urs site specific hazard analysis and development of earthquake

URS Site-Specific Seismic Hazard Analysis and Development of Earthquake Ground Motions for

the Anchorage Port Modernization Project, Alaska

Appendix E

F I N A L R E P O R T

SITE-SPECIFIC SEISMIC HAZARD ANALYSES AND DEVELOPMENT OF EARTHQUAKE GROUND MOTIONS FOR THE ANCHORAGE PORT MODERNIZATION PROJECT, ALASKA

Prepared for Municipality of Anchorage 632 W. 6th Avenue Anchorage, AK 99519-6650

21 November 2014

Ivan Wong, Patricia Thomas, Judith Zachariasen, Jacqueline Bott, and Fabia Terra

URS Corporation Seismic Hazards Group 1333 Broadway, Suite 800 Oakland, California 94612

26819091

TABLE OF CONTENTS

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Section 1 ONE Introduction ..................................................................................................................... 1-1 1.1 Scope of Work ......................................................................................... 1-1 1.2 Acknowledgments.................................................................................... 1-3

Section 2 TWO Seismic Hazard Analysis Methodology ........................................................................ 2-1 2.1 Seismic Source Characterization ............................................................. 2-2

2.1.1 Source Geometry ......................................................................... 2-2 2.1.2 Fault Recurrence .......................................................................... 2-3 2.1.3 Time-Dependent Model ............................................................... 2-4

2.2 Ground Motion Prediction Models .......................................................... 2-5

Section 3 THREE Seismotectonic Setting and Historical Seismicity ....................................................... 3-1 3.1 Seismotectonic Setting ............................................................................. 3-1 3.2 Historical Seismicity ................................................................................ 3-3

3.2.1 Pre-Instrumental Seismicity ......................................................... 3-3 3.2.2 Instrumental Seismicity ............................................................... 3-3 3.2.3 1964 Great Alaskan Earthquake .................................................. 3-4

Section 4 FOUR Seismic Source Characterization .................................................................................. 4-1 4.1 Crustal Faults ........................................................................................... 4-1

4.1.1 Crustal Faults In the Vicinity of the Port of Anchorage .............. 4-1 4.1.2 Neogene and Younger Faults In the Site Region ......................... 4-2 4.1.3 Neogene Faults Not Included In the Seismic Source

Characterization ........................................................................... 4-9 4.2 Crustal Background Seismicity................................................................ 4-9 4.3 Alaskan Subduction Zone ...................................................................... 4-11

4.3.1 Megathrust ................................................................................. 4-11 4.3.2 Wadati-Benioff Zone ................................................................. 4-14

Section 5 FIVE Ground Motion Prediction Models ................................................................................ 5-1 Section 6 SIX PSHA Results .................................................................................................................. 6-1

6.1 Hazard Results ......................................................................................... 6-1 6.2 Comparison With USGS National Hazard Maps..................................... 6-2 6.3 Comparison With 2008 Port Study .......................................................... 6-2

Section 7 SEVEN DSHA Results ................................................................................................................. 7-1 Section 8 EIGHT Development of Time Histories ..................................................................................... 8-1 Section 9 NINE References ...................................................................................................................... 9-1

TABLE OF CONTENTS

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Tables

1 Seismic Source Parameters for Faults in the Vicinity of the Port of Anchorage

2 Seismic Source Parameters for Alaskan Subduction Zone

3 Uniform Hazard Spectra

4 Modal M, D, and

5 Comparison of 2014 and 2008 Probabilistic Values in g’s

6 Seed Time Histories

7 Properties of Spectrally-Match Time Histories

Figures

1 Areal Image of Anchorage and Site Vicinity

2 Aleutian and Alaskan Subduction Zone and Large Historical Earthquakes (M 6.5), 1898 to 2014

3 Historical Seismicity and Significant Earthquakes (M 3.0), 1898 to 2014, Within 200 km of the Port

4 Brownian Passage Time Model

5 Seismic Hazard Model Logic Tree

6 Alaskan Subduction Zone

7 Isoseismal Map of the 28 March 1964 M 9.2 Great Alaska Earthquake

8 Neogene and Quaternary Faults Within 200 km of the Port Considered in the Hazard Analyses

9 Neogene and Quaternary Faults and Folds in the Cook Inlet Area

10 Stepp Plots for Estimating Completeness Intervals

11 Crustal Earthquakes Used in Recurrence Calculations 1988 to 2014

12 Crustal Background Earthquake Recurrence

13 Seismicity Cross-Section Through Alaskan Subduction Zone Near Anchorage

14 Preferred Model of Megathrust and Wadati-Benioff Zone Used in Hazard Analysis

15 Intraslab Earthquakes Used in Recurrence Calculations 1911 to 2014

16 Intraslab Earthquake Recurrence

17 Seismic Hazard Curves for Peak Horizontal Acceleration

18 Seismic Hazard Curves for 1.0 Sec Horizontal Spectral Acceleration

19 Seismic Hazard Curves for 3.0 Sec Horizontal Spectral Acceleration

20 Seismic Source Contributions to Mean Peak Horizontal Acceleration Hazard

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21 Seismic Source Contributions to Mean 1.0 Sec Horizontal Spectral Acceleration Hazard

22 Seismic Source Contributions to Mean 3.0 Sec Horizontal Spectral Acceleration Hazard

23 Sensitivity of Mean Peak Horizontal Acceleration Hazard to Time-Dependent Rates for Megathrust

24 Sensitivity of Mean 1.0 Sec Horizontal Acceleration Hazard to Time-Dependent Rates for Megathrust

25 Sensitivity of Mean 3.0 Sec Horizontal Acceleration Hazard to Time-Dependent Rates for Megathrust

26 Magnitude and Distance Contributions to the Mean Peak Horizontal Acceleration Hazard at 72-Year Return Period

27 Magnitude and Distance Contributions to the Mean Peak Horizontal Acceleration Hazard at 475-Year Return Period

28 Magnitude and Distance Contributions to the Mean Peak Horizontal Acceleration Hazard at 2,475-Year Return Period

29 Magnitude and Distance Contributions to the Mean 1.0 Sec Horizontal Spectral Acceleration Hazard at 72-Year Return Period


31 Magnitude and Distance Contributions to the Mean 1.0 Sec Horizontal Spectral Acceleration Hazard at 2,475-Year Return Period



34 Magnitude and Distance Contributions to the Mean 3.0 Sec Horizontal Spectral Acceleration Hazard at 2,475-Year Return Period

35 Sensitivity of the Peak Horizontal Acceleration Hazard From Crustal Sources to the Selection of Ground Motion Models

36 Sensitivity of the Peak Horizontal Acceleration Hazard From the Intraslab to the Selection of Ground Motion Models

37 Sensitivity of the Peak Horizontal Acceleration Hazard From the Megathrust to the Selection of Ground Motion Models

38 Sensitivity of the 3.0 Sec Horizontal Spectral Acceleration Hazard From Crustal Sources to the Selection of Ground Motion Models

39 Sensitivity of the 3.0 Sec Horizontal Spectral Acceleration Hazard From the Intraslab to the Selection of Ground Motion Models

40 Sensitivity of the 3.0 Sec Horizontal Spectral Acceleration Hazard From the Megathrust to the Selection of Ground Motion Models

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41 5%-Damped Uniform Hazard Spectra at 72, 475, and 2,475-Year Return periods

42 Sensitivity of Median and 84th Percentile Deterministic Spectra for M 7.5 Intraslab Event to Ground Motion Models

43 Sensitivity of Median and 84th Percentile Deterministic Spectra for M 9.2 Megathrust Event to Ground Motion Models

44 Median Deterministic Spectra for Intraslab and Megathrust Events Compared to UHS at 72, 475, and 2,475-Year Return Periods

45 Scaled Response Spectra for Seeds Used in Spectral Matching for Intraslab/Crustal Events for the 72-Year Return Period UHS

46 Scaled Response Spectra for Seeds Used in Spectral Matching for Intraslab/Crustal Events for the 475-Year Return Period UHS

47 Scaled Response Spectra for Intraslab Seeds Used in Spectral Matching for the 2,475-Year Return Period UHS

48 Scaled Response Spectra for Megathrust Seeds Used in Spectral Matching for the 2,475-Year Return Period UHS

49 Seed Time History – Horizontal 1997 Michoacan Earthquake Caleta De Campos Seed

50 Time Histories 2001 Nisqually Earthquake Kitsap County Airport, Bremerton (KIMR)

51 Time Histories 2001 Nisqually Earthquake Pierce County East Precinct, Puyallup (PCEP)

52 Seed Time Histories 2011 Tohoku Earthquake MYGH12 Seed

53 Seed Time Histories 2010 Maule Chile Earthquake Constitucion Seed

54 Response Spectra for Time History Spectrally Matched to 72-Year UHS Target 1997 Michoacan – Caleta De Campos (090) Seed

55 Time History Spectrally Matched to 72-Year UHS Target 1997 Michoacan – Caleta De Campos (090) Seed



58 Response Spectra for Time History Spectrally Matched to 72-Year UHS Target 2001 Nisqually – KIMR (ENE) Seed

59 Time History Spectrally Matched to 72-Year UHS Target 2001 Nisqually – KIMR (ENE) Seed

60 Response Spectra for Time History Spectrally Matched to 72-Year UHS Target 2001 Nisqually – KIMR (ENN) Seed

61 Time History Spectrally Matched to 72-Year UHS Target 2001 Nisqually – KIMR (ENN) Seed

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62 Response Spectra for Time History Spectrally Matched to 72-Year UHS Target 2001 Nisqually – PCEP (ENE) Seed

63 Time History Spectrally Matched to 72-Year UHS Target 2001 Nisqually – PCEP (ENE) Seed

64 Response Spectra for Time History Spectrally Matched to 72-Year UHS Target 2001 Nisqually – PCEP (ENN) Seed

65 Time History Spectrally Matched to 72-Year UHS Target 2001 Nisqually – PCEP (ENN) Seed





70 Response Spectra for Time History Spectrally Matched to 475-Year UHS Target 2001 Nisqually – KIMR (ENE) Seed

71 Time History Spectrally Matched to 475-Year UHS Target 2001 Nisqually – KIMR (ENE) Seed

72 Response Spectra for Time History Spectrally Matched to 475-Year UHS Target 2001 Nisqually – KIMR (ENN) Seed

73 Time History Spectrally Matched to 475-Year UHS Target 2001 Nisqually – KIMR (ENN) Seed

74 Response Spectra for Time History Spectrally Matched to 475-Year UHS Target 2001 Nisqually – PCEP (ENE) Seed

75 Time History Spectrally Matched to 475-Year UHS Target 2001 Nisqually – PCEP (ENE) Seed

76 Response Spectra for Time History Spectrally Matched to 475-Year UHS Target 2001 Nisqually – PCEP (ENN) Seed

77 Time History Spectrally Matched to 475-Year UHS Target 2001 Nisqually – PCEP (ENN) Seed

78 Response Spectra for Time History Spectrally Matched to 475-Year UHS Target 2001 Tohoku – MYGH12 (E) Seed

79 Time History Spectrally Matched to 475-Year UHS Target 2001 Tohoku – MYGH12 (E) Seed

80 Response Spectra for Time History Spectrally Matched to 475-Year UHS Target 2001 Tohoku – MYGH12 (N) Seed

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81 Time History Spectrally Matched to 475-Year UHS Target 2001 Tohoku – MYGH12 (N) Seed

82 Response Spectra for Time History Spectrally Matched to 2,475-Year UHS Target 1997 Michoacan – Caleta De Campos (090) Seed

83 Time History Spectrally Matched to 2,475-Year UHS Target 1997 Michoacan – Caleta De Campos (090) Seed

84 Response Spectra for Time History Spectrally Matched to 2,475-Year UHS Target 1997 Michoacan – Caleta De Campos (360) Seed

85 Time History Spectrally Matched to 2,475-Year UHS Target 1997 Michoacan – Caleta De Campos (360) Seed

86 Response Spectra for Time History Spectrally Matched to 2,475-Year UHS Target 2001 Nisqually – PCEP (ENE) Seed

87 Time History Spectrally Matched to 2,475-Year UHS Target 2001 Nisqually – PCEP (ENE) Seed

88 Response Spectra for Time History Spectrally Matched to 2,475-Year UHS Target 2001 Nisqually – PCEP (ENN) Seed

89 Time History Spectrally Matched to 2,475-Year UHS Target 2001 Nisqually – PCEP (ENN) Seed

90 Response Spectra for Time History Spectrally Matched to 2,475-Year UHS Target 2001 Tohoku – MYGH12 (E) Seed

91 Time History Spectrally Matched to 2,475-Year UHS Target 2001 Tohoku – MYGH12 (E) Seed

92 Response Spectra for Time History Spectrally Matched to 2,475-Year UHS Target 2001 Tohoku – MYGH12 (N) Seed

93 Time History Spectrally Matched to 2,475-Year UHS Target 2001 Tohoku – MYGH12 (N) Seed

94 Response Spectra for Time History Spectrally Matched to 2,475-Year UHS Target 2010 Maule, Chile – Constitucion (E) Seed

95 Time History Spectrally Matched to 2,475-Year UHS Target 2010 Maule, Chile – Constitucion (E) Seed

96 Response Spectra for Time History Spectrally Matched to 2,475-Year UHS Target 2010 Maule, Chile – Constitucion (N) Seed

97 Time History Spectrally Matched to 2,475-Year UHS Target 2010 Maule, Chile – Constitucion (N) Seed

Executive Summary

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At the request of the Municipality of Anchorage, URS Corporation has performed a site-specific probabilistic seismic hazard analysis (PSHA) and a deterministic seismic hazard analysis (DSHA) for the Anchorage Port Modernization Project. Maximum Considered Earthquake (MCE), Contingency Level Earthquake (CLE), and Operating Level Earthquake (OLE) ground motion parameters can be developed from these hazard results based on site response analyses. These three design earthquakes have corresponding exceedance probabilities of 2%, 10%, and 50% in 50 years or return periods of 2475, 475, and 72 years, respectively.

The Port of Anchorage is situated in one of the most seismically active regions in the U.S. The Alaskan subduction zone, which underlies the Port, is the source of the 1964 moment magnitude (M) 9.2 Great Alaskan earthquake. Intraslab earthquakes within the subduction zone and crustal faults such as the Castle Mountain fault will generate future strong ground shaking at the Port.

The primary objective of this study is to estimate the future levels of ground motions at the site that will be exceeded at the specified probabilities for the MCE, CLE, and OLE. Available geologic and seismologic data including inputs used in the U.S. Geological Survey’s (USGS) Alaska hazard maps (Wesson et al., 1999; 2007) have been used to evaluate and characterize potential seismic sources, the likelihood of earthquakes of various magnitudes occurring on those sources, and the likelihood of the earthquakes producing ground motions over a specified level. An unique aspect of PSHA is that we included a time-dependent model for the section of the Alaskan subduction zone megathrust that ruptured in 1964. A DSHA was also performed to compare with the PSHA results. Time histories for the three levels of design were developed based on the PSHA results.

Four types of seismic sources were included in the hazard analysis: 1) crustal faults, 2) crustal background seismicity, 3) the Alaskan subduction zone megathrust, and 4) the Wadati-Benioff zone. Probabilities of activity, fault dimensions and orientations, rupture characteristics, maximum magnitudes, recurrence rates/intervals, and recurrence models were assigned to each seismic source. There were a total of 12 crustal faults that were modeled including for example, the Castle Mountain-Caribou and Denali fault systems and several faults in Cook Inlet. The eastern section of the megathrust consisting of both the Prince William Sound/Western Yakutat and Kodiak segments was modeled as both segmented and unsegmented. The Semidi segment of the megathrust was also included in the analysis. The eastern section was modeled both time-dependently with a weight of 0.8 and time-independently with a weight of 0.2. The recurrence intervals were based on a robust paleoseismic record.

State-of-the-art ground motion prediction models were assigned to each seismic source. For crustal sources, we used the PEER Next Generation of Attenuation-West 2 models. For the subduction zone sources we gave 0.5 weight to the new model of Abrahamson et al. (2014b). Other models used were combinations of either Youngs et al. (1997), Zhao et al. (2006), or Atkinson and Boore (2003).

The products of the PSHA were hazard curves, deaggregation, and uniform hazard spectra (UHS). The hazard was calculated for a VS30 (time-averaged shear-wave velocity in the top 30 m) of 760 m/sec. The UHS are summarized in Table ES-1. The short-period hazard is controlled by the intraslab zone. At long periods, the intraslab zone controls at shorter return periods and the megathrust at longer return periods. A DSHA was also performed to calculate median and 84th percentile acceleration response spectra for a M 7.5 intraslab earthquake at a depth of 30 km

Executive Summary

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beneath Anchorage and a M 9.2 repeat of 1964 at a rupture distance of 35 km. A total of 11 pairs of horizontal time histories were developed for the three specified return periods.

The hazard results in this study are comparable to the results from the 2008 Port analysis except at a 2,475 year return period. At a return period of 72 years, the 2014 hazard is comparable to or slightly lower than in 2008. At 475 years, the 2014 results are 10% higher at short and moderate periods than in 2008 and about 20% lower at long period. For a return period of 2,475 years, the current short and moderate period hazard is 30% higher than in 2008 and about the same at long periods. The major updates in this study include the use of current state-of-art ground motion prediction models for both the crustal and subduction zone ground motion models, revision to the recurrence intervals, and time-dependent modeling of the megathrust. The downdip geometry of the megathrust was also updated and the uncertainties in the geometry were better incorporated into the PSHA than in 2008.

Table ES-1 Uniform Hazard Spectra in g’s

Spectral Period 72-Year Return Period

475-Year Return Period

2,475-Year Return Period

0.01 0.148 0.379 0.758 0.05 0.223 0.566 1.114 0.10 0.346 0.873 1.733 0.15 0.354 0.909 1.839 0.20 0.324 0.846 1.731 0.30 0.240 0.639 1.324 0.40 0.187 0.509 1.069 0.50 0.146 0.404 0.862 0.75 0.091 0.263 0.587 1.00 0.064 0.192 0.442 1.50 0.036 0.112 0.269 2.00 0.024 0.076 0.187 3.00 0.013 0.043 0.107 4.00 0.009 0.027 0.069 5.00 0.006 0.019 0.046 7.50 0.003 0.011 0.024 10.00 0.002 0.007 0.016

SECTIONONE Introduction

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1. Section 1 ONE Introduction

At the request of the Municipality of Anchorage, URS Corporation has performed a site-specific probabilistic seismic hazard analysis (PSHA) and a deterministic seismic hazard analysis (DSHA) for the Anchorage Port Modernization Project (Figure 1) and a firm rock site condition. Maximum Considered Earthquake (MCE), Contingency Level Earthquake (CLE), and Operating Level Earthquake (OLE) ground motion parameters can be developed from these hazard results based on site response analyses. These three design earthquakes have corresponding exceedance probabilities of 2%, 10%, and 50% in 50 years or return periods of 2475, 475, and 72 years, respectively.

The Port of Anchorage is situated in one of the most seismically active regions in the U.S. (Figures 2 and 3). The Alaskan subduction zone, which underlies the Port, is the source of the 1964 moment magnitude (M) 9.2 Great Alaskan earthquake (Figure 2). Intraslab earthquakes within the subduction zone and crustal faults such as the Castle Mountain fault will generate future strong ground shaking at the Port (Figure 3).

The primary objective of this study is to estimate the future levels of ground motions at the site that will be exceeded at the specified probabilities for the MCE, CLE, and OLE. Available geologic and seismologic data including inputs used in the U.S. Geological Survey’s (USGS) Alaska hazard maps (Wesson et al., 1999; 2007) have been used to evaluate and characterize potential seismic sources, the likelihood of earthquakes of various magnitudes occurring on those sources, and the likelihood of the earthquakes producing ground motions over a specified level. An unique aspect of PSHA is that we included a time-dependent model for the section of the Alaskan subduction zone megathrust that ruptured in 1964. A DSHA was also performed to compare with the PSHA results. Time histories for the three levels of design were developed based on the PSHA results.

1.1 SCOPE OF WORK The previous seismic hazard analyses of the Port was completed in April 2007 by URS (Wong et al., 2008). In June 2013, a site-specific seismic hazard analysis was performed by URS (2013) for the Port Access Bridge for the Alaska Department of Transportation and Public Facilities. The following are the tasks required to meet the objectives of the updated analyses for the Port.

