towards a reliable seismic microzonation in tehran,...

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Available at: http://www.ictp.it/ ~ pub_off IC/2006/104 (Revised) United Nations Educational, Scientific and Cultural Organization and International Atomic Energy Agency THE ABDUS SALAM INTERNAIONAL CENTRE FOR THEORETICAL PHYSICS TOWARDS A RELIABLE SEISMIC MICROZONATION IN TEHRAN, IRAN H. Hamzehloo International Institute of Earthquake Engineering and Seismology, Tehran, Islamic Republic of Iran, F. Vaccari and G.F. Panza Department of Earth Sciences, University of Trieste, Trieste, Italy and The Abdus Salam International Centre for Theoretical Physics, ESP Section, Trieste, Italy. Abstract A hybrid method for the calculation of realistic synthetic seismograms in laterally heterogeneous, anelastic media has been used to model the ground motion in Tehran city. The synthetic records compare reasonably well with the observed ground motion due to the 2004 Firozabad Kojor earthquake located 60 km north of Tehran. The ratio between the response spectrum for the signals calculated along a laterally varying structure, Sa(2D), and that for the signals at the bedrock regional reference structure, Sa(1D), shows a high amplification of seismic waves in Tehran. The procedure can be readily implemented for the entire Tehran city, which experienced large historical earthquakes in the past, simply by extending the analysis, made so far, in space and to different scenario earthquakes, consistent with the local and regional tectonics. MIRAMARE – TRIESTE December 2006

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Available at: http://www.ictp.it/~pub_off IC/2006/104 (Revised)

United Nations Educational, Scientific and Cultural Organization

and International Atomic Energy Agency

THE ABDUS SALAM INTERNAIONAL CENTRE FOR THEORETICAL PHYSICS

TOWARDS A RELIABLE SEISMIC MICROZONATION IN TEHRAN, IRAN

H. Hamzehloo

International Institute of Earthquake Engineering and Seismology, Tehran, Islamic Republic of Iran,

F. Vaccari and G.F. Panza Department of Earth Sciences, University of Trieste, Trieste, Italy

and The Abdus Salam International Centre for Theoretical Physics, ESP Section,

Trieste, Italy.

Abstract

A hybrid method for the calculation of realistic synthetic seismograms in laterally heterogeneous, anelastic media has been used to model the ground motion in Tehran city. The synthetic records compare reasonably well with the observed ground motion due to the 2004 Firozabad Kojor earthquake located 60 km north of Tehran. The ratio between the response spectrum for the signals calculated along a laterally varying structure, Sa(2D), and that for the signals at the bedrock regional reference structure, Sa(1D), shows a high amplification of seismic waves in Tehran. The procedure can be readily implemented for the entire Tehran city, which experienced large historical earthquakes in the past, simply by extending the analysis, made so far, in space and to different scenario earthquakes, consistent with the local and regional tectonics.

MIRAMARE – TRIESTE

December 2006

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1. Introduction

Tehran, the capital of Iran, is located in a very high seismic zone at the foot of the

Alborz Mountains, which is part of the Alpine-Himalayan seismic belt. The

distribution of historical earthquakes (Fig.1) around Tehran shows that the region has

been experiencing eight large destructive earthquakes with magnitude greater than 7

from 4th B.C to 1830 (Ambraseys and Melville, 1982). These large historical

earthquakes caused severe damage to Shahre Ray City, which is a part of Tehran city

at present (Table 1). The last large historical event was the 1830 earthquake with

magnitude 7.1, which occurred approximately 100 km from the city. The closest

historical event regaeding to the city was the 855 earthquake with magnitude 7.1. The

most important instrumental earthquakes, which occurred in this region, are the 1962

Buin Zahra earthquake with magnitude MW 7.2, the 2002 Changureh (Avaj)

earthquake with magnitude MW 6.5, and the 2004 Firozabad Kojor earthquake with

magnitude MW 6.3 (Table 1). The strong ground motion network in Tehran recorded

three large to strong earthquakes from 1990 to 2004. These records are related to the

1990 Manjil-Rudbar earthquake with magnitude MW=7.3, the 2002 Changureh (Avaj)

earthquake with magnitude MW=6.5 and the 2004 Firozabad Kojor earthquake with

magnitude MW=6.3 (Fig. 1).

