and soil) is shown in Fig-ure 6-9.


PGA Values for Differing Depth Values in Two Layer Model.

y = -4E-11x6 + 2E-08x5 - 4E-06x4 + 0.0005x3 - 0.0312x2 + 0.9811x - 11.878R2 = 0.8563

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 20 40 60 80 100 120 140

Depth (feet)

PGA

(g)

Depth Poly. (Depth )

Figure 6-9 The relation between PGA values and depth difference in a two-layer model. Sand was used for the two-layer model. The Rock layer shear wave velocity was 9842 f/s.

For the two-layer soil profile, R-squared was calculated as 0.8563. The formula for the 6th degree poly-nomial is:

Y = -4E-11x6+2E -0.8x5 - 4E- 0.6x4+0.0005x3 - 0.0312x2 + 0.9811x -11.878 In which X = soil thickness (in feet) and Y = PGA in g. The formula given above is considered in order to extract more information on the data behaviour. On the other hand, this was not that helpful and these formulas are kept because they are also in the methodology of the sensitivity analysis. The graph shows two peaks, one between 32 and 59 feet and the second between 85 and 98 feet. Both of the value pairs refer to an important increase and decrease in PGA values. The difference reaches 0.25 g in the first crest. The first crest corresponds to the first 18 meters of the soil profile and the second till 30 meters ( Figure 6-9 uses feet as unit). As a result, it could be inferred that the most important depth for one-layer models is the upper 30 meters. Though, the rest of the values seem to have a steady pattern, they can be considered as secondary important value pairs. To understand these pairs also, new values and calculations are needed. The next step was to analyse the three layer model (Figure 6-10).


PGA Values and Thickness Relation Using the Two-layer Model.

0

0.05

0.1

0.15

0.2

0 50 100 150 200 250 300 350

Thickness (feet)

PGA

(g)


Figure 6-10 Two-layer model for the analysis of thickness and PGA values sensitivity results.

The analysis for a three-layer model with Sand and Clay layers was done for the range of 0 - 328 feet (100 meters) with an interval of 3.28083 feet. The same dynamic properties were used; for Clay layer the plasticity index was “0” and for Sand layer it was “1”.Damping was 5 percent as always. Additional to the two-layer input parameters attributes, the Clay layer had 1840 f/s shear wave velocity. The curve of Sand has the R-squared model as 0.959. The formula for the 6th degree polynomial that suits the curve is:

Y = -1E -15x6 + 2E -12x5 -1E-0.9x4 + 4E-0.7 x3 -5E-0.5x2 + 0.0037x+ 0.0976

For Clay the R-squared is 0.8735. Both of the layers have good correlation with the trend line created. The formula for Clay is:

Y = -1E-15x6+ 2E -12x5 -1E-09x4 +4E-0.7x3 -5E-0.5x2 + 0.003x + 0.0692

The graph has 4 peaks but they do not show a great increase or decrease for PGA in pattern. Both the curves look alike but Clay has less PGA values than the Sand layer. As the thickness increases both curves gradually decrease in PGA values. The range between 6.5 and 150 feet gives the highest PGA val-ues, therefore this range should be considered as most important. The variation in PGA is from 0.09 till 0.2, which is also not a big difference but it shows the sensitive area.

6.6. Conclusions on the Sensitivity Analysis

For the most part, sensitivity analysis gave complex results for the all parameters assessed (such as shear wave velocity, input motions, unit weight and thickness). Though tried, it is very difficult to obtain a sim-ple pattern for these input parameters. Since the parameters and the calculations both are very sensitive, it is not advised to use the expert assumptions.


In order to give some range of values for the input parameters, a general estimation which is based on the graphs and the interpretations will be given. The range of values that can be interpreted from the graphs for shear wave velocity is for two-layer model, the range is between 100 and the 3000 m/s which has basically different pattern then the 3000-10000 part of the graph. The PGA difference ranges around 0.4 g. But this pattern changes significantly in three-layer model. Almost a linear correlation can be seen, but this is not realistic, since the shear wave velocities decrease, as the PGA’s gets higher in theory. Only Clay layer shows a decrease till 250 f/s and it is also awkward because the two layers should not behave so much differently. The consequences that create this pattern could be related to the assumption that the soil layers chosen have shear wave veloci-ties assigned beyond their properties. For the input motions and their range of PGA values, there could be some estimation values. The range for the scenario earthquakes for 1 and 2, PGA changes from 0.1 to 1.1 g. And this value did not include the third scenario, which will be discussed further. This result also coincides with the PGA map created using the generalized profile, which has values ranging from 0.56 to 1.40 g. Using both ranges it could be summarized as 0.1 till 1.40 g is the range of PGA values for the city; Lalitpur. Additionally spectral ac-celeration read from the generalized profile calculations gave SA starting from 0.7 till 4.9 g for different frequencies (1, 2, 3 and 5). The maximum value will be discussed in detail in following chapter. Unit weight showed no change in two-layer model. Three-layer model showed PGA values ranging from 0.12 to 0.22 g. This pattern could be interpreted that unit weight has very less affect on the PGA values comparing to the other ones. The other input parameter Thickness showed, the biggest change for 32 – 59 feet corresponding 0.15-0.38 g. But, continued some sinusoidal behaviour through the other thickness for the two-layer model. Three-layer model also showed some sinusoidal pattern and the biggest range created a difference of 0.08-0.2 g for the range 3-100 feet. The changes in g show that this parameter is not significant as input motion. As a conclusion, the most important parameter seemed to be the input motion; then shear wave velocity, then thickness and unit weight.