Task 1 – Seismic Source Characterization

The seismic source model used for the Port Access Bridge (URS, 2013) was reviewed and updated. The seismic source model includes all local and regional faults significant to the site in terms of ground shaking hazard. The USGS is currently updating their model for the 2015 Alaska hazard maps. We communicated with researchers working on the seismotectonics, seismicity, and active faulting in the site region including scientists from the USGS and Alaska Geological Survey (AGS) to assess whether our 2013 model needed to be updated. The fault parameters that need to be defined in order to characterize an active (seismogenic) fault for ground motion hazard assessments include: the geometry and rupture dimensions of the fault; the size of the maximum earthquake; the nature (style) and amount of slip on the fault expected for the maximum earthquake; and the rate and nature of earthquake recurrence.



Task 2 – Evaluation of Historical and Contemporary Seismicity

The regional historical seismicity catalog was updated with seismicity data from the AGS. We updated our earthquake recurrence rates for the Wadati-Benioff zone (intraslab) and crustal background seismicity.

Task 3 – Selection of Ground Motion Prediction Models

State-of-the-art ground motion prediction models were selected for the three types of seismic sources considered in the PSHA: subduction zone megathrust and intraslab, and crustal faults. The recently released Pacific Earthquake Engineering Research Center (PEER) NGA (Next Generation of Attenuation) West2 models for crustal earthquakes not used in the 2007 Port study were used in this study. Recent models for subduction zones were reviewed and selected for use in the PSHA and DSHA.

Task 4 – Probabilistic and Deterministic Seismic Hazard Analyses

Based on our regional seismic source model and ground motion prediction models, we calculated site-specific probabilistic ground motions for 2%, 10%, and 50% probabilities of exceedance in 50 years (return periods of 2475, 475, and 72 years for the MCE, CLE, and OLE, respectively). The hazard was calculated for a firm rock site condition (NEHRP B/C 760 m/sec). The PSHA methodology used in this study allows for the explicit inclusion of the range of possible interpretations in components of the seismic hazard model, including seismic source characterization and ground motion estimation. Epistemic uncertainties in models and parameters are incorporated into the hazard analysis through the use of logic trees. Horizontal Uniform Hazard Spectra (UHS) at 5% damping were calculated. The hazard was deaggregated at peak ground acceleration (PGA), 1.0, and 3.0 sec to characterize the controlling earthquakes.

Deterministic response spectra for maximum earthquakes on the intraslab zone and megathrust were calculated for a firm rock site condition. The probabilistic and deterministic spectra were compared. We also compared our PSHA results with the 2007 USGS National Hazard Maps.

Task 5 – Development of Time Histories

We developed 11 sets of three-component acceleration time histories for the 2,475, 475, and 72-year return period UHS for use in site response analysis to develop the MCE, OLE, and CLE spectra. The specific number of sets and type for each design level were selected based upon the hazard deaggregation results. The seed time histories were actual strong motion records such as from the 2011 Tohoku-Oki, Japan earthquake.

Task 6 – Final Report

A draft final report that described the analysis approach and summarized the results of the study was produced and transmitted for review. Review comments will be addressed and a Final Report will be produced.



1.2 ACKNOWLEDGMENTS Our appreciation to Don Anderson of CH2MHill and Todd Cowles of the Port of Anchorage for their support of this study. The seismic hazard analyses were performed by the following personnel of URS Corporation:

Seismic Source Characterization Judith Zachariasen, Jacqueline Bott, and Ivan Wong

PSHA Patricia Thomas and Ivan Wong

Development of Time Histories Jacqueline Bott and Fabia Terra

Report Preparation Ivan Wong, Patricia Thomas, Jacqueline Bott, and Fabia Terra

Ivan Wong served as the URS Project Manager. Out thanks to Melinda Lee and Deb Fournier for their assistance in preparing this report.

SECTIONTWO Seismic Hazard Analysis Methodology


2. Section 2 TWO Seismic Hazard Analysis Methodology

The PSHA approach used in this study is based on the model developed principally by Cornell (1968). The occurrence of earthquakes on a fault is assumed to be a Poisson process. The Poisson model is widely used and is a reasonable assumption in regions where data are sufficient to provide only an estimate of average recurrence rate (Cornell, 1968). When there are sufficient data to permit a real-time estimate of the occurrence of earthquakes, the time-dependent probability of exceeding a given value can be modeled as an equivalent Poisson process in which a variable average recurrence rate is assumed. The occurrence of ground motions at the site in excess of a specified level is also a Poisson process, if (1) the occurrence of earthquakes is a Poisson process, and (2) the probability that any one event will result in ground motions at the site in excess of a specified level is independent of the occurrence of other events.

The probability that a ground motion parameter "Z" exceeds a specified value "z" in a time period "t" is given by:

p(Z > z) = 1-e-(z)•t (2-1)

where (z) is the annual mean number (or rate) of events in which Z exceeds z. It should be noted that the assumption of a Poisson process for the number of events is not critical. This is because the mean number of events in time t, (z)•t, can be shown to be a close upper bound on the probability p(Z > z) for small probabilities (less than 0.10) that generally are of interest for engineering applications. The annual mean number of events is obtained by summing the contributions from all sources, that is:

(z) = n n(z) (2-2)

where n(z) is the annual mean number (or rate) of events on source n for which Z exceeds z at the site. The parameter n(z) is given by the expression:

n(z) = i j ßn(mi)•p(R=rj|mi)•p(Z>z|mi,rj) (2-3)

where:

ßn(mi) = annual mean rate of recurrence of earthquakes of magnitude increment mi on source n;

p(R=rj|mi) = probability that given the occurrence of an earthquake of magnitude mi on source n, rj is the closest distance increment from the rupture surface to the site;

p(Z > z|mi,rj) = probability that given an earthquake of magnitude mi at a distance of rj, the ground motion exceeds the specified level z.

The calculations were made using the computer program HAZ38 developed by Norm Abrahamson. This program has been validated in the Pacific Earthquake Engineering Research (PEER) Center-sponsored “Validation of PSHA Computer Programs” Project (Thomas et al., 2010).



2.1 SEISMIC SOURCE CHARACTERIZATION Two types of earthquake sources are characterized in this PSHA: (1) fault sources; and (2) areal source zones (Section 4). Fault sources are modeled as three-dimensional fault surfaces and details of their behavior are incorporated into the source characterization. Areal source zones are regions where earthquakes are assumed to occur randomly. Seismic sources are modeled in the hazard analysis in terms of geometry and earthquake recurrence.

The geometric source parameters for faults include fault location, segmentation model, dip, and thickness of the seismogenic zone. The recurrence parameters include recurrence model, recurrence rate (slip rate or average recurrence interval for the maximum event), slope of the recurrence curve (b-value), and maximum magnitude. Clearly, the geometry and recurrence are not totally independent. For example, if a fault is modeled with several small segments instead of large segments, the maximum magnitude is lower, and a given slip rate requires many more small earthquakes to accommodate a cumulative seismic moment. For areal source zones, only the areas, seismogenic thickness, maximum magnitude, and recurrence parameters (based on the historical earthquake record) need to be defined.

Uncertainties in the seismic source parameters as described below, which were sometimes large, were incorporated into the PSHA using a logic tree approach (Figure 4). In this procedure, values of the source parameters are represented by the branches of logic trees with weights that define the distribution of values. A sample logic tree is shown on Figure 4. In general, three values for each parameter were weighted and used in the analysis. Statistical analyses by Keefer and Bodily (1983) indicate that a three-point distribution of 5th, 50th, and 95th percentiles weighted 0.185, 0.63, and 0.185 (rounded to 0.2, 0.6, and 0.2), respectively, is the best discrete approximation of a continuous distribution. Alternatively, they found that the 10th, 50th, and 90th percentiles weighted 0.3, 0.4, and 0.3, respectively, can be used when limited available data make it difficult to determine the extreme tails (i.e., the 5th and 95th percentiles) of a distribution. Note that the weights associated with the percentiles are not equivalent to probabilities for these values, but rather are weights assigned to define the distribution. We generally applied these guidelines in developing distributions for seismic source parameters with continuous distributions (e.g., Mmax, fault dip, slip rate or recurrence) unless the available data suggested otherwise. Estimating the 5th, 95th, or even 50th percentiles is typically challenging and involves subjective judgment given limited available data.

2.1.1 Source Geometry In the PSHA, it is assumed that earthquakes of a certain magnitude may occur randomly along the length of a given fault or segment. The distance from an earthquake to the site is dependent on the source geometry, the size and shape of the rupture on the fault plane, and the likelihood of the earthquake occurring at different points along the fault length. The distance to the fault is defined to be consistent with the specific ground motion prediction model used to calculate the ground motions. The distance, therefore, is dependent on both the dip and depth of the fault plane, and a separate distance function is calculated for each geometry and each ground motion model. The size and shape of the rupture on the fault plane are dependent on the magnitude of the earthquake; larger events rupture longer and wider portions of the fault plane. We modeled the rupture dimensions for fault sources following the magnitude-rupture area and rupture-width relationships of Wells and Coppersmith (1994). However, this relationship gives very large and



unrealistic aspect ratios for large magnitude events (M > 8). For the megathrust, the relations were modified to give aspect ratios of two for large magnitude events while resulting in similar aspect ratios as those of Wells and Coppersmith (1997) at M 7.

2.1.2 Fault Recurrence The recurrence relationships for the faults are modeled using the truncated-exponential, characteristic earthquake, and the maximum magnitude recurrence models (Section 4.1.1). These models are weighted (Figure 4) to represent our judgment on their applicability to the sources. For the areal source zones, only a truncated-exponential recurrence relationship is assumed to be appropriate.

We have used the general approach of Molnar (1979) and Anderson (1979) to arrive at the recurrence for the truncated-exponential model. The number of events exceeding a given magnitude, N(m), for the truncated-exponential relationship is

N(m)= (m )10 -10

1-10o

-b(m-m ) -b( m -m )

-b( m -m )

o u o

u o (2-4)

where (mo) is the annual frequency of occurrence of earthquakes greater than the minimum magnitude, mo; b is the Gutenberg-Richter parameter defining the slope of the recurrence curve; and mu is the upper-bound magnitude event that can occur on the source. A mo of M 5.0 was used for the hazard calculations because smaller events are not considered likely to produce ground motions with sufficient energy to damage well-designed structures.

We have included the model where faults rupture with a "characteristic" magnitude on specific segments; this model is described by Aki (1983) and Schwartz and Coppersmith (1984). For the characteristic model, we have used the numerical model of Youngs and Coppersmith (1985). In the characteristic model, the number of events exceeding a given magnitude is the sum of the characteristic events and the non-characteristic events. The characteristic events are distributed uniformly over a + 0.25 magnitude unit around the characteristic magnitude, and the remainder of the moment rate is distributed exponentially using the above equation with a maximum magnitude 0.25 unit lower than the characteristic magnitude (Youngs and Coppersmith, 1985).

The maximum magnitude model can be regarded as an extreme version of the characteristic model. We adopted the model proposed by Wesnousky (1986). In the maximum magnitude model, there is no exponential portion of the recurrence curve, i.e., events are modeled with a normal distribution about the characteristic magnitude with a sigma of 0.25. The distribution is truncated at 0.5 units above the characteristic magnitude.

The recurrence rates for the fault sources are defined by either the slip rate or the average return time for the maximum or characteristic event and the recurrence b-value. The slip rate is used to calculate the moment rate on the fault using the following equation defining the seismic moment:

Mo = A D (2-5)



where Mo is the seismic moment, is the shear modulus, A is the area of the rupture plane, and D is the slip on the plane. Dividing both sides of the equation by time results in the moment rate as a function of slip rate:

oM = A S (2-6)

where oM is the moment rate and S is the slip rate. Mo has been related to moment magnitude, M, by Hanks and Kanamori (1979):

M = 2/3 log Mo - 10.7 (2-7)

Using this relationship and the relative frequency of different magnitude events from the recurrence model, the slip rate can be used to estimate the absolute frequency of different magnitude events.

The average return time for the characteristic or maximum magnitude event defines the high magnitude (low likelihood) end of the recurrence curve. When combined with the relative frequency of different magnitude events from the recurrence model, the recurrence curve is established.

2.1.3 Time-Dependent Model In contrast to the Poisson model, a time-dependent renewal process model embodies the expectation that after one earthquake on a fault segment, another earthquake on that segment is unlikely until sufficient time has elapsed for stress to gradually re-accumulate. Such models require a minimum of two parameters, and typically include knowledge of the time of the most recent rupture. One is the mean recurrence interval, μ = λ, and the other describes the variability of recurrence intervals and can be related to the variance, 2 of the distribution. (For the Poisson distribution, =μ). We define this variability of recurrence times as the aperiodicity or COV, =/μ.

The BPT model (Matthews et al., 2002) is a renewal model that describes the statistical distribution of rupture times. The BPT distribution is also known as the inverse Gaussian distribution. The probability density is defined by

exp } (2-8)

and is illustrated on Figure 5 for a mean rate of 1 and a suite of aperiodicity values. The exponential (Poisson) is shown for comparison. The hazard function (instantaneous failure rate), hBPT(t), is always zero at t = 0. It increases to achieve a maximum value at a time greater than the mode of fBPT(t), and from there decreases toward an asymptotic value of hBPT(t) Figure 5b). Thus, a BPT process always attains a finite quasi-stationary state in which the failure rate is independent of elapsed time. For an aperiodicity of 0.5, this quasi-stationary state is reached by 1.5 times the mean recurrence rate. After that point, conditional probabilities will not continue to increase (Figure 5d). When the aperiodicity = 1/2, the asymptotic failure rate is 1/μ, which equals the asymptotic failure rate for a Poisson process with the same μ. In practice, the behavior of a BPT model is similar to that of a delayed Poisson



process, for which the failure rate is zero up to a finite time following an event and then steps up to an approximately constant failure rate at all succeeding times.

The behavior of a BPT model depends strongly on the value of . For smaller values of , fBPT(t) is more strongly peaked and remains close to zero longer. For larger values, the “delay” or “dead time” becomes shorter, fBPT(t) becomes increasingly Poisson-like, and its mode decreases. The hazard function in the quasi-stationary state increases with decreasing values of and becomes Poisson-like with increasing values (Figure 5b).

Equivalent Poisson rupture rates can be back-calculated from the BPT rupture probabilities by solving for an equivalent Poisson rupture rate which produces the same rupture probability using the Poisson model. Equivalent Poisson rates can be used in the standard PSHA methodology to compute time-dependent hazard.

2.2 GROUND MOTION PREDICTION MODELS To characterize the ground motions at a specified site as a result of the seismic sources considered in the PSHA, we used empirical ground motion prediction equations (models) for spectral accelerations. The models used in this study were selected on the basis of the appropriateness of the site conditions and tectonic environment for which they were developed (Figure 4; Section 4.2).

The uncertainty in ground motion prediction models was included in the PSHA by using the lognormal distribution about the median values as defined by the standard deviation associated with each model. Three standard deviations about the median value were included in the analysis.

SECTIONTHREE Seismotectonic Setting and Historical Seismicity


3. Section 3 THREE Seismotectonic Setting and Historical Seismicity

The seismotectonic setting and historical seismicity of the site region are described below.

3.1 SEISMOTECTONIC SETTING Anchorage is in one of the most seismically active parts of the United States (Figures 2 and 3). Earthquakes in southern Alaska result primarily from interactions between the Pacific and North American plates (Figure 6). Northwestward motion of the Pacific plate relative to the North American plate is accommodated by subduction of the Pacific plate at the Aleutian megathrust and by dextral transform faulting in southeastern Alaska on the Queen Charlotte and Fairweather fault zones (Figure 6). Most damaging earthquakes in Alaska have occurred on the main megathrust zone plate boundary interface (Figure 2). Zoback and Zoback (1991) state that the direction of maximum principal stress in the Aleutian subduction zone area is north-northwest, consistent with the direction of relative motion between the Pacific and North American plates. Convergence across the Aleutian trench in the eastern part of the subduction zone, where Anchorage lies, occurs at a rate of about 5.4 cm/yr, and transform motion occurs at a slightly slower rate across the transform boundary to the southeast (Demets and Dixon, 1999). The eastern end of the subduction zone is complex because of the change from subduction, where the plates converge nearly perpendicularly, to the transform boundary defined by the Queen Charlotte and Fairweather fault zones (Figure 6).

Earthquakes occur in several settings within the Aleutian subduction zone: (a) bending-moment normal fault events in the Pacific plate near and seaward of the trench, (b) interplate (megathrust) earthquakes that have a maximum depth of seismic coupling of about 35 to 40 km (Tichelaar and Ruff, 1993), (c) within the down-going slab (Wadati-Benioff zone) to depths of about 150 km in the Gulf of Alaska region (Davies and House, 1979), and (d) within the upper North American plate, north of the plate interface. Davies and House (1979) and Tichelaar and Ruff (1993) argue that low levels of seismicity in the megathrust zone to about 40 km depth suggest that these shallow zones are dominated by great earthquakes and their aftershocks, with little inter-event seismicity. Conversely, the Wadati-Benioff zone below about 40 km shows relatively continual seismicity. Earthquakes within the Pacific plate, south of the Aleutian trench, are relatively rare.

Figure 2 shows subduction zone and other large Alaskan earthquakes since 1898. It is clear from this figure that most large historical earthquakes in the area are related to the subduction zone. The Aleutian subduction zone experienced four great earthquakes in the twentieth century, including three of the largest earthquakes of the century (Figure 2). The 1964 M 9.2 Great Alaskan earthquake (Figure 7), which was centered near the northern margin of Prince William Sound, was a subduction zone megathrust earthquake (Section 3.2.3). Dip-slip fault movement of as much as 20 m and a related tsunami accompanied the 1964 earthquake. Surface deformation was noted over a zone about 350 km wide (Plafker, 1969; Carver and Plafker, 2008).

The Queen Charlotte-Fairweather fault system forms the dextral transform boundary between the Pacific and North American plates to a latitude of about 57.75 degrees (Figure 6). Several large historical earthquakes have occurred along these faults, including the 1949 M 8.1 Queen Charlotte earthquake, the 1972 M 7.4 Sitka earthquake, and the 1958 M 7.7 Lituya earthquake.

The subduction and transform systems meet in an area of collision in southern Alaska centered on what Perez and Jacob (1980) call the Yakutat block (Figure 6). In this region, the Aleutian trench shallows and the plate boundary turns southeast. The Transition fault forms the boundary



of the Yakutat block with the Pacific plate (Figure 6). The Yakutat block is tightly coupled to the Pacific plate; it moves northeastward at about 5 cm/yr in a direction about 10 to 20 degrees to the west (counterclockwise) of the Pacific plate’s direction. Northeast of the Transition fault, the Yakutat block is separated from the Saint Elias block on the east by the northern extent of the Fairweather fault (Plafker et al., 1994) (Figure 6). The eastern part of the block is underthrusting beneath the North American continent along a series of thrust and oblique-slip faults that sole into the Yakutat décollement, which is largely creeping (Elliott, 2011). In the northwestern part of the Yakutat block, the décollement feeds into the megathrust along which the western Yakutat block is subducting beneath the North American plate. The buoyant Yakutat block subducts at a shallow dip angle and may be welded to and subducting with the Pacific plate (Brocher et al., 1994).

Large historical earthquakes (e.g., 1899 and 1979) have occurred in the Yakutat block. Plafker and Thatcher (2008), analyzing uplift data, argue that the September 1899 sequence of three large (ca. M 7-8) earthquakes occurred on a complex system of north-dipping thrust and oblique-slip faults within the Yakutat block. Their modeled slip is extremely large for crustal faults, so it may involve slip on the deeper décollement surface. Doser (2006) suggested that the 4 September 1899 earthquake occurred on the Pamplona fault zone, which forms part of the deformation front between the Yakutat block and southern Alaska (Lahr and Plafker, 1980; Worthington et al., 2008; Elliott, 2011).

The 2002 M 7.9 Denali earthquake, which was a crustal event, was the largest earthquake to affect onshore areas of the U.S. since the 1906 San Francisco earthquake. The epicenter of the Denali earthquake was north-northeast of Anchorage, near where the strike of the Denali fault changes from northwest to northeast (Figure 3). The Denali fault defines the northeast boundary of the Saint Elias block, and farther to the north it separates the Wrangell block from the North American plate (Plafker et al., 1994). The Denali fault is predominantly a right-lateral strike slip fault. The Totschunda fault system is a right-lateral splay of the Denali fault that separates the Saint Elias and Wrangell blocks (Plafker et al., 1977; 1994a). The 2002 Denali earthquake resulted from rupture of the central Denali fault and the western Totschunda fault. To the north and west, the Denali fault curves to a more westerly and then southwesterly strike. At the longitude of Anchorage it strikes to the southwest. The Castle Mountain and Lake Clark faults are southeast of and roughly parallel to the Denali fault (Figure 6).