The occurrence of large to strong earthquakes in Iran, which cause loss of life and

property (e.g. the 1978 Tabas, the 1990 Manjil- Rudbar and the 2003 Bam

earthquakes), makes one of the main goals of seismologists and earthquake engineers

to estimate the expected ground motion in a very high-seismicity zone like Tehran

city.

Different investigators have studied the microzonation of Tehran (e.g., JICA, 2000;

Jafari, 2002; Haghshenas 2005). The Japan International Cooperation Agency (JICA)

had studied seismic microzoning of the Greater Tehran area based on the location of

the scenario earthquakes on the Ray, Mosha and north Tehran faults (Fig.2). In that

study, based on the scenario earthquakes and fault model, the empirical Green’s

function method (Irikura and Kamae, 1993) was used to construct the waveform at the

bedrock. A small event with magnitude 3.9 (mb) which occurred on the Mosha fault

was considered as seed for the scenario earthquake ground motion (Fig.2). The

amplification of the subsurface was analysed using a one-dimensional response

analysis, based on the ground classification and soil properties. The waveform at the

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ground surface was then calculated from the waveform at the engineering bedrock and

by the subsurface amplification function (JICA, 2000).

Jafari (2002) investigated the microzonation of Tehran based on the estimation of

peak ground acceleration, which was estimated using a probabilistic earthquake

hazard analysis. Then, based on the analysis of refraction and down hole methods, the

shear wave velocity in the Tehran region has been estimated. The peak ground

acceleration at the surface has been calculated from the estimated peak acceleration at

the bedrock and the shear wave velocity at the surface. The probabilistic seismic

hazard analysis (PSHA) is, in general, based on the triple integration of magnitudes,

distances, and faults. Therefore a peak ground acceleration, which is calculated by

PSHA, is contributed by several faults at various distances and varies with the given

probability. The results are strongly influenced by variations of seismicity parameters,

sources and attenuation relationships. PSHA provides a scalar estimate of some

measure of shaking intensity (e.g. peak ground acceleration, response spectra,..), and

these estimates change every once in a while, as soon as new data, that show some

unexpected behavior become available. Klügel et al (2006), proposed a new

methodology based on the probabilistic interpretation of deterministic or scenario-

based hazard analysis. The scenario-based approach removes the ambiguity in the

results of probabilistic seismic hazard which relies on the projection of the Gutenberg-

Richter equation. Klügel (2007), based on a consistent interpretation of earthquake

occurrence as a stochastic process, demonstrates that the mathematical model of

Probabilistic Seismic Hazard Analysis (PSHA), as it is in use today, is inaccurate and

leads to systematic errors in the calculation process.

Haghshenas (2005) and Haghshenas et al., (2003) installed 13 temporary

seismological stations on geotechnically representative sites, from February to June

2002. Two stations were installed on the bedrock in the northern and south-eastern

parts of Tehran, a few on consolidated coarse grained deposits in the northern part,

and the rest in the southern part, which is covered with fine grained deposits. The

main objective of this study was the experimental estimation of the amplification

effect of the local soil (Haghshenas, 2005). In addition, the ambient noise was

recorded at more than 60 locations within the city. These noise data, plus the data of

more than 130 other sites recorded during previous microzonation projects by the

International Institute of Earthquake Engineering and Seismology (IIEES), were

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processed to help in the interpolation of the experimental transfer functions obtained

for the 13 seismological stations. Various experimental techniques were used by

Haghshenas (2005) to quantify the amplification and the prolongation of ground

motion: standard site/reference spectral ratio, receiver function, H/V spectral ratio on

noise, group delay method and sonogram. The results reveal a large site effect

affecting both the amplitude and duration of ground motion on the majority of the

studied sites. In particular, the south-western part of the city experiences an

amplification level reaching 7-8, contrasting with the moderate values (factor 2 to 3)

predicted in previous studies with a 1D approach (Jafari, 2002). In addition, this

amplification occurs on a very broad frequency band, starting at very low frequency

(0.3-0.4 Hz) (Haghshenas, 2005).

In this study, we simulate the seismic ground motions in Tehran along a north south

profile and compare the synthetic signals with the records of the 2004 Firozabad

Kojor earthquake (MW=6.3), which occurred at an epicentral distance of about 60 km.

We use a dense set of synthetic signals, calibrated against the few relevant records, to

draw some conclusions about local seismic wave amplification in Tehran.

