FINAL REPORT
2013 UPDATE TO THE SITE-SPECIFIC SEISMIC HAZARD ANALYSES AND DEVELOPMENT OF SEISMIC DESIGN GROUND MOTIONS
STANFORD UNIVERSITY, CALIFORNIA
Prepared for Stanford University Stanford, California
28 April 2014
Patricia Thomas, Ivan Wong, and Judith Zachariasen URS Corporation Seismic Hazards Group 1333 Broadway, Suite 800 Oakland, California 94612
Robert Darragh and Walt Silva Pacific Engineering & Analysis 856 Seaview Dr. El Cerrito, CA 94530
TABLE OF CONTENTS
Executive Summary ...... ES-1
Section 1 ONE Introduction ...... 1-1
1.1 Scope of Work ...... 1-1 1.2 Acknowledgments...... 1-2
Section 2 TWO Seismic Hazard Analyses Methodologies ...... 2-1
2.1 Probabilistic Seismic Hazard Analysis ...... 2-1 2.2 Seismic Source Characterization ...... 2-2 2.2.1 Source Geometry ...... 2-2 2.2.2 Fault Recurrence ...... 2-3 2.3 Ground Motion Characterization ...... 2-4 2.4 Deterministic Seismic Hazard Analysis ...... 2-4
Section 3 THREE Campus Geotechnical Characterization ...... 3-1
Section 4 FOUR Inputs to Analyses ...... 4-1
4.1 Seismic Sources ...... 4-1 4.1.1 Faults ...... 4-1 4.1.2 Background Seismicity ...... 4-7 4.2 Ground Motion Prediction Models ...... 4-7
Section 5 FIVE PSHA Results ...... 5-1
Section 6 SIX DSHA Results ...... 6-1
Section 7 SEVEN Site Response Analysis ...... 7-1
Section 8 EIGHT Design Response Spectra for New Buildings ...... 8-1
8.1 ASCE 7-10 Methodology ...... 8-1 8.2 MCER and DRSR for Zones 1, 2 and 3 ...... 8-1 8.3 MCER and DRSR for Zone 0 ...... 8-2 8.4 Design Acceleration Parameters ...... 8-3
Section 9 NINE Design Response Spectra for Existing Buildings...... 9-1
9.1 ASCE 41-13 Methodology ...... 9-1 9.2 BSE-1E and BSE-2E for Zones 1, 2, and 3 ...... 9-1 9.3 BSE-1E and BSE-2E for Zone 0 ...... 9-2
Section 10 TEN Comparison With 2010 Spectra and General Code Spectra ...... 10-1
10.1 Comparison of Site-Specific and General Code Design Spectra ...... 10-1 10.1.1 Design Spectra for New Buildings ...... 10-1
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10.1.2 Design Spectra for Existing Buildings ...... 10-1 10.2 Comparison With 2010 Spectra ...... 10-2 10.2.1 Design Spectra for New Buildings ...... 10-2 10.2.2 Design Spectra for Existing Buildings ...... 10-2
Section 11 ELEVEN Conditional Mean Spectra ...... 11-1
11.1 CMS Implementation ...... 11-1 11.2 Example CMS at Stanford ...... 11-2
Section 12 TWELVE Final Remarks ...... 12-1
Section 13 THIRTEEN References ...... 1
Appendix A-1 Bay Area Time-Independent Seismic Source Parameters
Tables
3-1 VS30 and NEHRP Site Classes
8-1 MCER (BSE-2N) and DRSR (BSE-1N) Spectra 8-2 Design Acceleration Parameters 9-1 BSE-1E and BSE-2E Spectra 10-1 Factors Impacting 84th Percentile Deterministic for Zone 0
Figures
1-1 Historical Seismicity in the San Francisco Bay Region (M 3.0) 1800-2013 1-2 Active Faults in the San Francisco Bay Region 1-3 Active Faults in the Vicinity of the Site 2-1 Seismic Hazard Model Logic Tree 3-1 SASW Survey Locations and Quaternary Geology
3-2 All SASW VS Profiles
3-3 West Campus SASW VS Profiles
3-4 North-Central Campus SASW VS Profiles
3-5 East Campus SASW VS Profiles
3-6 Comparison of Lognormal Average VS Profiles for East and North Central Campus
3-7 West Campus VS Profiles 5-1 Locations of Hazard Computations 5-2 Seismic Hazard Curves for Peak Horizontal Acceleration for Site 1 and Reference Site Condition
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5-3 Seismic Hazard Curves for 1.0 sec Horizontal Spectral Acceleration for Site 1 and Reference Site Condition 5-4 Comparison of Peak Horizontal Acceleration Hazard for all Sites at Reference Site Condition 5-5 Comparison of 1.0 sec Horizontal Spectral Acceleration Hazard for all Sites at Reference Site Condition 5-6 Seismic Source Contributions to Peak Horizontal Acceleration Hazard for Site 1 and Reference Site Condition 5-7 Seismic Source Contributions to 1.0 Sec Horizontal Spectral Acceleration Hazard for Site 1 and Reference Site Condition 5-8 Magnitude and Distance Contributions to the Mean Peak Horizontal Acceleration Hazard at 225-Year Return Period for Site 1 5-9 Magnitude and Distance Contributions to the Mean Peak Horizontal Acceleration Hazard at 975-Year Return Period for Site 1 5-10 Magnitude and Distance Contributions to the Mean Peak Horizontal Acceleration Hazard at 2,475-Year Return Period for Site 1 5-11 Magnitude and Distance Contributions to the Mean 1.0 Sec Horizontal Spectral Acceleration Hazard at 225-Year Return Period for Site 1 5-12 Magnitude and Distance Contributions to the Mean 1.0 Sec Horizontal Spectral Acceleration Hazard at 975-Year Return Period for Site 1 5-13 Magnitude and Distance Contributions to the Mean 1.0 Sec Horizontal Spectral Acceleration Hazard at 2,475-Year Return Period for Site 1 5-14 Sensitivity of the Peak Horizontal Acceleration Hazard to the Selection of Ground Motion Models for Site 1 and Reference Site Condition 5-15 Sensitivity of the 1.0 Sec Horizontal Spectral Acceleration Hazard to the Selection of Ground Motion Models for Site 1 and Reference Site Condition 5-16 5%-Damped Uniform Hazard Spectra at Reference Site Condition 6-1 Sensitivity of 84th Percentile Horizontal Acceleration Response Spectrum for the M 8.0 San Andreas Maximum Earthquake at 5.5 km to Ground Motion Models 6-2 Sensitivity of 84th Percentile Horizontal Acceleration Response Spectrum for the M 8.0 San Andreas Maximum Earthquake at 7.5 km to Ground Motion Models 6-3 84th Percentile Horizontal Acceleration Response Spectrum for the M 8.0 San Andreas Maximum Earthquake 6-4 Comparison of 84th Percentile Deterministic Spectra Using NGA-West1 and NGA- West2 Ground Motion Models 7-1 Example Randomized Velocity Profiles for North-Central/East Campus for One Bedrock Depth 7-2 Site-Specific Amplification Factors for Ground Motion Level of 0.5 g (PGA) 7-3 5%-Damped Uniform Hazard Spectra for Sites 1, 2, and 3 at the Ground Surface
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7-4 84th Percentile Horizontal Acceleration Response Spectrum for the M 8.0 San Andreas Maximum Earthquake at the Ground Surface 7-5 Comparison of Uniform Hazard Spectra and 84th Percentile Deterministic Spectra for Sites 1, 2, and 3 at the Ground Surface 7-6 5%-Damped Uniform Hazard Spectra at 225-Year Return Period for Site 0 7-7 5%-Damped Uniform Hazard Spectra at 975-Year Return Period for Site 0 7-8 5%-Damped Uniform Hazard Spectra at 2,475-Year Return Period for Site 0 7-9 84th Percentile Horizontal Acceleration Response Spectrum for the M 8.0 San Andreas Maximum Earthquake at 5.5 km for West Campus 7-10 Comparison of 84th Percentile Deterministic Response Spectra to the 2,475-Year Return Period UHS for West Campus 7-11 Design Ground Motion Zones 8-1 Methodology to Determine Site-Specific Design Ground Motions According to ASCE 7- 10 8-2 84th Percentile Horizontal Acceleration Response Spectrum for Zones 1, 2, and 3 Adjusted to Maximum Direction
8-3 Deterministic MCER for Zones 1, 2, and 3
8-4 Probabilistic MCER for Zones 1, 2, and 3
8-5 Site-Specific MCER for Zones 1, 2, and 3
8-6 Site-Specific DRSR for Zones 1, 2, and 3
8-7 Site-Specific MCER and DRSR for Zones 1, 2, and 3
8-8 Horizontal and Vertical Site-Specific MCER for Zones 1, 2, and 3
8-9 Horizontal and Vertical Site-Specific DRSR for Zones 1, 2, and 3 8-10 84th Percentile Horizontal Acceleration Response Spectra for Zone 0 Adjusted to Maximum Direction
8-11 Deterministic MCER for Zone 0
8-12 Probabilistic MCER for Zone 0
8-13 Site-Specific MCER for Zone 0
8-14 Site-Specific DRSR for Zone 0
8-15 Horizontal and Vertical Site-Specific MCER for Zone 0
8-16 Horizontal and Vertical Site-Specific DRSR for Zone 0 9-1 Methodology to Compute Site-Specific Design Ground Motions According to ASCE 41- 13 and 9-2 Site-Specific BSE-2E for Zones 1, 2, and 3 9-3 Site-Specific BSE-1E for Zones 1, 2, and 3 9-4 Site-Specific BSE-2E and BSE-1E for Zones 1, 2, and 3 9-5 Horizontal and Vertical Site-Specific BSE-2E for Zones 1, 2, and 3 9-6 Horizontal and Vertical Site-Specific BSE-1E for Zones 1, 2, and 3
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9-7 Site-Specific BSE-2E for Zone 0 9-8 Site-Specific BSE-1E for Zone 0 9-9 Horizontal and Vertical Site-Specific BSE-2E for Zone 0 9-10 Horizontal and Vertical Site-Specific BSE-1E for Zone 0
10-1 Site-Specific MCER for Zones 1, 2, and 3 Compared to ASCE 7-10 General MCER Spectra
10-2 Site-Specific DRSR for Zones 1, 2, and 3 Compared to ASCE 7-10 General DRSR Spectra
10-3 Site-Specific MCER for Zone 0 Compared to ASCE 7-10 General MCER Spectra
10-4 Site-Specific DRSR for Zone 0 Compared to ASCE 7-10 General DRSR Spectra 10-5 Site-Specific BSE-2E for Zones 1, 2, and 3 Compared to ASCE 41-13 General BSE-2E Spectra 10-6 Site-Specific BSE-1E for Zones 1, 2, and 3 Compared to ASCE 41-13 General BSE-1E Spectra 10-7 Site-Specific BSE-2E for Zone 0 Compared to ASCE 41-13 General BSE-2E Spectra 10-8 Site-Specific BSE-1E for Zone 0 Compared to ASCE 41-13 General BSE-1E Spectra
10-9 Site-Specific MCER Spectra and DRSR for Zone 1 Compared to 2010 Site-Specific MCE Spectra and DRS
10-10 Site-Specific MCER Spectra and DRSR for Zone 2 Compared to 2010 Site-Specific MCE Spectra and DRS
10-11 Site-Specific MCER Spectra and DRSR for Zone 3 Compared to 2010 Site-Specific MCE Spectra and DRS 10-12 Site-Specific BSE-2E and BSE-1E for Zone 1 Compared to 2010 Site-Specific BSE-2 and BSE-1 10-13 Site-Specific BSE-2E and BSE-1E for Zone 2 Compared to 2010 Site-Specific BSE-2 and BSE-1 10-14 Site-Specific BSE-2E and BSE-1E for Zone 3 Compared to 2010 Site-Specific BSE-2 and BSE-1
11-1 Conditional Mean Spectra Conditioned to Site-Specific MCER Spectrum at 0.2 and 1.0 Sec
11-2 Example CMS Conditioned to Site-Specific DRSR at 1.0 Sec and Broadened in Required Period Range
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At the request of Stanford University, URS Corporation has updated the 2010 seismic hazard evaluation of the campus and revised the campus-wide design ground motions. Stanford University is located in the seismically active San Francisco Bay region within the San Andreas fault system. The west side of campus is located about 6 km from the San Andreas fault, which last ruptured in the 1906 moment magnitude (M) 7.9 “Great San Francisco” earthquake. As in the 2010 study, the levels of ground motions at a specified exceedance probability are estimated based upon a probabilistic seismic hazard analysis (PSHA). Scenario ground motions also are calculated through a deterministic seismic hazard analysis (DSHA) to compare with the probabilistic ground motions. A site response analysis was performed to incorporate the effects of the near-surface geology beneath the campus into the design ground motions. Seismic design ground motions for new and existing buildings following the recently updated standards of ASCE 7-10 Minimum Design Loads for Building and Other Structures and ASCE 41-13 Seismic Rehabilitation of Existing Buildings are developed. Specifically, site-specific risk-adjusted Maximum Considered Earthquake (MCER) spectra and Design Response Spectra (DRSR) following ASCE 7-10 and Basic Safety Earthquake (BSE)-1E, BSE-2E, BSE-1N and BSE-2N spectra consistent with ASCE 41-13 are developed. These standards include significant changes from the versions in effect in 2010, including the use of risk-targeted and maximum direction ground motions. In addition, changes to ASCE 41-13 include the definition of two sets of earthquake hazard parameters. The first, defined as BSE-1E and BSE-2E and used in performance analyses for existing buildings, are consistent with the reduced hazard level for existing state-owned buildings defined in the 2010 CBC. The second, defined as BSE-1N and BSE-2N, are equivalent to the MCER and DRSR of ASCE 7-10. The “N” suffix indicates new building standards equivalent hazard level. To be consistent with its Seismic Design Guidelines and its seismic design approach for existing buildings, Stanford elected to use BSE-1N and BSE-2N as the basis for the analysis and retrofit of existing buildings. The recently released Next Generation of Attenuation (NGA)-West2 ground motion prediction models were used in the PSHA and DSHA. The seismic source model used in the analyses remained essentially unchanged since the 2010 analyses. As in the 2010 study, a microzonation of the campus in terms of design ground motions was performed. Zones 1, 2 and 3 were slightly revised from 2010 and Zone 0 in the northwest corner of the campus was added. Zone 0 is an area of the campus that has relatively thin soil, 100 to 500 ft in thickness, so the site response analysis focused on this area to capture the range in design ground motions that are appropriate for this range in soil thickness.
In the computation of design spectra for new buildings (MCER and DRSR), the deterministic ground motions and probabilistic ground motions are compared and for the Stanford campus, the former is the lesser of the two and hence is the basis for the MCER and DRSR.
Horizontal and vertical MCER and DRSR spectra for the four zones are provided in Table 8-1. Vertical design ground motions were computed using V/H ratios. The ASCE 7-10 design ground motions are similar for Zones 1 to 3. For Zone 0, the design ground motions depend on whether the depth to bedrock is less than 300 or 300 ft and greater. Site-specific investigations are recommended to confirm the depth to bedrock within Zone 0 because of the significant
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differences in the two sets of design spectra. Comparison of the MCER and DRSR ground motions using ASCE 7-10 and the MCE and DRS determined in 2010 using ASCE 7-05 shows the former to be larger at long periods (> 1.0 sec) due to use of the NGA-West2 ground motion prediction models and maximum direction. Table 8-2 summarizes the design acceleration parameters following ASCE 7-10. Table 9-1 lists the horizontal and vertical design spectra for existing buildings (BSE-2E and BSE-1E) for the four campus zones. The BSE-2E and BSE-1E following ASCE 41-13 are larger than the 2010 spectra per ASCE 41-06 for the same reasons cited above for the ASCE 7-10 versus ASCE 7-05 design motions. Note that Stanford has decided to use BSE-1N and BSE-2N (equal to MCER and DRSR) for existing buildings. These spectra are also larger than the 2010 spectra for existing buildings for the reasons discussed above. Example Conditional Mean Spectra (CMS) are computed to illustrate the value in using CMS for design.
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1. Section 1 ONE Introduction At the request of Stanford University, URS Corporation has updated the 2010 seismic hazard evaluation of the campus (Wong et al., 2010) and revised the campus-wide design ground motions. Stanford University is located in the seismically active San Francisco Bay region within the San Andreas fault system. The west side of campus is located about 6 km from the San Andreas fault, which last ruptured in the 1906 moment magnitude (M) 7.9 “Great San Francisco” earthquake (Figures 1-1 to 1-3). In the 2010 study, it was recognized that the 2008 seismic design ground motions for the Stanford campus also developed by URS (Wong et al., 2008) were conservative because they were intended to cover a wide range of soil conditions that were not well constrained due to the lack of any site-specific shear-wave velocity (VS) data for the campus. As part of the 2010 study, spectral-analysis-of-surface-waves (SASW) surveys were performed at 15 locations on campus by Professor Kenneth Stokoe and the University of Texas at Austin (UTA) and the resulting VS data were used to microZone the campus based on site response analyses and the distance to the San Andreas fault. In the 2010 study, the levels of ground motions at a specified exceedance probability were estimated based upon a probabilistic seismic hazard analysis (PSHA). Scenario ground motions were also calculated through a deterministic seismic hazard analysis (DSHA) to compare with the probabilistic ground motions. A site response analysis was performed to incorporate the effects of the near-surface geology beneath the campus into the design ground motions. Seismic design ground motions following the standards of ASCE 7-05 Minimum Design Loads for Building and other Structures and ASCE 41-06 Seismic Rehabilitation of Existing Buildings were developed. Specifically, site-specific Design Response Spectra (DRS) following ASCE 7- 05 and Basic Safety Earthquake (BSE)-1 (10% in 50 years) and BSE-2 (2% in 50 years) spectra consistent with ASCE 41-06 were developed. In addition, site-specific DRS following the recently developed ASCE 7-10, e.g., use of maximum direction and risk-targeted spectra were developed for comparison purposes. ASCE 7-10 had not yet been adopted into the California Building Code (CBC) in 2010. In this present study, seismic design ground motions for the Stanford campus were updated in accordance with the revised criteria specified in ASCE 7-10 and ASCE 41-13. The newly updated Next Generation of Attenuation (NGA)-West 2 ground motion prediction models were used in the hazard analyses. The following describes the inputs into the PSHA and DSHA, the PSHA and DSHA results, the site response analysis, a new microzonation of the campus and the associated seismic design ground motions.