Bruhn and Haeussler (2006) use earthquake focal mechanisms and north- to northeast-trending structures in the Cook Inlet area to define a model of dextral transpression for the Cook Inlet area. In their model, collision and subduction of the Yakutat block is responsible for driving the Chugach and Kenai Mountains toward the Alaska Range, and the Castle Mountain fault allows the ranges to escape westward (Figure 6). Around the times of great earthquakes when the subduction zone plates are tightly locked, the stress field in the crust rotates from its present orientation, with maximum compression trending to the east, to compression oriented to the northwest. The Castle Mountain fault serves as the northern right-lateral fault in this model and numerous fold and fault-cored fold axes trend north-northeast to the south of this fault in the Cook Inlet area (Bruhn and Haeussler, 2006).



3.2 HISTORICAL SEISMICITY The Aleutian subduction zone experienced four great earthquakes in the 20th century, including three of the largest earthquakes of the century. From east to west, these included the 1964 Great Alaskan earthquake (M 9.2), the 1938 earthquake off the Alaska Peninsula (M 8.2), the 1957 Andreanof earthquake (M 9.1), and the 1965 Rat Island earthquake (M 8.7) (Figure 2).

3.2.1 Pre-Instrumental Seismicity Instrumentation in Alaska was sparse prior to the 1964 Great Alaskan earthquake. At the time there were only two instruments: one at Sitka, installed in 1904, and one at the University of Alaska at Anchorage, installed in 1935. After the M 9.2 event, four more instruments were put in, creating the regional network in central and southern Alaska (Page et al., 1991). In 1967 the Alaska Tsunami Warning Center was established, with six instruments, to respond to the pressing need for detecting potentially tsunamigenic earthquakes (Page et al., 1991).

There have been a total of 212 documented earthquakes above M 5.0 within 200 km of Anchorage (Figure 3). Three pre-instrumental earthquakes within 200 km of the Port of Anchorage have been larger than M 7.0. The 14 July 1899 M 7.2 and 19 September 1909 M 7.4 earthquakes occurred within 25 km of one another, approximately 140 km south of the site (Figure 3). The events occurred on the Kenai Peninsula, in the proximity of the Kenai lineament. An event occurred on 31 Jan 1912 M 7.0 within 15 km of the 1964 earthquake, approximately 130 km east of the site (Figure 3).

3.2.2 Instrumental Seismicity The 1964 earthquake introduced the need for more instrumentation in the Alaska region, including the Aleutian Islands. By the early 1970’s continental Alaska had over 40 instruments. With the onset of oil exploration in the late 1970’s, there were at least four 17-station regional networks in operation at one time (Page et al., 1991). There are currently about 203 stations in the Alaska Regional Seismic Network (ARSN); 182 operated by the Alaska Volcano Observatory, 18 by the West Coast and Alaska Tsunami Warning Center, and 3 by IRIS (ARSN, 2008). From 1996 to 2014 there were more than 2,500 earthquakes above M 3.0 within 200 km of the site (Figure 3).

There have been three events above M 7.0, within 200 km of the site recorded with modern instrumentation (Figure 3). The 4 May 1934 M 7.1 earthquake occurred within 25 km of the 1964 earthquake where severe shaking was felt in the town of Tyonek (Stover and Coffman, 1993). The ground shaking lasted 45 seconds and awakened people in Anchorage. The event was also felt in Cordova (Neumann, 1936). The closest large earthquake to the site occurred 90 km northwest of the Port. The 3 November 1943 M 7.4 earthquake was felt in Anchorage, McGrath, and Bethel (Figure 3). In Anchorage, doors swung and windows rattled (Bodle, 1945). In Bethel, the community closest to the epicenter, the ground shaking lasted 20 seconds and buildings swayed. Ice from nearby frozen lakes and streams cracked for an hour after the shock (Bodle, 1945).

The closest significant earthquake, 20 km southwest of the site, occurred on 25 June 1951 (Figure 3). This M 6.3 earthquake caused light fixtures to sway, parked cars to jump, and containers to fall from top shelves (Murphy and Cloud, 1953). The local radio station reported



that the phonographs rolled out of their files. The event was also felt in Cordova, Palmer and Spenard, where the strongest shaking was felt (Murphy and Cloud, 1953).

The most recent significant earthquake, the M 7.9 Denali earthquake, occurred on 3 November 2002. The Denali earthquake ruptured 320 km of the central Denali fault and part of the Totschunda fault (Carver et al., 2004). Modified Mercalli (MM) intensity V was felt in the vicinity of Anchorage. This corresponds to an approximate peak horizontal acceleration of 0.04 to 0.09 g using the relationship of Wald et al. (1999).

3.2.3 1964 Great Alaskan Earthquake The Great Alaskan earthquake of 28 March 1964 M 9.2 was one of the most violent earthquakes on record and is the second largest earthquake ever recorded (Kanamori, 1977). The earthquake was felt over 1.8 million square kilometers in Alaska, and the Yukon Territory and British Columbia, Canada (Figure 7; Hake and Cloud, 1966). Rupture initiated about 100 km east of Anchorage along the Prince William Sound asperity (e.g., Christensen and Beck, 1994; Johnson et al., 1996). The source mechanism for the 1964 earthquake is sinistral reverse slip with a displacement of about 20 m. The maximum resulting surface displacements were on the order of 10 m in Prince William Sound with smaller amounts of subsidence on the Kenai Peninsula towards Anchorage (Plaflker, 1969).

The greatest amount of damage from the earthquake occurred in Anchorage, which recorded an Modified Mercalli (MM) intensity VIII (Figure 7). Numerous landslides, rockslides and avalanches were triggered from the strong ground shaking in the area. In addition, fractures and cracking developed in unconsolidated deposits, while mud spouts, slumping, and boils were observed in areas of compaction (Hake and Cloud, 1966). Observers in Anchorage documented shaking lasting between 4 to 5 minutes. There were 15 deaths attributed to the earthquake and another 113 following the tsunami (USGS, 2008). The most destruction was attributed to four major landslides, two of which were near the site: L Street (approximately 3 km south of the site), and 2) and Turnagain Heights (approximately 6 km south of the site). The L Street slide was over 244 m wide and 0.8 km long with shearing at the base, causing buildings to slide off foundations and buildings at the head of the slide to topple over (Hake and Cloud, 1966). The Turnagain Heights slide was larger, 300 m by 2.4 km, leaving a 15 m vertical scarp. Over 70 homes were destroyed by the slide at Turnagain Heights (Hake and Cloud, 1966).

SECTIONFOUR Seismic Source Characterization


4. Section 4 FOUR Seismic Source Characterization

The following describes the seismic sources considered in the seismic source analyses including crustal faults, crustal background seismicity, and the Alaskan subduction zone (megathrust and Wadati-Benioff zone).

4.1 CRUSTAL FAULTS Crustal faults near Anchorage and in the site region included in the seismic source model are described below. Neogene faults that were not included are also discussed in this section.

4.1.1 Crustal Faults in the Vicinity of the Port of Anchorage In order to identify active and potentially active crustal faults in the vicinity of the site, we relied on the Neotectonic Map of Alaska (Plafker et al., 1994), and where appropriate, supplemented this compilation with additional published sources to include other faults and structures not included in the Plafker et al. (1994) map (Table 1; Figures 8 and 9). A relatively new Quaternary fault and fold database for Alaska has been published online by the Alaska Division of Geological and Geophysical Surveys (DGGS) (Koehler, 2013) and also reviewed it for new information. In contrast to the National Seismic Hazards Mapping Program (NSHMP) seismic hazard maps for Alaska (Wesson et al., 2007), which only includes the Castle Mountain fault as a potential near-field seismic source, we have expanded the number of seismic sources to include potentially active Quaternary faults capable of M ≥ 6.5 within 200 km of the Port (Figures 8 and 9). Of particular importance are several Quaternary-active and potentially Quaternary-active structures within the Cook Inlet (Table 1; Figure 9) that may significantly contribute to the seismic hazard of the Anchorage area (Haeussler et al., 2002). Although Wesson et al. (2007) recognized the existence of these structures, they did not include them in the 2007 seismic hazard map due to insufficient data. Our review of the literature also concludes that these faults are poorly understood. However, because of their potential to cause earthquakes of significant size that could impact the Port, we include them in our model, adopting many of the source parameters of Haeussler et al. (2002), which currently represents the best available science for the purposes of site-specific seismic hazards.

In certain cases, we also include Neogene faults within 200 km of the site if they are judged to be potentially active (Table 1; Figures 8 and 9). Our criteria include: 1) whether the fault is in a favorable orientation within the present stress regime to accommodate ongoing deformation; 2) if the fault is on-strike with another active structure; and 3) if there is adequate resolution in the geomorphology and geologic mapping to identify evidence of active faulting. This is particularly difficult to assess, because we did not conduct a geomorphic or geologic analysis of the faults ourselves. However, it is apparent that many of the existing studies are reconnaissance in nature (Hauessler and Saltus, 2004), and it is possible that subtle expressions indicative of active faulting have been missed. In order to accommodate this uncertainty, but also honor the consensus that these faults are not active, we generally assign a lower probability of activity to these faults. In our model, these considerations are applied to two faults: the Bruin Bay fault and the Lake Clark fault (Table 1; Figure 8). Finally, we include features labeled “suspicious” by Plafker et al. (1994) if they are judged to be in an orientation similar to other active faults in the region and have long enough mapped traces to warrant inclusion as a potentially significant seismic source. These features are also assigned a lower probability of activity in order to



account for the uncertainty that they may not have been active in the Quaternary. Finally, although the Denali fault lies outside of the 200 km radius surrounding Anchorage (Figure 8), we have included it due to its potential to generate large, M > 7.5, earthquakes (Table 1).

Preferred maximum magnitudes were calculated using the empirical relationship between magnitude and surface rupture length of Wells and Coppersmith (1994) and fault rupture area and magnitude of Hanks and Bakun (2002), weighted equally. Rupture depth in the Anchorage region is based on observations of shallow crustal earthquakes that show that the depth of seismicity is about 20 km (Lahr et al., 1986; Flores and Doser, 2005). For the Denali fault, we estimate a shallower depth of 15 km. An uncertainty of 5 km is used for seismogenic depths (Table 1). For crustal fault recurrence models, we weighted the characteristic, maximum magnitude, and truncated-exponential models 0.6, 0.3, and 0.1, respectively (Figure 5). The fault parameters used in the PSHA are listed in Table 1.

4.1.2 Neogene and Younger Faults in the Site Region

Bruin Bay Fault

The Bruin Bay Fault extends 515 km from its intersection with the Castle Mt –Lake Clark fault along the west side of Cook Inlet and into the Aleutian Peninsula (Figures 8 and 9). This fault has a reverse sense of motion and is regarded as a Late Tertiary fault, with a stratigraphic throw of 3 km (Nockleberg et al., 1994). The fault dips 45° to the northwest (Haeussler et al., 2000). Detterman et al. (1976) found no evidence of Holocene activity for the 115-km-long section of the fault southwest of the Castle Mountain fault and also note that a late Tertiary or Quaternary volcanic plug is not offset. Schmoll and Yehle (1987) did not find any evidence of activity along the Bruin Bay fault during the late Pleistocene of Holocene.

Despite the lack of demonstrable Quaternary activity along the Bruin Bay fault, we include it in our seismic source model due to its similar orientation to active structures in the Cook Inlet, suggesting that it is in a favorable orientation to accommodate strain in the compressional regime that currently dominates the Cook Inlet region. However, because there are no geomorphic observations that support Quaternary activity, we assign a probability of activity of 0.5 in order to account for the possibility that the fault may not be active (Table 1). Our preferred maximum magnitude is M 7.0 and is based on the historical record of seismicity that includes earthquakes approaching this magnitude (Table 1). Given the moderate dip of the fault and depth of seismicity in the region, it is possible that an earthquake of this magnitude on the Bruin Bay fault would be blind and not rupture the surface. This is an additional reason we give this fault some probability of being active even though it does not appear to have recent surface expression. There are no Quaternary slip rate estimates available for this fault. We assign a preferred slip rate of 0.1 mm/yr with large uncertainties (Table 1). This slip rate implies relatively long recurrence intervals and a level of activity that is low enough that geomorphic evidence of fault activity at the surface would be obscured in this environment.

Castle Mountain – Caribou Fault System

The Castle Mountain – Caribou Fault System extends about 180 km from the Copper River Basin to the Susitna Lowlands (Figures 8 and 9). Haeussler et al. (2002) describe the fault as having two parts a western and an eastern segment: the western segment of the fault includes a



62-km-long section with Holocene fault scarps, located between Houston and the Susitna River; Detterman et al. (1974) referred to this as the Susitna section. The western segment of the fault extends another 31 km west of the Susitna section and shows no evidence of Holocene activity. The 87-km-long eastern segment of the fault, which includes Detterman et al.'s (1976) Talkeetna section, shows evidence of Pleistocene activity, but no geologic evidence of Holocene activity (Detterman et al., 1974, Plafker et al., 1994). However, in contrast to the seismically quiescent western section of the fault, the eastern section has experienced two historical earthquakes, in 1984 and 1996. The 1984 M 5.7 Sutton Alaska earthquake had a right-lateral focal mechanism and occurred on a 75°, north-dipping fault plane at a depth of < 17 km (Lahr et al., 1986). The 1996 M 4.6 earthquake, located east of the 1984 earthquake also had a right-lateral focal mechanism (Haeussler et al., 2002). Neither of these earthquakes ruptured the surface.

We consider two rupture models in our seismic source model for the Castle Mountain fault (Table 1). We give high weight (0.8) to a segmented model, which is based on the paleoseismic data that shows that the western Castle Mountain fault has failed repeatedly during the Holocene, while the most recent activity of the eastern Castle Mountain fault is Latest Pleistocene. This is consistent with the tectonic model of the Castle Mountain fault and faults in the Cook Inlet of Haeussler et al. (2002), which would suggest that the eastern part of the Castle Mountain fault may not be entirely within the regime of dextral transpression between the Kenai-Chugach Mountains Block and the Alaska Range, implying a lower slip rate and level of activity. A lesser weight is given to an unsegmented Castle Mountain fault rupture that allows for the entire 180 km of the fault to rupture. While the paleoseismic data suggests that this mode of failure is not common, the activity of both segments during the late Quaternary and the relatively simple trace of the fault suggests that such a rupture is not inconceivable.

Maximum magnitudes for the two rupture models are shown in Table 1. If the entire 211 km of the fault were to rupture in a single event, an unlikely scenario, the maximum magnitude would be M 7.7 0.3.

Geologic data suggest a dextral-reverse oblique sense of slip for the fault, consistent with the focal mechanisms of the two historical earthquakes noted above, but the dominant sense of slip is debated. The fault is marked by a consistent north-side-up scarp. Detterman et al. (1974) state that late Tertiary movement is primarily dip-slip, with older movement dominantly dextral, but acknowledge the possibility of recent dextral slip. They report a 7-m dextral offset of a Holocene sand ridge on the Susitna section. Hauessler et al. (2002) dug nine trenches across the fault and found clear evidence for reverse faulting in most of them, with less robust evidence for some component of strike-slip faulting. Willis et al. (2007) assert that the fault is dominantly dextral, with a component of reverse slip. A seismic reflection profile across the fault indicates reverse slip causing shortening but does not resolve lateral slip (Hauessler et al., 2000). More recently, Koehler et al. (2011b) analyzed LiDAR data along the Castle Mountain fault and concluded that, based on scarp morphology and the absence of significant lateral offset of early Holocene channels, the fault has had primarily reverse motion, at least in the Holocene. The recent work interprets the offset sand ridge as a sand dune with no offset (R. Koehler, pers. comm., December 2011). We consider the fault as a dextral-reverse oblique fault in the source model.

The western section of the Castle Mountain fault is the only fault near Anchorage (Figure 9) with paleoseismic data that provides information on recurrence and slip rate. Detterman et al. (1974)



report that a 2.1-m-high scarp on the Susitna section was caused by an inferred 2.3 m of dip slip on a 75-degree north-dipping reverse fault with an unknown component of lateral slip. They constrained the age of offset to between about 200 and 1850 BP. Haeussler et al. (2002) conducted a paleoseismic trenching study in the central part of the fault and concluded, based on exposures of faulting and liquefaction features, that the main fault has ruptured three times during the past 2100 years, with an average recurrence of about 700 years between earthquakes. They report an additional event on a splay fault at about 2700 cal BP. The timing of the most recent event (MRE), about 600-700 years ago, led Haeussler et al. (2002) to suggest that a M 6 to 7 earthquake along the Castle Mountain fault may be likely in the near future. Koehler et al. (2011) question if there have been multiple late Holocene events on the western segment of the fault. Their LiDAR and field analysis suggests only one event has formed the Holocene scarp, given the lack of beveling along the scarp that might be expected on a multi-event scarp. This is consistent with the earlier work of Detterman et al. (1974) which found evidence for only one event in the past 1800 years. The event history compiled from trenches reported in Hauessler et al. (2002) was developed largely from paleoliquefaction features rather than directly from faulting relationships. Some of these features may have been caused by earthquakes on other faults than the Castle Mountain fault (R. Koehler, pers. comm., December, 2011).

The slip rate on the Castle Mountain fault is also uncertain and debated. Hauessler et al. (2002) report a post-glacial dip-slip rate on the main fault in a trench of 0.07 to 0.14 mm/yr. They conclude that there must be a substantial unknown component of strike-slip to explain the 700-year average recurrence interval. If, as Koehler et al. (2011) suggest, there have not been three earthquakes in the last 2100 years, the inference about lateral slip is no longer supported. Willis et al. (2007) used a latest Pleistocene channel margin, offset about 36 m, to provide a right-lateral slip rate of 2.9 ± 0.8 mm/yr, with a preferred rate of 3.1 ± 0.1 mm/yr. As noted above, Koehler et al. (2011b) used LiDAR data and field observations and concluded that there was no appreciable lateral offset of numerous abandoned Holocene stream channels and terrace margins. Thus they suggest that the Holocene lateral slip rate may be much lower than suggested by Willis et al. (2007). Koehler and Reger (2011) calculate a rate of 0.45 to 0.63 mm/yr for the fault, closer to the long-term slip rate of about 0.5 mm/yr indicated by Hauessler and Saltus (2004) and Fuchs (1980).

We include both recurrence interval and slip rate to reflect earthquake recurrence rates on the western Castle Mountain fault (Table 1). Because of the conflicting interpretations regarding the number of late Holocene events on the fault, coupled with the fact that the events in the Hauessler et al. (2002) trenches are identified largely from liquefaction features rather than faulting relationships, we assign higher weight (0.8) to the slip rate method (Table 1). The slip rate distribution reflects the diversity of opinion in the literature regarding the amount of Holocene displacement on the fault, with weight fairly evenly divided between the low slip rates inferred from an interpretation of minimal lateral offset of Holocene features (e.g. Koehler et al., 2011b) and higher slip rates inferred from an interpretation of significant offset of a latest Pleistocene channel (Willis et al., 2007).

Denali Fault

The Denali fault system is a zone of right-lateral faulting that extends in a broad arc across south-central Alaska (Figures 6 and 8) and accommodates relative motion between North America and the Yakutat Block to the south. This fault system has at least 38 km of total offset



during the past 38 m.y. (Reed and Lanphere, 1974) and geomorphic evidence of Holocene activity is clear along much of the fault (Plafker et al., 1977). Historically, the most notable large earthquake along the fault is the 2002 M 7.9 Denali fault earthquake that ruptured about 320 km of the central Denali fault and part of the Totschunda fault (Eberhart-Phillips et al., 2003; Figure 3). A M 7.2 to 7.4 earthquake in 1912 is also thought to have ruptured the central Denali fault (Carver et al., 2004; Figure 3).

Since the 2002 earthquake, new research has provided slip rates along the central Denali fault and shows that the late Pleistocene – Holocene slip rate is as much as 13.0 ± 2.9 mm/yr at longitude ~144.8° W and decreases westward to 9.4 ± 1.6 at longitude ~148.6° W and about 6.7 ± 1.2 mm/yr at longitude ~149.4° W (Meriaux et al., 2009; Matmon et al., 2006). This slip rate gradient is due to the partitioning of slip from the Denali fault to thrust faults north and west of the Denali fault (Matmon et al., 2006). Although the Denali fault system has been mapped extending through western Alaska to the Bering Sea, the end of the active fault is regarded to be at about 154.7° W (Wesson et al., 2007).