7. Discussion, conclusions and recommendations

In this chapter the general conclusions will be presented in two parts: discussions along with recommen-dations and conclusions. The two main objectives of this study were to estimate the strong ground mo-tions for soil site responses with the available data for Lalitpur, Nepal and to assess the sensitivity of the input parameters for response modelling in general. Both of them have been fulfilled, under special con-siderations.

7.1. Discussions and Recommendations

In view of the first objective an intensity map for Lalitpur was made using the generalized soil profiles derived from the layer model by Piya (2004) and Shake2000. The original map with 60 pixels of 500 by 500 meters was densified into smaller pixels and each point produced response parameters, such as PGA and the spectral acceleration (SA) values for specific frequencies. From these data it was possible to cre-ate a PGA map and resonance and intensity maps. The response spectrum (which relates the SA with fre-quency) is the link between the earthquake resistant design and the ground response modelling. It is basi-cally used directly as input in the dynamic analysis of structures. Therefore it is important to know the response of the soil. The four-layer soil profile was created on the basis of generalized subsurface model and interpreted parameter values. The geotechnical parameters were based on generic values based on experience and taken from literature. The result with the right scenario gave an approximated map with values for the city of Lalitpur. The question to be answered is how accurate the resulting PGA and SA maps are. The PGA values that were obtained from this study, using three earthquake scenarios that are all very close to Lalitpur (see chapter 4) were in the range of 0.2 to 0.4 g, if relatively low shear wave ve-locities are used, and from 0.4 to 1.4 if relatively high shear wave velocities are used. PGA values for Kathmandu valley have been estimated by JICA (2002) based on an earthquake scenario model that var-ies from 0.2g to 0.3g for the 1934 earthquake, whereas it is taken as 0.1g for the characterization of the earthquake zone of V according to the Indian standard IS 1093-1934. The assessments of the sensitivity of the response modelling input parameters, which is the second objec-tive, showed that they are very sensitive to certain input parameters. The results of the several runs in Shake2000 give the following priority of parameters importance;

1. Input motion 2. Shear wave velocity 3. Thickness 4. Unit weight

1. Input Motion

Initially, the importance of the parameters was also assumed like this list. Though, some of them did not show a clear pattern, it is clear that input motion is always very important input in any case. The best would be to use an earthquake that is a real record from the site. Since, it was not available, the other op-tions were used. The other options refer to the Shake2000 strong motion database and the databases that can be obtain through Internet (NGDC 2002; MCEER 2004). Based on discussions with experts (J.P.