2. Method

The computation of synthetic seismograms has been carried out by the hybrid method

see Panza, 1985; Panza and Suhadolc, 1987; Florsch et al., 1991; Panza et al., 2000;

Vaccari et al., 1989; Romanelli et al., 1996; Fah et al., 1993, 1994 . For a summary of

the international validation of the hybrid method, e.g. in the framework of UNESCO-

IUGS-IGCP projects, see Panza, et al. (2002.). In this method, synthetic signals are

first computed by the modal summation along the bedrock (1D) model, which is

defined as a stack of horizontal layers, each characterized by its thickness,

longitudinal and transversal wave velocity, density, and Q-factor, controlling the

anelastic attenuation. Then, these signals are numerically propagated through the

laterally varying local structure by the finite-difference scheme. The seismograms

were computed for frequencies reaching 10 Hz, and were subsequently filtered to f ≤6

Hz. These signals are numerically propagated through the laterally varying local

structure by the finite- difference grid is formed first, approximating the laterally

varying model. A grid step of 5 m is chosen, obeying the empirical condition that at

least 10 points per minimum wavelength are required. The resulting signals are used

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for the seismic microzoning, using as zoning criteria the "response spectra ratio"

(RSR), i.e., the spectral amplification defined by:

RSR=[Sa(2D)/Sa(1D)]

where Sa(2D) is the response spectrum (at 5% of damping) for the signals calculated

in the laterally varying structure, and Sa(1D) is the one calculated for signals at the

top of the counterpart bedrock regional reference structure.

The computation of synthetic seismograms has been carried out by the hybrid method

see Panza, 1985; Panza and Suhadolc, 1987; Florsch et al., 1991; Panza et al., 2000;

Vaccari et al., 1989; Romanelli et al., 1996; Fah et al., 1993, 1994 . For a summary of

the international validation of the hybrid method, e.g. in the framework of UNESCO-

IUGS-IGCP projects, see Panza, et al. (2002.). In this method, synthetic signals are

first computed by the modal summation along the bedrock (1D) model, which is

defined as a stack of horizontal layers, each characterized by its thickness,

longitudinal and transversal wave velocity, density, and Q-factor, controlling the

anelastic attenuation. Then, these signals are numerically propagated through the

laterally varying local structure by the finite-difference scheme. The seismograms

were computed for frequencies reaching 10 Hz, and were subsequently filtered to f ≤6

Hz. These signals are numerically propagated through the laterally varying local

structure by the finite- difference grid is formed first, approximating the laterally

varying model. A grid step of 5 m is chosen, obeying the empirical condition that at

least 10 points per minimum wavelength are required. The resulting signals are used

for the seismic microzoning, using as zoning criteria the "response spectra ratio"

(RSR), i.e., the spectral amplification defined by:

RSR=[Sa(2D)/Sa(1D)]

where Sa(2D) is the response spectrum (at 5% of damping) for the signals calculated

in the laterally varying structure, and Sa(1D) is the one calculated for signals at the

top of the counterpart bedrock regional reference structure.

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3. Structural Model

The urban area of Tehran has been developed on alluvial layers, accumulated on hard

rock. The uppermost geological formation basically represents the distribution of the

Pliocene and Quaternary alluvial and glacial deposits in the Tehran region. Seismic

structural models of Iran have been studied by different investigators (e.g. Giese et al.,

1984; Hatzfeld et al., 2003; Dehghani and Markis, 1984; Snyder and Barazangi,,

1986; Asudeh, 1982). Recently, the Turkish-Iranian plateau has been studied by

Maggi and Priestly (2005) using waveform tomography of surface waves. In this

study, we use the result of Maggi and Priestly (2005) to define the bedrock reference

model for the Tehran region.

The Turkish-Iranian plateau is characterized by Cong and Mitchell (1998) as having

relatively low shear wave velocities (VS) and high attenuation (Q<100 in the crust).

The information on Q variation within the Iranian plateau was obtained by studying

amplitude spectra of fundamental-mode and higher mode Rayleigh waves. In this

study we use the Q model defined by Cong and Mitchell (1998) for the bedrock

model, due to the lack of detailed information in the Tehran region.