Because of its potential to produce M 7.9 earthquakes such as the 2002 earthquake, we include it in our model as a seismic source (Table 1). Our seismic source model considers the three segments of the Denali fault closest to Anchorage (Table 1). We adopt a segmentation scheme that is modified from Plafker et al. (1994). The westernmost segment of the Denali fault is the 140 km-long Farewell segment (Figure 8). There is very little information in the published literature regarding the slip rate of this section of the fault and there is no paleoseismic data available that constrains the timing of the most recent event or recurrence of this section of the fault. We have assigned a preferred slip rate to this segment of 6.4 mm/yr, which is the average of the nearest available Late Pleistocene – Holocene slip rate (6.7 mm/yr, Meriaux et al., 2004) and the long-term slip rate of about 6 mm/yr, which is obtained from a pluton offset 38 km along the fault (Reed and Lanphere, 1974) and an assumption that activity on the Denali fault began around the time that Mt McKinley was uplifted, about 6 Ma (Plafker et al., 1992) (Table 1). The central 122 km-long Tonzona – Muldrow segment bisects the Alaska Range, and many of the highest peaks, including Mt McKinley, are located south of this segment of the fault. Due to much of the fault being under glacial cover, very little is known about the fault, and Plafker et al. (1994) show this segment of the fault as “suspicious” in terms of its activity. Given the lack of data, we assign it the same slip rate distribution as the Farewell segment (Table 1).

The easternmost segment we consider in the seismic source model is the Muldrow-Alsek segment (Figure 8; Table 1). This segment is modified from what appears on the map of Plafker et al. (1994). While the western extent of the segment remains the same, we have defined the eastern end of this segment as the westernmost extent of rupture during the 2002 Denali fault earthquake, for a total segment length of 150 km. In addition to being a segment boundary defined by the 2002 earthquake, the segment boundary is also a geometric segment boundary, where the fault changes strike from northeast-striking to the west to more west-northwest-striking along the section that ruptured during the 2002 earthquake. This is also the only segment of the Denali fault in our seismic source model with robust slip rate data, which range from as much as about 10.5 mm/yr along the eastern-most part of this section (Matmon et al., 2006) to about 6.7 mm/yr in the central part (Meriaux et al., 2009). We adopt an average rate of about 8.5 mm/yr and a distribution between 6 and 11 mm/yr in our seismic source model to represent the slip rate for this segment of the fault (Table 1).



Preliminary results of paleoseismic studies along the section of the fault west of the 2002 rupture suggest that the MRE was relatively recent based on geomorphically fresh fault scarps. The MRE occurred between 100 and 370 years before the 2002 rupture and the penultimate event occurred between 550 and 680 years before 2002, suggesting that the fault has a recurrence interval on the order of several hundred years between large earthquakes (Schwartz et al., 2005; Koehler et al., 2011c).

We consider three rupture models in our seismic source model and, due to a lack of paleoseismic data to better constrain the rupture models, we have weighted each equally (Table 1). An unsegmented model that ruptures all three segments of the fault is considered because there is little paleoseismic data available to constrain the location and extent of past ruptures along the three segments included in our model. The slip rate distribution for this model is centered on the average of the late Pleistocene rate of 6.7 mm/yr obtained from the westernmost site of Meriaux et al. (2009) and the long-term rate of about 6 mm/yr, as noted described above for the Farewell segment (Table 1). The maximum is the preferred latest Pleistocene rate at the eastern end of the fault of about 9.4 mm/yr (Matmon et al., 2006) and the minimum is 3 mm/yr, reflecting an average value over the full length of the fault assuming the slip rate decreases to near zero at the western end. Furthermore, at the scale of the map by Plafker et al. (1994), there are no large geometric discontinuities that would suggest any kind of segmentation along the western Denali fault. The maximum rupture length of 410 km for the combined three segments is also similar to other large strike-slip ruptures such as the 1906 earthquake, which ruptured about 420 km of the northern San Andreas fault in California (Lawson, 1908). The maximum magnitude for this scenario is estimated at M 8.1 0.3.

The second rupture model is a segmented model and is based on the segmentation depicted in terms of fault activity on the map of Plafker et al. (1994) (Table 1). We do not favor this model over the other rupture models because there is considerable uncertainty about whether the Tonzona-Muldrow segment is an individual rupture segment. As classified by Plafker et al. (1994), this segment is labeled as “suspicious”. Much of this segment is under the cover of glaciers or in rugged terrain that would make a comparison of relative activity to the adjacent segments difficult. For this reason, we assign this rupture scenario an equal weight relative to the other models. Maximum magnitudes of the segments are similar at M 7.5 to 7.6 0.3. Slip rates in this model are as described above for each segment (Table 1). For the Farewell and Tonzona-Muldrow segments, which have poorly constrained slip rates, the maximum slip rate is the rate at the eastern end of the fault (Matmon et al., 2006) and the minimum rate is assigned to be 1 mm/yr, reflecting the possible decrease of faulting to zero at the western end.

Our third model is a M 7.9 earthquake that is allowed to float anywhere along the three segments (Table 1). We use the 2002 Denali fault earthquake, which ruptured about 320 km of the central Denali fault, as an analog to a rupture that could occur along the western Denali fault. In the case of the 2002 rupture, it has been implied that the endpoints of the rupture were largely controlled by the timing of the most recent event along the unruptured parts of the fault adjacent to the 2002 rupture (Schwartz et al., 2005). Because there is little information about the timing and frequency of earthquakes along the three segments included in our seismic source model, we consider this a viable rupture model and give it equal weight relative to the other rupture models (Table 1). The slip rate in this model is similar to that on the Farewell and Tonzona-Muldrow segments.



Lake Clark Fault

The 247 km-long Lake Clark fault is a right-oblique fault that extends from its intersection with the Bruin Bay and Castle Mountain faults to Lake Clark (Figures 8 and 9). It is on strike with, and has been proposed as a continuation of the Castle Mountain fault, but is considered to have a lower rate of activity that that fault. The slip rate on the fault is poorly constrained. A 5 km offset of a 38.6 Ma intrusive suggests a slip rate of around 0.1 mm/yr (Reed and Lanphere, 1972; Plafker et al., 1975). Haeussler and Saltus (2004), however, interpret aeromagnetic data to indicate that the fault has moved a total of 26 km right laterally since 34 to 39 Ma, giving a long term strike-slip rate of 0.7 mm/yr. More recent reconnaissance mapping of the eastern section of the fault and surrounding glacial deposits by Koehler and Reger (2011) indicates that the fault has not offset Naptowne (11 to 30 ka) glacial deposits. They also found no definitive evidence for faulting of penultimate (marine isotope stage [MIS]4) glacial deposits (ca. 60 to 75 ka). However, convex-up stream profiles along two fault-crossing rivers suggest possible vertical displacement since MIS4. In addition, MIS4 drift appears to blanket a pre-existing scarp, suggesting that older deposits may be faulted. Koehler and Reger (2011) state that MIS6 drift (ca. 130 to 180 ka) may be offset.

Haeussler and Saltus (2004) suggest that post-late Tertiary deformation along the Castle Mountain fault is transferred to the transpressional structures in Cook Inlet, perhaps explaining the lack of Late Tertiary and younger deformation on the Lake Clark fault. Reconnaissance studies by Plafker et al. (1974; 1975) found no evidence for offset glacial features and concluded that the fault was active during the Neogene (Plafker et al., 1994). However, Schmoll and Yehle (1987) report some evidence for Pleistocene movement, but no Holocene movement along the fault near its intersection with the Castle Mountain Fault.

Although the available geologic literature regards the Lake Clark fault as a fault with little or no Quaternary deformation, we include it in our seismic source model because: 1) it is on strike with the Holocene-active Castle Mountain fault, making it a possible extension of that fault and 2) although the fault is classified by Plafker et al. (1994) as a Neogene structure, Schmoll and Yehle (1987) report contradictory evidence of Quaternary activity along the eastern-most section of the fault. We have assigned a lower probability of activity (0.7) to this fault to account for the possibility that it has not been active during the Quaternary (Table 1). We include segmented and unsegmented rupture models for the Lake Clark fault. However, we prefer a model that allows an M 7.0 earthquake to float along the fault (Table 1). This magnitude is favored based on historical seismicity in the Cook Inlet region (Flores and Doser, 2005), which has experienced earthquakes of about this magnitude. We also feel that an earthquake of this size best represents the maximum magnitude that would rupture the surface and produce the observations of Quaternary deformation observed by Schmoll and Yehle (1987) along a limited section of the fault.

We assign a slip rate distribution to reflect the uncertainty in activity level and the wide range of possible slip rates based on the sparse studies to date, with a lower preferred rate, which allows for activity but ensures that earthquakes are infrequent enough to explain the lack of evidence for active faulting along this fault (Table 1). We adopt a preferred rate of 0.1 mm/yr, with some weight to a very low rate of 0.01 mm/yr to reflect the lack of clear late Quaternary activity and to the high long-term slip rate of 0.7 mm/yr (Table 1).



Parker Lake Fault

Little is known about this short, ~16 km-long fault that is classified by Plafker et al. (1994) as a suspicious feature (Figure 8). Due to a similar northeast strike to other active faults in the region, we assign this fault an oblique right-lateral-reverse sense of motion. We assign this fault a probability of activity of 0.5 with a preferred slip rate of 0.1 mm/yr with large uncertainties (0.01 – 1 mm/yr) to account for the many unknowns related to this largely unstudied feature (Table 1). The maximum magnitude if the fault were to rupture is M 6.5 0.3.

Pass Creek – Dutch Creek Fault

This largely unstudied 68-km-long fault zone is classified as Late Pleistocene-active by Plafker et al. (1994) (Figure 8). We assume this fault is right-lateral-reverse due to a similar orientation to the Denali fault, which suggests that it may accommodate right-lateral motion in the region. Because the fault bounds the southern part of the Alaska Range, the fault may accommodate reverse motion as well. There is no published slip rate information available for this fault. Similar to our treatment for other faults in the region without any estimates of slip rate, we assign a preferred slip rate of 0.1 mm/yr, with large uncertainties (0.01 to 1 mm/yr) (Table 1). The maximum magnitude is estimated at M 7.2 0.3.

Unnamed Fault Near Palmer

This 56-km-long feature is classified as “suspicious” by Plafker et al. (1994) (Figure 8). Because of a trend that is essentially parallel to the Castle Mountain fault, we consider this a potentially active feature and assign it a right-lateral-reverse sense of motion and a probability of activity of 0.5 (Table 1). There are no slip rate data available for this fault, so we assign it our preferred default slip rate of 0.1 mm/yr for faults in the model that do not have a published slip rate (Table 1). The maximum magnitude is M 7.1 0.3.

Cook Inlet Folds

While little is known about these faults in the Cook Inlet, the proximity of these structures to the Port of Anchorage make them, next to the Castle Mountain fault, the closest shallow crustal seismic sources (Figure 9). Haeussler et al. (2000) suggest that these faults may present a greater short-term hazard than 1964-type subduction zone earthquakes. Our source characterization includes structures capable of M ≥ 6.5 earthquakes and identified by Haeussler et al. (2000) as Quaternary-active or potentially Quaternary-active. We also include the Turnagain Arm structure because it is the closest potentially Quaternary-active structure to the site (Figure 9). Because very little additional information about these structures exists with which to characterize them, we mostly adopt the source parameters of Haeussler et al. (2000), who measured the structure lengths in their dataset and used the magnitude versus rupture length relationships of Wells and Coppersmith (1994) to calculate preferred earthquake moment magnitudes. In some instances, where the on-trend continuity of two or more structures suggests they have a potential to rupture together, we have combined the structures and calculated a preferred maximum magnitude. Haeussler et al. (2000) note that, although the base of the seismogenic crust may be as deep as 35 km, they do not believe that these faults extend to this depth. For this reason, we did not attempt to calculate a preferred maximum magnitude using alternate methods such as magnitude vs. area relationships, and believe that the magnitudes of Haeussler et al. (2000) are the most reasonable estimates available given the sparse data.



Slip rates are unknown for most of the structures in Cook Inlet. Using assumptions of the start of deformation in the region and balanced cross-sections, Haeussler et al. (2000) calculated slip rates for the North Cook Inlet, Middle Ground Shoal and Granite Point structures. Although Haeussler et al. (2000) indicate some preference for their higher estimates of the slip rates, we find the 2.72 mm/yr slip rate calculated for the Middle Ground Shoal and Granite Point structures to be too high, making them comparable to the Castle Mountain fault in terms of activity. Instead, we prefer slip rate estimates that are based on a 5.3 Ma start of deformation, but give some weight (0.2) to both their lower and upper bounds (Table 1). Slip rates for structures without any data are assigned on a case-by-case basis and discussed in Table 1.

4.1.3 Neogene Faults Not Included in the Seismic Source Characterization Several potential faults or structures in the vicinity of Anchorage that appear on the map of Plafker et al. (1994) are not included as seismic sources on Table 1. These structures are discussed below.

Little Susitna River Scarp

This mapped structure is not included because it is likely that this feature is a fluvial terrace riser. This interpretation is based on the presence of a similar, opposite facing feature located on the other side of the Susitna River that suggests a fluvial origin for this scarp (Peter Haeussler, USGS, written communication, 2007).

Patton Bay Faults

This fault zone, located on Montague Island, ruptured during the 1964 earthquake and rupture is thought to have extended offshore for a total rupture length of 300 km (Plafker, 1967). It is likely that this fault zone is structurally linked to the subduction zone as an up-dip imbricate thrust fault and is not independently seismogenic (Plafker, 1971; Carver and McCalpin, 1996). We do not include these faults in our characterization of crustal fault seismic sources because activity along this zone is accounted for in the characterization of the subduction zone.

Kenai Lineament

This north-south trending feature is classified as “suspicious” by Plafker et al. (1994). Dames and Moore (1999) conducted field reconnaissance and concluded that scarps along this feature were non-tectonic in origin. We do not include this feature in our seismic source characterization.

Johnstone Bay Fault

The Johnstone Bay fault is portrayed by Plafker et al. (1994) as Holocene-active. Due to the similar orientation to the Patton Bay faults and its location on the upper plate above the subduction zone, we interpret this structure to be linked to the megathrust and likely not independently seismogenic.

4.2 CRUSTAL BACKGROUND SEISMICITY The hazard from crustal background (floating or random) earthquakes that are not associated with the known or mapped faults must be incorporated into the hazard analysis. Earthquake



recurrence estimates in the site region and maximum magnitudes are required to assess the hazard from background earthquakes. Background seismicity can be treated as an areal source zone where earthquakes are assumed to occur randomly or the historical seismicity can be assumed to be stationary in space and hence smoothed using a Gaussian filter. Both approaches were used in this PSHA.

In tectonically active areas such as the western U.S., the maximum magnitude for earthquakes not associated with known faults usually ranges from M 6 to 6½. Repeated events larger than these magnitudes probably produce recognizable fault-or fold-related features at the earth’s surface (e.g., Doser, 1985; dePolo, 1994). In this study, we adopt a value of M 7 ± ¼, however, because of the thick seismogenic crust that could conceal M 7-sized events. The best estimate value and one-sigma uncertainties are weighted in a logic tree similar to the maximum magnitude for the faults (Figure 4).

Completeness intervals were estimated for this catalog based on developing Stepp (1972) plots of the historical record (Figure 10). These intervals were used in the evaluation for earthquake recurrence.

The recurrence relationship was estimated using the maximum likelihood procedure developed by Weichert (1980) and the estimated completeness intervals for the region. Dependent events, such as aftershocks, foreshocks, and smaller events within an earthquake swarm, were also identified and removed from the catalog using the technique developed by Youngs et al. (2000). For this study, it was assumed that the crustal seismicity in the region shown in Figure 11 could be treated uniformly and that there were no significant differences in seismicity rates in the region. Crustal and intraslab earthquakes were identified for the recurrence calculations using the geometry of the subducting plate as modeled in this study (Section 4.3.1).

After adjusting the earthquake catalog for dependent events and completeness, 138 crustal events remained in the range M 4.5 to 7.3 from which to estimate the recurrence for the crustal background seismicity (Figure 12). Only one earthquake was M 7.0 and larger. It was assumed that very few, if any, of the events in the historical catalog were associated with the faults included in the PSHA. Given there were few crustal events larger than M 6.0, this assumption is probably valid.

The resulting mean and plus and minus one standard deviation recurrence relationship, assuming the truncated-exponential form of the Gutenberg-Richter relationship, log N = a – bM is shown on Figure 12. The resulting b- and a-values are 0.90 0.05 and -1.15, respectively.

Because of the limited duration and incompleteness of the historical catalog, uncertainties in the recurrence parameters can be large. To incorporate the uncertainties into the hazard analysis, we used three b-values, the best estimate, and plus and minus 0.1 values, weighted 0.6, 0.2, and 0.2, respectively. An inspection of the resulting recurrence intervals for M 5 and 6 events was performed to check the reasonableness of the three b-values. Although the a and b-values are correlated, the former was held fixed because it is better constrained by the small magnitude seismicity data.

The use of seismic source zones assumes that background earthquakes are uniformly (randomly) distributed throughout the seismogenic crust. However, some seismicity may also be stationary



through time (at least over the next few decades of interest) and thus the use of Gaussian smoothing.

In the Gaussian smoothing approach, we smoothed the historical seismicity on a grid at 0.1 degree intervals to incorporate a degree of stationarity. The version of Gaussian smoothing adopted in this study (Frankel, 1995) is the same as that used in the National Hazard Maps. This scheme addresses both the spatial stationarity of seismicity and its randomness. In the smoothing approach, we smoothed the historical background seismicity out to 500 km from the site to incorporate a degree of stationarity, using a spatial window of 15 km. Thus the hazard from seismicity that clusters in a specific seismic zone is retained spatially rather than being smoothed to a uniform distribution as in a seismic source zone. We weighted the use of a seismic source zone and Gaussian smoothing at 0.5 and 0.5, respectively.

4.3 ALASKAN SUBDUCTION ZONE The Alaskan subduction zone megathrust and Wadati-Benioff zone are described in the following. Table 2 lists the seismic source parameters.

4.3.1 Megathrust The Aleutian megathrust is defined by a northward-dipping Wadati-Benioff zone at the plate boundary interface. A seismicity cross-section through the subduction zone in the vicinity of Anchorage from Veilleux and Doser (2007) is shown on Figure 13. If this zone of seismicity intersected the surface, it would daylight near the Aleutian trench. Near Anchorage, relative motion is compressional and thrust faults predominate, whereas the western part of the subduction zone, where plate motion is oblique, is largely a transform boundary. Large historical earthquakes have ruptured much of the length of this megathrust. The four segments of the subduction zone considered in the PSHA were the Semidi, Kodiak, Prince William Sound, and the western Yakutat microplate (Yakataga segment) (Figure 13; Table 2).

The “Eastern section” of the subduction zone includes the Kodiak segment, centered on Kodiak Island, and the Prince William Sound segment (Figure 13). The Prince William Sound and Kodiak segments ruptured in the 1964 Alaska earthquake. Recent work by Shennan et al. (2009), however, suggests that the prior two megathrust events on those segments, at ca. 900 BP and ca. 1500 BP, also ruptured the western part of the Yakutat block, adding about 15% to the seismic moment release compared to 1964.

The Yakutat microplate has been variously described as an oceanic plateau (e.g. Worthington et al., 2012; Christesen et al., 2010), an allochthonous fragment of continental terrane (Plafker, et al., 1994), and oceanic crust (Bruns, 1983). The western part of the block is subducting under the North American plate, whereas the eastern portion meets the North American plate in a collisional regime characterized by accretion and underplating along a series of crustal thrust faults soling into a décollement under the Saint Elias block (Elliott, 2011; Worthington et al., 2012). The microplate is buoyant compared to the oceanic crust of the Pacific plate and the subduction is low angle. Veilleux and Doser (2007) use relocated earthquakes to conclude that the subducted Yakutat block is nearly flat in the easternmost part of the subduction zone. Brocher et al. (1994) analyzed wide angle seismic reflection and refraction profiles and determined it is dipping 3 to 4 degrees. The 2007 National Seismic Hazard map model for



Alaska, acknowledging the complexity of the Yakutat region, simplified it to include the Yakutat microplate as a subduction source, the Yakataga segment. It was characterized in that model as a flat surface at 15 km depth. More recently, Elliott (2011) analyzed GPS data and modeled the western Yakutat microplate, from the Bering Glacier west, subducting with a 5 degree dip and extending at least 200 km to the northwest under Prince William Sound.

The subduction of the Yakutat microplate and its interaction with the subducting Pacific plate are complex and poorly understood. Based on the Elliott (2011) model, however, the subducting Yakutat plate underlies much the same region as the northeastern part of the subducting Pacific slab. Freymueller et al. (2008a) argue that the Yakutat plate subducts under the north American plate at a very shallow dip while the Pacific plate subducts at a slightly steeper dip under the subducting Yakutat slab, yielding two separate but overlapping subduction interfaces. Brocher et al. (1994) argue that there are not two Wadati-Benioff zones and rather the Yakutat and Pacific plates subduct together as a composite plate. Given the complexity, different interpretations, and distance from the site, and in light of the paleoseismic data suggesting the western Yakutat microplate has ruptured with the Prince William Sound and Kodiak segments of the Pacific plate in single event, in this model of the subduction zone, we simplify the region and combine the western Yakutat microplate megathrust with the Prince William Sound megathrust into a single segment (PWS/WY), capable of rupturing together. In this model, the 1964 rupture would represent a partial rupture of the segment, or an event somewhat smaller than the maximum event, while the 900 BP and 1500 BP events would represent full rupture events.