Avouac, personal communication) and considering the geological setting of the area, a synthetic strong motion was used in the analysis for the worst scenario (M; 8; R: 48km). The results were good for the PGA and intensity maps, but when the values in the response spectrum reached very high accelerations (4 g). The maximum of the strong motions recorded are around 2.38 g so far in the databases on Internet. The reason to have such high accelerations depends on the soft and thick soils that are used and the very severe scenario chosen. But these could not be solely the reason, because it should be possible to calculate realistic values in the given situation. To understand this behaviour other sources of information were as-sessed. Another study also had high SA values (RIED 2000), reaching 5.9 g. The input signal that was used in this study used a synthetic one and was derived with a Green function analysis (A mathematical representation that, in reference to earthquake shaking, is used to represent the ground motion caused by instantaneous slip on a small part of a fault) from the Quindio Earthquake (1999) In every component of the acceleration time histories it could be seen that the peak were over 0.4 g. The highest acceleration was 0.58 g in the North-South component. To use the earthquake record from the soil site gives already the amplification of the soil. Secondly, the record was synthetically generated. The earthquake record that was used in this study is also synthetic but it is not certain if it is a surface record, or a record measured on hard Rock. Additionally, it should not be surface record since the software is for calculating the soil site response in respect to seismic waves coming from Rock. A recording in soil would help to assess the quality of the result modelled by Shake2000. From the both studies it could be interpreted that using synthetic motions could reveal results exceeding limitations if not handled with special attention in 1D linear response analysis software. This statement is true for synthetic and real motions when the input signal is above 0.45 g, as explained in a late stage of this research by one of the developers of the Shake2000 software (Ordonez, personal communication). It was advised by several researches that SHAKE (meaning also other versions) should not be used if the input motion exceeds a given limit. Actually, using the input motions beyond this acceleration means that the earthquake has a major magnitude, such as 8 and above. So, it should be correct to use SHAKE for moderate levels of shaking, generally between 0.15 –0.35 g. And it would be suitable for earthquake re-sistant design procedures since beyond this limit it is really hard to construct a resistant building for a rea-sonable cost especially in developing countries. Under these circumstances, Shake2000 is advised to be used only for the moderate levels of shakings. Secondly, when choosing an input motion to run the analysis, the parameters that should be evaluated are not only the magnitude and distance but also the input signals maximum acceleration in the time history components (North-South; East-West; Vertical). 2. Shear wave velocity Coming back to the priority list; the behaviour of the model under different shear wave velocities did not lead to clear results in the sensitivity analysis. The expected decrease of acceleration with increasing shear wave velocities was not shown in the resulting graphs. In fact, the results were contrary to that. The rea-son for the resulting pattern could be very much related to the analysis technique at first hand. The as-sumption of having a very wide range of shear wave values for a single layer could not show realistic val-ues, since every material has its own ranges. For this parameter, more detailed analysis should be carried out. For example, the behaviour can be assessed to different soil layers and crosschecked with the real geotechnical values.


But this situation could also be argued in another way. If we consider that the theoretically shear wave velocities could get higher as PGA values gets higher, then the explanation could refer to the soil reacting more stiff to the shear waves produced by the input motion. High shear wave velocities relates to high shear modulus and this results in more stiff soils. Depending on the input signal characteristics this could refer to high amplifications in high frequencies and high PGA and SA values. Another subject that should be pointed out is the 30-meter shear wave velocity approach (Borcherdt 1994). He proposed that certain period of amplification factors used to scale design spectrum could be calculated as a continuous function of mean shear wave velocity in the top 30 m. But this was not seen in the analysis of Darragh and Idriss study (1997) where they have assessed the shear wave velocity for the top 30 meters in two sites in California and found that the variation was about 60%, therefore not very applicable. This could be also assessed using defined shear wave velocities and 30 meters thickness using sensitivity analysis (For the same soil profile, different Vs and thickness pairs could be assessed for PGA values and see their difference) Shear wave velocity changes with depth also. And this is also an important effect and should be consid-ered in more detailed studies. If the change in shear wave velocity is not known initially, some derived formulas can be used (refer to (Ni, Siddharthan et al. 1997)). Due to time constraints, the increase of shear wave velocity was depth has not been taken into account in this study. 3. Thickness Thickness showed two important peaks around the first 30 meters and slightly in the three-layer model. This range revealed important changes in PGA values. Also, it was obvious that through great thickness the PGA value was decreasing. This could be interpreted that very thick sediments are considered stiffer regarding to the calculations. Also for the thickness-acceleration relation, the resulting correlation was opposite to the one expected initially. The initial hypothesis that acceleration would increase with increas-ing depth (keeping all other factors constant), had to be rejected. With increasing depth, acceleration values were decreasing. Above statement refers to the general behaviour of the curve obtained for thickness and PGA values. On the other hand the curve also showed a sinusoidal pattern, which could also be much related to the stand-ing waves, formed while the waves are at specific depths.

5. Unit Weight Unit weight has shown very slight differences in the analysis and it appears to be the least important pa-rameter, because it showed less correlation with PGA values in the sensitivity analysis. It is debatable whether it is appropriate not to include this parameter in the calculations. A better understanding of all the parameters and the calculation is needed to support such an idea. In this study the difference between the use of saturated and dry unit weights was not evaluated due to time constraints. On the other hand, it was noted that the pore water is very effective on the strong ground motion and should not be left out in the assessment of seismic hazard (Ni, Siddharthan et al. 1997).


Based on the results of the sensitivity analysis done in this research, several recommendations can be made for future work:

1. The input motion used should be under the 0.45 g limit so that the software works properly. 2. It will be better to assess these (Vs, UW, Thickness and input motion) parameters in several

situations, such as the material was generally accepted as Sand and Clay; this could be also done to others (Silt, Gravel etc).

3. The range of the geotechnical data, such as unit weight or shear wave velocities should be more accurate, better using actual test data from the project area.