1.1 SCOPE OF WORK As described in our proposed scope of work dated 17 September 2013, the following tasks were to be performed: Task 1 – Geotechnical Site Characterization We will review any new available geologic and geotechnical information collected since 2010 to determine whether the VS profiles developed in the 2010 study need to be updated. The current site response microzonation of the campus will be reviewed to assess its current applicability. Seismic design ground motions will now be calculated for Zone 0, which was defined in the
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2010 study. Efforts will be focused on characterizing this Zone in terms of a range of VS profiles. Task 2 – Site-Specific PSHA and DSHA Based on our updated 2013 seismic source model for the San Francisco Bay region and the 2013 NGA-West2 ground motion prediction models, we will calculate site-specific probabilistic ground motion hazard curves. The hazard will be calculated for a reference site condition that will be input into the site response analysis. The seismic source model includes the characterization of the major faults (e.g., San Andreas, Hayward) from the Working Groups on California Earthquake Probabilities (2003; 2008) and builds upon other U.S. Geological Survey (USGS) studies. The model has been reviewed by the USGS and California Geological Survey (CGS). Uncertainties in models and parameters are incorporated into the hazard analysis through the use of logic trees. We will carry out sensitivity analyses to assess the impact of various parameters to be specified by the Stanford Seismic Advisory Committee (SAC) and Project Manager. Sensitivity analyses will include, at a minimum, seismic source deaggregation, the sensitivity to ground motion prediction models, and site effects. Deterministic analyses for a M 8.0 maximum earthquake will be performed. Task 3 – Site Response Analyses Based on the hazard results from Task 2, RVT (random vibration theory) equivalent-linear site response analyses will be performed by Dr. Walt Silva to develop hazard curves and deterministic spectra at the ground surface for the design ground motion zones. Task 4 – Development of Site-Specific Design Ground Motions Based on Tasks 1 to 3, maximum- direction horizontal Uniform Hazard Spectra (UHS) at 5% damping and 225, 975, and 2,475-return periods will be calculated. BSE-1E and BSE-2E ground motions (both for existing and new building equivalent) per ASCE 41-13 and MCER and DRSR per ASCE 7-10. Site-specific BSE-1E, BSE-2E, MCER and DRSR spectra will be developed for the campus at the ground surface for each of the campus zones. The vertical design spectra will be calculated from the horizontal spectra using V/H ratios. The site-specific spectra will be compared against the code -based spectra. Example Conditional Mean Spectra (CMS) will be computed at selected periods for the DRSR spectra. All spectra will be provided digitally. Task 5 – Final Report and Meetings A draft final report that describes the analysis approach and summarizes the results of the study will be produced and transmitted to Stanford University for review. Meetings with the SAC are included in this task. Review comments will be addressed and a Final Report will be produced.
1.2 ACKNOWLEDGMENTS This project was supported by Stanford University. Our thanks to the Project Manager Dr. Fouad Bendimerad and Jean Barnes for their support and assistance in this study. Thanks also to Melinda Lee who assisted in the preparation of the report, to Laura Knutson for discussions on the campus geology and to Eliza Nemser for her peer review of the report.
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a e F T Walnut Creek es r l r - Mt. Diablo - t d a aR m er t u n e p T l North Stanford University l a t r i s a s z a c n y C t Mt. Diablo - M f f ic a a u l i u u l in d lt l e South W w Oakland l t C e a s y a t f n e a Tracy Dublin s r u y a n l o Livermore t n T B S V osit r l . Pleasantone P a a H r c ck a o y Haywardy n Las f B w a a u N u t S a W e . i l a r ll t f d C ia a n m u a s l G l t a r v e S e g A r Stanford a o F r s i P o e fault n f i G M a n t u s O l u F s t l oo Hayward o a th Fa ill Southeast S ul T . t ( hr C b u s Extension lin t f a d) a u Zone la lt v e r a s
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Z ay S an ar te ge -V n e t r fa ± ge u l l SAF - San Andreas Fault es t
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105 0 10 Miles Faults with surface rupture 05 10 20 30 40 Blind faults and zones Kilometers Segment boundaries Fault Source: URS Seismic Source Model
Project No. 26818815 ACTIVE FAULTS IN THE Figure Stanford University SAN FRANCISCO BAY REGION 1-2 Palo Alto, CA 122.67° W 122.5° W 122.33° W 122.17° W L 122° W 121.83° W as 37.83° N 37.83° N T C r f a u n a a t m u l i l c p l li a t C n s e W Oakland a Mt. Diablo - n e y s o South t n e Dublin r Livermore n s T Pleasanton V ta e 37.67° N r 37.67° N S r a . o Posi H n c a a as y Hayward yw L f a r a d S N u A . l t F C W P a ill S l ia a e a m n v s n i e n r G s a u s r la 37.5° N 37.5° N e g o r Stanford i o Stanford
f fault a University u l t Hayward Fo Southeast oth ill Extension T 37.33° N 37.33° N hr Zone us t fa ult
37.17° N 37.17° N Sa Z rg ay en an t f te au -V lt er ± ge l SAF - San Andreas Fault es
122.67° W 122.5° W 122.33° W 122.17° W 122° W 121.83° W
0 1 2 3 4 5 Miles Faults with surface rupture 0 4 8 12 16 20 Blind faults and zones Kilometers Segment Boundaries Fault Source: URS Seismic Source Model
Project No. 26818815 ACTIVE FAULTS IN THE Figure Stanford University VICINITY OF THE SITE 1-3 Palo Alto, CA SECTIONTWO Seismic Hazard Analyses Methodologies
2. Section 2 TWO Seismic Hazard Analyses Methodologies The PSHA and DSHA methodologies are described below.
2.1 PROBABILISTIC SEISMIC HAZARD ANALYSIS The seismic hazard 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 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 (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(z) (2) n
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) = ßn(mi)•p(R=rj|mi)•p(Z>z|mi,rj) (3) i j 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
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(PEER) Center-sponsored “Validation of PSHA Computer Programs” Project (Thomas et al., 2010).
2.2 SEISMIC SOURCE CHARACTERIZATION Two types of earthquake sources are characterized in this seismic hazard analysis: (1) fault sources; and (2) areal source zones (Section 4.1). 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, 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 2-1). 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 in Figure 2-1. 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.
2.2.1 Source Geometry In a 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 attenuation relationship 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 attenuation relationship. The
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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 following the magnitude-rupture area and rupture width relationships of Wells and Coppersmith (1994).
2.2.2 Fault Recurrence The recurrence relationships for the faults are modeled using the exponentially truncated Gutenberg-Richter, characteristic earthquake, and the maximum magnitude recurrence models (Section 4.1.1). These models are weighted (Figure 2-1) to represent our judgment on their applicability to the sources. For the areal source zones, only an 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 exponentially truncated model. The number of events exceeding a given magnitude, N(m), for the truncated exponential relationship is
ouo 10-b(m-m )-b(-10 m -m ) N(m)= ( o ) m -b( muo-m ) 1-10 (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 that the 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 units 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 (5)
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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:
M o = A S (6)
where M o 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 (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.
2.3 GROUND MOTION CHARACTERIZATION To characterize the ground motions in the PSHA and DSHA, we use empirical ground motion prediction models for response spectral acceleration. The models used in this study are selected on the basis of the appropriateness of the site conditions and tectonic environment for which they were developed. The uncertainty in ground motion prediction is included in the PSHA by using the log-normal distribution about the median values as defined by the standard error associated with each model. Three standard deviations about the median value are included in the analysis.
2.4 DETERMINISTIC SEISMIC HAZARD ANALYSIS The deterministic approach involves the following steps:
Identification of potential seismic sources that could affect the site and estimation of the maximum earthquake that could reasonably be expected from these sources.
Development of the range of maximum ground motions likely to occur at the site due to the maximum earthquake for each seismic source based on state-of-the-art ground motion attenuation relationships.
Selection of the controlling deterministic earthquake with the potential for generating the strongest ground motions at the site.
Characterization of the controlling deterministic earthquake in terms of peak ground acceleration, acceleration response spectra, duration of strong ground shaking, and/or other parameters as deemed appropriate.
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The first step, which is required in any earthquake hazards assessment, requires a characterization of all significant seismic sources that could produce ground motions of engineering significance at the site (Section 4.1). In the DSHA, no earthquake recurrence rate information is used. A description of the DSHA results is contained in Section 6.
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 2-5 SOURCE GROUND MOTION SEISMIC ACTIVITYGEOMETRY MAXIMUM EARTHQUAKE SLIP RATES MODELS SOURCES (Rupture Length, MAGNITUDE RECURRENCE Seismogenic Depth, MODEL and Dip)
San Andreas M - 0.3 Characteristic (See Table A-1) (0.2) (0.7) San Gregorio
Boore et al. (2013) See Table A-1 for (0.25) Hayward-Rodgers Creek Yes fault rupture length M (See Table A-1) (See Table A-1 and width, and dip. (0.6) for weights) Abrahamson et al. Calaveras (2013) (0.25) Concord-Green Valley M + 0.3 Maximum Magnitude (See Table A-1) (0.2) (0.3) Campbell and Cordelia Bozorgnia (2013) (0.25) Greenville No
Chiou and West Napa Youngs (2013) (0.25) Mt Oso
Background earthquakes
• • •
Project No. 26818815 SEISMIC HAZARD Figure Stanford University MODEL LOGIC TREE 2-1 Palo Alto, California SECTIONTHREE Campus Geotechnical Characterization
3. Section 3 THREE Campus Geotechnical Characterization Stanford University is located in the eastern foothills of the Santa Cruz Mountains. The main physiographic features around the site are the Santa Cruz Coast Range to the west, the San Francisco Bay and the Diablo Range to the east, and the Santa Clara Valley which stretches between the two mountain ranges (Figure 1-1). Prior to the 2010 URS analysis, the available subsurface information was limited to data obtained from a few previous geotechnical field investigations performed on the campus and at sites in the immediate vicinity of the campus (Woodward-Clyde Consultants [WCC], 1995). These data included:
A 315-ft (96-m) deep boring drilled by Woodward-Lundgren & Associates (1973) for ground motion studies of the Stanford Medical Center Expansion, Phase –I.
A 487-ft (148-m) deep boring drilled by WCC (1991) for the seismic study of the Veterans Administration Hospital replacement.
VS profile from downhole seismic wave velocity conducted at the Palo Alto VA Hospital site by WCC (1990).
Bedrock contour map prepared for south San Francisco Bay region (Hazelwood, 1976). The campus is underlain by late Pleistocene alluvium and terrace deposits consisting of stiff to very stiff silty clay and sandy clay and dense gravelly silty sand strata. These alluvial deposits vary in thickness from a few feet at the southwest end of the campus (near Juniperro Serra Boulevard) to about 120 ft (37 m) at the northeast end (near El Camino Real). The alluvium is underlain by Santa Clara formation (very stiff to hard, reddish brown, sandy and silty clays with occasional gravel) to a depth of about 430 ft (131 m). A poorly consolidated weathered rock, consisting of gravelly shale, sandstone and claystone (locally known as the Merced Formation) was encountered below the Santa Clara formation during the WCC (1990) drilling at the VA Hospital in Palo Alto. Based on the bedrock contour map (Hazelwood, 1976), Franciscan group crystalline rock is expected to be located approximately 1,100 feet beneath the campus although the SASW surveys suggest it could be shallower at least in the west campus area (see below).
Due to the lack of VS data for the Campus, VS data were collected as part of the 2010 URS study. SASW surveys at 15 locations were performed on campus from 2 to 7 August 2009 (Table 3-1). The surveys were carried out by UTA under the supervision of Professor Kenneth Stokoe.
The survey locations are shown on Figure 3-1 and the resulting VS profiles are shown in Figure 3-2. The VS profiles show similar trends except for three profiles in the west campus area: the Foothills, Equestrian Center, and Electioneer Road (Figure 3-3), which exhibit strong velocity contrasts at depth indicating the possible presence of Franciscan rock (VS > 2,500 ft/sec).
The remaining VS profiles were examined to see if they could be grouped together geographically based on similarities in their profiles and near-surface geology. The most obvious groupings were sites on the north-central campus and east campus based on the VS profiles (Figures 3-4 and 3-5). The north-central campus VS profiles were, in general, faster (stiffer) than the east campus. We also considered the division of the VS profiles into two groups based on the surficial geologic map of Witter et al. (2006): (1) north-central campus where the sites are generally situated on late Pleistocene alluvial fan deposits (Qpf) and early to mid
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Pleistocene alluvial fan and stream terrace deposits (Qof) and (2) east campus where Holocene floodplain deposits (Qhf2) and Holocene natural levee deposits (Qhl) are the predominant units (Figure 5).
Base case VS profiles were computed for the north-central campus and east campus by computing a lognormal mean of the grouped profiles (Figures 3-4 and 3-5). Figure 3-6 compares the base case VS profiles for the two campus areas and a lognormal mean of all profiles from the two areas. Despite apparent differences in the VS profiles in each zone, the north-central and east base case VS profiles (lognormal means) are quite similar. A lognormal average of all north- central and east campus VS profiles was used as the base case in profile randomization (Section 7). Since the SASW data did not reach rock beneath the north-central and east campus, the depth to a rock-like VS of 3,280 ft/sec (1 km/sec) was varied in the site response analyses consistent with the NGA models use of Z1.0. The VS of 3,280 ft/sec is also a rough average of the Franciscan rock VS encountered at the three sites in west campus (Figure 3-3).
At Electioneer Road, rock (VS > 2,500 ft/sec) was encountered at a depth of 290 ft (Figure 3-3). To the west at the Foothill site, rock (VS > 3,500 ft/sec) was, as expected, shallower at a depth of about 100 ft (Figure 3-3). Hence, we varied the depth to rock for the north-central/east campus using values of 300, 350, 400, and 500 ft in the site response analysis (Section 7) since we expect rock to be at a depth of about 300 ft as observed at Electioneer Road or deeper. For west campus, there were only two SASW surveys at Electioneer Road and the Equestrian Center (Figure 3-1). We are disregarding the Foothills site because there are no campus facilities or planned facilities southwest of Junipero Serra Boulevard. In addition to the two SASW surveys, two shallow downhole velocity surveys were performed in 2012 by JR Associates as part of the geotechnical investigations for the Stanford Campus Energy System Improvements (CESI) project. The downhole velocity surveys were completed in borings EB-7 and EB-13 to depths of approximately 100 ft. These borings are located to the northwest of Fremont Drive and Searsville Road, within the west campus area (Figure 3-1). The VS profiles are shown on Figure 3-7 along with the lognormal average, which is used as the base case profile in the site-response analysis of the west campus (Section 7). There are no known borings that encounter Franciscan rock so based solely on the two SASW sites, we estimate that Franciscan rock occurs at depths of 100 to 500 ft. The top of Franciscan rock was varied in the site response analysis between 100 and 500 ft (Section 7).
In the PSHA and DSHA, we performed the calculations using a generic soil VS30 of 270 m/sec. The site response analysis was then carried out adjusting the hazard to the site-specific site conditions (Section 7). The VS30 value was chosen because a robust mean VS profile based on a large data set of profiles from Pacific Engineering & Analysis was available for use in the site response analysis.
A VS30 (average shear-wave velocity in the top 30 m) value was computed for each site from its VS profile and a NEHRP site class assigned (Table 3-1). These site classes can be used for code- based design if deemed appropriate.