4. Local structure model for Tehran

We consider the north-south profile in Tehran, as shown in Figure 3. The

classification of alluvial deposits according to Rieben (1966) has been used for the

description of layers (Table 2). Layer 1 is the youngest deposit, which is composed of

fine material such as silt and clay. The second layer includes conglomeratic young

alluvial deposits. Layer 3 essentially includes conglomeratic with a few lenses of

sandstone, siltstone and mudstone. Since no direct measurements are available along

the profile, the physical parameters of the local structure model have been considered

based on the results which have been estimated by Jafari (2002) and the Japan

International Cooperation Agency (JICA, 2000), as summarized in Table 2. Based on

the refraction method and the down-hole method VS has been estimated for north and

south Tehran. The geoseismic profile in the north of Tehran shows that VS is changing

from 250 m/sec to 700 m/sec, while VP is changing from 450 m/sec to 1200 m/sec

from the free surface to 25 m of depth (Jafari, 2002). The geoseismic profile in the

south of Tehran shows that VS is changing from 120 m/sec to 735 m/sec, while VP is

changing from 285 m/sec to 1410 m/sec from the free surface to 30 m of depth (Jafari,

2002). Fifty boreholes have been used to measure VS based on suspension PS logging

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method and down-hole PS logging method by JICA (2000). Based on this study, JICA

(2000) proposed a local structure model in the north-south direction in the west of

Tehran, which has been considered as a local structure for generating our synthetic

seismograms. This is the only detailed study about the local structure which was

available to us.

5. Results

On May 28, 2004, an earthquake with magnitude MW=6.3 occurred at about 60 km

north of Tehran and was strongly felt in the town. This earthquake was recorded by

the Building and Housing Research Center (BHRC) at 146 stations, of which 28

stations belong to the Tehran strong ground motion network. Figure 4 shows the

location of these stations and the location of the north-south profile we have

considered in this study. As can be seen from Figure 4, some of the BHRC stations

are located on or are very close to the north-south profile, and therefore have been

considered as a benchmarks of our modeling in this study. The focal mechanism

parameters of the 2004 Firozabad-Kojoe event, according to Harvard CMT are:

strike=119o, rake= 720 and dip=24o. These values have been used to compute with

the hybrid method and the synthetic seismograms, shown in Figures 5 to 7, along the

considered profile. We consider t33, t22, t23 and t35 stations for the comparison

between synthetic and observed signals at Azadi Hotel, Institute of Geophysics,

Building and Housing Research Center and Amir Kabir University, respectively.

These stations are in the free field or in one storey buildings. For some of the stations,

such as t9 at Yademan Tower, the data was not available. Stations t10, t2, t16, t29 are

located in multi storey buildings, others are quite far from the profile, as t11 and t30

stations. The comparison between observed and simulated records at the four stations,

t33, t22, t23 and t35, are shown in Figures 8 to 11. Figures 12 and 13 show the

comparison between observed and simulated response spectra at the same four

stations. The corresponding value of peak ground acceleration (P.G.A.), peak ground

velocity (P.G.V.) and peak ground displacement (P.G.D.) are given in Tables 3 to 5.

6. Discussions

Three component synthetic seismograms have been computed for a north-south

profile in Tehran city using, as source, the CMT focal mechanism of the 2004

Firozabad-Kojor earthquake. A quite reliable agreement can be seen between

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observed and simulated P.G.A., P.G.V. and P.G.D. (Tables 3 to 5). The differences

between observed and simulated signals can be reasonably explained by the

uncertainty in the geometry and physical parameters of the bedrock and the local

model, and are well within the range of uncertainties that can be dealt with by

Engineering Seismology and Seismic Engineering. A set of parametric tests, made

perturbing the mechanical properties of the uppermost part of the bedrock model,

show that the differences can be strongly reduced by a proper modification of the

mechanical properties of the uppermost layers of the bedrock model. However, since

a reliable comparison was obtained between observed and simulated transverse

components at t33, t22, t23 and t35 stations, we limit our discussion to the signals

obtained with the models shown in Table 2 and Fig. 3. In spite of the lack of

information about lateral variations of Q, P and S wave velocities for subsurface

layers, even a rough estimate of lateral structural parameters has been able to capture

most of the interesting features of the ground motion. This is not surprising if one

considers that to have an increment of one degree in macroseismic intensity, a

doubling of peak values is necessary. To get this doubling, from changes in structural

parameters, requires indeed the introduction of large variations.