4. Trial number of the sensitivity analysis could be increased 5. A more sophisticated sensitivity/uncertainty (Computer Algebra methods etc) analysis could be

applied improve the detection of relationship patterns. Linear approach Though the non-linearity is accounted for through the use of modulus reduction curves and damping, the linear approach used in this study could also be less representative then a non-linear approach that in-cludes the soil sites non-linearity, which is very important to thick soft soil sites. Not only the input signal created the high accelerations in the response spectrums, but also the deep soft soil deposits produced them. Deep soft soils are a special case for the geotechnical problems, especially in response models. Many settlements are constructed over quaternary basins, with lacustrine deposits such as Kathmandu, Lalitpur, Mexico etc. And also, these soils could also be saturated and create more complex behaviour for an earthquake. So it is important to understand these soil sites in detail. A better response analysis for such sites uses the non-linear approach. It is mentioned that soft soils are also responsible of creating such high accelerations. The reason for this statement comes from the analysis details, which depends on the dynamic material properties used and the input motions combination. If the input motion used causes shear strains (Angular displacement of a structural member due to a force acting across it, measured in radius) greater than the shear strain used to define the dynamic material properties, the acceleration values get higher (Ordonez, personal communica-tion). The solution for this is to use a material that covers these levels of shear strains. But, in case of ac-tual boreholes, or even the generalized four-layer model, it is not possible to change the material. Above all, if the input motion is producing more than %3 shear strain then the linear approach is not applicable in Shake (Ordonez, personal communication). A supporting statement summarizes that the soft soils may plastify, soften and fail in given specific levels of input acceleration (Seed, Dickenson et al. 1992). They also mention that linear approaches do not pro-duce good results when this failing and softening happens. In the analysis the peak shear stresses within critical soil zones may exceed the actual dynamic strengths of soils and the result gives over prediction of PGA’s in high frequency motions. The same study assess the linear and non-linear approaches gives the following result response spectrum (Figure 7.1) The input motion that is used for the analyses is a transverse (S-waves) component of the Yerba Buena Island record which is scaled to A max= 0.07g (Seed, Dickenson et al.). The given graph shows that linear approach results in higher SA values than, the non-linear (MARDES; non-linear soft-ware) approach. The site has also similar characteristics as Lalitpur; deep soft soils of San Francisco Bay region. Another point that should be referred is that the input signal they are using is real and does not exceed the 0.45 g limit but the calculated results show moderate-high accelerations.


Figure 7-1 The response spectrum showing the linear and non-linear approach results; SHAKE is linear and MARES is the non-linear. Compare the maximum and the difference between the two.

Then, with high shear strains and specific material it is advised to use the non-linear approach. When it is required to analyse a worst scenario case, which has higher accelerations then 0.45 g, the analysis ap-proach should be non-linear, if not the linear approach also predicts proficiently. Response Modelling If we consider that every geotechnical parameter needed for an ideal soil site response analysis is gath-ered, the earthquake is recorded at that site and the general subsurface geology is known in 3D, one of the best analyses could be done. On the other hand there are still some gaps that are very hard to fill. These gaps refer to the assumptions that are accepted from the beginning. This is the linearity of the soil sites, though they are not. The subsurface geology is very complex in pattern. The soil is weathered, moved, eroded, deposited and experienced many other processes. And therefore expecting a linear approach from the site is very difficult. It seems to be it would be more realistic if the non-linear site effects were consid-ered in 2D or 3D (Aki 1993). For direct non-linear approaches the software that can be used are DESRA 2 (Lee and Finn 1978) and the CHARSOIL (Streeter, Wylie et al. 1974). The improved version of DESRA2 could also be found (Ni, Siddharthan et al. 1997).

7.2. General Conclusions

• The resonance maps that are created from the generalized profile could be appropriate for smaller scale projects, but for larger scales it is not sufficiently accurate. First, when compared to actual borehole log results in the response spectra are very different. Secondly, the used scenario earth-quake was not suitable for the software (Shake2000) to make the realistic calculations.

• If the ideal site response study is done, the results of the sensitivity and the comparison of the

methods show that the linear response analysis still needs uncertainty / sensitivity analysis.


• Using similar earthquake signals (magnitude and distance) for the same site shows that there are

significant changes in the response spectra. One signal can result in high accelerations in a spe-cific frequency and another signal can result in different behaviour. This was assessed for the ac-tual boreholes and the generalized profile. And the result demonstrates also that it is very impor-tant to use an input signal that is characteristics for the region. This is also true for the synthetic signals generated. The study of Guatteri, Mai et al (2002), showed that variation in the specific source zone parameters, such as fault and slip type, rupture velocity and slip velocity has a great effect on the type of ground motion that is generated.