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Table 3-1
VS30 and NEHRP Site Classes
Location VS30 (m/sec) NEHRP Site Class Abram’s Court 274 D Arboretum Road 325 D Children’s Center 294 D Electioneer Road 376 C Enchanted Broccoli Forest 295 D Equestrian Center 328 D Escondido Mall 351 D Foothills 400 C Manzanita Fields 329 D New Concert Hall 315 D Parking Structure #1 336 D Roble Field 328 D Sand Hill Fields 372 C The Oval 321 D Wilbur Hall 307 D EB-7 (CESI) 399 C EB-13 (CESI) 416 C
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Qhl
Qhly
Qhf um Road Qhc Arboret Qhly
Qhf1 EAST Qhl CAMPUS
Qhf2 1 #
e STANFORD r s u d t N l e STADUIM e c w i u F r t C l l S o i n H g c e n r d i t n k r H C a a a h S ll i P ld l re a n v s
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E n t l e rEB-13 e r c
t r EB-7 i o d n l e Abram's Court Qhc e i F e E a r sco t Field nd i R Roble ido n Qht Ma a Qof o ll z a n
d a M r l e l t NORTH-CENTRAL a n Qpf H e af r C CAMPUS u n b a l i adf i r t W br s e af H2O u q E br Qhf Qhc WEST rest CAMPUS colli Fo ted Bro Enchan
Qht Qf af lls othi 37.42° N 37.42° N Qhf Fo br Qht af af br Qhc Qha af Qpa af af
Geologic Map Source: Witter et al. , 2006 122.17° W
0 150 300 450 600 750 Yards Vs Zones
0 200 400 600 800 1,000 SASW Line Meters Blind faults ±
r Downhole velocity survey
Project No. 26818815 SASW SURVEY LOCATIONS AND Figure Stanford University QUATERNARY GEOLOGY 3-1 Palo Alto, CA 0.00
100.00
200.00 Depth (ft)
300.00
400.00 0 1000 2000 3000 4000 Shear Wave Velocity, Vs, ft/s
Project No. 26818815 ALL SASW VS PROFILES Figure Stanford University 3-2 California 0.00
Electioneer Rd Equestrian Center Foothills
100.00
200.00 Depth (ft)
300.00
400.00 0 1000 2000 3000 4000 Shear Wave Velocity, Vs, ft/s
Project No. 26817493 WEST SASW CAMPUS VS PROFILES Figure Stanford University 3-3 California 0.00
Roble Field Sand Hill Fields Wilbur Hall Enchanted Broccoli Forest Manzanita Field Escondido Mall Abram's Court 100.00 Lognormal Average
200.00 Depth (ft)
300.00
400.00 0 1000 2000 3000 4000 Shear Wave Velocity, Vs, ft/s
Project No. 26817493 NORTH-CENTRAL SASW CAMPUS VS PROFILES Figure Stanford University 3-4 California 0.00
Arboretum Rd Children's Center New Concert Hall Parking Structure #1 100.00 The Oval Lognormal Average
200.00 Depth (ft)
300.00
400.00 0 1000 2000 3000 4000 Shear Wave Velocity, Vs, ft/s
Project No. 26817493 EAST CAMPUS SASW VS PROFILES Figure Stanford University 3-5 California 0.00
East NorthCentral NorthCentral/East Profiles
100.00
200.00 Depth (ft)
300.00
400.00 0 1000 2000 3000 4000 Shear Wave Velocity, Vs, ft/s
Project No. 26817493 COMPARISON OF LOGNORMAL AVERAGE V PROFILES FOR EAST Figure Stanford University S 3-6 California AND NORTH-CENTRAL CAMPUS 0.00
Electioneer Rd Equestrian Center EB-7 CESI EB-13 CESI Average
100.00
200.00 Depth (ft)
300.00
400.00 0 1000 2000 3000 4000 Shear Wave Velocity, Vs, ft/s
Project No. 26817493 WEST CAMPUS VS PROFILES Figure Stanford University 3-7 California SECTIONFOUR Inputs to Analyses
4. Section 4 FOUR Inputs to Analyses The following section describes the characterization of the seismic sources considered in the analyses, the geologic site conditions beneath the campus, and the empirical ground motion attenuation relationships selected and used.
4.1 SEISMIC SOURCES Seismic source characterization is concerned with three fundamental elements: (1) the identification, location, and geometry of significant sources of earthquakes; (2) the maximum sizes of the earthquakes associated with these sources; and (3) in the PSHA, the rate at which they occur. The source parameters for the significant faults in the site region (generally within about 100 km) are characterized for input into the hazard analyses (Figures 1-2 and 1-3). Areal source zones, used to represent background earthquakes, are also characterized and used in the PSHA.
4.1.1 Faults The fault model used in this study is adopted from a model developed as part of the California Department of Water Resources’ Delta Risk Management Strategy Project (Wong et al., 2008). Each seismic source is characterized using the latest available geologic, seismologic, and paleoseismic data and the currently accepted models of fault behavior developed by the Working Group on Northern California Earthquake Potential (WGNCEP, 1996) and the 2002 California Geological Survey’s (CGS) seismic source model used in the USGS National Hazard Maps (Cao et al., 2003). Characterizations of the major faults in the San Francisco Bay region, the San Andreas, Hayward/Rodgers Creek, Concord/Green Valley, San Gregorio, Greenville, and Mt. Diablo thrust faults, are adopted from the 1999 and 2002 Working Groups on California Earthquake Probabilities (WGCEP, 2003). Figures 1-2 and 1-3 show the locations of the faults relative to campus and Table A-1 summarizes the fault source parameters used in this analysis. Faults are included that are judged to be at least potentially active and that may contribute to the probabilistic hazard because of their maximum earthquakes and/or proximity to the transmission system. In this analysis, most faults are modeled as single, independent, planar sources extending the full extent of the seismogenic crust. Thus, fault dips are averages estimated through the seismogenic crust. Generally, in western California, the seismogenic crust ranges from 11 to 15 km thick based on well-located contemporary seismicity (e.g., Oppenheimer and MacGregor-Scott, 1992). Fault zones are modeled as multiple, parallel planes within the Zone boundaries (e.g., Briones zone) (Table A-1; Figures 1-2 and 1-3). Recurrence rates for many of the faults within the San Francisco Bay region are either poorly understood or unknown due to a lack of reliable paleoseismic data. Thus, we express fault activity as an average annual slip rate (in mm/yr) rather than recurrence intervals (years between events). The uncertainty in slip rates and other input parameters are accommodated in the PSHA through the use of logic trees (Figure 2-1). Uncertainties in determining recurrence models can significantly impact the hazard analysis. We consider truncated exponential, maximum-magnitude, and characteristic recurrence models, with various weights depending on source geometry and type of rupture model. Historical seismicity and paleoseismic investigations along faults in the western U.S. (e.g., San Andreas fault) suggest
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that characteristic behavior is more likely for individual faults (Schwartz and Coppersmith, 1984). Therefore, we generally favor the characteristic model for all fault sources (weight of 0.70) while the maximum magnitude model is weighted 0.30 (Figure 2-1). The most significant seismic source to campus is the San Andreas fault because of its proximity, potential for generating large earthquakes (M 7) and high activity rates (Figures 1-2 and 1-3). Probably the most significant historical earthquakes to Stanford were the 1838 M 6.8 Peninsula, 1906 M 7.9 and 1989 Loma Prieta M 6.9 earthquakes, which occurred on or near the San Andreas faults (Figure 1-1). The three closest and significant major faults to campus, the San Andreas, San Gregorio, and Hayward faults, are discussed below in addition to the Stanford fault, which crosses the campus (Figure 1-3).
San Andreas Fault System The dominant active fault in California is the San Andreas fault. The fault extends from the Gulf of California, Mexico, to Point Delgada on the Mendocino Coast in northern California, a total distance of 1,200 km. The San Andreas fault accommodates the majority of the motion between the Pacific and North American plates. This fault is the largest active fault in California and is responsible for the largest known earthquake in Northern California, the 1906 M 7.9 San Francisco earthquake (Wallace, 1990). Movement on the San Andreas fault is right-lateral strike-slip, with a total offset of some 560 km (Irwin, 1990). In northern California, the San Andreas fault is clearly delineated, striking northwest, parallel to the vector of plate motion between the Pacific and North American plates. Over most of its southern extent, the San Andreas fault is a relatively simple, linear fault trace. Immediately south of the San Francisco Bay area, however, the fault splits into a number of branch faults or splays, including the Calaveras and Hayward faults (Figure 1-2). In the San Francisco Bay area, the main trace of the San Andreas fault forms a linear depression along the San Francisco Peninsula, occupied by the Crystal Springs and San Andreas Lake Reservoirs (Figure 1-2). Geomorphic evidence for Holocene faulting includes fault scarps in Holocene deposits, right-laterally offset streams, shutter ridges, and closed linear depressions (Hall, 1984; Wallace, 1990). The 1906 earthquake resulted from rupture of the fault from San Juan Bautista north to Point Delgada, a distance of approximately 475 km. The average slip on the fault was 5.1 m in the area north of the Golden Gate and 2.5 m in the Santa Cruz Mountains (WGNCEP, 1996). Based on differences in geomorphic expression, fault geometry, paleoseismic chronology, slip rate, seismicity, and historical fault ruptures, the San Andreas fault is divided into a number of fault segments. Each of these segments may be capable of rupturing independently or in conjunction with adjacent segments. In the San Francisco Bay area, these segments include the Santa Cruz Mountains, Peninsula, and North Coast segments. Based on the lengths of the fault segments, they are capable of producing estimated mean maximum earthquakes of M 7.0, 7.15, and 7.45, respectively (WGCEP, 2003). The 1906 earthquake was the result of rupture of the Offshore (northernmost segment north of Point Arena), North Coast, Peninsula, and Santa Cruz Mountains segments. Two- or three-segment ruptures also may be possible (WGCEP, 2003). We estimate that the maximum earthquakes associated with these potential multi-segment ruptures may range from M 7.4 to M 7.7 (Table A-1). Based on geodetic, geologic and paleoseismic data, the fault slip rate for the San Andreas fault south of the Golden Gate is 17 - 3/+ 7 mm/yr (Hall et al., 1999). North of the Golden Gate, the
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slip rate increases to 24 ± 5 mm/yr (Niemi and Hall, 1992). The San Gregorio fault, which merges with the San Andreas fault north of the Golden Gate, has a slip rate of 7 ± 3 mm/yr (WGCEP, 2003). WGCEP (2003) assigns a mean recurrence interval of 378 years to a M 7.9 1906-type event on the San Andreas fault with a large uncertainty. They estimate a 21% probability of occurrence of a M 6.7 or larger earthquake on the San Andreas fault in northern California in the time period between 2002 and 2031. Recent investigations by Niemi (2002) indicate that the repeat time for large earthquakes on the North Coast segment may be less than 250 years. WGCEP (2003) characterized the San Francisco Peninsula segment of the San Andreas fault as having the second highest probability of all Northern California faults (21%) for having one or more M 6.7 or greater earthquakes from 2002 to 2031. To the north, the Peninsula segment moves offshore at Daly City, where a prominent fault valley and numerous sags marked its predevelopment trace. The southern boundary of the Peninsula segment is near the Town of Los Gatos, at the surface projection of the northern limit of the 1989 Loma Prieta earthquake rupture Zone (McNally and Ward, 1990; WGCEP, 2003). Southeast along the San Francisco Peninsula the fault valley is occupied by San Andreas Lake, the reservoir that gave the fault its name (Lawson, 1895), Lower and Upper Crystal Springs reservoirs, and the towns of Woodside and Portola Valley. Southeast of Portola Valley, the San Andreas fault enters the Santa Cruz Mountains, its path marked by tectonically controlled geomorphic features. Few detailed paleoseismic field studies have been successfully performed on the Peninsula segment because much of the fault is covered by water, modified by development, or lacks stratigraphic conditions conducive for recording ground-rupturing earthquakes. Paleoseismic studies at the Filoli site, about 1.7 km southeast of Upper Crystal Springs Reservoir, resulted in an estimate of a late Holocene slip rate of 17 4 mm/yr for the peninsula segment (Clahan, 1996; Hall et al., 1999). Hall et al. (1999) document 4.1 m of offset of approximately 330-year- old channel deposits. Because the 1906 rupture caused approximately 2.5 m of offset, Hall et al. (1999) suggest that the penultimate earthquake (likely the 1838 earthquake) was accompanied by 1.6 m of surface offset. This line of reasoning is used to argue that the Peninsula segment ruptures not just during 1906-type events, but also in smaller, perhaps M 7 earthquakes (Hall et al., 1999; WGCEP, 2003). Relatively limited slip on the Peninsula segment during the 1906 earthquake also has been used to argue for smaller events occurring between 1906-type events (WGCEP, 2003).
Hayward-Rodgers Creek Fault System The Hayward fault extends for 100 km from the area of Mount Misery, east of San Jose, to Point Pinole on San Pablo Bay (Figure 1-2). The northern continuation of this fault system, north of San Pablo Bay, is the Rodgers Creek fault. The two faults are separated by a 5-km-wide right step or bend beneath San Pablo Bay. Systematic right-lateral geomorphic offsets and creep offset of cultural features are documented along the entire length of the Hayward fault by Lienkaemper (1992; 2006). The last major earthquake on the Hayward fault, in October 1868, occurred along the southern segment of the fault (Figure 1-2). This approximate M 6.8 event caused toppling of buildings in Hayward and other localities within about 5 km of the fault. Ground shaking was strong throughout the Bay area at a Modified Mercalli intensity VII and greater (Toppozada et al., 1981). Surface rupture associated with this earthquake is thought to have extended for approximately 30 km, from Warm Springs to at least as far north as San
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Leandro, with a maximum reported displacement of about 1 m. The Hayward fault is considered the most likely source of the next major earthquake in the San Francisco Bay area (WGCEP, 2003). Between large earthquakes, the Hayward fault also moves by aseismic creep. Measurements along the fault over the last two decades show that the creep rate is 5 to 9 mm/yr (Lienkaemper and Galehouse, 1997). Paleoseismic trenching along the northern Hayward fault indicates that the last surface rupturing earthquake along this part of the fault was sometime between 1626 and 1724 (Lienkaemper et al., 1999). This study also indicated at least four surface-rupturing earthquakes in the last 2,250 years. The WGCEP (2003) assigns maximum earthquakes of M 6.5 and 6.7, and recurrence intervals of 387 and 371 years, for the northern and southern segments of the Hayward fault, respectively. Recent studies by Lienkaemper and Williams (2007) indicate that there have been 10 earthquakes along the southern Hayward fault since about 170 A.D. resulting in an average recurrence interval of 170 years. The last five events have an average recurrence interval of 140 50 years. Rupture of the entire fault Zone would generate an earthquake of M 7.0. The WGCEP (2003) considers the Hayward-Rodgers Creek fault system the most likely source of the next M 6.7 or larger earthquake in the Bay Area, with a 27 percent probability of occurring in the time period 2002 to 2031. Their model also incorporates a scenario where the Hayward fault ruptures along with the Rodgers Creek fault. Rupture of the entire length of both faults would generate a maximum earthquake of M 7.3. Rupture of the Rodgers Creek fault and the northern segment of the Hayward fault would generate a maximum event of M 7.1. The Rodgers Creek fault is 44 km long (Figure 1-2) and its geomorphic expression is similar to that of the Hayward fault. At its northern end, the Rodgers Creek fault is separated from the Healdsburg fault by a 3-km-wide right step, and separated from the Maacama fault by a 10-km- wide right step (Wagner and Bortugno, 1982). Holocene activity along the Rodgers Creek is indicated by a series of fault scarps in Holocene deposits, side-hill benches, right-laterally offset streams, and closed linear depressions. Microseismicity is nearly absent along much of the length of the fault suggesting that it is a seismic gap and the site of an impending earthquake (Wong, 1991). Paleoseismic investigations by Schwartz et al. (1992) revealed three events in 925 to 1,000 years. This gives a preferred recurrence of 230 years for a maximum earthquake of M 7.0. The most recent earthquake occurred on the fault sometime between 1438 to 1654 AD (Schwartz et al., 1992). The calculated slip rate for the Rodgers Creek fault is 9 ± 2 mm/yr.
San Gregorio Fault Zone This northwest-striking fault is the principal active fault west of the San Andreas fault in the coastal region of central California (Figure 1-2). The fault extends from offshore of Point Sur, northward to Bolinas Lagoon, where it merges with the North Coast segment of the San Andreas fault (Figure 2). WGCEP (2003) considers the northern end of the fault Zone to be about at the latitude of Golden Gate and the southern end to be about 20 km south of Point Sur, with uncertainties of about ± 10 km on each and a total length of about 175 km. The USGS Quaternary fault database considers the fault Zone to extend northward all the way to Bolinas Lagoon and, at the southern end, to include the Sur fault, for a total fault length of 212 km (Bryant and Cluett, 1999). WGCEP (2003) divides the fault into northern and southern rupture segments with the boundary at a prominent step in the middle of Monterey Bay (Jennings, 1994).
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The fault is largely offshore, with only two short sections, from Moss Beach/Seal Cove to Pillar Point and from Mussel Rock/Pescadero to Point Año Neuvo, occurring on land (Figure 1-2). Because of the limited onshore extent of the fault, the fault is relatively poorly understood and data to characterize the fault Zone come entirely from the northern segment. Simpson et al. (1997; 1998) carried out a paleoseismic investigation along the Seal Cove section of the fault, where they demonstrated late Holocene right-lateral movement. They obtained a slip rate on the Seal Cove strand of 3.5 to 4.5 mm/yr from an offset 80 ka channel. In the Point Año Nuevo section, the San Gregorio fault consists of several subparallel splays, including the Coastways and Frijoles faults and the Año Nuevo thrust, spanning a roughly 3-km-wide zone. Slip rates have only been directly measured across some strands, leading to high uncertainties in the slip rate across the entire fault zone. Weber and Cotton (1981), Weber (1994) and Weber et al. (1995) report slip rates of 4 to 11 mm/yr for the entire Zone in this region based on offsets of creeks and marine shoreline angles over the last 100 ky, as summarized in WGCEP (2003), which used a rate of 7 3 mm/yr for the northern segment. This rate is consistent with a model in which slip from the San Andreas fault is transferred to the San Gregorio fault, and the San Andreas slip rate decreases from 24 to 17 mm/yr south of the faults’ intersection. There are no measured slip rate data for the southern segment. WGCEP (2003), however, assumes that at least 2 mm/yr is transferred to the Monterey Bay-Tularcitos-Navy-Chupines fault system and assign a slip rate of 3 2 mm/yr to the southern segment. Paleoseismic data for the San Gregorio fault are limited. The most recent surface-faulting event on the Seal Cove strand occurred sometime between A.D. 1270 and A.D. 1775 (Simpson et al. 1997, 1998). The penultimate event occurred between A.D. 680 and A.D. 1400. Recent studies analyzing marsh stratigraphy along the same fault strand at Pillar Point Marsh corroborated the Simpson et al. date of the most recent event, constraining it to have occurred between 500 yrs cal BP and present (Koehler et al., 2005), with a preferred date between A.D. 1667-1802 (Simpson and Knudsen, 2000). Koehler et al. (2004) estimate an average recurrence interval of 1500 to 3000 years from the marsh data at Pillar Point. Paleoseismic data from the Año Neuvo onshore section of the fault are similarly limited. Thornberg and Weber (1998) conducted a paleoseismic study at Cascade Ranch near Point Año Neuvo and found evidence for three to four events in deposits at most 6000 to 8000 years old, yielding a minimum average recurrence interval of 1500 to 2000 years. By contrast, Soujourner et al. (2000) studied the Coastways fault near Mussel Rock and found no evidence of faulting in 4000 year-old deposits exposed in a cross-fault trench, nor in < 10-ka fluvial terraces that span the fault, suggesting little or no Holocene activity on this strand of the San Gregorio fault. Based on geological and paleoseismic data, the San Gregorio fault comprises two segments: a northern segment extending from Bolinas Lagoon to Monterey Bay and a southern segment from Monterey Bay to Point Sur. The fault is modeled as either unsegmented, where the entire fault ruptures, generating an earthquake of M 7.5, or segmented, where the northern and southern segments rupture independently, generating earthquakes of M 7.2 and 7.0, respectively. We also consider a M 6.9 ‘floating’ earthquake which can rupture any part of the fault. Based on the slip rate estimates of 4 to 11 mm/yr (WGCEP, 2003) derived from observations along the onshore Año Nuevo section of the fault, we adopt a preferred slip rate of 7 mm/yr for the unsegmented and northern segment models, with lower and upper bound estimates of 4 mm/yr and 10 mm/yr, respectively. The slip rate for the southern segment is 3 mm/yr ( 2 mm/yr).