In the model of the subduction zone, we include two rupture models for the Eastern section (Table 2). In the “unsegmented” model, the PWS/WY and Kodiak segments rupture together. In the segmented model, PWS/WY and Kodiak rupture independently. Paleoseismic data through nine events in the Prince William Sound area and through five or six events in Kodiak indicate that earthquakes in both segments occurred at the same time within the uncertainties of radiocarbon ages (Carver and Plafker, 2008; Hutchinson and Crowell, 2007). This leads us to favor the unsegmented model, but we give moderate weight to the segmented model because the paleoseismic events could represent independent ruptures in relatively rapid succession (Table 2).

Figure 14 shows geometric models used for the megathrust and slab in the hazard analysis. Geodetic modeling of the megathrust indicates a very shallow dip. In a joint inversion of tsunami waveforms and geodetic data, Johnson et al. (1996) model the Prince William Sound segment as dipping 3 to 4 degrees and the Kodiak segment as 8 to 10 degrees. Similarly, Savage et al. (1999) model a megathrust as dipping 5 degrees based on geodetic data. Brocher et al. (1994) estimate the dip of the megathrust as 9 to 10 degrees based on wide-angle seismic reflection data. Ichinose et al. (2007) model the Prince William Sound and Kodiak segments as dipping 12 degrees based on modeling of the 1964 rupture using teleseismic data. At the bottom of the megathrust, the downgoing slab steepens in dip based on relocated seismicity (Figure 13).

Given the range in dips, we consider two models for the megathrust (Table 2). In the model that is given the highest weight of 0.8, the megathrust dips 6 3 degrees (weighted 0.8, 0.1, 0.1, respectively). The megathrust is extended to depths where it is matched to the model of the slab based on the relocated seismicity (Figure 14). This results in the maximum depth of the megathrust ranging from 24 to 62 km. In the second model, which is assigned a weight of only



0.2, the megathrust has steeper dips of 9.25 3 degrees based primarily on the analysis of Ichinose et al. (2007). This model is also extended downward to match the slab as modeled by the relocated seismicity of Veilleux and Doser (2007). Maximum depths of the megathrust range from 34 to 62 km.

The brown areas shown on Figure 14 are treated as locked and capable of producing great megathrust earthquakes. The un-shaded part of the slab is greater than 45 km in depth, and is the part that is considered not capable of producing great earthquakes like the subduction zone. Zweck et al. (2002) use GPS data to model the locked and slipping parts of the plate interface. They conclude that the present extent of the locked plate boundary closely resembles the area of the interface that broke in the 1964 earthquake. The area to the northwest of this locked patch is experiencing postseismic creep parallel to the direction of plate motion. The boundary between these locked and creeping patches trends to the northwest and is very near Anchorage. This is also the location where the subducting slab begins to bend and dip more steeply (Figure 14).

The USGS (Wesson et al., 2007) cites paleoseismology studies in the eastern part of the megathrust by Plafker and Rubin (1994), Combellick (1994), Bartsch-Winkler and Schmoll (1992), Hamilton and Shennan (2005), Hamilton et al. (2005), and Shennan and Hamilton (2006) to assign an average recurrence time of 650 years for the Prince William Sound (1964 rupture zone) segment (Table 2). A more recent compilation of paleoseismic data by Carver and Plafker (2008), however, suggests a slightly shorter average recurrence interval. For the PWS/WY and Kodiak segments, we calculate mean recurrence intervals/rates via the approaches described in the Central and Eastern U.S. (CEUS) Seismic Source Characterization (SSC) for Nuclear Facilities (EPRI/DOE/NRC, 2012). We apply the approach described in 5.3.3.1.2 (“Earthquake Recurrence Intervals”) of the CEUS-SSC report which computes a distribution of recurrence intervals based on paleoseismic data incorporating statistical uncertainty due to limited sample size. The CEUS-SSC approaches result in discrete five-point approximations to continuous probability distributions of mean recurrence intervals/rates that define weighted branches in the fault logic tree (Table 2). As discussed in the CEUS-SSC report, these probability distributions quantify the uncertainty in the mean recurrence intervals/rates that arise from relatively small samples sizes of past earthquakes.

In our calculations of mean recurrence rates/intervals, we do not incorporate the input uncertainties discussed in Section 5.3.3.3 (“Incorporating Uncertainty in the Input”) of the CEUS-SSC report – namely uncertainties in the time interval T over which past earthquakes have occurred or in the earthquake occurrence times. The reason we do not is that we find the impacts of incorporating these uncertainties on the probability distributions of mean recurrence rates/intervals to be negligible. In other words, the impacts of the input uncertainties are found to be negligible in comparison to the uncertainty arising from the relatively small sample sizes of past earthquakes.

The distributions of recurrence intervals were based on the in Carver and Plafker (2008): 10 events which ruptured the PWS and Kodiak segments and 5 events that ruptured the Kodiak segment alone. The resulting distributions are provided in Table 2. The distributions have a mean recurrence interval of 590 years for the PWS segment and 600 years for the Kodiak segment.

The USGS also cites evidence in Nishenko and Jacob (1990) and Carver et al. (2003) to conclude that the southwestern part of the 1964 rupture zone (the Kodiak Island segment)



ruptures separately as well, more frequently than the segment to the east. The Carver and Plafker (2008) compilation identifies one event in Kodiak, at ca. 500 BP, in the 2000 year record that has no correlative in the Prince William Sound segment. We allow for the possibility that the Kodiak segment ruptures somewhat more frequently by assigning it a slightly shorter recurrence interval than PWS/WY in the segmented model and, in the “unsegmented” model, by allowing additional ruptures of only the Kodiak segment along with the unsegmented full rupture events (Table 2). The recurrence interval of these "extra" Kodiak events is not known, but we include alternatives of 1000 and 2000 years to reflect the one event in the 2000 year Kodiak record (Table 2).

Rupture of the Prince William Sound and Kodiak segments was also modeled as time-dependent using the BPT model. As described in Section 2.1.3, equivalent Poisson recurrence intervals were calculated. The number of events on these segments is statistically too small to adequately compute COVs for this specific source. Instead, a range of COVs (0.3, 0.5 and 0.7, weighted 0.2, 0.6, 0.2) was selected based on an analysis of global dataset by Ellsworth et al. (1999) . This range of COV has been used in the UCERF2 and UCERF3 forecasts. Given the short time since the 1964 event, the BPT model predicts very low rupture probabilities for all values of COV. Hence, equivalent poisson rates, based on a time interval of 50 years, are very long (Table 2). A weight of 0.8 was assigned to the time-dependent model based on the quality and robustness of the paleoseismic record.

The Semidi segment is located between the Kodiak segment and the Shumagin gap (Figure 13). The Semidi segment, according to geodetic analyses, is nearly fully coupled (70 to 90%) whereas in the adjacent Shumagin gap, the plates are largely decoupled (Fletcher et al., 2001; Fournier and Freymueller, 2007; Freymueller and Beavan, 1999). An M 8.2 earthquake occurred on the Semidi segment in 1938 (Figure 2). Johnson and Satake (1994) used modeling of waveforms from the earthquake to infer that the rupture plane dipped about 10 degrees and extended to a depth of about 30 km. More recently, modeling of GPS velocities suggests an effective slip rate for the Semidi segment of about 45 mm/yr, dip of about 6 to 10 degrees and a locking depth of about 23 to 30 km (Fletcher, 2002; Fournier and Freymueller, 2007). We include a characteristic event on this segment with a weight of 0.6 for M 8.2, based on the 1938 earthquake magnitude, and 0.2 for earthquakes of M 7.9 and 8.5 (Table 2).

For the megathrust, we weighted the characteristic and maximum magnitude recurrence models 0.5 and 0.5, respectively. For megathrust earthquakes larger than M 8.0, the USGS (Wesson et al., 2007) weighted equally the characteristic model and the maximum magnitude model for the Prince William Sound and Kodiak segments. For earthquakes between M 7 and 8, the USGS used the same probability of occurrence throughout the megathrust zone, and based the likelihood on an average of the entire zone’s instrumental seismicity. The USGS did not use a moment-balancing approach to estimate the frequency of earthquakes in this area because of the varying (both spatially and temporally) aseismic moment release.

4.3.2 Wadati-Benioff Zone In the PSHA, we model the Wadati-Benioff zones as staircasing blocks, each 18 to 25 km thick from 30 to 120 km deep. Figure 14 is a cross-section oriented northwest to southeast showing slab seismicity in the vicinity of Anchorage. The arrows show areas of concentrated seismicity down-dip of the locked portion of the plate interface and near the southwestern edge of the subducted Yakutat block. These areas are interpreted to be conjugate vertical faults with



northeast and northwest strikes. Focal mechanisms and inversion of first motion data in this area indicate that the subducted Pacific plate is experiencing east-west compression as a result of its collision with the southwestern edge of the subducted Yakutat block (Veilleux and Doser, 2007).

Similar to our evaluation of crustal background seismicity, recurrence was calculated for the intraslab zone (Figures 15 and 16). A maximum magnitude of M 7½ ¼ was adopted based on the historical record of earthquakes in the Alaskan subduction zone (Figure 3). The truncated-exponential recurrence model was assigned a weight of 1.0. A total of 514 events were used in the recurrence calculations. The resulting b-value is 1.12 (Figure 16). Table 2 lists the seismic source parameters for the intraslab zone.

SECTIONFIVE Ground Motion Prediction Models


5. Section 5 FIVE Ground Motion Prediction Models

The traditional approach for estimating ground motions in seismic hazard analysis utilizes ground motion prediction models (also called attenuation relationships), which are derived from strong motion data. Attenuation is defined as the decrease in amplitude or intensity of seismic waves with distance. This decrease results from a number of factors including geometrical spreading, damping or absorption by the earth, scattering, reflection, refraction, diffraction, and wave conversion.

Empirical ground motion prediction models have been developed in regions where there are numerous strong ground motion recordings by applying statistical regression methods to these data. Because the data correspond to geologic conditions and earthquakes typical of the region, they are generally applicable only in that region. However, they may also be used in another area with similar seismotectonic characteristics.

To predict ground motions in the PSHA, we have used recently developed NGA-West 2 ground motion prediction models appropriate for tectonically active regions such as southern Alaska. These new models, developed as part of the NGA Project sponsored by the PEER Center Lifelines Program, have been recently published in the journal Earthquake Spectra. The NGA-West 1 Project began in 2003 and the first set of five models became available. The NGA-West 1 models had a substantially better scientific basis than current models (e.g., Abrahamson and Silva, 1997) because they are developed through the efforts of five selected developer teams working in a highly interactive process with other researchers who have: (a) developed an expanded and improved database of strong ground motion recordings and supporting information on the causative earthquakes, the source-to-site travel path characteristics, and the site and structure conditions at ground motion recording stations; (b) conducted research to provide improved understanding of the effects of various parameters and effects on ground motions that are used to constrain attenuation models; and (c) developed improved statistical methods to develop attenuation relationships including uncertainty quantification. The NGA-West 1 models benefited greatly from a large amount of new strong motion data from large earthquakes (M > 7) at close-in distances (< 25 km). Data include records from the 1999 M 7.6 Chi Chi, Taiwan, 1999 M 7.4 Kocaeli, Turkey, and 2002 M 7.9 Denali, Alaska earthquakes. Review of the NGA models indicate that, in general, ground motions particularly at short-periods (e.g., PGA) are significantly reduced particularly for very large magnitudes (M 7.5) compared to previous models.

In 2010, the NGA-West2 Project began as a follow-up to the original NGA-West1 Project. The NGA-West2 models were developed based on an expanded database, with a number of more recent well recorded earthquakes added including Wenchuan, China, numerous moderate magnitude California events down to M 3.0, and several Japanese, New Zealand, and Italian earthquakes. The NGA-West2 models are now state-of-the-practice. For example, the models were used in the 2014 USGS National Seismic Hazard Maps. In this study, the models of Campbell and Bozorgnia (2014), Chiou and Youngs (2014), Abrahamson et al. (2014a), and Boore et al. (2014) are used. The models are weighted equally in the PSHA. As requested, a VS30 value of 760 m/sec was used in the NGA models.

Other input parameters include Z2.5, the depth to the VS of 2.5 km/sec (a proxy for basin effects), which is only used in one model, Campbell and Bozorgnia (2014). Abrahamson et al. (2014a) and Chiou and Youngs (2014) use Z1.0, the depth to the VS of 1.0 km/sec. In the absence of site-

SECTIONFIVE Ground Motion Prediction Models


specific data, the authors provide an equation for default values based on the VS30 at the site. We used the default values of 0.045 km for the Z2.5 value and the average Z1.0 value of 0.607 km. Other parameters such as depth to the top of rupture (zero for all surficial faults unless specified otherwise), dip angle, and rupture width are specified for each fault or calculated within the PSHA code.

As noted by Atik and Youngs (2014) the development of the NGA-West2 models was a collaborative effort with many interactions and exchanges of ideas among the developers and the developers indicated that an additional epistemic uncertainty needs to be incorporated into the median ground motions in order to more fully represent an appropriate level of epistemic uncertainty. Hence, for each of the four NGA-West2 models an additional epistemic uncertainty on the median ground motion was included. The three-point distribution and model of Atik and Youngs (2014) was applied (Figure 5). The model is a function of magnitude, style of faulting, and spectral period.

For the Alaskan subduction zone, we principally used the new model by Abrahamson et al. (2014) developed for the BCHydro PSHA Project. This model was developed specifically for the Cascadia subduction zone but it also is applicable to other subduction zones worldwide since it is based principally on global subduction zone data. The subduction zone strong motion database used in the development of the BCHydro model is the most comprehensive compiled to date. Regional variations were considered in the model. In our judgment, it is the best subduction zone model that is currently available. For the megathrust, we assigned a weight of 0.5 to Abrahamson et al. (2014b) and 0.25 weight each to the model of Youngs et al. (1997), which has been the model most commonly used in previous state-of-the-practice and Zhao et al. (2006) which is based on Japanese data. For the intraslab, Abrahamson et al. (2014b), Zhao et al. (2006), and Atkinson and Boore (2003) were assigned weights of 0.5, 0.25, and 0.25, respectively. The latter model is also based on global data.

SECTIONSIX PSHA Results


6. Section 6 SIX PSHA Results

The following describes the hazard results from the PSHA and comparisons with USGS National Hazard Maps for Alaska. The natural period of interest is between 2 and 3 sec.

6.1 HAZARD RESULTS The results of the PSHA are presented in terms of ground motion as a function of annual frequency of exceedance (AFE). AFE is the reciprocal of the average return period. Figure 17 shows the mean, median (50th percentile), 5th, 15th, 85th, and 95th percentile hazard curves for peak horizontal ground acceleration (PGA). The 1.0 and 3.0 sec horizontal spectral acceleration (SA) hazard are shown on Figures 18 and 19. These fractiles indicate the range of uncertainties about the mean hazard. At a return period of 2475 years, there is more than a factor of 2 between the 5th and 95th percentile PGA values (Figure 17). At the specified return periods of 72, 475, and 2475 years, the PGA, 1.0, and 3.0 sec SA values are listed in Table 3.

The contributions of the various seismic sources to the mean PGA hazard are shown on Figure 20. The intraslab zone dominates the PGA hazard at all return periods. At long-period ground motions at a period of 1.0 and 3.0 sec or more, the intraslab zone controls the hazard at the shorter return periods (Figures 21 and 22). At longer return periods, the 1964 rupture controls the long-period hazard. The Castle Mountain fault, the closest and most significant crustal fault to the site, is not a major contributor to the hazard at the site (Figures 20 to 22).

Figures 23 to 25 illustrate the sensitivity to the use of time-dependent rates for the megathrust. The curves on these figures show the total hazard from all seismic sources and the hazard from the megathrust alone for two cases: 1) fully time-independent and 2) time-dependent rates weighted 0.8 and time-independent rates weighted 0.2. Note that contributions from sources other than the megathrust are time-independent for both cases. As expected, the time-dependent hazard from the megathrust is significantly smaller than the time-independent hazard because of the short elapsed time since the 1964 earthquake. The impact on the total 3.0 sec spectral acceleration hazard is a factor of 1.85 in ground motion at a return period of 2,475 years (Figure 25). The impact on total hazard is slightly less for PGA and 1.0 sec spectral acceleration where the relative contribution of the megathrust to the total hazard is lower (Figures 23 and 24).

By deaggregating the PGA, 1.0, and 3.0 sec SA hazard by magnitude and distance bins, Figures 26 to 34 illustrate the contributions by events. At a 72-year return period, the PGA hazard comes from a range of events associated with the crust, slab, and megathrust (Figure 26). At 475 years, the PGA hazard is controlled by the intraslab events with some contribution from the megathrust (Figure 27). At 2475 years, the megathrust contribution becomes much more prominent (Figure 28). At 1.0 and 3.0 sec SA, the pattern is similar (Figures 29 to 34).

Table 4 lists the modal magnitude (Mmode) and distance (Dmode), and epsilon (mode) at PGA, 1.0, and 3.0 sec SA hazard corresponding to the period ranges of interest for the Port. Epsilon is the difference between the logarithm of the ground motion amplitude and the mean logarithm of ground motion (for that M and R) measured in units of the standard deviation (σ) of the logarithm of the ground motion. The controlling earthquakes reflect the distributions shown in Figures 26 to 34.

Figures 35 to 40 illustrate the sensitivity of the mean PGA and 3.0 sec horizontal SA hazard to the choice of the three types of ground motion prediction models. Each hazard curve is labeled

SECTIONSIX PSHA Results


with one of the models calculated using only that model. Figures 35 and 38 show the crustal ground motion prediction models including the models, which have been adjusted for the additional epistemic uncertainty on the median estimates. The models produce similar hazard curves. The intraslab models give similar hazard curves except for the Atkinson and Boore (2003) model (Figures 36 and 39). The megathrust models show widely varying hazard curves reflecting significant uncertainty between the three models.

Firm rock UHS at 5% damping for return periods of 72, 975, and 2475 years are shown on Figure 41.

6.2 COMPARISON WITH USGS NATIONAL HAZARD MAPS In 1996, the USGS released a “landmark” set of National Hazard Maps of the conterminous U.S. for earthquake ground shaking, which was a significant improvement from previous maps they had developed (Frankel et al., 1996). These maps were the result of the most comprehensive analyses of seismic sources and ground motion attenuation ever undertaken on a national scale. The maps are the basis for the NEHRP Maximum Considered Earthquake maps, which are used in the International Building Code. The maps are for NEHRP site class B/C (firm rock). In 1999 and 2007, similar maps for Alaska were developed by Wesson et al. (1999; 2007).

For a 2475-year return period (2% exceedance probability in 50 years), the 2007 USGS Alaska map indicates a firm rock PGA of 0.69 g for the Port. The site-specific PGA computed in this study for the same return period is 0.76 g, about 10% higher than the USGS value. Similarly, the USGS 2475-year return period 0.2 and 1.0 sec SA values are 1.55 g and 0.52 g (Wesson et al., 2007) compared to this study’s values of 1.73 g and 0.44 g, respectively. These differences are small and not surprising given the differences in approaches and inputs. The primary reason may be the ground motion prediction models used in this study compared to the USGS study are totally different.

6.3 COMPARISON WITH 2008 PORT STUDY The hazard results in this study are comparable to the results from the 2008 Port analysis except at a 2,475 year return period (Table 5). At a return period of 72 years, the 2014 hazard is comparable to or slightly lower than in 2008. At 475 years, the 2014 results are 10% higher at short and moderate periods than in 2008 and about 20% lower at long period. For a return period of 2,475 years, the current short and moderate period hazard is 30% higher than in 2008 and about the same at long periods (Table 5). The major updates in this study include the use of current state-of-art ground motion prediction models for both the crustal and subduction zone earthquakes, revision to the megathrust recurrence intervals, and time-dependent modeling of the megathrust. The downdip geometry of the megathrust was also updated and the uncertainties in the geometry were better incorporated into the PSHA than in 2008.

SECTIONSEVEN DSHA Results


7. Section 7 SEVEN Dsha Results

The deterministic approach involves the following steps:

Identify the potential seismic sources that could affect the site and estimation of the maximum earthquakes that could reasonably be expected from these sources.

Develop the range of maximum ground motions that are likely to occur at the site due to the maximum earthquakes for each seismic source using state-of-the-art ground motion attenuation relationships and/or ground motion numerical modeling.