• One of the research questions was if it would be possible to use a simplified two-layer model

shear wave velocity instead of multi-layer soil profiles. Looking at the sensitivity analysis and the profiles compared, it can be interpreted that this is not advisable, because soil profile produces important changes in sensitivity analysis.

• Another question was whether it is possible to establish relationship between a two-layer and a

multi-layer profile for a single parameter. The patterns, especially for shear wave and thickness parameters, are not clear enough to derive any such relationship.

• Initially, shear wave velocity was of great concern and it was opted to simplify this parameter.

This simplification in any dimension (defining standards etc) would help the analysis, lower the costs and make it easier, since expensive geophysical methods were going to be omitted. How-ever, the sensitivity analysis demonstrates that the shear wave velocity of the soil (which relates to the shear modulus of the soil) is too important to dismiss or generalise too much.

• The generalised 2.5 D boundary layer subsurface model did not accurately predict the correct re-

sponse at 14 specific locations where more detailed subsurface information was available in the form of borehole record.

• When using either a Linear or non-linear approach it is advised to give attention on the parameter

sensitivity because of the fully non-linear soils also employ parameters which can be difficult to evaluate, but which can have a significant impact on resulting calculations (Seed, Dickenson et al.). Particularly when large magnitude and large duration earthquakes are simulated, which result in exceedance of the shear strength of the soil, and in turn results in high strain values, cannot be accurately validated in the SHAKE-based modelling approach.


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Appendix A: Input Strong Ground Motion (3 Scenario) MAE Center RR 2B Synthetic, M= 8, R= 48km (hypocentral distance) seismogram records for accelera-tion, velocity and displacement records.

MAE Center RR-2B Project - Synthetic Ground Motion - Ground Surface

Acc

eler

atio

n (g

)

Time (sec)

-0.1

-0.2

-0.3

-0.4

-0.5

0.0

0.1

0.2

0.3

0.4

0.5

0 20 40 60 80 100


Velo

city

(ft/s

ec)

Time (sec)

-0.5

-1.0

-1.5

-2.0

0.0

0.5

1.0

1.5

0 20 40 60 80 100


Dis

plac

emen

t (ft)

Time (sec)

-0.2

-0.4

-0.6

0.0

0.2

0.4

0.6

0.8

0 20 40 60 80 100


Los Angeles Simulated strong ground motion M= 7.1 D= 17.5 km (epicentral) files for acceleration, velocity and displacement records.

Los Angeles 2% in 50 years; Elysian Park (simulated); M: 7.1; D: 17.5 Km; 1.19g;

Acc

eler

atio

n (g

)

Time (sec)

-0.5

-1.0

-1.5

0.0

0.5

1.0

1.5

0 5 10 15 20 25 30


Velo

city

(ft/s

ec)

Time (sec)

-1

-2

-3

-4

-5

0

1

2

3

4

0 10 20 30 40


Dis

plac

emen

t (ft)

Time (sec)

-0.5

-1.0

-1.5

0.0

0.5

1.0

0 10 20 30 40


SAC steel Northridge 1994 M=6.7, D= 6.4 km (epicentral) seismogram records for acceleration, velocity and displacement records.

Sylm n Northridge,17 Jan 94,04:31PST; Sylmar, Olive View FF

Acc

eler

atio

n (g

)

Time (sec)

-0.2

-0.4

-0.6

-0.8

0.0

0.2

0.4

0.6

0 10 20 30 40 50 60


Velo

city

(ft/s

ec)

Time (sec)

-1

-2

0

1

2

3

4

5

0 20 40 60 80


Dis

plac

emen

t (ft)

Time (sec)

-0.5

-1.0

0.0

0.5

1.0

1.5

0 20 40 60 80


Appendix B: Soil Profile Information On Calculations Done In Shake2000.

meter KN/m3 m/s m/s

No. Well_ID Modified Description Soil ID Thickness feet UW pcf kcf Vs- SET 1 ft/s Vs-SET2 ft/s