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Stanford Fault The Stanford fault Zone comprises several northwest-striking, west-dipping, left-stepping en echelon oblique-reverse faults at the northern end of the Foothills thrust belt, east of the San Andreas fault, that links the San Andreas and Monte Vista faults (Fenton and Hitchcock, 2001; Angell et al., 1998). It is considered to be a blind fault, underlying the Stock Farm monocline, that has caused warping of Plio-Pleistocene and younger deposits (Fenton and Hitchcock, 2001). Angell et al. (1998) depict the Stanford fault as a steeply west-dipping inverted normal fault that ramps up from a deeper fault rooting into the San Andreas fault at about 10 km depth. Earlier studies by Willis (1924) showed the Stanford fault merging with the Hermit fault and ultimately the San Andreas fault, although the subsurface geometry was poorly constrained. Roering et al. (1996) modeled the fault as a blind west-dipping reverse fault. Bullard et al. (2004) refining previous work reported by Angell et al. (1998), conducted a geomorphic analysis of Quaternary terraces surfaces in the vicinity of the Stanford fault Zone to assess the rate of Quaternary activity on the faults. They determined that the majority of latest Pleistocene to Holocene activity was concentrated on the Stanford fault. A terrace estimated by Angell et al. (1998) to be ca. 15 ka was vertically displaced across the fault 5 to 8 m, and an undated but younger terrace was displaced about 3 m. At another location, a terrace, estimated from radiocarbon dates to be 5 ka, was displaced vertically about 3 m. On the basis of these investigations, Bullard et al. (2004) estimated that the latest Quaternary vertical displacement rate across the Stanford fault was about 0.6 mm/yr, consistent with what Angell et al. (1998) reported. We model the Stanford fault as a west-dipping reverse fault with dips ranging from 45 to 75 degrees (Table A-1). Angell et al. (1998) modeled the upper part of the fault with a 75-degree dip merging at 5 km depth into a shallower fault with a 45-degree dip. They proposed that the faults of the Stanford fault Zone merge into the San Andreas fault between 8 and 12 km, and we use these values to constrain the depth of faulting. For slip rate, we use the latest Pleistocene to Holocene vertical displacement rates reported by Angell et al. (1998) and Bullard et al. (2004) with the range in dips to obtain a range of slip rates between 0.4 and 1.0 mm/yr (Table A-1). Hitchcock and Kelson (1999) studied the Monte Vista, Cascade, and other range bounding faults south of the Stanford fault and proposed that slip triggered by San Andreas fault ruptures, such as that produced in the 1989 Loma Prieta earthquake, could account for all of the late Quaternary geologic slip rate of 0.25 to 0.4 mm/yr observed on those structures. Thus they argued that reverse oblique faults of the Foothills thrust system may not act as independent seismogenic sources but rather rupture sometimes or always as triggered slip events consequent to rupture of the San Andreas fault and that such a scenario should be considered in assessing seismic hazard. Although the Stanford fault has clear evidence of latest Pleistocene to Holocene deformation, given the observations of Hitchcock and Kelson (1999), we consider the possibility that the fault does not act as an independent seismogenic source, but only ruptures in conjunction with the San Andreas fault in triggered slip events. The slip rate Hitchcock and Kelson (1999) associate with triggered or postseismic slip on the Foothills faults, 0.25 to 0.4 mm/yr, is about half that documented on the Stanford fault. There is no conclusive evidence, given that higher triggered slip around the Stanford fault was not reported following the Loma Prieta earthquake, that all the slip on the Stanford fault occurs in triggered slip events, although some of it may be. Modeling
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by Angell et al (1998) suggests the Stanford fault merges with the San Andreas fault below about 10 km depth, well within the range of earthquake nucleation. Thus the fault is large and deep enough to generate surface deforming earthquakes without being triggered by another fault. Given these considerations, we assign a probability of 0.7 that the Stanford fault is an independent active seismic source (Table A-1).
4.1.2 Background Seismicity To account for the hazard from background (floating or random) earthquakes that are not associated with known or mapped faults, regional seismic source zones are used in the PSHA. In most of the western U.S., the maximum magnitude of earthquakes not associated with known faults usually ranges from M 6 to 6½. Repeated events larger than these magnitudes generally produce recognizable fault-or-fold related features at the earth’s surface (e.g., dePolo, 1994). Examples of background earthquakes are the 1986 M 5.7 Mt. Lewis and 31 October 2007 M 5.6 Alum Rock earthquakes, both of which occurred east of San Jose and resulted in no discernable surface rupture. Earthquake recurrence estimates of the background seismicity within each seismic source Zone are required. The site region is divided into two regional seismic source zones: the Coast Ranges and Central Valley. The recurrence parameters for the Coast Ranges source Zone are adopted from Youngs et al. (1992). They calculate values for background earthquakes based on the historical seismicity record after removing earthquakes within 10-km-wide corridors along each of the major faults. The recurrence values for the Central Valley Zone are adopted from URS Corporation/Jack Benjamin & Associates (2007). The a-values are normalized per year and per km2. Maximum earthquakes for both zones of M 6.5 0.3 are used in the PSHA. Recurrence Parameters
Source Zone b a Coast Ranges 0.72 -3.68 Central Valley 1.14 -0.73
4.2 GROUND MOTION PREDICTION MODELS To estimate the ground motions for crustal earthquakes in the PSHA and DSHA, we have used recently developed ground motion prediction models appropriate for tectonically active crustal regions. The crustal models, developed as part of the NGA-West2 Project sponsored by PEER Center Lifelines Program, were published in May 2013. The NGA-West1 Project began in the mid-1990s and in 1998, the first set of models became available (e.g., Abrahamson et al., 2013). The NGA West-1 models had a substantially better scientific basis than past relationships, which generally dated around 1997 (e.g., Abrahamson and Silva, 1997), because they were developed through the efforts of five selected ground motion prediction developer teams working in a highly interactive process with other researchers who: (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)
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conducted research to provide improved understanding of the effects of various parameters and effects on ground motions that are used to constrain models; and (c) developed improved statistical methods to develop ground motion 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 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. The NGA-West2 models were developed based on an expanded strong motion database compared to the initial NGA database. A number of more recent well recorded earthquakes were added to the NGA-West2 database including the Wenchuan, China, numerous moderate magnitude California events down to M 3.0, and several Japanese, New Zealand, and Italian earthquakes. The NGA-West2 models by Chiou and Youngs (2013), Campbell and Bozorgnia (2013), Abrahamson et al. (2013), and Boore et al. (2013) were used in the PSHA and DSHA. The models were weighted equally in the hazard analyses (Figure 2-1). The model by Idriss (2013) was not used because it is only appropriate for rock (VS30 450 to 1,200 m/sec).
Other input parameters include Z1.0, the depth of a VS of 1.0 km/sec and Z2.5, the depth to a VS of 2.5 km/sec. Both parameters were used by some of the developers as proxies for basin effects. Z1.0 is used by Chiou and Youngs (2013) and Abrahamson et al. (2013) and Z2.5 is only used in one model, Campbell and Bozorgnia (2013). Due to the lack of site-specific data, the default values of Z1.0 and Z2.5, based on the VS30 from equations provided by the developers, were used in the PSHA. Z1.0 and Z2.5 were 0.475 and 1.98 for a VS30 value of 270 m/sec, respectively. Other parameters such as depth to the top of rupture (zero for all faults that intersect the surface unless specified otherwise), dip angle, rupture width, and aspect ratio were specified for each fault or calculated within the PSHA code. Rupture directivity was not included in the PSHA or DSHA in consultation with Dr. Norm Abrahamson. It is believed that the effects of rupture directivity are included in the NGA-West2 database, with a preference of forward directivity sites. In addition, the maximum direction spectra include the directivity effects at the site. It would be overly conservative to add additional modeling of rupture directivity to the response spectra.
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5. Section 5 FIVE Psha Results Based on the 2010 study, it was anticipated that microzonation of the campus will be based on the distance to the San Andreas fault. Hence a PSHA was performed for four sites from southwest to northeast (Figure 5-1). Site 0 lies within the West area defined by the VS profiles. Sites 1 to 3 lie within the North-Central and East areas at varying distances from the San Andreas fault. The hazard curves for peak horizontal ground acceleration (PGA) and 1.0 sec spectral acceleration (SA) are shown on Figures 5-2 and 5-3 for Site 1, respectively, and a reference site condition of 270 m/sec. Comparisons of the mean hazard curves for PGA and 1.0 sec SA for all sites are shown on Figures 5-4 and 5-5. For the same site condition, the probabilistic hazard varies very little across campus. The contributions of the various seismic sources to the mean PGA and 1.0 sec SA hazard are shown on Figures 5-6 and 5-7. As expected, because of the proximity to the site, the San Andreas fault is the largest contributor to the short-and long-period hazard. The Stanford fault also contributes only a small percentage to the hazard at the site because of its relatively low slip rate and 0.7 probability of activity (Table A-1) (Figures 5-6 and 5-7). Figures 5-8 through 5-13 illustrate the contributions by sources, after deaggregating the mean PGA and 1.0 sec horizontal SA hazard by magnitude, distance and epsilon bins for the 225, 975, and 2,475-year return periods. Epsilon is the difference between the logarithm of the ground motion amplitude and the modal logarithm of ground motion (for that M and R) measured in units of the standard deviation (σ) of the logarithm of the ground motion. For all return periods, the PGA and 1.0 sec SA hazard are dominated by events in the magnitude range of M 6.75 to 8.0 at distances from 5 to 10 km corresponding to events on the San Andreas fault. The modal magnitude and distance for all three hazard levels and all sites is a M 7.1 at 7.5 km. The sensitivities of the PGA and 1.0 sec SA hazard to selection of ground motion models are shown on Figures 5-14 and 5-15, respectively. At PGA, Boore et al. (2013) gives the highest hazard, while Campbell and Bozorgnia (2013) gives the lowest. At 1.0 sec, Chiou and Youngs (2013) gives higher hazard than the other models. The UHS for the return period of 225, 975, and 2,475 years for the reference site condition of VS30 of 270 m/sec are shown on Figure 5-16 for all four sites. These UHS reflect the geometric mean of expected horizontal ground motions, as predicted by the NGA-West2 models.
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 5-1 122.17° W
Site 3 G Site 2 G
Site 1 Site 0 G G
± SAF - San Andreas Fault
122.17° W
0 0.080.160.240.32 0.4 Miles
0 0.10.20.30.40.5 Kilometers
Project No. 26818815 Figure Stanford University LOCATIONS OF HAZARD COMPUTATIONS 5-1 Palo Alto, CA 1 1
5th and 95th Percentile 15th and 85th Percentile 50th Percentile Total Mean Hazard
0.1 10
0.01 100 eunPro (years) Period Return
0.001 1,000 Annual Exceedence Frequency
0.0001 10,000
VS30 = 270 m/sec Geometric Mean
1E-5 100,000 0 0.25 0.5 0.75 1 1.25 1.5 Peak Ground Acceleration (g)
Project No. 26818815 SEISMIC HAZARD CURVES FOR Figure Stanford University PEAK HORIZONTAL ACCELERATION 5-2 Palo Alto, CA FOR SITE 1 AND REFERNCE SITE CONDITION 1 1
5th and 95th Percentile 15th and 85th Percentile 50th Percentile Total Mean Hazard
0.1 10
0.01 100 eunPro (years) Period Return
0.001 1,000 Annual Exceedence Frequency
0.0001 10,000
VS30 = 270 m/sec Geometric Mean
1E-5 100,000 0 0.25 0.5 0.75 1 1.25 1.5 Spectral Acceleration (g)
Project No. 26818815 SEISMIC HAZARD CURVES FOR 1.0 SEC Figure Stanford University HORIZONTAL SPECTRAL ACCELERATION 5-3 Palo Alto, CA FOR SITE 1 AND REFERENCE SITE CONDITION 1 1
Site 0 Site 1 Site 2 Site 3
0.1 10
0.01 100 eunPro (years) Period Return
0.001 1,000 Annual Exceedence Frequency
0.0001 10,000
VS30 = 270 m/sec Geometric Mean 1E-5 100,000 0 0.25 0.5 0.75 1 1.25 1.5 Peak Ground Acceleration (g)
Project No. 26818815 COMPARISON OF PEAK HORIZONTAL Figure Stanford University ACCELERATION HAZARD FOR ALL SITES 5-4 Palo Alto, CA AT REFERNCE SITE CONDITION 1 1
Site 0 Site 1 Site 2 Site 3
0.1 10
0.01 100 eunPro (years) Period Return
0.001 1,000 Annual Exceedence Frequency
0.0001 10,000
VS30 = 270 m/sec Geometric Mean 1E-5 100,000 0 0.25 0.5 0.75 1 1.25 1.5 Spectral Acceleration (g)
Project No. 26818815 COMPARISON OF 1.0 SEC HORIZONTAL SPECTRAL Figure Stanford University ACCELERATION HAZARD FOR ALL SITES 5-5 Palo Alto, CA AT REFERNCE SITE CONDITION 1 1
0.1 10
Other less significant sources not listed.
VS30 = 270 m/sec 0.01 Geometric Mean 100 eunPro (years) Period Return
0.001 1,000 Annual Exceedance Frequency
0.0001 10,000
1E-005 100,000 0 0.25 0.5 0.75 1 1.25 1.5 Peak Ground Acceleration (g)
Project No. 26818815 SEISMIC SOURCE CONTRIBUTIONS TO PEAK Figure Stanford University HORIZONTAL ACCELERATION HAZARD 5-6 Palo Alto, CA FOR SITE 1 AND REFERENCE SITE CONDITION 1 1
0.1 10
Other less significant sources not listed.