Select the maximum earthquake with the potential for generating the strongest ground motions at the site.

Characterize the maximum earthquake in terms of peak ground acceleration, acceleration response spectra, duration of strong ground shaking, and/or other parameters as deemed appropriate.

The first step, which is required in any assessment of earthquake hazards, requires a characterization of all significant seismic sources that will produce ground motions of engineering significance at the site (Section 4). In a deterministic analysis, no earthquake recurrence rate information is used.

Based on the ground motion prediction models used in the PSHA described in Section 5, 5%-damped acceleration response spectra were calculated for the sources most significant to the Port. The Alaskan subduction zone megathrust and intraslab zone are deemed the most significant seismic sources to the Port within a deterministic framework. Previous analyses indicate the Castle Mountain fault, the closest significant crustal fault to the Port, is not important (Wong et al., 2008; URS, 2013). The two maximum earthquake scenarios included in the DSHA: (1) a M 7.5 intraslab earthquake about 30 km beneath Anchorage; and (2) a repeat of the 1964 earthquake, a M 9.2 megathrust earthquake at a distance of 35 km. The VS30 used in the DSHA was 760 m/sec similar to the PSHA.

Figures 42 to 43 show the weighted median (50th%) and 84th% acceleration response spectra for a critical damping value of 5%. On Figure 44, the median deterministic spectra are compared with the three UHS. The median intraslab spectrum, which is the higher of the two deterministic spectra except beyond 0.8 sec lies between the 475 and 2,475-year return period UHS. The median megathrust spectrum lies below the 475-year UHS at short periods and is above it at longer periods (Figure 44).

SECTIONEIGHT Development of Time Histories


8. Section 8 EIGHT Development of Time Histories

We developed 11 pairs of horizontal-component time histories. Because the response spectrum of a time history has peaks and valleys that deviate from the design response spectrum (target spectrum), it is necessary to modify the motion to improve its response spectrum compatibility. We used two spectral matching approaches as embodied in the computer codes RSPMatch and RASCALS. The procedure proposed by Lilhanand and Tseng (1988), as modified by Norm Abrahamson (written communication, 1999) in the computer code RSPMatch09, was used to develop the acceleration time histories through spectral matching to the target (seed) spectrum. This time-domain procedure has been shown to be superior to previous frequency-domain approaches because the adjustments to the time history are only done at the time at which the spectral response occurs resulting in only localized perturbations on both the time history and the spectra (Lilhanand and Tseng, 1988).

Time histories were also developed by combining a Fourier amplitude spectrum (which is generated by matching the target) with a phase spectrum from an observed strong ground motion recording using the technique described by Silva and Lee (1987). This approach is implemented in the computer program RASCALS (Silva and Lee, 1987). To improve the fit to the target spectrum, additional spectral matching is performed using the response spectrum computed from the synthetic time history. Additionally, a baseline correction is included by high-pass filtering the record at 10 sec. The result is a synthetic time history, which closely matches the target spectrum and which possesses realistic integrations to velocity as well as displacement.

The 11 pairs for the three return periods were selected based upon the results of the PSHA. For the 72-year return period, the hazard was dominated by the intraslab earthquakes and so pairs of horizontal components from three intraslab events were used as seed time histories (Table 6). For the 475-year return period, three pairs of intraslab and one pair of megathrust earthquake time histories were used as seeds. For the 2,475-year return period where the contributions from the intraslab earthquakes and the Alaskan subduction zone megathrust were almost equal, two pairs each were used as seed time histories (Table 6).

To match the target spectra, time histories for events should be of similar magnitude and distance (for duration) as the event dominating the spectrum as most importantly spectral shape. The horizontal design target spectra are the three UHS. Comparisons of spectral shapes targeted at the period of interest, 2 to 3 sec, are shown in Figures 45 to 47. Table 6 lists the selected seed time histories and they are shown on Figures 49 to 53.

The spectral matches and the resulting time histories are shown in Figures 54 to 97. The matches are good over most frequencies except at very low frequencies or long periods, e.g., 5 to 10 sec. Table 7 lists the properties of the spectrally-matched time histories including Arias intensities and durations.

SECTIONNINE References


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W:\X_WCFS\PROJECTS\PORT_OF_ANCHORAGE 2014\PORT OF ANCHORAGE PSHA UPDATE_NOV14.DOCX

Table 1 Seismic Source Parameters for Faults in the Vicinity of the Port of Anchorage

Fault Name

Probability of

Activity Rupture Model Section Name

Rupture Length (km)

Preferred MMax

1

(M) 0.3 Sense of

Slip Dip

(degrees)

Rupture Depth (km)

Slip Rate (Mm/Yr)

Recurrence Interval Comments

Bruin Bay Fault 0.5 Floating (1.0) N/A 7.0 Reverse 30 NW (0.2)45 NW (0.6)60 NW (0.2)

20±5 0.01 (0.2) 0.1 (0.6) 1.0 (0.2)

Schmoll and Yehle (1987) found no geologic evidence of activity on the Bruin Bay fault or related structures during late Pleistocene or Holocene time (the last ~120,000 years) and the fault is classified as a Neogene fault by Plafker et al. (1994). However, there is some uncertainty whether there are enough Quaternary deposits spanning the fault to entirely preclude Quaternary activity, so the probability of activity is set as 0.5. Based on the lack of activity during the past 120,000 years, we assign a slip rate that is low, with broad uncertainties. Our preferred slip rate is based on a maximum geologic slip rate based on the 3000 m of throw (Detterman and Reed, 1980) that predates the emplacement of Oligocene plutons across the fault (Nockleberg et al., 1994). Also, because the fault is in a favorable orientation for activity in the present stress regime, we believe that it may be capable of producing earthquakes. We assign a preferred Mmax in a floating earthquake model based on the historical 1933 M 6.9 earthquake that occurred in the Cook Inlet, suggesting that earthquakes of at least this size, along parallel structures, are possible in the region.

Castle Mountain – Caribou Fault System

1.0 Unsegmented (0.2)

211 7.7 Reverse-RL 50 N (0.3) 75 N (0.7)

20±5 0.5 (0.4) 1.0 (0.4) 2.9 (0.1) 3.6 (0.1)

The Holocene-active Castle Mountain Fault System is modeled as a segmented fault due to repeated Holocene activity along the western section, with only Pleistocene activity identified on the eastern section (Haeussler et al., 2002). This is the only fault in the Anchorage area with both a slip rate and a Late Holocene earthquake chronology. Trenching studies suggest the fault has ruptured three times during the past 2100 years (Haeussler et al., 2002). Alternative interpretations, however, suggest only one event in the late Holocene (Koehler et al., 2011a; Detterman et al., 1974). We include the recurrence data in the model, but give it low weight due to the uncertainty in interpretation. Differing interpretations of slip rate, which differ by a factor of five or more, also result in a broad distribution of slip rates. Because of the apparent along-strike continuity of the fault in map view between the western and eastern sections, we also include an unsegmented rupture model. However, this is given a relatively low weight because of the paleoseismic record that clearly shows the western Castle Mountain fault has repeatedly failed during the Holocene, while the eastern Castle Mountain fault has not. Due to this lack of activity, and the suggestion that the slip rate should decrease to the east due to being on the edge of the Yakutat – North America collision that may drive the Castle Mountain fault, we assign the eastern Castle Mountain – Caribou fault system a lower slip rate of about half of the western Castle Mountain slip rate.

Segmented (0.8)

Western 100 7.4 Reverse-RL 50 N (0.3) 75 N (0.7)

20±5 0.5 (0.3) 1.0 (0.3) 2.9 (0.3) 3.6 (0.1) Slip rate wt: 0.8

700 (0.4) 5,000 (0.3) 7,000 (0.3) R.I. wt: 0.2

Eastern (plus Caribou)

111 7.4 Reverse-RL 50 N (0.3) 75 N (0.7)

20±5 0.1 (0.5) 1.5 (0.4) 1.8 (0.1)



Fault Name

Probability of


Rupture Length (km)

Preferred MMax

1

(M) 0.3 Sense of

Slip Dip

(degrees)

Rupture Depth (km)

Slip Rate (Mm/Yr)


Denali Fault System 1.0 Unsegmented (0.33)

410 8.1 RL 90 (0.5) 75 SE (0.5)

15±5 3.0 (0.2) 6.4 (0.6) 9.4 (0.2)

We consider the three segments of the Denali Fault System closest to the 200 km radius surrounding the Port of Anchorage in our source model. Three rupture models are given equal weight: Due to the relatively continuous trace, an unsegmented model is considered. The segmented model is proposed based on the apparent segmentation portrayed on the map of Plafker et al., 1994). We include a floating earthquake that is based on the length of the two longest segments. This length (290 km) is also similar to the 2002 Denali earthquake rupture length and magnitude, which may be a typical large magnitude earthquake for this fault. This is given equal weight as the segmented model, given the large uncertainties whether there are actual rupture segments along this part of the fault. The slip rate for all models except the Muldrow-Alsek segment is an average of the long term slip rate (38 km over 6 Ma, Matmon et al, 2006) and Late Quaternary slip rate of Meriaux et al, 2004; 2009), both of which are about the same. Uncertainties are assigned in order to include the higher value of Matmon and others (2006) for the western Denali Fault. The lower end of the slip rate is assigned based on the suggestion that the slip rate may taper to zero towards the west (Wesson et al. 2007).

Segmented (0.34)

Muldrow - Alsek

150 7.6 RL 90 (0.5) 75 SE (0.5)

15±5 6 (0.2) 8.5 (0.6) 11 (0.2)

Tonzona - Muldrow

122 7.5 RL 90 (0.5) 75 SE (0.5)

15±5 1.0 (0.2) 6.4 (0.6) 9.4 (0.2)

Farewell 140 7.5 RL 90 (0.5) 75 SE (0.5)

15±5 1.0 (0.2) 6.4 (0.6) 9.4 (0.2)

Floating (0.33)

290 7.9 RL 90 (0.5) 75 SE (0.5)

15±5 1.0 (0.2) 6.4 (0.6) 9.4 (0.2)

Lake Clark Fault 0.7 Unsegmented (0.1)

247 7.9 RL - Reverse

75 N (0.5) 90 N (0.5)

20±5 0.01 (0.2) 0.1 (0.6) 0.7 (0.2)

Plafker et al. (1975) observed no evidence of Quaternary movement along this fault and the fault is shown as a Neogene fault on the map of Plafker et al. (1994). However, Schmoll and Yehle (1987) report some evidence for Pleistocene movement, but no Holocene movement along the fault near its intersection with the Castle Mountain Fault. Koehler and Reger (2011) find unfaulted 11-30 ka glacial deposits across the eastern section of the fault; 60 ka deposits may be unfaulted. This uncertainty is reflected in a lower probability of activity. We include three rupture models to characterize the behavior of this fault. Very little weight is given to an unsegmented rupture model, based on an apparent discontinuous trace between the western and eastern sections. We give high weight to a floating earthquake model with a magnitude set at near the threshold of surface rupture. This is our preferred rupture model because it implies that, if the fault is active, displacements would be relatively small, and geomorphic evidence of recent activity would be quickly erased and not identifiable in this climate. The slip rate is poorly constrained for the Lake Clark Fault. Estimates of long-term average slip rate vary between 0.1 mm/yr and 0.7 mm/yr since ca. 39 Ma (Plafker et al., 1975; Reed and Lanphere, 1972; Hauessler and Saltus, 2004). The preferred slip rate estimate is based on Plafker et al. (1975) which is based on 5 km of total offset during the past 38 Ma. We assign a minimum slip rate of 0.01mm/yr to reflect the notion that, if this fault is active, it has a very low slip rate and consequently, very little in terms of a geomorphic signature indicative of active tectonics. A low weight is assigned to a higher slip rate reflecting the aeromagnetic data.

Segmented (0.3)

West 116 7.5 RL - Reverse

75 N (0.5) 90 N (0.5)

20±5 0.01 (0.2) 0.1 (0.6) 0.7 (0.2)

East 131 7.6 RL - Reverse

75 N (0.5) 90 (0.5)

20±5 0.01 (0.2) 0.1 (0.6) 0.7 (0.2)

Floating (0.6)

N/A 7.0 RL - Reverse

75 N (0.5) 90 (0.5)

20±5 0.01 (0.2) 0.1 (0.6) 0.7 (0.2)

Parker Lake Fault 0.5 Unsegmented 16 6.5 RL - Reverse

75 N (0.3) 90 (0.4) 75 S (0.3)

20±5 0.01 (0.2) 0.1 (0.6) 1.0 (0.2)

Little is known about this short, possible fault, identified as “suspicious” by Plafker et al. (1994). This feature is sub-parallel to the Castle Mountain fault and many of the fault parameters assigned to it are based on this. We assign this feature a nominal slip rate with relatively large uncertainties.

Pass Creek – Dutch Creek Fault

1.0 Unsegmented 68 7.2 RL - Reverse

45 N (0.3) 60 N (0.4) 75 N (0.3)

20±5 0.01 (0.2) 0.1 (0.6) 1.0 (0.2)

Little is known about this fault zone, identified as a Late Pleistocene fault by Plafker et al. (1994). No slip rates are available for this fault. Because of this lack of data we assign this fault a nominal slip rate.



Fault Name

Probability of


Rupture Length (km)

Preferred MMax

1

(M) 0.3 Sense of

Slip Dip

(degrees)

Rupture Depth (km)

Slip Rate (Mm/Yr)


Unnamed Fault near Palmer

0.5 Unsegmented 56 7.1 RL - Reverse

75 N (0.5) 90 N (0.5)

20±5 0.01 (0.2) 0.1 (0.6) 1.0 (0.2)

Little is known about this short, possible fault, identified as “suspicious” by Plafker et al. (1994). This feature is sub-parallel to the Castle Mountain fault and many of the fault parameters assigned to it are based on this. We assign this feature a nominal slip rate with relatively large uncertainties.

COOK INLET – BLIND SOURCES Cook Inlet – Middle Ground Shoal + Granite Point

1.0 Unsegmented 44 6.8 Reverse – RL?

45 NW (0.3)60 NW (0.4)75 NW (0.3)

20±5 0.39 (0.2) 0.82 (0.6) 2.72 (0.2)

This pair of structures deforms Pliocene deposits and may deform Quaternary sediments (Haeussler et al., 2000). Slip rate is based on the range of possible slip rates reported by Haeussler et al. (2000).

Cook Inlet – Naptown + Sunrise Lake + Beaver Creek


45 NW (0.3)60 NW (0.4)75 NW (0.3)

20±5 0.39 (0.2) 0.82 (0.6) 2.72 (0.2)

These structures deform Pliocene deposits and may deform Quaternary sediments and may be a composite of several smaller structures (Haeussler et al., 2000). There are no independent slip rate estimates available. We have applied the range of possible slip rates reported by Haeussler et al. (2000) for the Middle Ground Shoal as a proxy for these structures.

Cook Inlet – North Cook Inlet


45 NW (0.3)60 NW (0.4)75 NW (0.3)

20±5 0.04 (0.2) 0.08 (0.6) 0.27 (0.2)

The North Cook Inlet anticline likely folds Quaternary sediments (Haeussler et al., 2000) and has been attributed as one of the possible sources of the 1933 M 6.9 earthquake (Haeussler et al., 2000; Flores and Doser, 2005). We use this magnitude as the preferred Mmax for this structure. Slip rate is based on Haeussler et al., 2000.

Cook Inlet – Ivan River-Lewis River-Beluga River

1.0 Unsegmented 40 6.9 Reverse 45 NW (0.3)60 NW (0.4)75 NW (0.3)

20±5 0.04 (0.2) 0.08 (0.6) 0.27 (0.2)

Based on geomorphic evidence and the presence of gas fields, Haeussler et al. (2000) suggest that these anticlines are active. Given that these anticlines form a fairly continuous northwest trending zone, we have combined these structures to form one potential seismic source. Because this structure is near the source area of the 1933 M 6.9 Cook Inlet earthquake, we assign a preferred M max based on the magnitude of that earthquake. There are no slip rates available for these structures, we assign a slip rate based on the slip rate of the North Cook Inlet fault (Haeussler et al., 2000).

Cook Inlet – Turnagain Arm

1.0 Unsegmented 22 6.4 (0.5) 6.9 (0.5)

Reverse 45 SE (0.3) 60 SE (0.4) 75 SE (0.3)

20±5 0.04 (0.2) 0.08 (0.6) 0.27 (0.2)

Little is known about this structure, which is the closest structure to the Port of Anchorage with possible Quaternary activity. Haeussler et al. (2000) identified this as a possible Quaternary structure capable of a M 6.4 earthquake. However, this structure is of similar length as the North Cook Inlet structure, which may have produced an earthquake as large as M 6.9 in the 1933 earthquake. For this reason, we assign a preferred Mmax that is much larger than the empirical relationships would suggest.

1. Preferred Mmax estimated using the empirical relations of Wells and Coppersmith (1994) and Hanks and Bakun (2002), weighted equally. Preferred Mmax for structures in Cook Inlet are from the estimated magnitudes of Haeussler et al. (2000).


Table 2 Seismic Source Parameters for Alaskan Subduction Zone

Fault Name

Probability of

Activity Rupture Model Source

Rupture Length (km)

Preferred MMax (M)

B-Value Dip (degrees)

Rupture Depth (km)

Slip Rate (mm/yr)

Recurrence Interval (Yrs)

Poisson Time-Dependent Equivalent Poisson

COV = 0.3 (0.2) COV = 0.5 (0.6) COV = 0.7 (0.2) Eastern section (Western Yakutat/Prince William Sound/Kodiak)

1.0 Unsegmented (0.7)

Kodiak + PWS/WY

N/A 9.1 (0.2) 9.2 (0.6) 9.3 (0.2)

1.000 Model 1 (0.8) 3.0 N (0.1) 6.0 N (0.8) 9.0 N (0.1) Model 2 (0.2) 6.25 N (0.1) 9.25 N (0.8) 12.25 N (0.1)

Top: 5 Bottom: Model 1 (0.8) 24 (0.1) 43 (0.8) 61.5 (0.1) Model 2 (0.2) 33.5 (0.1) 47.5 (0.8) 61.5 (0.1)

325 (0.101) 430 (0.244) 550 (0.31) 720 (0.244) 1050 (0.101) Wt mean: 590

> 2,000,000 5060 (0.101) 43,150 (0.244) 480,700 (0.31) > 2,000,000 (0.345)

840 (0.101) 2660 (0.244) 9560 (0.244) > 1,000,000 (0.101)

Kodiak (additional)

N/A 8.2 (0.2) 8.5 (0.6) 8.8 (0.2)

1.000 5.0 N (0.2) 7.0 N (0.6) 9.0 N (0.2)

Top: 5 Bottom: 30 (0.5) 50 (0.5)

> 2,000,000 > 2,000,000 > 1,000,000

Segmented (0.3)

PWS/WY N/A 9.1 (0.2) 9.2 (0.6) 9.3 (0.2)

1.000 Model 1 (0.8) 3.0 N (0.1) 6.0 N (0.8) 9.0 N (0.1) Model 2 (0.2) 6.25 N (0.1) 9.25 N (0.8) 12.25 N (0.1)

Top: 5 Bottom: Model 1 (0.8) 24 (0.1) 43 (0.8) 61.5 (0.1) Model 2 (0.2) 33.5 (0.1) 47.5 (0.8) 61.5 (0.1)

325 (0.101) 430 (0.244) 550 (0.31) 720 (0.244) 1050 (0.101) Wt mean: 590

> 2,000,000 5060 (0.101) 43,150 (0.244) 480,700 (0.31) > 2,000,000 (0.345)

840 (0.101) 2660 (0.244) 9560 (0.244) > 1,000,000 (0.101)

Kodiak

N/A 8.2 (0.2) 8.5 (0.6) 8.8 (0.2)

1.000 5.0 N (0.2) 7.0 N (0.6) 9.0 N (0.2)

Top: 5 (1.0) Bottom: 30 (0.5) 50 (0.5)

250 (0.101) 370 (0.244) 520 (0.31) 770 (0.244) 1370 (0.101) Wt mean: 600

> 2,000,000 (0.899) 46,000 (0.101)

1160 (0.101) 12,000 (0.244) 267,400 (0.31) > 2,000,000 (0.345)

380 (0.101) 1340 (0.244) 7020 (0.31) 101,800 (0.244) > 2,000,000 (0.101)

Semidi 1.0 Unsegmented (1.0)

N/A 7.9 (0.2) 8.2 (0.6) 8.5 (0.2)

0.710 6 N (0.5) 10 N (0.5)

Top: 5 Bottom: 20 (0.2) 24 (0.6) 28 (0.2)

40.0 (0.2) 45.0 (0.6) 50.0 (0.2)

Intraslab 1.0 7.25 (0.3) 7.50 (0.4) 7.75 (0.3)