1 B -23 Clayey Silt 1 4 13.1 17 108 0.11 250 820 500 1640

Medium to coarse Sand 2 11.08 36.4 18 115 0.11 600 1968 450 1476

Silty Sand 2 12.2 40.0 18 115 0.11 600 1968 450 1476

Gravelly Sandy Clay 3 18.28 60.0 16 102 0.10 300 984 600 1968

Sandy Clay 3 30.48 100.0 16 102 0.10 300 984 600 1968

Sandy Clay 3 97.37 319.5 16 102 0.10 300 984 600 1968

Sandy Gravel 4 42.47 139.3 20 127 0.13 1000 3281 700 2297

Sandy Clay 3 33.43 109.7 16 102 0.10 300 984 750 2461

Sandy Clay 3 54.86 180.0 16 102 0.10 300 984 750 2461

Rock 5 0.0 22 140 0.14 3000 9842 3000 9842

2 B - 24 Clay 1 41.14 135.0 16 102 0.10 300 984 600 1968

Gravels and Boulders 2 18.9 62.0 20 127 0.13 1000 3281 1850 6070

Rock 3 0.0 22 140 0.14 3000 9842 3000 9842

3 B - 25 Clay 1 105.76 347.0 16 102 0.10 300 984 600 1968

Gravelly Clay 1 6.1 20.0 16 102 0.10 300 984 850 2789

Gravel 2 22.55 74.0 20 127 0.13 1000 3281 1700 5577

Rock 3 1.71 5.6 22 140 0.14 3000 9842 3000 9842

4 B1 Fine Sand 1 6.4 21.0 18 115 0.11 600 1968 750 2461


Fine to medium Sand 1 2.74 9.0 18 115 0.11 600 1968 750 2461

Fine to coarse Sand 1 6.1 20.0 18 115 0.11 600 1968 800 2625

Clay 2 70.26 230.5 16 102 0.10 300 984 600 1968

Clay 2 5.94 19.5 16 102 0.10 300 984 600 1968

Clay 2 83.31 273.3 16 102 0.10 300 984 600 1968

Gravelly Clay 2 38.55 126.5 16 102 0.10 300 984 850 2789

Gravelly Sand with Clay 3 9.14 30.0 18 115 0.11 300 984 1200 3937

Clay 2 97.54 320.0 16 102 0.10 300 984 600 1968

Fine to Corse Sand 1 5.72 18.8 18 115 0.11 600 1968 1200 3937

Sandy Clay 2 9.16 30.1 16 102 0.10 300 984 800 2625

Sandy Clay 2 15.24 50.0 16 102 0.10 300 984 800 2625

Gravelly Sand with Clay 3 21.32 69.9 18 115 0.11 300 984 1100 3609

Sandy Clay 2 15.25 50.0 16 102 0.10 300 984 800 2625

Clayey Sand 1 6.09 20.0 18 115 0.11 600 1968 1000 3281

Silty Sandy Clay 2 9.14 30.0 16 102 0.10 300 984 1000 3281

Medium to coarse Sand 2 24.39 80.0 18 115 0.11 600 1968 1100 3609

Clayey Sand 2 24.39 80.0 18 115 0.11 600 1968 1000 3281

Sandy Clay 1 6.1 20.0 16 102 0.10 300 984 800 2625

Rock 4 22 140 0.14 3000 9842

5 DMG 13 Clay 1 55 180.4 16 102 0.10 300 984 600 1968

Clayey Sand 2 10 32.8 18 115 0.11 600 1968 1000 3281

Clay 1 21 68.9 16 102 0.10 300 984 600 1968

Clayey Silty Sand 2 3 9.8 18 115 0.11 600 1968 1100 3609

Clay 1 64 210.0 16 102 0.10 300 984 600 1968


medium to coarse Sand 2 5 16.4 18 115 0.11 600 1968 1200 3937

Clay 1 5 16.4 16 102 0.10 300 984 600 1968

Medium to coarse Sand 2 11 36.1 18 115 0.11 600 1968 1200 3937

Clay 1 6 19.7 16 102 0.10 300 984 600 1968

Medium to coarse Sand 2 10 32.8 18 115 0.11 600 1968 1200 3937

Clay 1 5 16.4 16 102 0.10 300 984 600 1968


Clay 1 4 13.1 16 102 0.10 300 984 600 1968


Clay 1 17 55.8 16 102 0.10 300 984 600 1968


Clay 1 6 19.7 16 102 0.10 300 984 600 1968


Clay 1 29 95.1 16 102 0.10 300 984 600 1968

Rock 3 0.0 22 140 0.14 3000 9842 3000 9842

6 AG 68 Clayey Silt 1 6 19.7 17 108 0.11 450 1476 750 2461