VS30 = 270 m/sec 0.01 Geometric Mean 100 eunPro (years) Period Return
0.001 1,000 Annual Exceedance Frequency
0.0001 10,000
1E-005 100,000 0 0.25 0.5 0.75 1 1.25 1.5 Spectral Acceleration (g)
Project No. 26818815 SEISMIC SOURCE CONTRIBUTIONS TO 1.0 SEC Figure Stanford University HORIZONTAL SPECTRAL ACCELERATION HAZARD 5-7 Palo Alto, CA FOR SITE 1 AND REFERENCE SITE CONDITION Epsilon >2 1to2 0to1 -1 to 0 -2 to -1 Proportion
Magnitude
Distance (km)
Project No. 26818815 MAGNITUDE AND DISTANCE CONTRIBUTIONS Figure Vs30 = 270 m/sec Stanford University TO THE MEAN PEAK HORIZONTAL ACCELERATION 5-8 Palo Alto, CA HAZARD AT 225-YEAR RETURN PERIOD FOR SITE 1 Epsilon >2 1to2 0to1 -1 to 0 -2 to -1 Proportion
Magnitude
Distance (km)
Project No. 26818815 MAGNITUDE AND DISTANCE CONTRIBUTIONS Figure Vs30 = 270 m/sec Stanford University TO THE MEAN PEAK HORIZONTAL ACCELERATION 5-9 Palo Alto, CA HAZARD AT 975-YEAR RETURN PERIOD FOR SITE 1 Epsilon >2 1to2 0to1 -1 to 0 -2 to -1 Proportion
Magnitude
Distance (km)
Project No. 26818815 MAGNITUDE AND DISTANCE CONTRIBUTIONS Figure Vs30 = 270 m/sec Stanford University TO THE MEAN PEAK HORIZONTAL ACCELERATION 5-10 Palo Alto, CA HAZARD AT 2,475-YEAR RETURN PERIOD FOR SITE 1 Epsilon >2 1to2 0to1 -1 to 0 -2 to -1 Proportion
Magnitude
Distance (km)
Project No. 26818815 MAGNITUDE AND DISTANCE CONTRIBUTIONS TOTHEMEAN1.0SECHORIZONTAL Figure Vs30 = 270 m/sec Stanford University SPECTRAL ACCELERATION HAZARD 5-11 Palo Alto, CA AT 225-YEAR RETURN PERIOD FOR SITE 1 Epsilon >2 1to2 0to1 -1 to 0 -2 to -1 Proportion
Magnitude
Distance (km)
Project No. 26818815 MAGNITUDE AND DISTANCE CONTRIBUTIONS TOTHEMEAN1.0SECHORIZONTAL Figure Vs30 = 270 m/sec Stanford University SPECTRAL ACCELERATION HAZARD 5-12 Palo Alto, CA AT 975-YEAR RETURN PERIOD FOR SITE 1 Epsilon >2 1to2 0to1 -1 to 0 -2 to -1 Proportion
Magnitude
Distance (km)
Project No. 26818815 MAGNITUDE AND DISTANCE CONTRIBUTIONS TOTHEMEAN1.0SECHORIZONTAL Figure Vs30 = 270 m/sec Stanford University SPECTRAL ACCELERATION HAZARD 5-13 Palo Alto, CA AT 2,475-YEAR RETURN PERIOD FOR SITE 1 1 1
Abrahamson et al. (2013) Chiou and Youngs (2013) Campbell and Bozorgnia (2013) Boore et al. (2013) Total Mean Hazard 0.1 10
0.01 100 eunPro (years) Period Return
0.001 1,000 Annual Exceedence Frequency
0.0001 10,000
VS30 = 270 m/sec Geometric Mean
1E-5 100,000 0 0.25 0.5 0.75 1 1.25 1.5 Peak Ground Acceleration (g)
Project No. 26818815 SENSITIVITY OF THE PEAK HORIZONTAL ACCELERATION HAZARD TO THE Figure Stanford University SELECTION OF GROUND MOTION MODELS 5-14 Palo Alto, CA FOR SITE 1 AND REFERENCE SITE CONDITION 1 1
Abrahamson et al. (2013) Chiou and Youngs (2013) Campbell and Bozorgnia (2013) Boore et al. (2013) Total Mean Hazard 0.1 10
0.01 100 eunPro (years) Period Return
0.001 1,000 Annual Exceedence Frequency
0.0001 10,000
VS30 = 270 m/sec Geometric Mean 1E-5 100,000 0 0.25 0.5 0.75 1 1.25 1.5 Spectral Acceleration (g)
Project No. 26818815 SENSITIVITY OF THE 1.0 SEC HORIZONTAL SPECTRAL ACCELERATION HAZARD TO THE Figure Stanford University SELECTION OF GROUND MOTION MODELS 5-15 Palo Alto, CA FOR SITE 1 AND REFERENCE SITE CONDITION 3.00
2.75
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0.00 0.01 0.1 1 10 Period (s)
Site 0 Site 1 Site 2 Site 3
Project No. 26818815 5%-DAMPED UNIFORM HAZARD SPECTRA Figure Stanford University 5-16 Palo Alto, CA AT REFERENCE SITE CONDITION SECTIONSIX DSHA Results
6. Section 6 SIX Dsha Results 5%-damped 84th-percentile horizontal acceleration response spectra are calculated for the maximum earthquake on the San Andreas fault (M 8.0) for a range of source-to-site distances from 5.5 to 7.5 km using the same NGA-West2 models used in the PSHA. A VS30 of 270 m/sec was also used for the generic firm soil site conditions (Section 3). Figures 6-1 and 6-2 show the geometric mean 84th-percentile acceleration response spectrum and the individual spectra from the four ground motion models used at distances of 5.5 and 7.5 km, respectively. The range in spectra represent the epistemic uncertainty in the ground motion modeling. Figure 6-3 compares the geometric mean spectra of the four NGA models for all distances modeled. The 84th percentile spectra for the campus are larger than in the 2010 study. Figure 6-4 compares the geometric means from the four ground motion models for a M 8.0 at 6.0 and 7.5 km using the NGA-West1 and NGA-West2 models. For both distances, the NGA-West2 ground motions are higher, especially at periods between 0.2 and 1.0 sec.
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 6-1 3 San Andreas fault
M 8.0, Rrup =5.5km Vs30 = 270 m/sec
Z1.0 = 0.47 km (ASK 2013), 0.48 km (CY 2013)
Z2.5 = 1.98 km (CB 2013)
PGA = 0.78 g 2 Spectral Acceleration (g) 1
5% Damping Geometric Mean
0 0.01 0.1 1 10 Period (s)
Abrahamson et al. (2013) Boore et al. (2013) Campbell and Bozorgnia (2013) Chiou and Youngs (2013) Wt Mean
Project No. 26818815 SENSITIVITY OF 84th PERCENTILE HORIZONTAL ACCELERATION RESPONSE SPECTRUM FOR THE Figure Stanford University M 8.0 SAN ANDREAS MAXIMUM EARTHQUAKE 6-1 Palo Alto, CA AT 5.5 KM TO GROUND MOTION MODELS 3 San Andreas fault
M 8.0, Rrup =7.5km Vs30 = 270 m/sec
Z1.0 = 0.47 km (ASK 2013), 0.48 km (CY 2013)
Z2.5 = 1.98 km (CB 2013)
PGA = 0.71 g 2 Spectral Acceleration (g) 1
5% Damping Geometric Mean
0 0.01 0.1 1 10 Period (s)
Abrahamson et al. (2013) Boore et al. (2013) Campbell and Bozorgnia (2013) Chiou and Youngs (2013) Wt Mean
Project No. 26818815 SENSITIVITY OF 84th PERCENTILE HORIZONTAL ACCELERATION RESPONSE SPECTRUM FOR THE Figure Stanford University M 8.0 SAN ANDREAS MAXIMUM EARTHQUAKE 6-2 Palo Alto, CA AT 7.5 KM TO GROUND MOTION MODELS 2 San Andreas fault M 8.0 Vs30 = 270 m/sec
Z1.0 = 0.47 km (ASK 2013), 1.6 0.48 km (CY 2013)
Z2.5 = 1.98 km (CB 2013)
1.2
0.8 Spectral Acceleration (g)
0.4
5% Damping Geometric Mean
0 0.01 0.1 1 10 Period (s)
Rupture Distance 5.5 km 6.0 km 6.60 km 7.25 km 7.5 km
Project No. 26818815 84th PERCENTILE HORIZONTAL Figure Stanford University ACCELERATION RESPONSE SPECTRUM FOR THE 6-3 Palo Alto, CA M 8.0 SAN ANDREAS MAXIMUM EARTHQUAKE 2
San Andreas fault M 8.0 Vs30 = 270 m/sec
Z1.0 = 0.47 km (ASK 2013), 1.6 0.48 km (CY 2013)
Z2.5 = 1.98 km (CB 2013)
1.2
0.8 Spectral Acceleration (g)
0.4
5% Damping Geometric Mean
0 0.01 0.1 1 10 Period (s)
M 8.0 at 6.0 km, NGA West 2 (2013) M 8.0 at 7.5 km, NGA West 2 (2013) M 8.0 at 6.0 km, NGA West 1 (2008) M 8.0 at 7.5 km, NGA West 1 (2008)
Project No. 26818815 COMPARISON OF 84TH PERCENTILE DETERMINISTIC SPECTRA USING Figure Stanford Univeristy 6-4 Palo Alto, California NGA WEST 1 AND NGA WEST 2 GROUND MOTION MODELS SECTIONSEVEN Site Response Analysis
7. Section 7 SEVEN Site Response Analysis A site response analysis was performed using the same approach as in 2010 (Wong et al., 2010). The computational scheme employed to compute the amplification factors uses random vibration theory (RVT) (Silva and Lee, 1987). In this approach, as embodied in the computer program RASCALS, the control motion power spectrum is propagated through the 1-D soil profile.
To perform the site response analysis, representative base case VS profiles of the site (Section 2) and shear modulus (G/Gmax) reduction and damping curves are required. For the dynamic material properties, the EPRI (1993) sand curves and Peninsular Range curves (Silva et al., 1997) were used to cover the range of nonlinear behavior at the site. The two dynamic material models were weighted equally when combining the site response analyses results obtained from the two velocity models.
In order to randomly vary the base case VS profile, a profile randomization scheme based on a correlation model was used (Silva et al., 1997). Profile depth (depth to competent material) is also varied on a site-specific basis using a uniform distribution. The depth range is generally selected to reflect expected variability over the structural foundation as well as uncertainty in the estimation of depth to competent material. To accommodate variability in shear modulus reduction and hysteretic damping curves on a generic basis, the curves are independently randomized about the base case values. A lognormal -2 distribution is assumed with a σln of 0.35 at a cyclic shear strain of 3 x 10 %.
For each combination of base case velocity profile and depth to bedrock, 30 randomized VS profiles were generated. For example, Figure 7-1 shows the 30 randomized VS profiles for one bedrock depth and the north-central/east campus base case velocity profile. Associated with each 30 randomized profile was a set of randomized dynamic material property curves. Based on RASCALS runs for the 30 VS profiles for each base case, a probability distribution of amplification factors was calculated. Figure 7-2 shows the median amplification factors for each combination of material properties and velocity profile for a ground motion level of 0.5 g (PGA) for the north-central and east campus.
The suite of amplification factors with respect to generic firm soil (VS30 270 m/sec) were applied to the generic soil hazard curves. From these amplified curves, hazard-consistent site- specific UHS were calculated for return periods of 225, 975, and 2,475 years for sites 1, 2, and 3 (Figure 7-3). The median amplification factors were applied to the median horizontal acceleration response spectra for the M 8.0 San Andreas maximum earthquake (VS30 270 m/sec) to arrive at the median deterministic site-specific spectra for the suite of distances. The 84th-percentile spectra were then calculated using the aleatory sigma from each of the four NGA models (Figure 7-4). Figure 7-5 compares the site-specific 2,475-year return period UHS and 84th percentile M 8.0 deterministic spectra at the ground surface. As expected for sites in seismically active regions with many active faults, the 84th percentile deterministic spectra are lower than the 2,475-year return period UHS. Hence, MCER and DRSR will be controlled by the 84th percentile deterministic spectra (Section 8.1). Note that these ground surface spectra exhibit the unsmoothed characteristics of spectra derived from actual strong motion data. In this case, the bump in the spectra centered at about 1.5 sec is
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 7-1 SECTIONSEVEN Site Response Analysis
probably due to modeling the soil/rock contrast at varying depths. Given the absence of data on where this contact is, the bump is probably broader than what would be observed in actual strong motion data. For west campus, a suite of amplification factors were developed based on the near-surface velocity profile (Figure 11) and five depths to bedrock (Section 2). Thirty randomized velocity profiles were generated for each of the resulting base case velocity profiles. The amplification factors were applied to the generic soil hazard curves to obtain hazard-consistent site-specific UHS for return periods of 225, 975, and 2,475 years for site 0 (Figures 7-6 to 7-8). The site- specific ground motions vary significantly for the range of bedrock depths. As bedrock becomes shallower (100 and 200 ft depths), the ground motions amplification in the 0.1 to 0.5 period range becomes significant. In addition, as the peak ground motion increases, the uncertainty in the amplification factors increases. As the depth to bedrock increases, the amplification due to the soil/rock contrast shifts to longer periods. For bedrock depths of 300 ft or greater, the 2,475- year UHS have a bump in the 1.0 to 2.0 sec period range (Figure 7-8). The median amplification factors and aleatory sigma for the ground motion models were applied to the median horizontal acceleration response spectrum for the M 8.0 San Andreas maximum earthquake (VS30 270 m/sec) at 5.5 km to arrive at the 84th percentile deterministic spectra for west campus (Figure 7-9). The sensitivity to depth to bedrock is similar to that of the UHS discussed above. Figure 7-10 compares the site-specific 2,475-year return period UHS and the 84th percentile deterministic spectra for west campus. For all bedrock depths, the 2,475-year return period UHS exceeds the 84th percentile deterministic spectra. The microzonation of campus developed in 2010 was re-examined in light of the revised ground motions. As noted in 2010, the deterministic ground motions for most of campus (west area excepted) are generally a function of distance to the San Andreas fault. Given the similarities in base case VS profiles for north-central and east campus areas, site response effects are not significant in the campus microzonation for these areas. Based on examination of the deterministic spectra, the north-central and east areas (Figure 3-1) were divided into 3 zones similar to the 2010 study (Figure 7-11). The boundaries between zones 1 to 3 reflect a constant distance to the San Andreas fault. Note that changes from these boundaries from the 2010 study are due to strictly enforcing the distance to the San Andreas fault in this study. For west campus (Zone 0 in the 2010 study), the boundaries are defined by near-surface geology (shallow alluvium over bedrock at varying depths). The golf course, which was included in Zone 0 in the 2010 study, was excluded from Zone 0 in the current study after discussions with the Project Manager. As discussed above, the ground motions in the western part of campus are significantly impacted by the depth of the bedrock. Bedrock was determined to be at approximately 130 ft depth at Electioneer Road and close to 300 ft depth at the Equestrian Center based on the SASW surveys (Figures 3-1 and 3-3). Bedrock depth is unknown for much of the west campus area. Given the significant differences in ground motions for the various depths to bedrock modeled, design spectra are developed for bedrock depth less than 300 ft and greater than 300 ft. Design of structures in Zone 0 should confirm the depth of bedrock at the site to determine which design spectra to use.
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 7-2 Shear-Wave Velocity (m/sec) 0 500 1000 1500 2000 2500 3000 0 0
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Project No. 26818815 EXAMPLE RANDOMIZED VELOCITY PROFILES FOR NORTH-CENTRAL/EAST CAMPUS Figure Stanford University 7-1 Palo Alto, CA FOR ONE BEDROCK DEPTH 3.00
2.75 M1P1
2.50 M1P2 M1P3
2.25 M1P4 M2P1 M2P2 2.00 M2P3 M2P4 1.75
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M1 = EPRI sand modulus reduction and damping curves (EPRI, 1993) M2 = Peninsular Range modulus reduction and damping curves (Silva et al., 1997) P1 = 300 ft to 1.0 km/sec velocity P1 = 350 ft to 1.0 km/sec velocity P1 = 400 ft to 1.0 km/sec velocity P1 = 500 ft to 1.0 km/sec velocity
Project No. 26818815 SITE-SPECIFIC AMPLIFICATION FACTORS Figure Stanford University FOR GROUND MOTION LEVEL OF 0.5 g (PGA) 7-2 Palo Alto, CA 3.25
3.00
2.75
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1.00 225-year UHS 0.75
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0.25 5% Damping Geometric Mean
0.00 0.01 0.1 1 10 Period (s)
Site 1 Site 2 Site 3
Project No. 26818815 5%-DAMPED UNIFORM HAZARD SPECTRA Figure Stanford University FOR SITES 1, 2, AND 3 7-3 Palo Alto, CA AT THE GROUND SURFACE 1.75
1.50
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RRUP =6.0km RRUP =6.6km RRUP =7.25km RRUP =7.5km
Project No. 26818815 84th PERCENTILE HORIZONTAL ACCELERATION RESPONSE SPECTRUM FOR THE M 8.0 Figure Stanford University SAN ANDREAS MAXIMUM EARTHQUAKE AT 6.0, 6.6, 7-4 Palo Alto, CA 7.25 AND 7.5 KM AT THE GROUND SURFACE 3.25
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2,475-YEAR UHS 84TH PERCENTILE DETERMINISTIC SPECTRA Site 1 M 8.0 at 6.0 km Site 2 M 8.0 at 6.6 km Site 3 M 8.0at7.25km M 8.0 at 7.5 km
Project No. 26818815 COMPARISON OF UNIFORM HAZARD SPECTRA Figure Stanford University AND 84TH PERCENTILE DETERMINISTIC SPECTRA 7-5 Palo Alto, CA FOR SITES 1, 2, AND 3 AT THE GROUND SURFACE 2.50
5% Damping Geometric Mean
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Depth to Bedrock 100 ft 200 ft 300 ft 400 ft 500 ft
Project No. 26818815 5% DAMPED UNIFORM HAZARD SPECTRA Figure Stanford University AT 225-YEAR RETURN PERIOD 7-6 Palo Alto, CA FOR SITE 0 5.00
5% Damping
4.50 Geometric Mean
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Depth to Bedrock 100 ft 200 ft 300 ft 400 ft 500 ft
Project No. 26818815 5% DAMPED UNIFORM HAZARD SPECTRA Figure Stanford University AT 975-YEAR RETURN PERIOD 7-7 Palo Alto, CA FOR SITE 0 7.00
5% Damping 6.50 Geometric Mean
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Depth to Bedrock 100 ft 200 ft 300 ft 400 ft 500 ft
Project No. 26818815 5% DAMPED UNIFORM HAZARD SPECTRA Figure Stanford University AT 2,475-YEAR RETURN PERIOD 7-8 Palo Alto, CA FOR SITE 0 2.50
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Depth to Bedrock 100 ft 200 ft 300 ft 400 ft 500 ft
Project No. 26818815 84th PERCENTILE HORIZONTAL ACCELERATION RESPONSE SPECTRA FOR Figure Stanford University 7-9 Palo Alto, CA THE M 8.0 SAN ANDREAS MAXIMUM EARTHQUAKE AT 5.5 KM FOR WEST CAMPUS 7.00
5% Damping 6.50 Geometric Mean
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84th Percentile Deterministic, Depth to Bedrock 2,475-year UHS, Depth to Bedrock 100 ft 100 ft 200 ft 200 ft 300 ft 300 ft 400 ft 400 ft 500 ft 500 ft
Project No. 26818815 COMPARISON OF 84th PERCENTILE DETERMINISTIC RESPONSE SPECTRA TO THE Figure Stanford University 2,475-YEAR RETURN PERIOD UHS 7-10 Palo Alto, CA FOR WEST CAMPUS 122.17° W
3 e n o Z
2 e n o Z
1 e n o Z
0 e n o Z
37.42° N 37.42° N
122.17° W Geologic Map Source: Witter et al. , 2006 0 190 380 570 760 950 Yards Design Ground Motion Zones
0 275 550 825 1,100 1,375 Meters ±
Project No. 26818815 Figure Stanford University DESIGN GROUND MOTION ZONES 7-11 Palo Alto, CA SECTIONEIGHT Design Response Spectra for New Buildings
8. Section 8 EIGHT Design Response Spectra for New Buildings The development of design ground motions for new buildings is discussed in this section and site-specific design spectra are presented. For new buildings, the California Building Code (CBC) 2014 requires that design motions be developed in accordance with ASCE Standard 7-10. Design ground motions for the four zones were computed following ASCE 7-10, resulting in Risk-Targeted Maximum Considered Earthquake (MCER) and DRSR spectra. 8.1 ASCE 7-10 METHODOLOGY The criteria for site-specific design ground motions is provided in ASCE 7-10, Chapter 21 Site- Specific Ground Motion Procedures for Seismic Design. Figure 8-1 provides a flowchart for the procedure for computing the site-specific MCER and DRSR according to ASCE 7-10. First, a PSHA and DSHA are performed for generic rock conditions. Next, a site-response analysis is performed resulting in site amplification functions to adjust both the probabilistic ground motions (2,475-year return period UHS) and thedeterministic ground motions (84th percentile deterministic response spectrum) to the ground surface. One change implemented in ASCE 7-10 relative to previous versions of the code is the use of maximum direction ground motions. Ground motion prediction models (i.e., NGA-West1 and NGA-West2) provide the geometric mean (specifically GMRotI50 for NGA-West1 and GMRotD50 for NGA-West2) of the horizontal components. Scaling factors have been developed (e.g., 2009 NEHRP Provisions) to convert to maximum direction. These scale factors are applied to the 2,475-year UHS and 84th percentile deterministic spectra. Another change implemented in ASCE 7-10 is the development of risk-targeted spectra. Previous building codes have used the 2,475-year return period (2% in 50 year exceedance frequency) ground motions as the probabilistic MCE. ASCE 7-10 requires estimation of ground motions that are expected to achieve a 1% probability of collapse in 50 years. To obtain these probabilistic ground motions, the hazard curve is iteratively integrated with a lognormal probability density function representing the collapse fragility. For a site-specific analysis, ASCE 7-10 Chapter 21 provides two methods to calculate the probabilistic ground motions. Method 1 corrects the site-specific 2,475-year return period UHS to risk-targeted ground motions by applying a risk coefficient, CR. These risk-coefficients have been calculated for the continental U.S. by the USGS and are based on the 2008 USGS hazard curves, which are the basis for the 2008 USGS National Seismic Hazard Maps. Method 2 computes the risk-targeted ground motions by directly integrating the site-specific hazard curve with a collapse fragility function. For this study, Method 1 was used to compute the MCER and DRSR. As in previous versions (ASCE 7-05 and CBC 2010), ASCE 7-10 caps the probabilistic ground motions with the site-specific deterministic ground motions; thus the site-specific MCER is the minimum of the probabilistic MCER and the deterministic MCER (Figure 8-1). The site-specific DRSR is the minimum of 2/3rds the MCER and 80% of the general code spectra for the appropriate site class.