1.12 0.1 30-120


Table 3 Uniform Hazard Spectra

Spectral Period 72-Year Return

Period 475-Year Return

Period 2,475-Year Return

Period 0.01 0.148 0.379 0.758 0.05 0.223 0.566 1.114 0.10 0.346 0.873 1.733 0.15 0.354 0.909 1.839 0.20 0.324 0.846 1.731 0.30 0.240 0.639 1.324 0.40 0.187 0.509 1.069 0.50 0.146 0.404 0.862 0.75 0.091 0.263 0.587 1.00 0.064 0.192 0.442 1.50 0.036 0.112 0.269 2.00 0.024 0.076 0.187 3.00 0.013 0.043 0.107 4.00 0.009 0.027 0.069 5.00 0.006 0.019 0.046 7.50 0.003 0.011 0.024 10.00 0.002 0.007 0.016


Table 4 Modal M, D and

Return Period (years)

PGA 1.0 sec SA 3.0 sec SA M* D* * M* D* * M* D* *

72 6.1 45 0.75 6.3 45 1.25 7.1 35 0.25 475 6.9 45 1.25 9.3 35 0.25 9.3 35 0.5 2475 9.3 35 0.75 9.3 35 0.75 9.3 35 0.75


Table 5 Comparison of 2014 and 2008 Probabilistic Values in g’s

Return Periods (yrs) PGA 0.3 Sec SA 1.0 Sec SA

72 0.15 (0.16)* 0.24 (0.26) 0.06 (0.10) 475 0.38 (0.34) 0.64 (0.59) 0.19 (0.24)

2,475 0.76 (0.58) 1.32 (1.02) 0.44 (0.44) * 2008 values in parentheses


Table 6

Seed Time Histories

Year Earthquake Station Mag ClstD VS30 Components 72-YRP 475-YRP 2,475-YRP 1997 Michoacan Caleta de Campos 7.1 33 unknown E-W, N-S X X X 2001 Nisqually KIMR 6.8 66 1937 E-W, N-S X X 2001 Nisqually PCEP 6.8 62 1445 E-W, N-S X X X 2011 Tohoku, Japan MYGH12 9 53 unknown E-W, N-S X X 2010 Maule Chile Constitucion 8.8 39 unknown E-W, N-S X


Table 7 Properties of Spectrally-Matched Time Histories

Year Earthquake Station Mag ClstD Component PGA (g) PGV (cm/s) PGD (cm) 5-95% AI(m/sec) 5-95% Dur(sec) 72-Year UHS 1997 Michoacan Caleta de Campos 7.1 33 090 0.148 6.09 1.39 0.445 15.9

360 0.147 6.10 1.59 0.433 16.9 2001 Nisqually KIMR 6.8 66 E 0.145 5.13 1.90 0.155 15.7

N 0.150 5.45 1.17 0.137 21.4 2001 Nisqually PCEP 6.8 62 E 0.145 5.69 1.77 0.244 19.1

N 0.147 6.15 1.85 0.246 18.9 475-Year UHS 1997 Michoacan Caleta de Campos 7.1 33 090 0.381 13.58 4.42 1.548 13.8

360 0.375 15.87 4.69 1.304 14.3 2001 Nisqually KIMR 6.8 66 E 0.377 13.37 6.01 0.494 7.8

N 0.386 14.88 4.75 0.377 9.2 2001 Nisqually PCEP 6.8 62 E 0.377 13.92 4.88 0.576 9.9

N 0.373 19.05 3.90 0.671 11.7 2011 Tohoku MYGH12 9.0 53 E 0.380 17.63 6.15 4.770 117.1

N 0.330 22.02 6.57 4.993 118.9 2,475-Year UHS 1997 Michoacan Caleta de Campos 7.1 33 090 0.764 30.98 11.75 3.253 13.4

360 0.762 39.41 8.95 2.819 13.8 2001 Nisqually PCEP 6.8 62 E 0.759 37.60 15.51 1.622 5.8

N 0.760 35.95 11.78 1.304 7.8 2010 Maule Constitucion 8.8 39 E 0.670 34.23 12.67 19.663 82.3

N 0.627 36.22 11.81 18.582 76.3 2011 Tohoku MYGH12 9.0 53 E 0.748 36.82 13.58 17.695 116.8

N 0.649 49.72 15.48 19.935 118.6

G

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SS

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Turnagain Arm149.7° W

149.7° W

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61.5° N 61.5° N

61.3° N 61.3° N

61.2° N 61.2° N

61° N 61° N

Anchorage PortModernization Project

F0 20 4010

Kilometers

0 3015

Miles

Project No. 26819091

Anchorage PortModernization Project,

Alaska

Figure

1

AREAL IMAGE OF ANCHORAGEAND SITE VICINITY

G

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1964

ALEUTIAN AND ALASKAN SUBDUCTION ZONEAND LARGE HISTORICAL EARTHQUAKES

(M >= 6.5), 1898 TO 2014

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¯Project No. 26819091


Alaska

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1951 M6.3

18990714

19431103

19340504

1912013119640328

19120707

20021103Denali Fault

Bruin

Bay

Fau

lt

Lake

Clark

Fau

lt

Chugach - St. Elias Fault

Castle Mountain Fault

Ken

ai L

inea

men

t

Rude River F

ault

Caribou Fault

Patto

n Bay

Fau

lt

Totschunda FaultDen

ali F

ault

Bruin

Bay

Fau

lt

Denali Fault

Pass

Creek

-

Dutch

Creek

Fau

lt

Littl

e Su

sitn

a

Riv

er S

carp

Hicks Creek FaultParker L

ake

Fault

East Boulder Creek Fault

Lunch Gulch Fault

John

son

Bay

Fau

lt

Cache Creek Fault

Matanuska Glacier Fault

Lake Creek Fault

Totschunda Fault

0 50 100 150 20025

Kilometers

Seismicity above M3.0Magnitudes

! 3.0 - 4.0

! 4.0 - 5.0

, 5.0 - 6.0

, 6.0 - 7.0

%, 7.0 - 9.2

[� Site

200 km radius around Port of Anchorage

Anchorage_100 km_Buffer

FaultsActivity

Historic

Holocene

Late Pleistocene

Quaternary

Neogene

Suspicious

Unnamed

¯

HISTORICAL SEISMICITY AND SIGNIFICANT EARTHQUAKES (M >= 3.0), 1898 TO 2014,

WITHIN 200 KM OF THE PORT



Alaska

Figure

3

GROUND MOTIONPREDICTION MODELS

SOURCEGEOMETRY(Dip, Closest

Distance, Depth)

ACTIVITY MAXIMUMMAGNITUDE

EARTHQUAKERECURRENCE

MODEL

M(0.6)

M - 0.3(0.2)

M + 0.3(0.2)

SEISMICSOURCES

Subduction Zone

Intraslab

Boore et al. (2014)(0.25)

Abrahamson et al. (2014a)

(0.25)

Campbell and Bozorgnia (2014)(0.25)

Chiou and Youngs (2014)(0.25)

Yes

No

Bruin Bay

Castle Mtn.

Subduction Zone

Megathrust

HistoricalSeismicityRecurrence

(1.0)

RECURRENCEMETHOD

Atkinson and Boore (2003)(0.25)

SeeText

Lake Clark

...

Denali

Maximum Magnitude

(0.3)

Characteristic(0.7)

Zhao et al. (2006)(0.25)

Youngs et al. (1997)(0.25)

Zhao et al. (2006)(0.25)

SEISMIC HAZARD MODEL LOGIC TREE

Figure4

Project NO. 26819091


Alaska

median + 1.645*σµ (M, SOF, T)

(0.2)

ADDITIONALEPISTEMIC

UNCERTAINTYON MEDIAN GROUND

MOTION

median - 1.645*σµ (M, SOF, T)

(0.2)

median(0.6)

Abrahamson et al. (2014b)

(0.50)

Abrahamson et al. (2014b)

(0.50)


Alaska


BROWNIAN PASSAGE TIME MODELFigure5

(a) (b)

(c) (d)

((

((((

((

((

((

((

((

((

((

((

((

((

((

(( ((

((

((

(((( ((

((

G

Denali fault

Aleutian M

egathrust

Queen Charlotte fault

Fairweather -

North American Plate

YakutatBlock

Saint Elias

Block

Wrangell Block

Transition fault

Pacific Plate

Ala

ska

Ran

geC

ook

Inle

tKen

ai M

tns.

Chugach Mtns.Castle Mtn. fault

0 125 250 375 500 62562.5

Kilometers

Legend

G Site Location

FaultsActivity

Historic

Holocene

Late Pleistocene

Quaternary

Neogene

Suspicious

Megathrust SystemActivity

(( Historic

(( Late Pleistocene

(( Neogene

¯ALASKAN SUBDUCTION ZONE



Alaska

Figure

6

ISOSEISMAL MAP OF THE 28 MARCH 1964 M 9.2

GREAT ALASKA EARTHQUAKE

Source: Stover and Coffman (1993)

Site

Figure7

Project NO. 26819091


Alaska

((

((

((

(((( ((

((

(( ((

G

Farewell

Tonzo

na-Muldro

w

Muldrow-Alsek

Bruin

Bay

Fau

lt

Lake C

lark

Fault

Chugach - St. Elias Fault


Ken

ai L

inea

men

t

Rude River F

ault

Caribou Fault

Patto

n Bay

Fau

lt

Totschunda FaultDen

ali F

ault

Bruin

Bay

Fau

lt

D e n a l i F a u l t

D e n a l i F a u l t

Pass

Creek

-

Dutch

Cre

ek F

ault

Littl

e Su

sitn

a

Riv

er S

carp

Hicks Creek FaultParker L

ake

Fault

East Boulder Creek Fault

Lunch Gulch Fault

John

son

Bay

Fau

lt

Cache Creek Fault

Matanuska Glacier Fault

Lake Creek Fault

Totschunda Fault

0 50 100 150 20025

Kilometers

Legend

G Site Location

200 km radius around Port of Anchorage

Anchorage_100 km_Buffer

FaultsActivity

Historic

Holocene

Late Pleistocene

Quaternary

Neogene

Suspicious

Unnamed

¯

NEOGENE AND QUATERNARY FAULTSWITHIN 200 KM OF THE PORT

CONSIDERED IN THE HAZARD ANALYSES




Alaska

Figure

8

F

F

F

F

F

F

FF

F

F

F

F

F

F

F

FF

F

F

F

F

FF

G

Bruin

Bay

Fau

lt

Lake C

lark F

ault


Kas

ilot

Big Lake - P

ittman

Ken

ai F

ield

Bel

l Isl

and

Falls

Cre

ek F

ield

Sw

an L

ake

Was

illa S

t 1 -

Nee

dham

Nor

th C

ook

Inle

tB

irch

Hill

Nap

tow

n -

Sun

rise

Lake

-

Bea

ver

Cre

ek

Turn

agai

n Ar

m

Lorr

aine

-

Ala

ska

Gul

f

Pin

cher

Cre

ek

Mid

dle

Gro

und

Sho

al F

ield

Stir

ling

Fie

ld

Beaver Creek

Wes

t For

k F

ield

Swanson River Field

Gra

nite

Poi

nt F

ield

Bel

uga

Riv

er F

ield

Red

oubt

Sho

al

Fie

ld

Ivan River Field

Stump Lake Field

0 20 40 60 80 10010

Kilometers

Legend

G Site Location

Cook Inlet folds

F > Quaternary or Unknown

F Quaternary or Suspected Quaternary

Faults<all other values>

Activity

Historic

Holocene

Late Pleistocene

Quaternary

Neogene

Suspicious

¯

NEOGENE AND QUATERNARY FAULTS AND FOLDS IN THE COOK INLET AREA



Alaska

Figure

9


Figure10

STEPP PLOTS FOR ESTIMATINGCOMPLETENESS INTERVALSAnchorage Port

Modernization ProjectAlaska


0.00

0.01

0.10

1.00

10.00

100.00

1 10 100

Annual Cummulative Number of Events

Year

Crustal Earthquakes

M 3.0 ‐3.5

M 3.5‐4.0

M 4.0‐4.5

M 4.5‐5.0

M 5.0‐5.5

M 5.5‐6.0

M6.0‐6.5

M6.5‐7.0

M7.0‐7.5

0.01

0.10

1.00

10.00

100.00

1000.00

1 10 100

Annual Cummulative Number of Events

Year

Intraplate Earthquakes

M 3.0 ‐3.5

M 3.5‐4.0

M 4.0‐4.5

M 4.5‐5.0

M 5.0‐5.5

M 5.5‐6.0

M6.0‐6.5

M6.5‐7.0

M7.0‐7.5

G

Area used for crustal recurrence calculations

145°0'0"W

145°0'0"W

150°0'0"W

150°0'0"W

155°0'0"W

155°0'0"W

64°0'0"N 64°0'0"N

63°0'0"N 63°0'0"N

62°0'0"N 62°0'0"N

61°0'0"N 61°0'0"N

60°0'0"N 60°0'0"N

59°0'0"N 59°0'0"N

CRUSTAL EARTHQUAKES USED IN THERECURRENCE CALCULATIONS

1988 TO 2014

0 50 100 150 20025Kilometers

±Magnitude

4.0 - 5.0

5.1 - 5.5

5.6 - 6.0

6.1 - 6.5

6.6 - 7.5



Alaska

Figure

11


4 5 6 7Magnitude

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

Cum

ulat

ive

Num

bero

fAnn

ualE

vent

s/km

2

N=138Log N = -1.15 - (0.90 0.05) ML

Area = 210,930 km2

Magnitude Time No. ofRange Period Events

4.00 4.50 1980-2014 794.50 5.00 1980-2014 335.00 5.50 1980-2014 145.50 6.00 1932-2014 86.00 6.50 1925-2014 36.50 7.00 1925-2014 07.00 7.30 1898-2014 1

CRUSTAL BACKGROUNDEARTHQUAKE RECURRENCE

Figure12


Alaska


SEISMICITY CROSS-SECTION THROUGH ALASKANSUBDUCTION ZONE NEAR ANCHORAGE

Source: Veilleux and Doser, 2007

(NW) (SE)

Figure13


Alaska


((((

((((

((

((

((

((

((

((

((

((

((

((

((

((

((

((

((

((

((

((

((

((

((((

((

((

((

((

[�

5 km depth

30 km depth

40 km depth

60 km depth

95 km depth

Semidi

Kodiak

Prince

Will

iam

Sou

nd /

Yaka

taga35 km

depth45 km

depth75 km

depth

145°0'0"W

145°0'0"W

150°0'0"W

150°0'0"W

155°0'0"W

155°0'0"W160°0'0"W

62°0'0"N

62°0'0"N

61°0'0"N61°0'0"N

60°0'0"N60°0'0"N

59°0'0"N59°0'0"N

58°0'0"N58°0'0"N

57°0'0"N57°0'0"N

56°0'0"N56°0'0"N

55°0'0"N55°0'0"N

PREFERRED MODEL OF MEGATHRUST WADATI-BENIOFF ZONE USED IN

THE HAZARD ANALYSIS

0 75 150 225 30037.5

Kilometers

±

[� Site(( (( Megathrust



Alaska

Figure

14

Area Use

d in

Recurre

nce C

alculatio

n

145°0'0"W

145°0'0"W

150°0'0"W

150°0'0"W

155°0'0"W

155°0'0"W160°0'0"W

64°0'0"N

63°0'0"N

63°0'0"N

62°0'0"N

62°0'0"N

61°0'0"N

61°0'0"N

60°0'0"N

60°0'0"N

59°0'0"N

59°0'0"N

58°0'0"N58°0'0"N

57°0'0"N57°0'0"N

56°0'0"N56°0'0"N

INTRASLAB EARTHQUAKES USED IN THERECURRENCE CALCULATIONS

1911 TO 2014

0 80 160 240 32040Kilometers

±Magnitude

4.5 - 5.0

5.0 - 5.5

5.5 - 6.0

6.0 - 6.5

6.5 - 7.5



Alaska

Figure

15

4 5 6 7Magnitude

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

Cum

ulat

ive

Num

bero

fAnn

ualE

vent

s/km

2

N=495Log N = 0.61 - (1.12 0.04) ML

Area = 380,000 km2

Magnitude Time No. ofRange Period Events

4.50 5.00 1980-2014 3695.00 5.50 1980-2014 865.50 6.00 1980-2014 216.00 6.50 1932-2014 146.50 7.00 1932-2014 57.00 7.30 1898-2014 0

INTRASLAB EARTHQUAKE RECURRENCE Figure16


Alaska


0.01 0.1 1Peak Ground Acceleration (g)

1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100

1x101An

nual

Freq

uenc

yof

Exce

eden

ce

Figure17

SEISMIC HAZARD CURVES FORPEAK HORIZONTAL ACCELERATION

100,000

10,000

1,000

100

10

1

0.1

Return

Period(years)

5th and 95th Percentile15th and 85th Percentile50th PercentileTotal Mean Hazard


Alaska


0.01 0.1 1Spectral Acceleration (g)

1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100An

nual

Freq

uenc

yof

Exce

eden

ce

Figure18

SEISMIC HAZARD CURVES FOR 1.0 SECHORIZONTAL SPECTRAL ACCELERATION

100,000

10,000

1,000

100

10

1

Return

Period(years)



Alaska



1x10-5

1x10-4

1x10-3

1x10-2

1x10-1An

nual

Freq

uenc

yof

Exce

eden

ce

Figure19

SEISMIC HAZARD CURVES FOR 3.0 SECHORIZONTAL SPECTRAL ACCELERATION

100,000

10,000

1,000

100

10

Return

Period(years)



Alaska



1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100

1x101An

nual

Freq

uenc

yof

Exce

edan

ce

100,000

10,000

1,000

100

10

1

0.1

Return

Period(years)

Figure20

Project No. 26819091Anchorage Port


SEISMIC SOURCE CONTRIBUTIONS TO MEANPEAK HORIZONTAL ACCELERATION HAZARD


1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100An

nual

Freq

uenc

yof

Exce

edan

ce

100,000

10,000

1,000

100

10

1

Return

Period(years)

Figure21



SEISMIC SOURCE CONTRIBUTIONS TOMEAN 1.0 SEC HORIZONTAL SPECTRAL

ACCELERATION HAZARD


1x10-5

1x10-4

1x10-3

1x10-2

1x10-1An

nual

Freq

uenc

yof

Exce

edan

ce

100,000

10,000

1,000

100

10

Return

Period(years)

Figure22



Alaska

SEISMIC SOURCE CONTRIBUTIONS TOMEAN 3.0 SEC HORIZONTAL SPECTRAL

ACCELERATION HAZARD


1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100An

nual

Exce

edan

ceFr

eque

ncy

100,000

10,000

1,000

100

10

1

Return

Period(years)

Figure23



Alaska

SENSITIVITY OF MEAN PEAK HORIZONTALACCELERATION HAZARD TO

TIME-DEPENDENT RATES FOR MEGATHRUST


1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100An

nual

Exce

edan

ceFr

eque

ncy

100,000

10,000

1,000

100

10

1

Return

Period(years)

Figure24



Alaska

SENSITIVITY OF MEAN 1.0 SEC HORIZONTALSPECTRAL ACCELERATION HAZARD TO



1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100An

nual

Exce

edan

ceFr

eque

ncy

100,000

10,000

1,000

100

10

1

Return

Period(years)

Figure25



Alaska

SENSITIVITY OF MEAN 3.0 SEC HORIZONTALSPECTRAL ACCELERATION HAZARD TO


Magnitude

Distance (km)

Prop

ortio

n

Magnitude

Epsilon2 to 31 to 20 to 1-1 to 0-2 to -1


Alaska

Project No. 26819091 MAGNITUDE AND DISTANCE CONTRIBUTIONSTO THE MEAN PEAK HORIZONTAL

ACCELERATION HAZARDAT 72-YEAR RETURN PERIOD

Figure26VS30 = 760 m/sec

Magnitude

Distance (km)

Prop

ortio

n

Magnitude



Alaska


ACCELERATION HAZARDAT 475-YEAR RETURN PERIOD


Magnitude

Distance (km)

Prop

ortio

n

Magnitude



Alaska


ACCELERATION HAZARDAT 2,475-YEAR RETURN PERIOD


Magnitude

Distance (km)

Prop

ortio

n

Magnitude



Alaska

Project No. 26819091 MAGNITUDE AND DISTANCE CONTRIBUTIONSTO THE MEAN 1.0 SEC HORIZONTALSPECTRAL ACCELERATION HAZARD

AT 72-YEAR RETURN PERIOD


Magnitude

Distance (km)

Prop

ortio

n

Magnitude



Alaska




Magnitude

Distance (km)