Silt 1 23 75.5 17 108 0.11 450 1476 800 2625

Clay 2 120 393.7 16 102 0.10 300 984 600 1968

Silt 1 14 45.9 17 108 0.11 450 1476 800 2625

Gravelly Sand 3 15 49.2 18 115 0.11 600 1968 1450 4757

Gravel and boulder mixed 4 11 36.1 20 127 0.13 1000 3281 1850 6070

Rock 5 0.0 22 140 0.14 3000 9842 3000 9842

7 BHD 3 Clay 1 129 423.2 16 102 0.10 300 984 600 1968


Silty Clayey Sand 2 15 49.2 18 115 0.11 600 1968 1000 3281

Clay 1 25 82.0 16 102 0.10 300 984 600 1968

Rock 3 0.0 22 140 0.14 3000 9842 3000 9842

8 P -29 Clay 1 174 570.9 16 102 0.10 300 984 600 1968

Sand and Gravel 2 44 144.4 20 127 0.13 1000 3281 1450 4757

Rock 3 0.0 22 140 0.14 3000 9842 3000 9842

9 P 37 Sandy Clay 1 30.6 100.4 16 102 0.10 300 984 900 2953

Clayey Sand 2 3.9 12.8 18 115 0.11 600 1968 1000 3281

Coarse Sand 2 5.5 18.0 18 115 0.11 600 1968 1200 3937

Medium Sand 2 5 16.4 18 115 0.11 600 1968 1200 3937

Clay 1 13.5 44.3 16 102 0.10 300 984 600 1968

Clayey Sand 2 93 305.1 18 115 0.11 600 1968 1000 3281

Medium Sand 2 3 9.8 18 115 0.11 600 1968 1200 3937

Sandy Clay 1 8 26.2 16 102 0.10 300 984 900 2953

Coarse Sand 2 4.5 14.8 18 115 0.11 600 1968 1200 3937

Sandy Clay 1 5.5 18.0 16 102 0.10 300 984 900 2953

Gravelly Sand 2 5.5 18.0 18 115 0.11 600 1968 1450 4757

Clay 1 2 6.6 16 102 0.10 300 984 600 1968

Gravelly Sand 2 8 26.2 18 115 0.11 600 1968 1450 4757

Clay 1 6 19.7 16 102 0.10 300 984 600 1968

Gravelly Sand 2 4.5 14.8 18 115 0.11 600 1968 1450 4757

Clay 1 69 226.4 16 102 0.10 300 984 600 1968

Gravelly Sand 2 15 49.2 18 115 0.11 600 1968 1450 4757


Clay 1 1 3.3 16 102 0.10 300 984 600 1968

Coarse Sand 2 4.5 14.8 18 115 0.11 600 1968 1200 3937

Clay 1 10.5 34.4 16 102 0.10 300 984 600 1968

Coarse Sand 2 4 13.1 18 115 0.11 600 1968 1200 3937

Clay 1 2 6.6 16 102 0.10 300 984 600 1968

Coarse Sand 2 44.1 144.7 18 115 0.11 600 1968 1200 3937

Clay 1 1.4 4.6 16 102 0.10 300 984 600 1968

Coarse Sand 2 20 65.6 18 115 0.11 600 1968 1200 3937

Rock 3 22 140 0.14 3000 9842 3000 9842

0.0

10 PR 16 Clay 1 45 147.6 16 102 0.10 300 984 600 1968

Boulders 2 3 9.8 21 134 0.13 1500 4921 2000 6562

Limestone /Rock 3 26.65 87.4 22 140 0.14 3000 9842 3000 9842

0.0

11 SPT 39 Sandy Clay 1 0.7 2.3 16 102 0.10 300 984 900 2953

medium Sand 2 0.3 1.0 18 115 0.11 600 1968 1100 3609

medium Sand 2 0.7 2.3 18 115 0.11 600 1968 1100 3609

Clayey Sand 2 0.3 1.0 18 115 0.11 600 1968 1000 3281

Clayey Sand 2 1 3.3 18 115 0.11 600 1968 1000 3281

Clayey Sand 2 0.35 1.1 18 115 0.11 600 1968 1000 3281

Clayey Sand 2 0.1 0.3 18 115 0.11 600 1968 1000 3281

Clayey Sand 2 0.75 2.5 18 115 0.11 600 1968 1000 3281

Clay 1 0.25 0.8 16 102 0.10 300 984 600 1968

Sandy Clay 1 0.55 1.8 16 102 0.10 300 984 900 2953

Clay 1 1.45 4.8 16 102 0.10 300 984 600 1968


Rock 3 0.0 22 140 0.14 3000 9842 3000 9842

12 SPT 25 Silty Clay 1 1 3.3 16 102 0.10 300 984 700 2297