8.2 MCER AND DRSR FOR ZONES 1, 2 AND 3
The procedure described in Section 8.1 was followed to obtain site-specific MCER and DRSR for Zones 1, 2 and 3. For each of these zones, the intermediate spectra are similar, thus the process is illustrated in this section for Zone 1.
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Figures 8-2 to 8-6 illustrate the development of the site-specific MCER and DRSR for Zones 1, 2 and 3. Figure 8-2 shows the conversion of the 84th percentile deterministic spectra from geometric mean to maximum direction. The scaling factors in the 2009 NEHR Provisions (Table C21.2.1) are used. The maximum direction 84th percentile deterministic spectrum is then compared to the ASCE 7-10 lower limit for site-specific deterministic spectra (Figure 8-3). The lower limit is determined from the code for both NEHRP site classes C and D due to the variation of soils within the zones. The lower limit exceeds the site-specific deterministic spectrum at periods less than approximately 0.2 sec. The envelope of these spectra is the deterministic MCER spectrum per ASCE 7-10. Figure 8-4 shows the adjustment of the site-specific 2,475-year return period UHS to the maximum direction, risk-targeted probabilistic spectrum. First, the maximum direction scaling factors are applied and then the risk-coefficient. The risk coefficient, CR, is defined as CRS at periods less than or equal to 0.2 sec and CR1 for periods greater than or equal to 1.0 sec, with linear interpolation used to define CR for periods between 0.2 and 1.0 sec. There is little risk adjustment for the zones, with the minimum CRS and CR1 of 0.973 and 0.925, respectively. Figure 8-5 then compares the site-specific maximum direction, risk-targeted UHS (the probabilistic MCER spectrum per ASCE 7-10) with the site-specific deterministic MCER. The minimum of these two is the site-specific MCER. The deterministic MCER controls the MCER at all periods except 4 sec and greater.
In Figure 8-6, two-thirds of the site-specific MCER is compared with the lower limit of 80% of the ASCE 7-10 code general DRSR for site classes C and D. The envelope of these is the site- specific DRSR.
Figure 8-7 summarizes the site-specific MCER and DRSR for the three zones. Response spectra are shown log-linear and linear-linear to highlight different period ranges. For short periods (less than 0.2 sec), the spectra are controlled by the lower limit deterministic spectrum of ASCE 7-10 and there is little difference between the spectra for the three zones. At longer periods, the MCER and DRSR are controlled by the site-specific deterministic spectra. For the range of distances for Zones 1 to 3 (6.0 to 7.5 km), there is little difference in the deterministic ground motions (Section 7, Figure 7-5). Horizontal MCER and DRSR are provided in Table 8-1. Vertical design spectra were computed using the median V/H ratios of Gülerce and Abrahamson (2011). Figures 8-8 and 8-9 show the horizontal and vertical response spectra for the MCER and DRSR levels for all zones. The median V/H ratios are a function of magnitude, distance, VS30 and level of shaking as defined by the corresponding PGA for a VS30 of 1,100 m/sec (PGA1,100). The 84th percentile deterministic spectra control the horizontal MCER and DRSR, so a magnitude M 8.0 at distances of 6.0, 6.6 and 7.25 km were used for Zones 1, 2 and 3, respectively. A VS30 value of 330 m/sec was used corresponding to the site-specific velocity profile. The PGA1,100 was determined separately for the MCER and DRSR spectra based on the magnitude, distance and epsilon required to match the MCER or DRSR at PGA. Horizontal and vertical MCER and DRSR are provided in Table 8-1.
8.3 MCER AND DRSR FOR ZONE 0
Figures 8-10 to 8-14 show the development of the MCER and DRSR for Zone 0 following the methodology of ASCE 7-10 discussed in Section 8.1. MCER and DRSR were developed for two
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cases: bedrock depths less than 300 ft and bedrock depths greater than or equal to 300 ft. As discussed in Sections 3 and 7, the depth to bedrock is unknown for much of Zone 0. However, we estimate that the bedrock depth ranges between 100 and 500 ft and likely increases towards the northeast within Zone 0. Figure 8-10 shows the 84th percentile deterministic spectra adjusted to maximum direction. These spectra are then compared to the minimum deterministic spectra allowed by ASCE 7-10 on Figure 8-11 to arrive at the deterministic MCER. The probabilistic MCER is the 2,475-year return period UHS adjusted to maximum direction and a risk coefficient is applied (Figure 8-12). The final site-specific MCER for Zone 0 is the lesser of the probabilistic and deterministic MCER (Figure 8-13). MCER deterministic spectra control the MCER at periods less than 1.0 to 2.0 sec. The DRSR are shown on Figure 8-14. The DRSR are two-thirds the MCER, but not less than 80% the ASCE 7-10 general DRSR for site classes C and D. The site-specific MCER and DRSR for Zone 0 are provided in Table 8-1.
Vertical design spectral were computed for the MCER and DRSR levels using the V/H ratios of Gülerce and Abrahamson (2011), as described above for Zones 1, 2 and 3. Figures 8-15 and 8- 16 (and Table 8-1) provide the horizontal and vertical MCER and DRSR spectra for Zone 0. 8.4 DESIGN ACCELERATION PARAMETERS Design acceleration parameters as per ASCE 7-10, Section 21.4 are provided in Table 8-2 for all zones. The site-specific SDS is taken as the 0.2 sec SA, except not less than 90 percent of the SA at any period greater than 0.2 sec. The SD1 parameter is the greater of the site-specific 1.0 sec SA and twice the 2.0 sec SA. SMS and SM1 are 1.5 times SDS and SD1, respectively.
ASCE 7-10 also requires the calculation of the MCEG PGA, which is used in liquefaction analyses. The site-specific MCEG PGA is the lesser of the 2,475-year return period PGA (geometric mean) and the 84th percentile PGA (geometric mean). For all zones, the MCEG PGA is the site-specific 84th percentile PGA (geometric mean). Values are provided in Table 8-2.
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Table 8-1
MCER (BSE-2N) and DRSR (BSE-1N) Spectra
Zone 0 Spectra, Bedrock Depth < 300 feet Horizontal Vertical MCER Horizontal Vertical DRSR Period (sec) MCER (BSE-2N) (BSE-2N) per DRSR (BSE-1N) (BSE-1N) per per ASCE 7-10 ASCE 7-10 per ASCE 7-10 ASCE 7-10 0.01 0.89 0.72 0.60 0.43 0.03 0.92 1.16 0.61 0.67 0.05 1.14 2.01 0.76 1.13 0.075 1.56 2.53 1.04 1.38 0.10 1.87 2.44 1.25 1.32 0.15 2.11 1.86 1.41 1.01 0.20 2.41 1.47 1.61 0.81 0.25 2.56 1.20 1.70 0.68 0.30 2.55 1.05 1.70 0.61 0.35 2.55 0.94 1.70 0.55 0.40 2.55 0.85 1.70 0.51 0.45 2.54 0.80 1.70 0.49 0.50 2.54 0.76 1.69 0.47 0.55 2.42 0.72 1.61 0.45 0.60 2.30 0.68 1.54 0.43 0.65 2.20 0.66 1.47 0.42 0.70 2.10 0.64 1.40 0.41 0.75 2.01 0.63 1.34 0.40 0.80 1.95 0.62 1.30 0.40 0.85 1.89 0.61 1.26 0.39 0.90 1.83 0.60 1.22 0.39 0.95 1.78 0.60 1.19 0.38 1.00 1.73 0.59 1.15 0.38 1.10 1.59 0.58 1.06 0.37 1.20 1.47 0.57 0.98 0.37 1.30 1.35 0.56 0.90 0.36 1.40 1.25 0.55 0.83 0.36 1.50 1.15 0.54 0.77 0.35 1.60 1.07 0.52 0.72 0.34 1.70 1.00 0.49 0.67 0.33 1.80 0.93 0.47 0.62 0.31 1.90 0.87 0.45 0.58 0.30 2.00 0.81 0.44 0.54 0.29 2.25 0.73 0.40 0.49 0.26 2.50 0.67 0.36 0.44 0.24 2.75 0.61 0.33 0.40 0.22 3.00 0.55 0.31 0.37 0.20 3.50 0.44 0.24 0.30 0.16 4.00 0.35 0.18 0.23 0.12 4.50 0.29 0.14 0.20 0.10 5.00 0.24 0.11 0.16 0.08 5.50 0.22 0.10 0.15 0.07 6.00 0.20 0.09 0.13 0.06 6.50 0.18 0.08 0.12 0.06 7.00 0.16 0.08 0.11 0.05 7.50 0.15 0.07 0.10 0.05 10.00 0.10 0.04 0.07 0.03
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Table 8-1 (continued)
Zone 0 Spectra, Bedrock Depth >= 300 feet Horizontal Vertical MCER Horizontal Vertical DRSR Period (sec) MCER (BSE-2N) (BSE-2N) per DRSR (BSE-1N) (BSE-1N) per per ASCE 7-10 ASCE 7-10 per ASCE 7-10 ASCE 7-10 0.01 0.69 0.73 0.54 0.45 0.03 0.86 1.17 0.59 0.71 0.05 1.03 2.03 0.70 1.18 0.075 1.25 2.54 0.83 1.42 0.10 1.50 2.50 1.00 1.39 0.15 1.56 1.88 1.06 1.06 0.20 1.61 1.48 1.07 0.83 0.25 1.65 1.21 1.10 0.70 0.30 1.69 1.04 1.13 0.61 0.35 1.70 0.92 1.13 0.55 0.40 1.71 0.83 1.14 0.50 0.45 1.72 0.77 1.15 0.47 0.50 1.73 0.71 1.15 0.44 0.55 1.70 0.68 1.13 0.43 0.60 1.67 0.66 1.11 0.41 0.65 1.64 0.63 1.09 0.40 0.70 1.61 0.61 1.08 0.39 0.75 1.59 0.59 1.06 0.38 0.80 1.57 0.58 1.05 0.37 0.85 1.55 0.57 1.03 0.37 0.90 1.53 0.57 1.02 0.37 0.95 1.51 0.56 1.01 0.36 1.00 1.50 0.55 1.00 0.36 1.10 1.48 0.55 0.99 0.36 1.20 1.47 0.54 0.98 0.35 1.30 1.45 0.54 0.97 0.35 1.40 1.44 0.53 0.96 0.35 1.50 1.43 0.53 0.95 0.35 1.60 1.35 0.50 0.90 0.33 1.70 1.29 0.48 0.86 0.32 1.80 1.22 0.45 0.81 0.30 1.90 1.16 0.43 0.77 0.29 2.00 1.10 0.41 0.73 0.27 2.25 1.02 0.39 0.68 0.26 2.50 0.95 0.37 0.63 0.24 2.75 0.89 0.35 0.59 0.23 3.00 0.83 0.33 0.55 0.22 3.50 0.64 0.26 0.43 0.17 4.00 0.48 0.20 0.32 0.13 4.50 0.38 0.16 0.26 0.11 5.00 0.29 0.12 0.20 0.08 5.50 0.27 0.11 0.18 0.07 6.00 0.24 0.10 0.16 0.07 6.50 0.22 0.09 0.15 0.06 7.00 0.20 0.08 0.13 0.06 7.50 0.18 0.07 0.12 0.05 10.00 0.11 0.05 0.07 0.03
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Table 8-1 (continued)
Zone 1 Spectra Horizontal Vertical MCER Horizontal Vertical DRSR Period (sec) MCER (BSE-2N) (BSE-2N) per DRSR (BSE-1N) (BSE-1N) per per ASCE 7-10 ASCE 7-10 per ASCE 7-10 ASCE 7-10 0.01 0.86 0.72 0.57 0.43 0.03 0.86 1.16 0.57 0.67 0.05 1.03 2.01 0.69 1.13 0.075 1.25 2.53 0.83 1.38 0.10 1.47 2.44 0.98 1.32 0.15 1.56 1.86 1.04 1.01 0.20 1.60 1.47 1.07 0.81 0.25 1.64 1.20 1.09 0.68 0.30 1.70 1.05 1.13 0.61 0.35 1.73 0.94 1.15 0.55 0.40 1.75 0.85 1.17 0.51 0.45 1.80 0.80 1.20 0.49 0.50 1.84 0.76 1.23 0.47 0.55 1.80 0.72 1.20 0.45 0.60 1.77 0.68 1.18 0.43 0.65 1.74 0.66 1.16 0.42 0.70 1.71 0.64 1.14 0.41 0.75 1.69 0.63 1.13 0.40 0.80 1.67 0.62 1.11 0.40 0.85 1.64 0.61 1.10 0.39 0.90 1.62 0.60 1.08 0.39 0.95 1.61 0.60 1.07 0.38 1.00 1.59 0.59 1.06 0.38 1.10 1.56 0.58 1.04 0.37 1.20 1.53 0.57 1.02 0.37 1.30 1.50 0.56 1.00 0.36 1.40 1.47 0.55 0.98 0.36 1.50 1.45 0.54 0.97 0.35 1.60 1.39 0.52 0.92 0.34 1.70 1.33 0.49 0.88 0.33 1.80 1.27 0.47 0.85 0.31 1.90 1.22 0.45 0.81 0.30 2.00 1.16 0.44 0.78 0.29 2.25 1.05 0.40 0.70 0.26 2.50 0.94 0.36 0.63 0.24 2.75 0.85 0.33 0.57 0.22 3.00 0.76 0.31 0.51 0.20 3.50 0.58 0.24 0.39 0.16 4.00 0.42 0.18 0.28 0.12 4.50 0.34 0.14 0.23 0.10 5.00 0.27 0.11 0.18 0.08 5.50 0.24 0.10 0.16 0.07 6.00 0.22 0.09 0.15 0.06 6.50 0.20 0.08 0.13 0.06 7.00 0.18 0.08 0.12 0.05 7.50 0.16 0.07 0.11 0.05 10.00 0.11 0.04 0.07 0.03
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Table 8-1 (continued)
Zone 2 Spectra Horizontal Vertical MCER Horizontal Vertical DRSR Period (sec) MCER (BSE-2N) (BSE-2N) per DRSR (BSE-1N) (BSE-1N) per per ASCE 7-10 ASCE 7-10 per ASCE 7-10 ASCE 7-10 0.01 0.77 0.72 0.52 0.42 0.03 0.86 1.15 0.57 0.67 0.05 1.03 2.00 0.69 1.12 0.075 1.29 2.54 0.86 1.40 0.10 1.47 2.42 0.98 1.31 0.15 1.54 1.83 1.03 1.00 0.20 1.57 1.43 1.05 0.79 0.25 1.59 1.17 1.06 0.66 0.30 1.65 1.02 1.10 0.59 0.35 1.68 0.91 1.12 0.54 0.40 1.71 0.83 1.14 0.50 0.45 1.74 0.78 1.16 0.47 0.50 1.77 0.73 1.18 0.45 0.55 1.73 0.69 1.15 0.43 0.60 1.70 0.66 1.13 0.41 0.65 1.67 0.64 1.11 0.40 0.70 1.64 0.62 1.09 0.39 0.75 1.62 0.60 1.08 0.38 0.80 1.59 0.59 1.06 0.38 0.85 1.57 0.59 1.05 0.38 0.90 1.55 0.58 1.04 0.37 0.95 1.53 0.57 1.02 0.37 1.00 1.52 0.56 1.01 0.36 1.10 1.49 0.55 0.99 0.36 1.20 1.46 0.54 0.97 0.35 1.30 1.43 0.53 0.95 0.35 1.40 1.41 0.53 0.94 0.34 1.50 1.39 0.52 0.92 0.34 1.60 1.32 0.49 0.88 0.32 1.70 1.26 0.47 0.84 0.31 1.80 1.20 0.45 0.80 0.30 1.90 1.14 0.43 0.76 0.28 2.00 1.09 0.41 0.73 0.27 2.25 0.98 0.37 0.65 0.25 2.50 0.87 0.34 0.58 0.22 2.75 0.78 0.31 0.52 0.20 3.00 0.69 0.28 0.46 0.19 3.50 0.53 0.22 0.35 0.14 4.00 0.38 0.16 0.26 0.11 4.50 0.31 0.13 0.21 0.09 5.00 0.25 0.10 0.16 0.07 5.50 0.23 0.10 0.15 0.06 6.00 0.21 0.09 0.14 0.06 6.50 0.19 0.08 0.13 0.05 7.00 0.17 0.07 0.12 0.05 7.50 0.16 0.07 0.11 0.05 10.00 0.10 0.04 0.07 0.03