Prop

ortio

n

Magnitude



Alaska


AT 2,475-YEAR RETURN PERIOD


Magnitude

Distance (km)

Prop

ortio

n

Magnitude



Alaska




Magnitude

Distance (km)

Prop

ortio

n

Magnitude



Alaska


AT 2,475-YEAR RETURN PERIOD



1E-005

0.0001

0.001

0.01

0.1

1An

nual

Freq

uenc

yof

Exce

eden

ce

100,000

10,000

1,000

100

10

1

Return

Period(years)

Figure35Anchorage Port


Project No. 26819091 SENSITIVITY OF THE PEAK HORIZONTALACCELERATION HAZARD FROM CRUSTAL

SOURCES TO THE SELECTION OFGROUND MOTION MODELS

Abrahamson et al. (2014a)Abrahamson et al. (2014a) -

+/- additional epistemic uncertainty on medianChiou and Youngs (2014)Chiou and Youngs (2014) -

+/- additional epistemic uncertainty on medianCampbell and Bozorgnia (2014)Campbell and Bozorgnia (2014) -

+/- additional epistemic uncertainty on medianBoore et al. (2014)Boore et al. (2014) -

+/- additional epistemic uncertainty on medianWt. Total Mean Hazard


1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100An

nual

Freq

uenc

yof

Exce

edan

ce

100,000

10,000

1,000

100

10

1

Return

Period(years)



Project No. 26819091 SENSITIVITY OF THE PEAK HORIZONTALACCELERATION HAZARD FROM THEINTRASLAB TO THE SELECTION OF

GROUND MOTION MODELS

Zhao et al. (2006)Abrahamson et al. (2014b)Atkinson and Boore (2003)Total Mean Hazard from the Intraslab


1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100An

nual

Exce

eden

ceFr

eque

ncy

100,000

10,000

1,000

100

10

1

Return

Period(years)



Project No. 26819091 SENSITIVITY OF THE PEAK HORIZONTALACCELERATION HAZARD FROM THE

MEGATHRUST TO THE SELECTION OFGROUND MOTION MODELS

Zhao et al. (2006)Youngs et al. (1997)Abrahamson et al. (2014b)Total Mean Hazard from the Megathrust


1E-005

0.0001

0.001

0.01An

nual

Freq

uenc

yof

Exce

eden

ce

100,000

10,000

1,000

100

10

Return

Period(years)



Project No. 26819091 SENSITIVITY OF THE 3.0 SEC HORIZONTALSPECTRAL ACCELERATION HAZARD FROM

CRUSTAL SOURCES TO THE SELECTIONOF GROUND MOTION MODELS

Abrahamson et al. (2014a)Abrahamson et al. (2014a) -

+/- additional epistemic uncertainty on medianChiou and Youngs (2014)Chiou and Youngs (2014) -

+/- additional epistemic uncertainty on medianCampbell and Bozorgnia (2014)Campbell and Bozorgnia (2014) -

+/- additional epistemic uncertainty on medianBoore et al. (2014)Boore et al. (2014) -

+/- additional epistemic uncertainty on medianWt. Total Mean Hazard


1x10-5

1x10-4

1x10-3

1x10-2

1x10-1An

nual

Freq

uenc

yof

Exce

edan

ce

100,000

10,000

1,000

100

10

Return

Period(years)



Project No. 26819091 SENSITIVITY OF THE 3.0 SEC HORIZONTALSPECTRAL ACCELERATION HAZARD FROM

THE INTRASLAB TO THE SELECTION OFGROUND MOTION MODELS

Zhao et al. (2006)Abrahamson et al. (2014b)Atkinson and Boore (2003)Total Mean Hazard from the Intraslab


1x10-5

1x10-4

1x10-3

1x10-2

1x10-1An

nual

Exce

eden

ceFr

eque

ncy

100,000

10,000

1,000

100

10

Return

Period(years)



Project No. 26819091 SENSITIVITY OF THE 3.0 SEC HORIZONTALSPECTRAL ACCELERATION HAZARD FROMTHE MEGATHRUST TO THE SELECTION OF

GROUND MOTION MODELS

Zhao et al. (2006)Youngs et al. (1997)Abrahamson et al. (2014b)Total Mean Hazard from the Megathrust

0.01 0.1 1 10Period (s)

0.00

0.50

1.00

1.50

2.00Sp

ectra

lAcc

eler

atio

n(g

)

Figure41

5%-DAMPED UNIFORM HAZARD SPECTRAAT 72, 475 AND 2,475-YEAR RETURN PERIODS


Alaska


72-Year Return Period UHS475-Year Return Period UHS2,475-Year Return Period UHS

5% Damping

0.01 0.1 1 10Period (s)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Spec

tralA

ccel

erat

ion

(g)

Figure42

SENSITIVITY OF MEDIAN AND 84TH PERCENTILEDETERMINISTIC SPECTRA FOR M 7.5 INTRASLAB

EVENT TO GROUND MOTION MODELSAnchorage Port



84th Percentile DeterministicWt. MeanAtkinson and Boore 2006Abrahamson et al. 2014bZhao et al. 2006

5% Damping

0.01 0.1 1 10Period (s)0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Spec

tralA

ccel

erat

ion

(g)

MedianWt. MeanAtkinson and Boore 2006Abrahamson et al. 2014bZhao et al. 2006

0.01 0.1 1 10Period (s)

0.00

0.50

1.00

1.50

2.00

2.50

Spec

tralA

ccel

erat

ion

(g)

Figure43

SENSITIVITY OF MEDIAN AND 84TH PERCENTILEDETERMINISTIC SPECTRA FOR M 9.2 MEGATHRUST

EVENT TO GROUND MOTION MODELS


Alaska


84th Percentile DeterministicWt. MeanYoungs 1997Abrahamson et al. 2014bZhao et al. 2006

5% Damping

0.01 0.1 1 10Period (s)0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Spec

tralA

ccel

erat

ion

(g)

MedianWt. MeanYoungs 1997Abrahamson et al. 2014bZhao et al. 2006

0.01 0.1 1 10Period (s)

0.00

0.50

1.00

1.50

2.00Sp

ectra

lAcc

eler

atio

n(g

)

Figure44

MEDIAN DETERMINISTIC SPECTRA FORINTRASLAB AND MEGATHRUST EVENTS

COMPARED TO UHS AT 72, 475AND 2,475 YEAR RETURN PERIODS


Alaska


72-year UHS475-year UHS2475-year UHSMedian Deterministic, M 7.5 Intraslab EarthquakeMedian Deterministic, M 9.2 Megathrust Earthquake

5% Damping

0.1 1 10 100Frequency (Hz)

0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)

MICH-CALE-360MICH-CALE-090NISQ-KIMR-ENENISQ-KIMR-ENNNISQ-PECP-ENENISQ-PECP-ENN

72-YRP UHS

Figure45

SCALED RESPONSE SPECTRA FOR SEEDSUSED IN SPECTRAL MATCHING FOR

INTRASLAB/CRUSTAL EVENTSFOR THE 72-YEAR RETURN PERIOD UHS




0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)

MICH-CALE-000MICH-CALE-090NISQ-KIMR-ENENISQ-KIMR-ENNNISQ-PECP-ENENISQ-PECP-ENNTOHOKU-MYGH12-ETOHOKU-MYGH12-N

475-YRP UHS

Figure46

SCALED RESPONSE SPECTRA FOR SEEDSUSED IN SPECTRAL MATCHING FOR

INTRASLAB/CRUSTAL EVENTSFOR THE 475-YEAR RETURN PERIOD UHS




0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)

MICH-CALE-000MICH-CALE-090NISQ-PECP-ENENISQ-PECP-ENN

2,475-YRP UHS

Figure47

SCALED RESPONSE SPECTRA FOR INTRASLABSEEDS USED IN SPECTRAL MATCHING

FOR THE 2,475-YEAR RETURN PERIOD UHSAnchorage Port




0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)

TOHOKU-MYGH12-ETOHOKU-MYGH12-NMAULE-CONST-EMAULE-CONST-N

2,475-YRP UHS

Figure48

SCALED RESPONSE SPECTRA FOR MEGATHRUSTSEEDS USED IN SPECTRAL MATCHING

FOR THE 2,475-YEAR RETURN PERIOD UHSAnchorage Port



0 20 40 60 80Time (sec)

-0.4

0

0.4Ac

cele

ratio

n(g

) Horizontal 1 (South)Acceleration

0 20 40 60 80Time (sec)

-0.4

0

0.4

Acce

lera

tion

(g) Horizontal 2 (East)

Acceleration

Figure49

1996 MICHOACAN EARTHQUAKEMw = 7.1, DEPTH = 33 kM

STATION CALETA DE CAMPOS, MEXICOHYPOCENTRAL DISTANCE 37 kM

Project No. 26819091SEED TIME HISTORY - HORIZONTAL1997 MICHOACAN EARTHQUAKE

CALETA DE CAMPOS SEEDAnchorage Port


0 20 40 60 80 100Time (sec)

-0.2

-0.1

0

0.1

0.2Ac

cele

ratio

n(g

) EastPGA = 0.163 g

0 20 40 60 80 100Time (sec)

-0.2

-0.1

0

0.1

0.2

Acce

lera

tion

(g) North

PGA = 0.150 g

Figure50

TIME HISTORIES2001 NISQUALLY EARTHQUAKE

KITSAP COUNTY AIRPORT, BREMERTON (KIMR)

NEHRP Site Class = CVs30 = 1937 ft/s

Hypocentral Distance = 66 km Project No. 26819091


Alaska

0 20 40 60 80 100Time (sec)

-0.2

-0.1

0

0.1

0.2Ac

cele

ratio

n(g

) EastPGA = 0.204 g

0 20 40 60 80 100Time (sec)

-0.2

-0.1

0

0.1

0.2

Acce

lera

tion

(g) North

PGA = 0.213 g

Figure51

TIME HISTORIES2001 NISQUALLY EARTHQUAKE

PIERCE COUNTY EAST PRECINCT, PUYALLUP(PCEP)

NEHRP Site Class = CVs30 = 1445 ft/s

Hypocentral Distance = 62 km Project No. 26819091


Alaska

0 20 40 60 80 100 120 140 160 180 200 220 240Time (sec)

-0.6

-0.2

0.2

0.6Ac

cler

atio

n(g

) ENE

0 20 40 60 80 100 120 140 160 180 200 220 240Time (sec)

-0.6

-0.2

0.2

0.6

Accl

erat

ion

(g) ENN

Figure52

SEED TIME HISTORIES2011 TOHOKU EARTHQUAKE

MYGH12 SEED

Tohoku, Japan 2011 M9.0MYGH12

Epicentral dist = 88 kmFault dist = 53 km

PGA=0.54g



Alaska

0 20 40 60 80 100 120 140Time (sec)

-0.6

-0.2

0.2

0.6Ac

cler

atio

n(g

) Horizontal 1

0 20 40 60 80 100 120 140Time (sec)

-0.6

-0.2

0.2

0.6

Accl

erat

ion

(g) Horizontal 2

Figure53

SEED TIME HISTORIES2010 MAULE CHILE EARTHQAUKE

CONSTITUCION SEED

Maule, Chile 2010 M8.8Constitucion

Epicentral dist = 70 kmFault dist = 39 km

PGA=0.64g



Alaska


0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)

TargetSpectrally- Matched Time History

Figure54

RESPONSE SPECTRA FOR TIME HISTORYSPECTRALLY-MATCHED TO 72-YEAR UHS

TARGET 1997 MICHOACAN -CALETA DE CAMPOS (090) SEED


Modernization Project,Alaska

0 10 20 30 40 50 60Time (sec)

-0.25

0.00

0.25Ac

cele

ratio

n(g

)

-0.5

0

0.5

0 10 20 30 40 50 60Time (sec)

-10

0

10

Velo

city

(cm

/s)

-20

0

20

0 10 20 30 40 50 60Time (sec)

0

Dis

plac

emen

t(cm

)

0

0 10 20 30 40 50 60Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity

Spectrally- Matched Time HistoryRecorded Time History

Figure55

TIME HISTORY SPECTRALLY-MATCHEDTO 72-YEAR UHS

1997 MICHOACAN -CALETA DE CAMPOS (090) SEED


Alaska



0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure56





0 10 20 30 40 50 60Time (sec)

-0.25

0.00

0.25Ac

cele

ratio

n(g

)

-0.5

0

0.5

0 10 20 30 40 50 60Time (sec)

-10

0

10

Velo

city

(cm

/s)

-20

0

20

0 10 20 30 40 50 60Time (sec)

-5

0

5

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure57




Alaska



0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure58


TARGET 2001 NISQUALLY -KIMR (ENE) SEED



0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.25

0.00

0.25Ac

cele

ratio

n(g

)

-0.25

0

0.25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-10

0

10

Velo

city

(cm

/s)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-5

0

5

Dis

plac

emen

t(cm

)

-5

0

5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure59






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)

TargetSpectrally-Matched Time History

Figure60


TARGET 2001 NISQUALLY -KIMR (ENN) SEED



0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.25

0.00

0.25Ac

cele

ratio

n(g

)

-0.25

0

0.25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-10

0

10

Velo

city

(cm

/s)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-5

0

5

Dis

plac

emen

t(cm

)

-5

0

5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity

Spectrally-Matched Time HistoryRecorded Time History

Figure61






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure62


TARGET 2001 NISQUALLY -PCEP (ENE) SEED



0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.25

0.00

0.25Ac

cele

ratio

n(g

)

-0.25

0

0.25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-15

0

15

Velo

city

(cm

/s)

-15

0

15

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-5

0

5

Dis

plac

emen

t(cm

)

-5

0

5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure63






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure64


TARGET 2001 NISQUALLY -PCEP (ENN) SEED



0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.20

0.00

0.20Ac

cele

ratio

n(g

)

-0.2

0

0.2

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-10

0

10

Velo

city

(cm

/s)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-5

0

5

Dis

plac

emen

t(cm

)

-5

0

5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure65






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure66





0 10 20 30 40 50 60Time (sec)

-0.50

-0.25

0.00

0.25

0.50Ac

cele

ratio

n(g

)

-0.5

0

0.5

0 10 20 30 40 50 60Time (sec)

-50

0

50

Velo

city

(cm

/s)

-50

0

50

0 10 20 30 40 50 60Time (sec)

-10

0

10

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure67




Alaska



0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure68





0 10 20 30 40 50 60Time (sec)

-0.50

-0.25

0.00

0.25

0.50Ac

cele

ratio

n(g

)

-0.5

0

0.5

0 10 20 30 40 50 60Time (sec)

-50

0

50

Velo

city

(cm

/s)

-50

0

50

0 10 20 30 40 50 60Time (sec)

-10

0

10

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure69




Alaska



0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure70





0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.50

-0.25

0.00

0.25

0.50Ac

cele

ratio

n(g

)

-0.5

0

0.5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-20

0

20

Velo

city

(cm

/s)

-20

0

20

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-10

0

10

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure71






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure72





0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.25

0.00

0.25Ac

cele

ratio

n(g

)

-0.25

0

0.25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-25

0

25

Velo

city

(cm

/s)

-25

0

25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-10

0

10

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure73






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure74





0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.50

0.00

0.50Ac

cele

ratio

n(g

)

-0.5

0

0.5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-25

0

25

Velo

city

(cm

/s)

-25

0

25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-10

0

10

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure75






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure76





0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.50

-0.25

0.00

0.25

0.50Ac

cele

ratio

n(g

)

-0.5

0

0.5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-25

0

25

Velo

city

(cm

/s)

-25

0

25

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-10

0

10

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure77






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure78


TARGET 2012 TOHOKU -MYGH12 (E) SEED



0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-1.00

-0.50

0.00

0.50

1.00Ac

cele

ratio

n(g

)

-2

-1

0

1

2

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-50

0

50

Velo

city

(cm

/s)

-200

-100

0

100

200

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-20

-10

0

10

20

Dis

plac

emen

t(cm

)

-400

-200

0

200

400

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure79






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure80


TARGET 2011 TOHOKU -MYGH12 (N) SEED



0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-1.00

-0.50

0.00

0.50

1.00Ac

cele

ratio

n(g

)

-2

-1

0

1

2

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-50

0

50

Velo

city

(cm

/s)

-200

-100

0

100

200

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-20

-10

0

10

20

Dis

plac

emen

t(cm

)

-400

-200

0

200

400

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure81






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure82

RESPONSE SPECTRA FOR TIME HISTORYSPECTRALLY-MATCHED TO 2,475-YEAR UHS




0 10 20 30 40 50 60Time (sec)

-1.00-0.75-0.50-0.250.000.250.500.751.00

Acce

lera

tion

(g)

-0.5

0

0.5

0 10 20 30 40 50 60Time (sec)

-100

-50

0

50

100

Velo

city

(cm

/s)

-50

0

50

0 10 20 30 40 50 60Time (sec)

-30

-20

-10

0

10

20

30

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure83

TIME HISTORY SPECTRALLY-MATCHEDTO 2,475-YEAR UHS1997 MICHOACAN -

CALETA DE CAMPOS (360) SEED


Alaska



0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure84





0 10 20 30 40 50 60Time (sec)

-1.00-0.75-0.50-0.250.000.250.500.751.00

Acce

lera

tion

(g)

-0.5

0

0.5

0 10 20 30 40 50 60Time (sec)

-100

-50

0

50

100

Velo

city

(cm

/s)

-50

0

50

0 10 20 30 40 50 60Time (sec)

-30

-20

-10

0

10

20

30

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure85

TIME HISTORY SPECTRALLY-MATCHEDTO 2,475-YEAR UHS1997 MICHOACAN -

CALETA DE CAMPOS (090) SEED


Alaska



0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure86





0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-0.50

0.00

0.50Ac

cele

ratio

n(g

)

-0.5

0

0.5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-50

0

50

Velo

city

(cm

/s)

-50

0

50

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-20

-10

0

10

20

Dis

plac

emen

t(cm

)

-20

-10

0

10

20

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure87

TIME HISTORY SPECTRALLY-MATCHEDTO 2,475-YEAR UHS





0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure88





0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-1.00-0.75-0.50-0.250.000.250.500.751.00

Acce

lera

tion

(g)

-0.5

0

0.5

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-50

0

50

Velo

city

(cm

/s)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

-20

-10

0

10

20

Dis

plac

emen

t(cm

)

-10

0

10

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity

Matched Time HistoryRecorded Time History

Figure89






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure90





0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-1.00

-0.50

0.00

0.50

1.00Ac

cele

ratio

n(g

)

-2

0

2

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-50

0

50

Velo

city

(cm

/s)

-200

-100

0

100

200

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-40

-20

0

20

40

Dis

plac

emen

t(cm

)

-400

-200

0

200

400

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure91






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure92


TARGET 20012 TOHONKU -MYGH12 (N) SEED



0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-1.00

-0.50

0.00

0.50

1.00Ac

cele

ratio

n(g

)

-2

0

2

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-50

0

50

Velo

city

(cm

/s)

-200

-100

0

100

200

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

-40

-20

0

20

40

Dis

plac

emen

t(cm

)

-400

-200

0

200

400

0 25 50 75 100 125 150 175 200 225 250 275 300Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure93






0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure94


TARGET 2010 MAULE, CHILE -CONSTITUCION (E) SEED



0 20 40 60 80 100 120 140Time (sec)

-2.00

-1.00

0.00

1.00

2.00Ac

cele

ratio

n(g

)

-0.8

-0.4

0

0.4

0.8

0 20 40 60 80 100 120 140Time (sec)

-40

-20

0

20

40

Velo

city

(cm

/s)

-40

-20

0

20

40

0 20 40 60 80 100 120 140Time (sec)

-40

-20

0

20

40

Dis

plac

emen

t(cm

)

-40

-20

0

20

40

0 20 40 60 80 100 120 140Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure95


TARGET 2010 MAULE, CHILE -CONSTITUCION (E) SEED




0.00

0.01

0.10

1.00

10.00

Spec

tralA

ccel

erat

ion

(g)


Figure96


TARGET 2010 MAULE, CHILE -CONSTITUCION (N) SEED



0 10 20 30 40 50 60 70 80 90 100 110 120 130 140Time (sec)

-2.00

-1.00

0.00

1.00

2.00Ac

cele

ratio

n(g

)

-0.8

-0.4

0

0.4

0.8

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140Time (sec)

-40

-20

0

20

40

Velo

city

(cm

/s)

-40

-20

0

20

40

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140Time (sec)

-40

-20

0

20

40

Dis

plac

emen

t(cm

)

-40

-20

0

20

40

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140Time (sec)

0.0

0.5

1.0

Nor

mal

ized

Aria

sIn

tens

ity


Figure97


TARGET 2010 MAULE, CHILE -CONSTITUCION (N) SEED



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