Clayey Silt 2 0.45 1.5 17 108 0.11 450 1476 750 2461

Clayey Silt 2 0.55 1.8 17 108 0.11 450 1476 750 2461

fine Sandy Silt 2 0.45 1.5 17 108 0.11 450 1476 1000 3281

fine Sandy Silt 2 0.55 1.8 17 108 0.11 450 1476 1000 3281

fine Sandy Silt 2 0.45 1.5 17 108 0.11 450 1476 1000 3281

fine Sandy Silt 2 0.55 1.8 17 108 0.11 450 1476 1000 3281

Sandy Clay 1 0.45 1.5 16 102 0.10 300 984 900 2953

Rock 3 22 140.05 0.14 3000 9842 3000 9842

13 C40 Gravel and Sandy Silt 1 0.82 2.69 15 95.487 0.10 250 820 1200 3937

Clayey Silt and Gravel 2 0.88 2.89 16 101.85 0.10 300 984 700 2297

Clayey Silt and Gravel 2 1.30 4.27 18 114.58 0.11 400 1312 700 2297

Clayey Silt 3 3.00 9.84 17 108.22 0.11 350 1148 750 2461

Sandy Silt 4 5.48 17.98 17 108.22 0.11 350 1148 900 2953

Plastic Clayey Silt 5 3.97 13.03 17 108.22 0.11 350 1148 750 2461

Rock 6 22 140.05 0.14 3000 9842 3000 9842

14 C296 Silty Sand Gravel and cobble mixed 1 0.90 2.9529 15 95.487 0.10 250 820 300 984

Gravel 2 1.50 4.9215 18 114.58 0.11 350 1148 1400 4593

Rock 3 7.00 22.967 20 127.32 0.13 1000 3281 2500 8202

22 140.05 0.14 3000 9842 3000 9842

Shear Modu.lus 2431


6188


Appendix C: Generalized Soil Profile Frequency Values

Frequency Hertz

Profile No 0.3 1 2 3 5

1 0.27 1.98 2.41 1.34 0.84

2 0.18 0.74 1.31 1.98 1.1

3 0.17 2.87 1.88 1.97 1.1

4 0.2 1.74 2.31 1.92 0.81

5 0.25 1.76 2.31 1.66 0.79

6 0.27 1.66 2.08 1.67 0.73

7

8 0.13 0.59 2.21 4.37 1.65

9 0.17 2.9 2.21 2.39 1.14

10 0.13 3.2 3 1.44 1.64

11 0.28 1.85 2.34 1.63 0.79

12 0.42 3.19 1.62 1.06 0.81

13 0.11 1.7 3.5 4.9 1.62

14 0.09 0.48 0.89 1.9 4.6

15 0.18 4.4 3.56 2.25 1.08

16 0.11 3.12 2.88 1.49 1.61

17 0.18 3.3 1.71 1.21 1.01

18 0.19 1.65 1.98 1.8 0.83

19 0.37 3.5 1.49 1.19 0.77

20 0.14 5.84 2.03 2.85 1.38

21 0.14 6.03 2.41 2.7 1.52

22 0.18 3.9 3.25 2.6 1.1

23 0.16 2.5 2.4 1.71 1.1

24 1.2 1.93 2.08 3.31 1.77

25 0.26 1.67 1.44 0.98 0.68


26 0.29 1.15 1.85 1.31 0.93

27 0.2 1.2 1.48 1.1 0.9

28 0.24 1.31 1.24 1.25 0.77

29 1.04 2.15 1.2 1.98 1.31

30 0.11 0.46 0.7 1.11 1.68

31 0.11 0.65 4.7 2.6 2.3

32 0.15 5.52 2.06 2.9 1.35

33 0.15 2.54 2.75 2.56 1.27

34 0.17 1.74 2 1.59 0.83

35 0.2 1.95 2.15 1.78 0.85

36 0.22 2.4 2.5 1.24 0.86

37 0.27 2.2 2.35 1.2 0.83

38 0.21 2.8 1.9 1.15 0.84

39 0.13 5.9 2.07 2.1 1.43

40 0.15 2.06 2.01 1.6 0.91

41 0.21 1.61 1.77 1.31 0.8

42 0.21 1.73 1.75 1.36 0.74

43 0.18 0.92 2.07 1.4 0.86

44 0.12 1.34 1.2 1.74 1.87

45 0.14 1.9 2.11 1.77 0.91

46 0.22 1.62 1.7 1.4 0.82

47 0.28 1.7 1.76 1.83 0.74

48 0.29 1.81 1.55 1.74 0.73

49 0.24 1.85 2.29 1.35 0.77

50 0.21 3.4 1.75 1.33 0.85

51 0.21 1.83 2.23 1.58 0.78

52 0.28 0.75 1.91 1.44 0.76

53 0.14 1.29 2.5 3.6 1.9

54 0.57 3.6 1.46 0.96 0.84

55 0.22 2.1 2.06 1.11 0.77


56 0.35 3.42 1.42 0.97 0.86

57 0.4 3.13 1.13 0.95 0.69

58 0.26 1.54 1.4 0.96 0.68

59 0.33 2.56 1.88 1.05 0.81

60 0.27 3.4 1.49 1.11 0.78

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