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Table 8-1 (continued)
Zone 3 Spectra Horizontal Vertical MCER Horizontal Vertical DRSR Period (sec) MCER (BSE-2N) (BSE-2N) per DRSR (BSE-1N) (BSE-1N) per per ASCE 7-10 ASCE 7-10 per ASCE 7-10 ASCE 7-10 0.01 0.77 0.71 0.52 0.42 0.03 0.86 1.15 0.57 0.66 0.05 1.03 1.98 0.69 1.11 0.075 1.29 2.52 0.86 1.38 0.10 1.47 2.40 0.98 1.30 0.15 1.52 1.81 1.01 0.98 0.20 1.54 1.40 1.03 0.78 0.25 1.55 1.14 1.03 0.64 0.30 1.61 0.99 1.07 0.57 0.35 1.64 0.89 1.09 0.53 0.40 1.67 0.81 1.11 0.49 0.45 1.70 0.76 1.13 0.46 0.50 1.73 0.71 1.15 0.44 0.55 1.70 0.68 1.13 0.42 0.60 1.66 0.65 1.11 0.40 0.65 1.64 0.63 1.09 0.39 0.70 1.61 0.61 1.07 0.39 0.75 1.59 0.59 1.06 0.38 0.80 1.57 0.59 1.04 0.37 0.85 1.55 0.58 1.03 0.37 0.90 1.53 0.57 1.02 0.37 0.95 1.51 0.56 1.01 0.36 1.00 1.49 0.56 1.00 0.36 1.10 1.47 0.55 0.98 0.35 1.20 1.44 0.54 0.96 0.35 1.30 1.41 0.53 0.94 0.34 1.40 1.39 0.52 0.93 0.34 1.50 1.37 0.51 0.91 0.34 1.60 1.31 0.49 0.87 0.32 1.70 1.25 0.47 0.83 0.31 1.80 1.19 0.45 0.79 0.29 1.90 1.13 0.43 0.76 0.28 2.00 1.08 0.41 0.72 0.27 2.25 0.97 0.37 0.65 0.25 2.50 0.87 0.34 0.58 0.23 2.75 0.78 0.31 0.52 0.21 3.00 0.70 0.28 0.46 0.19 3.50 0.53 0.22 0.36 0.15 4.00 0.39 0.16 0.26 0.11 4.50 0.32 0.13 0.21 0.09 5.00 0.25 0.11 0.17 0.07 5.50 0.23 0.10 0.15 0.07 6.00 0.21 0.09 0.14 0.06 6.50 0.19 0.08 0.13 0.05 7.00 0.17 0.07 0.12 0.05 7.50 0.16 0.07 0.10 0.04 10.00 0.10 0.04 0.07 0.03
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Table 8-2 Design Acceleration Parameters
Zone 0 Zone 0 Bedrock < 300 Bedrock 300 Zone 1 Zone 2 Zone 3 ft ft
SS 1.99 1.99 1.91 1.84 1.69
S1 0.87 0.87 0.84 0.80 0.76
SDS 1.61 1.07 1.10 1.06 1.04
SD1 1.15 1.47 1.55 1.45 1.44
SMS 2.41 1.61 1.65 1.59 1.56
SM1 1.73 2.20 2.33 2.18 2.17
MCEG PGA 0.81 0.63 0.63 0.62 0.61
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Site Response Analysis (Section 7)
2,475-yr UHS at 84th Percentile Deterministic Ground Surface Spectrum at Ground Surface (Geomean) (Geomean)
Apply Maximum Direction Factors Apply Maximum Direction Factors
2,475-yr UHS at 84th Percentile Deterministic Ground Surface Spectrum at Ground Surface (Maximum Direction) Minimum Allowable (Maximum Direction) Deterministic Spectrum Apply Risk Coefficients (Method 1 of ASCE 7-10)
Deterministic MCE Probabilistic MCER R = maximum of 84th Percentile (1% Collapse Deterministic and Minimum Allowable in 50 years) Deterministic Spectrum
MCER = minimum of
Probabilistic MCER and
Deterministic MCER
2/3 MCE R 80% General Code DRSR for site class (ASCE 7-10 maps use NGA-West1 ground motion models)
DRSR = maximum of
2/3 MCER and
80%General DRSR
Project No. 26818815 METHODOLOGY TO DETERMINE Figure Stanford Univeristy SITE-SPECIFIC GROUND MOTIONS (MCER AND DRSR) 8-1 Palo Alto, California ACCORDING TO ASCE 7-10 2.00
1.75 Zone 1 San Andreas fault 1.50 M 8.0, Rrup =6.0km
1.25
1.00
0.75
0.50 Spectral Acceleration (g)
0.25 5% Damping 0.00 0.01 0.1 1 10 Period (s) 2.00
1.75 Zone 2 San Andreas fault 1.50 M 8.0, Rrup =6.6km 1.25
1.00
0.75
0.50 Spectral Acceleration (g) 0.25 5% Damping
0.00 0.01 0.1 1 10 Period (s) 2.00
1.75 Zone 3
1.50 San Andreas fault M 8.0, Rrup =7.5km 1.25
1.00
0.75
0.50 Geometric Mean (GMRotD50) Spectral Acceleration (g) Maximum Direction 0.25 5% Damping
0.00 0.01 0.1Period (s) 1 10 Project No. 26818815 th 84 PERCENTILE HORIZONTAL ACCELERATION Figure Stanford University RESPONSE SPECTRUM FOR ZONES , 2 AND 3 8-2 Palo Alto, CA ADJUSTED TO MAXIMUM DIRECTION 2.00
1.75 Zone 1 San Andreas fault 1.50 M 8.0, Rrup =6.0km
1.25
1.00
0.75
0.50 Spectral Acceleration (g)
0.25 5% Damping
0.00 0.01 0.1 1 10 Period (s) 2.00
1.75 Zone 2 San Andreas fault 1.50 M 8.0, Rrup =6.6km 1.25
1.00
0.75
0.50 Spectral Acceleration (g)
0.25
0.00 0.01 0.1 1 10 Period (s) 2.00
1.75 Zone 3 San Andreas fault 1.50 M 8.0, Rrup =7.5km 1.25
1.00
0.75
0.50 84th% Deter. spectrum (max. dir.) Spectral Acceleration (g) Min. Allowable Determ. Spectrum - Class C and D 0.25 Site-specific Deterministic MCER 0.00 0.01 0.1Period (s) 1 10 Project No. 26818815 Figure Stanford University DETERMINISTIC MCER FOR ZONES 1, 2 AND 3 8-3 Palo Alto, CA 3.50 Zone 1 5% Damping 3.00 Risk Coefficients:
2.50 CRS =0.973,CR1 =0.925
2.00
1.50
1.00 Spectral Acceleration (g) 0.50
0.00 0.01 0.1 1 10 Period (s) 3.50
3.00 Zone 2 5% Damping Risk Coefficients:
2.50 CRS =0.983,CR1 =0.934
2.00
1.50
1.00 Spectral Acceleration (g) 0.50
0.00 0.01 0.1 1 10 Period (s) 3.50 5% Damping 3.00 Zone 3 Risk Coefficients:
2.50 CRS = 0.989, CR1 =0.939
2.00
1.50
1.00 2,475-Year UHS - Geometric Mean
Spectral Acceleration (g) 2,475-Year UHS - Maximum Direction 0.50 Probabilistic MCER = Max Direction 2,475-year UHS * Risk Coefficient 0.00 0.01 0.1Period (s) 1 10 Project No. 26818815 Figure Stanford University PROBABILISTIC MCER FOR ZONES 1, 2 AND 3 8-4 Palo Alto, CA 3.50 5% Damping 3.00 Zone 1
2.50
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1.00 Site-specific deterministic MCER Spectral Acceleration (g) Site-specific probabilistic MCE 0.50 R
Site-specific MCER 0.00 0.01 0.1Period (s) 1 10
Project No. 26818815 Figure Stanford Univeristy SITE-SPECIFIC MCER FOR ZONES 1, 2 AND 3 8-5 Palo Alto, California 1.50
Zone 1 5% Damping 1.25
1.00
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2/3 Site-specific MCER Spectral Acceleration (g)
0.25 80% general DRSR -ClassCandD
Site-specific DRSR 0.00 0.01 0.1Period (s) 1 10
Project No. 26818815 Figure Stanford Univeristy SITE-SPECIFIC DRSR FOR ZONES 1, 2 AND 3 8-6 Palo Alto, California 2
5% Damping 1.8
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ASCE 7-10 Site-Specific MCER -Zone1 ASCE 7-10 Site-Specific DRSR - Zone 1
ASCE 7-10 Site-Specific MCER -Zone2 ASCE 7-10 Site-Specific DRSR - Zone 2
ASCE 7-10 Site-Specific MCER -Zone3 ASCE 7-10 Site-Specific DRSR - Zone 3
Project No. 26818815 SITE-SPECIFIC MCER AND DRSR Figure Stanford Univeristy FOR ZONES 1, 2, AND 3 8-7 Palo Alto, California 3
2 Spectral Acceleration (g) 1
5% Damping
0 0.01 0.1 1 10 Period (s)
Site-Specific Spectra
Horizontal ASCE 7-10 Site-Specific MCER -Zone1
Vertical ASCE 7-10 Site-Specific MCER -Zone1
Horizontal ASCE 7-10 Site-Specific MCER -Zone2
Vertical ASCE 7-10 Site-Specific MCER -Zone2
Horizontal Site-Specific MCER - Zone 3
Vertical ASCE 7-10 Site-Specific MCER -Zone3
Project No. 26818815 HORIZONTAL AND VERTICAL Figure SITE-SPECIFIC MCE Stanford Univeristy R 8-8 Palo Alto, California FOR ZONES 1, 2 AND 3 2
1.6
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Horizontal ASCE 7-10 Site-Specific DRSR - Zone 1
Vertical ASCE 7-10 Site-Specific DRSR -Zone1
Horizontal ASCE 7-10 Site-Specific DRSR - Zone 2
Vertical ASCE 7-10 Site-Specific DRSR -Zone2
Horizontal Site-Specific DRSR -Zone3
Vertical ASCE 7-10 Site-Specific DRSR -Zone3
Project No. 26818815 HORIZONTAL AND VERTICAL Figure SITE-SPECIFIC DRS Stanford Univeristy R 8-9 Palo Alto, California FOR ZONES 1, 2 AND 3 2.75
2.50 San Andreas fault Bedrock Depth < 300 ft M 8.0, R =5.5km 2.25 rup
2.00
1.75
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Spectral Acceleration (g) 0.75
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0.00 0.01 0.1 1 10 Period (s) 2.75
2.50 San Andreas fault Bedrock Depth >= 300 ft 2.25 M 8.0, Rrup =5.5km
2.00
1.75
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Spectral Acceleration0.75 (g)
0.50
0.25 5% Damping 0.00 0.01 0.1 1 10 Period (s)
Geometric Mean (GMRotD50) Maximum Direction
Project No. 26818815 th 84 PERCENTILE HORIZONTAL Figure Stanford University ACCELERATION RESPONSE SPECTRA FOR 8-10 Palo Alto, CA ZONE 0 ADJUSTED TO MAXIMUM DIRECTION 2.75
2.50 Bedrock Depth < 300 ft 2.25
2.00
1.75
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84th percentile deterministic spectrum (maximum direction)
Site-specific deterministic MCER Minimum Deterministic Spectrum - Class C Minimum Deterministic Spectrum - Class D
Project No. 26818815 Figure Stanford University DETERMINISTIC MCER FOR ZONE 0 8-11 Palo Alto, CA 8.00 7.50 7.00 Bedrock Depth < 300 ft 6.50 6.00 5.50 5.00 4.50 4.00 3.50 3.00 2.50 Spectral Acceleration (g) 2.00 1.50 1.00 0.50 5% Damping 0.00 0.01 0.1 1 10 Period (s) 8.00 7.50 7.00 Bedrock Depth >= 300 ft 6.50 6.00 5.50 5.00 4.50 4.00 3.50 3.00 2.50 Spectral Acceleration (g) 2.00 1.50 1.00 0.50 5% Damping 0.00 0.01 0.1 1 10 Period (s)
2,475-Year UHS - Geometric Mean 2,475-Year UHS - Maximum Direction
Probabilistic MCER - Max Direction 2,475-year UHS * Risk Coef.
Risk Coefficients for Zone 0: CRS = 0.961, CR1 = 0.914 Project No. 26818815 PROBABILISTIC MCE FOR ZONE 0 Figure Stanford University R 8-12 Palo Alto, CA 6 Bedrock Depth < 300 ft
4
Spectral Acceleration (g) 2
5% Damping
0 0.01 0.1 1 10 Period (s)
6 Bedrock Depth >= 300 ft
4
Spectral Acceleration2 (g)
5% Damping 0 0.01 0.1 1 10 Period (s)
Site-specific deterministic MCER,Zone0
Site-specific probabilistic MCER, Zone 0
Site-specific MCER, Zone 0
Project No. 26818815 Figure Stanford Univeristy SITE-SPECIFIC MCER FOR ZONE 0 8-13 Palo Alto, California 2
Bedrock Depth < 300 ft
1.6
1.2
0.8 Spectral Acceleration (g)
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0 0.01 0.1 1 10 Period (s) 2
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2/3 Site-specific MCER,Zone0
Site-specific DRSR,Zone0
80% general DRSR - Class C and D
Project No. 26818815 Figure Stanford Univeristy SITE-SPECIFIC DRSR FOR ZONE 0 8-14 Palo Alto, California 4
3
2 Spectral Acceleration (g)
1
5% Damping
0 0.01 0.1 1 10 Period (s)
Site-Specific Spectra
Horizontal ASCE 7-10 Site-Specific MCER - Zone 0, Bedrock < 300 ft
Vertical ASCE 7-10 Site-Specific MCER - Zone 0, Bedrock < 300 ft
Horizontal ASCE 7-10 Site-Specific MCER - Zone 0, Bedrock >= 300 ft
Vertical ASCE 7-10 Site-Specific MCER - Zone 0, Bedrock >= 300 ft
Project No. 26818815 HORIZONTAL AND VERTICAL Figure SITE-SPECIFIC MCE Stanford Univeristy R 8-15 Palo Alto, California FOR ZONE 0 2
1.6
1.2
0.8 Spectral Acceleration (g)
0.4
5% Damping
0 0.01 0.1 1 10 Period (s)
Site-Specific Spectra
Horizontal ASCE 7-10 Site-Specific DRSR - Zone 0, Bedrock < 300 ft
Vertical ASCE 7-10 Site-Specific DRSR - Zone 0, Bedrock < 300 ft
Horizontal ASCE 7-10 Site-Specific DRSR - Zone 0, Bedrock >= 300 ft
Vertical ASCE 7-10 Site-Specific DRSR - Zone 0, Bedrock >= 300 ft
Project No. 26818815 HORIZONTAL AND VERTICAL Figure SITE-SPECIFIC DRS Stanford Univeristy R 8-16 Palo Alto, California FOR ZONE 0 SECTIONNINE Design Response Spectra for Existing Buildings
9. Section 9 NINE Design Response Spectra for Existing Buildings The development of design ground motions for existing buildings is discussed in this section and site-specific design spectra are presented. For existing buildings, seismic design criteria are governed by ASCE Standard 41-13. This standard is a recent update to ASCE 41-06. Design ground motions for the four zones were computed following ASCE 41-13, resulting in BSE-1N, BSE-2N, BSE-1E and BSE-2E design spectra.