With this validation of synthetic signals against the pertinent observations it is natural

to use the modeling to estimate possible local effects (amplifications/reduction) along

the entire profile. This can be done computing the ratio between the response

spectrum (at 5% of damping) of the signals calculated in the laterally varying

structure, Sa(2D), and the response spectrum (at 5% of damping) of the signals in the

bedrock regional reference structure, Sa(1D). This ratio, shown in Fig. 14, clearly

indicates that the Quaternary sediments severely amplify the seismic wave ground

motion (Fig.14) and that a detailed study of the entire urban area is necessary for a

reliable assessment of the earthquake hazard in Tehran. The amplification level

reaches 6, which is in agreement with the results obtained by Haghshenas (2005). In

the presence of a high-velocity contrast between the sediments and the underlying

bedrock, these local surface waves can be reflected several times at the edges of the

basin, resulting in a long duration of the ground shaking inside the basin (Bard and

Bouchon, 1980). The numerical results show that the existence of a large velocity

gradient within the sediment cover does not change significantly the qualitative

seismic behavior of the two-dimensional deposits: local surface waves and/or two-

dimensional resonance patterns are observed in the case of homogeneous sediments

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(Bard and Gariel, 1986). Panza et al., (2000) report that the highest values of the

spectral amplification and the largest damage in Rome, due to the Fucino 1915 event,

are observed in the Tiber river bed. This is caused by the large amplitudes and long

duration of ground motion due to 1) low impedance of the alluvial sediments, 2)

resonance effects, and 3) excitation of local surface waves. Similar conclusions are

given by Fah et al. (1994).

Clearly the location of Tehran with respect to active faults and the location of large

historical earthquakes suggest the most important earthquake sources for the city. As

these are large events, such earthquakes must have quite extended lengths and widths.

The estimated maximum credible earthquake (MCE) for faults around Tehran varies

in the range of 6.2 to 7.3 by considering the length of the faults. The estimations of

MCE and the reliable modeling results for the 2004 Firozabad Kojor earthquake

indicate that a very powerful way to make a model prediction of the seismic ground

motion, during a severe earthquake in the city, is to consider different scenario events,

and this will be the subject of a future paper, based on ongoing investigations.

7. Conclusions

The satisfactory comparison between observed and synthetic waveforms allowed us to

propose a possible pattern of amplification of seismic waves along a representative

north-south profile in the west part of Tehran. The high amplification in Tehran city

clearly indicates that a seismic microzonation map, based on the described

methodology, is necessary for sound and sustainable land use planning and for the

specifications of building codes and practice to be used by city planners and civil

engineers. Our results indicate that this very important preventive planning tool can

be readily implemented for Tehran city, which experienced large historical

earthquakes in the past, simply by extending the analysis, made so far, in space and to

different scenario earthquakes, consistent with the local and regional tectonics.

Acknowledgments

We are thankful to Prof. K.R. Sreenivasan, Director of The Abdus Salam International

Centre for Theoretical Physics, Trieste Italy, and Prof. Ghafory-Ashtiany, Director of

International Institute of Earthquake Engineering and Seismology, Tehran, Iran, for

providing the facilities for this research work. We are also thankful to the Building

and Housing Research Center for providing the strong ground motion data used in this

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study. We thank Mrs. D. Grilli of ICTP Publication Office for the careful revision of

the English.

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Vaccari, F., Gregersen, S., Furlan, M., and Panza, G.F., 1989. Synthetic seismograms

in Laterally heterogeneous anelastic media by modal summation of P-SV waves,

Geophys. J. Int. 99, 285-295.

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Table 1. The most important earthquakes around Tehran.

Date Long. Lat. Magnitude Dist. To City (km) 4th BC 51.8 35.5 7.6 50.0

743 52.2 35.3 7.2 94.0 855 51.5 35.6 7.1 25.0

January 864 51 35.7 5.3 31.0 23/2/958 51.1 36 7.7 32.0

10/12/1119 49.9 35.7 6.5 129.0 May 1177 50.7 35.7 7.2 57.7 15/8/1485 50.5 36.7 7.2 126.0

1495 50.5 34.5 5.9 160.7 20/4/1608 50.5 36.4 7.6 102.0

1665 52.1 35.7 6.5 69.0 3/2/1678 50 37.2 6.5 198.0

1678 52.6 36.3 6.5 127.0 16/12/1808 50.3 36.4 5.9 115.0

1809 52.5 36.3 6.5 120.0 1825 52.6 36.1 6.7 119.0

27/3/1830 52.5 35.7 7.1 105.0 1/8/1868 52.5 34.9 6.4 143.0

20/10/1876 49.8 35.8 5.7 138.0 1/9/1962 49.81 35.71 7.2 137.0

20/6/1990 49.41 36.96 7.4 225 22/6/2002 48.94 35.85 6.5 220.0 28/5/2004 51.61 36.29 6.3 61.0

Table 2. Geophysical properties of sediments.

Layer

ρ (gr/cm3)

VP (km/sec)

QP VS (km/sec)

QS

1 (silt and clay) 1.8 0.45 60 0.25 25 2 (congolomeratic young alluvial deposits)

1.9 0.90 70 0.6 30

3 (congolomerates with a few lenses of sandstone, siltstone and mudstone)

2.0 1.20 125 0.7 50

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Table 3. Observed and simulated peak ground acceleration (cm/sec2).

PGA (cm/sec2) Radial

PGA(cm/sec2) Transverse

PGA(cm/sec2) Vertical

Station

Obs. Syn. Obs. Syn. Obs. Syn. T33 24.3 14.1 20.6 29.9 18.8 13.5 T22 22.5 8.6 22.2 15.6 14.5 5.6 T23 12.1 8.7 8.7 14.2 11.2 7.6 T35 10.9 14.6 22.2 17.4 14.0 10.7

Table 4. Observed and simulated peak ground velocity (cm/sec).

PGV (cm/sec) Radial

PGV(cm/sec) Transverse

PGV (cm/sec) Vertical

Station

Obs. Syn. Obs. Syn. Obs. Syn. T33 1.6 0.85 2.5 2.7 2.1 1.1 T22 1.6 0.9 1.8 1.4 1.4 0.53 T23 1.4 0.93 1.3 1.3 1.4 0.84 T35 1.4 1.1 2.0 1.3 1.3 1.0

Table 5. Observed and simulated peak ground displacement (cm).

PGD (cm) Radial PGD (cm) Transverse PGD(cm) Vertical Station Obs. Syn. Obs. Syn. Obs. Syn.

T33 0.6 0.09 0.8 0.52 0.8 0.1 T22 0.5 0.11 0.5 0.25 0.5 0.05 T23 0.4 0.1 0.4 0.23 0.4 0.1 T35 0.3 0.1 0.3 0.22 0.3 0.1

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Fig.1 Historical and instrumental earthquakes around Tehran city.

Fig.2 The Mosha fault, North Tehran Fault (N.T.F) and Ray Fault (R.F) models and

location of small events used by JICA (JICA, 2002).

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Fig.3 Local structure model for the north-south profile in Tehran, considered in this

study.

Fig.4 Location of the recording stations for the 2004 Firozabad Kojor earthquake and

the North-south profile, considered in this study.

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Fig.5 Synthetic seismograms along the profile considered in this study for the

transverse component of motion. Acceleration (cm/sec2), velocity (cm/sec) and displacement (cm).

Fig.6 Synthetic seismograms along the profile considered in this study for the radial

component of motion. Acceleration (cm/sec2), velocity (cm/sec) and displacement (cm).

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Fig.7 Synthetic seismograms along the profile considered in this study for the vertical

component of motion. Acceleration (cm/sec2), velocity (cm/sec) and displacement (cm).

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Fig.8 Observed and synthetic acceleration (cm/sec2), velocity (cm/sec) and

displacement (cm) at T22 station.

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Fig. 9 Observed and synthetic acceleration (cm/sec2), velocity (cm/sec) and

displacement (cm) at T23 station.

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Fig.10 Observed and synthetic acceleration (cm/sec2), velocity (cm/sec) and

displacement (cm) at T33 station.

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Fig.11 Observed and synthetic acceleration (cm/sec2), velocity (cm/sec) and displacement

(cm) at T35 station.

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Fig.12 Observed (black) and simulated (grey) response spectra at T33 (top) and T22

(bottom) stations.

Fig.13 Observed (black) and simulated (grey) response spectra at T23 (top) and T35

(bottom) stations.

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Fig.14 Spectral amplification along the profile due to the 2004 Firozabad Kojor

Earthquake. From top to bottom: vertical component, radial component and transverse component.