9.1 ASCE 41-13 METHODOLOGY The latest changes in the ASCE Standard Seismic Evaluation of Retrofit of Existing Buildings (ASCE 41-13) are made to be consistent with ASCE 7-10 and the 2009 NEHRP Provisions. Figure 9-1 illustrates the methodology of developing site-specific BSE-2E and BSE-1E according to ASCE 41-13. Note that ASCE 41-13 now provides two sets of earthquake hazard parameters: one equivalent to new buildings and one for existing buildings. The design levels for existing buildings (BSE-2E and BSE-1E) are based on probabilistic ground motions with 5% and 20% in 50-year exceedance frequencies (975-year and 225-year return period, respectively). The design levels for new building equivalence (BSE-2N and BSE-1N) are simply defined as the MCER and 2/3 MCER (DRSR) as defined in ASCE 7-10. MCER and DRSR are provided in Section 8 and Table 8-1. To be consistent with its Seismic Design Guidelines and its seismic design approach for existing buildings, Stanford elected to use BSE-2N and BSE-1N as the basis for the analysis and retrofit of existing buildings. BSE-2N and BSE-1N are equivalent to MCER and DRSR, respectively, and are provided in Table 8.1. As illustrated on the flowchart (Figure 9-1), BSE-2E and BSE-1E are based on the 975-year and 225-year UHS at the ground surface. These spectra are the result of a site-specific PSHA (Section 5) and a site-response analysis (Section 7). Scaling factors are then applied to convert the UHS from geometric mean horizontal spectra to maximum direction horizontal spectra. BSE-2E is defined as the site-specific 975-year return period UHS, but not less than BSE-2N. BSE-1E is defined as the site-specific 225-year return period UHS, but not less than BSE-1N. (Note that the deterministic caps included in ASCE 41-06 for BSE-2 and BSE-1 are now inherent in the use of BSE-2N and BSE-1N as caps for BSE-2E and BSE-1E. The site-specific BSE-2E and BSE-1E also must not be less than 80% of the code defined BSE-2E and BSE-1E general spectra for the appropriate site class.
9.2 BSE-1E AND BSE-2E FOR ZONES 1, 2, AND 3 Figure 9-2 illustrates the development of the site-specific BSE-2E spectra for Zones 1, 2 and 3. The BSE-2N spectra are less than the 975-year return period UHS (maximum direction) at most periods less than 0.75 sec. The BSE-2E spectrum is the lesser of these two spectra, but not less than 80% of the general code BSE-2E spectrum for site classes C and D. The code minimum controls the site-specific BSE-2E at very long periods (7.5 sec and greater). Figure 9-3 illustrates the development of the site-specific BSE-1E spectra for Zones 1, 2, and 3. The 225-year UHS (maximum direction) is compared to the site-specific BSE-1E and 80% of the general code BSE-1E spectrum for site classes C and D. The site-specific BSE-1E is controlled by the 225-year return period UHS at periods between 0.03 and 0.075 sec and periods between 0.5 and 5.0 sec. The code minimum controls the BSE-1E for periods greater than 5.0 sec. The
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BSE-1E spectrum is capped by the BSE-1N spectrum at periods less than 0.3 sec and periods between 0.075 and 0.5 sec. Figures 9-4 summarizes the site-specific BSE-2E and BSE-1E for all three zones. Response spectra are shown log-linear and linear-linear to highlight different period ranges. The spectra differ the most between 0.1 and 1.0 sec where they are controlled by the BSE-2N (MCER) and BSE-1N (DRSR) spectra. At periods greater than 1.0 sec, the spectra are very similar because the 975-year and 225-year return period UHS for the three zones are very similar (Section 7, Figure 7-5). Vertical design spectra were computed using the median V/H ratios of Gülerce and Abrahamson (2011). Figures 9-5 and 9-6 show the horizontal and vertical response spectra for the BSE-2E and BSE-1E levels for all zones. The median V/H ratios are a function of magnitude, distance, VS30 and level of shaking as defined by the corresponding PGA for a VS30 of 1,100 m/sec (PGA1,100). The modal magnitude and distance from deaggregating the hazard at the 225-year and 975-year levels were used (M 7.1 at 7.5 km for both hazard levels and all three zones). A VS30 value of 330 m/sec was used corresponding to the site-specific velocity profile. The PGA1,100 was determined separately for the BSE-2E and BSE-1E spectra based on the magnitude, distance and epsilon required to match the BSE-2E and BSE-1E at PGA. Horizontal and vertical BSE-2E and BSE-1E spectra are provided in Table 9-1.
9.3 BSE-1E AND BSE-2E FOR ZONE 0
Figures 9-7 and 9-8 show the BSE-2E and BSE-1E spectra for Zone 0. As with the MCER and DRSR developed in Section 8.1, BSE-2E and BSE-1E spectra are developed for sites with bedrock at depths less than 300 ft and for bedrock at depths equal or greater than 300 ft. For both of these conditions, the BSE-2E spectra are controlled by the MCER (BSE-2N) for periods less than approximately 1.0 sec and the 975-year UHS at longer periods (Figure 9-7). The BSE- 1E spectra are controlled by two-thirds the MCER (BSE-1N) at periods less than approximately 0.5 sec and the 225-year UHS for longer periods. Vertical design spectra were computed for the BSE-2E and BSE-1E spectra for Zone 0 using the approach described above. Figures 9-9 and 9-10 show the horizontal and vertical response spectra for the BSE-2E and BSE-1E levels. These spectra are also provided in Table 9-1.
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Table 9-1 BSE-2E and BSE-1E Spectra
Zone 0 Spectra, Bedrock Depth < 300 feet Horizontal BSE- Horizontal BSE- Vertical BSE-2E Vertical BSE-1E Period (sec) 2E per ASCE 1E per ASCE per ASCE 41-13 per ASCE 41-13 41-13 41-13 0.01 0.89 1.01 0.60 0.59 0.03 0.90 1.03 0.60 0.60 0.05 0.92 1.35 0.61 0.77 0.075 1.14 2.44 0.76 1.35 0.10 1.56 3.47 1.04 1.88 0.15 1.87 3.44 1.25 1.84 0.20 2.11 2.83 1.41 1.51 0.25 2.41 2.49 1.61 1.35 0.30 2.56 2.10 1.70 1.17 0.35 2.55 1.75 1.70 1.00 0.40 2.55 1.55 1.70 0.90 0.45 2.55 1.37 1.70 0.81 0.50 2.54 1.26 1.70 0.75 0.55 2.54 1.16 1.69 0.71 0.60 2.42 1.07 1.58 0.65 0.65 2.30 1.00 1.47 0.59 0.70 2.20 0.93 1.37 0.54 0.75 2.10 0.87 1.28 0.50 0.80 2.01 0.81 1.20 0.46 0.85 1.95 0.78 1.14 0.43 0.90 1.89 0.76 1.08 0.41 0.95 1.83 0.73 1.03 0.39 1.00 1.78 0.71 0.98 0.38 1.10 1.73 0.69 0.94 0.36 1.20 1.59 0.63 0.85 0.32 1.30 1.47 0.57 0.76 0.29 1.40 1.35 0.52 0.69 0.26 1.50 1.25 0.47 0.62 0.24 1.60 1.15 0.42 0.55 0.21 1.70 1.07 0.39 0.51 0.20 1.80 1.00 0.36 0.46 0.18 1.90 0.93 0.33 0.42 0.17 2.00 0.87 0.30 0.39 0.15 2.25 0.81 0.27 0.35 0.14 2.50 0.73 0.25 0.31 0.12 2.75 0.67 0.22 0.28 0.11 3.00 0.61 0.20 0.25 0.10 3.50 0.55 0.18 0.22 0.09 4.00 0.44 0.15 0.17 0.07 4.50 0.35 0.12 0.13 0.06 5.00 0.29 0.10 0.11 0.05 5.50 0.24 0.09 0.09 0.04 6.00 0.22 0.08 0.08 0.04 6.50 0.20 0.07 0.08 0.03 7.00 0.18 0.07 0.07 0.03 7.50 0.16 0.06 0.07 0.03 10.00 0.15 0.05 0.06 0.03
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Table 9-1 (continued)
Zone 0 Spectra, Bedrock Depth >= 300 feet Horizontal BSE- Horizontal BSE- Vertical BSE-2E Vertical BSE-1E Period (sec) 2E per ASCE 1E per ASCE per ASCE 41-13 per ASCE 41-13 41-13 41-13 0.01 0.69 0.71 0.48 0.45 0.03 0.77 0.81 0.54 0.50 0.05 0.86 1.14 0.53 0.62 0.075 1.03 1.95 0.64 1.04 0.10 1.25 2.43 0.83 1.36 0.15 1.50 2.39 1.00 1.33 0.20 1.56 1.82 1.06 1.03 0.25 1.61 1.45 1.06 0.81 0.30 1.65 1.20 1.07 0.68 0.35 1.69 1.04 1.10 0.60 0.40 1.70 0.94 1.11 0.55 0.45 1.71 0.85 1.13 0.51 0.50 1.72 0.79 1.13 0.48 0.55 1.73 0.74 1.14 0.46 0.60 1.70 0.71 1.08 0.43 0.65 1.67 0.69 1.03 0.40 0.70 1.64 0.66 0.98 0.38 0.75 1.61 0.64 0.94 0.35 0.80 1.59 0.71 0.89 0.33 0.85 1.57 0.81 0.88 0.33 0.90 1.55 1.14 0.87 0.33 0.95 1.53 1.95 0.87 0.32 1.00 1.51 2.43 0.86 0.32 1.10 1.50 2.39 0.85 0.32 1.20 1.42 1.82 0.81 0.31 1.30 1.36 1.45 0.77 0.29 1.40 1.30 1.20 0.74 0.28 1.50 1.24 1.04 0.71 0.27 1.60 1.19 0.94 0.68 0.26 1.70 1.13 0.85 0.65 0.25 1.80 1.08 0.79 0.62 0.24 1.90 1.02 0.74 0.59 0.23 2.00 0.97 0.71 0.56 0.22 2.25 0.93 0.69 0.53 0.21 2.50 0.85 0.66 0.48 0.19 2.75 0.78 0.64 0.43 0.17 3.00 0.72 0.71 0.38 0.16 3.50 0.66 0.81 0.34 0.14 4.00 0.51 1.14 0.25 0.10 4.50 0.37 1.95 0.17 0.07 5.00 0.29 2.43 0.13 0.06 5.50 0.22 2.39 0.09 0.04 6.00 0.19 1.82 0.09 0.04 6.50 0.17 1.45 0.08 0.04 7.00 0.16 1.20 0.07 0.03 7.50 0.14 1.04 0.07 0.03 10.00 0.12 0.94 0.06 0.03
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Table 9-1 (continued)
Zone 1 Spectra Horizontal BSE- Horizontal BSE- Vertical BSE-2E Vertical BSE-1E Period (sec) 2E per ASCE 1E per ASCE per ASCE 41-13 per ASCE 41-13 41-13 41-13 0.01 0.69 0.71 0.46 0.42 0.03 0.77 0.81 0.52 0.48 0.05 0.86 1.14 0.53 0.62 0.075 1.00 1.90 0.62 0.99 0.10 1.25 2.43 0.83 1.33 0.15 1.47 2.34 0.98 1.27 0.20 1.56 1.81 1.04 0.99 0.25 1.60 1.44 1.07 0.80 0.30 1.64 1.19 1.09 0.68 0.35 1.70 1.05 1.13 0.61 0.40 1.73 0.95 1.15 0.56 0.45 1.75 0.87 1.17 0.52 0.50 1.80 0.83 1.18 0.50 0.55 1.84 0.79 1.19 0.47 0.60 1.80 0.75 1.12 0.44 0.65 1.77 0.71 1.06 0.40 0.70 1.74 0.69 1.00 0.38 0.75 1.72 0.68 0.95 0.35 0.80 1.70 0.66 0.90 0.33 0.85 1.62 0.63 0.87 0.33 0.90 1.55 0.60 0.85 0.32 0.95 1.48 0.57 0.83 0.31 1.00 1.41 0.55 0.81 0.31 1.10 1.35 0.52 0.80 0.30 1.20 1.31 0.51 0.78 0.29 1.30 1.27 0.50 0.76 0.29 1.40 1.24 0.48 0.74 0.28 1.50 1.21 0.47 0.72 0.27 1.60 1.19 0.46 0.70 0.27 1.70 1.14 0.44 0.66 0.25 1.80 1.09 0.42 0.62 0.24 1.90 1.04 0.41 0.59 0.23 2.00 1.00 0.39 0.55 0.22 2.25 0.96 0.38 0.52 0.20 2.50 0.86 0.34 0.45 0.18 2.75 0.76 0.31 0.39 0.16 3.00 0.68 0.28 0.34 0.14 3.50 0.60 0.25 0.29 0.12 4.00 0.45 0.19 0.21 0.09 4.50 0.31 0.14 0.14 0.06 5.00 0.25 0.11 0.11 0.05 5.50 0.20 0.09 0.09 0.04 6.00 0.18 0.08 0.08 0.04 6.50 0.16 0.07 0.08 0.03 7.00 0.15 0.06 0.07 0.03 7.50 0.13 0.06 0.07 0.03 10.00 0.12 0.05 0.06 0.03
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Table 9-1 (continued)
Zone 2 Spectra Horizontal BSE- Horizontal BSE- Vertical BSE-2E Vertical BSE-1E Period (sec) 2E per ASCE 1E per ASCE per ASCE 41-13 per ASCE 41-13 41-13 41-13 0.01 0.69 0.71 0.46 0.42 0.03 0.77 0.81 0.52 0.48 0.05 0.86 1.14 0.52 0.60 0.075 0.98 1.86 0.61 0.97 0.10 1.26 2.41 0.82 1.29 0.15 1.47 2.34 0.98 1.27 0.20 1.54 1.79 1.03 0.97 0.25 1.57 1.41 1.05 0.78 0.30 1.59 1.16 1.06 0.66 0.35 1.65 1.02 1.10 0.59 0.40 1.68 0.93 1.12 0.55 0.45 1.71 0.85 1.14 0.51 0.50 1.74 0.80 1.16 0.49 0.55 1.77 0.76 1.18 0.47 0.60 1.73 0.72 1.10 0.43 0.65 1.70 0.68 1.03 0.39 0.70 1.67 0.66 0.98 0.37 0.75 1.64 0.64 0.92 0.35 0.80 1.62 0.63 0.88 0.33 0.85 1.55 0.60 0.86 0.32 0.90 1.49 0.58 0.84 0.31 0.95 1.43 0.55 0.82 0.31 1.00 1.37 0.53 0.80 0.30 1.10 1.32 0.51 0.78 0.29 1.20 1.28 0.50 0.76 0.29 1.30 1.24 0.48 0.74 0.28 1.40 1.21 0.47 0.72 0.27 1.50 1.18 0.46 0.71 0.27 1.60 1.16 0.45 0.69 0.26 1.70 1.11 0.43 0.65 0.25 1.80 1.06 0.41 0.61 0.23 1.90 1.01 0.40 0.57 0.22 2.00 0.97 0.38 0.54 0.21 2.25 0.93 0.36 0.51 0.20 2.50 0.83 0.33 0.44 0.17 2.75 0.74 0.30 0.38 0.15 3.00 0.65 0.27 0.33 0.13 3.50 0.58 0.24 0.28 0.12 4.00 0.43 0.18 0.20 0.09 4.50 0.30 0.13 0.14 0.06 5.00 0.24 0.10 0.11 0.05 5.50 0.19 0.10 0.09 0.04 6.00 0.17 0.09 0.08 0.04 6.50 0.16 0.08 0.07 0.03 7.00 0.14 0.07 0.07 0.03 7.50 0.13 0.07 0.06 0.03 10.00 0.11 0.04 0.06 0.03
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Table 9-1 (continued)
Zone 3 Spectra Horizontal BSE- Horizontal BSE- Vertical BSE-2E Vertical BSE-1E Period (sec) 2E per ASCE 1E per ASCE per ASCE 41-13 per ASCE 41-13 41-13 41-13 0.01 0.69 0.71 0.46 0.42 0.03 0.77 0.81 0.51 0.47 0.05 0.84 1.11 0.51 0.59 0.075 0.97 1.83 0.60 0.96 0.10 1.26 2.40 0.82 1.28 0.15 1.47 2.34 0.98 1.27 0.20 1.52 1.77 1.01 0.96 0.25 1.54 1.39 1.03 0.77 0.30 1.55 1.13 1.03 0.64 0.35 1.61 0.99 1.07 0.58 0.40 1.64 0.90 1.09 0.53 0.45 1.67 0.83 1.11 0.50 0.50 1.70 0.78 1.13 0.48 0.55 1.73 0.74 1.15 0.46 0.60 1.70 0.70 1.08 0.42 0.65 1.66 0.67 1.02 0.38 0.70 1.64 0.65 0.96 0.36 0.75 1.61 0.63 0.91 0.34 0.80 1.59 0.62 0.86 0.32 0.85 1.52 0.59 0.84 0.31 0.90 1.46 0.57 0.82 0.31 0.95 1.40 0.54 0.81 0.30 1.00 1.34 0.52 0.79 0.30 1.10 1.29 0.50 0.77 0.29 1.20 1.25 0.49 0.75 0.28 1.30 1.22 0.47 0.73 0.28 1.40 1.19 0.46 0.71 0.27 1.50 1.16 0.45 0.69 0.26 1.60 1.13 0.44 0.68 0.26 1.70 1.08 0.42 0.64 0.24 1.80 1.04 0.40 0.60 0.23 1.90 0.99 0.39 0.56 0.22 2.00 0.95 0.37 0.53 0.21 2.25 0.91 0.36 0.50 0.19 2.50 0.81 0.32 0.43 0.17 2.75 0.72 0.29 0.37 0.15 3.00 0.63 0.26 0.32 0.13 3.50 0.56 0.23 0.27 0.11 4.00 0.41 0.18 0.20 0.08 4.50 0.29 0.13 0.13 0.06 5.00 0.23 0.10 0.11 0.05 5.50 0.18 0.08 0.09 0.04 6.00 0.17 0.07 0.08 0.04 6.50 0.15 0.07 0.07 0.03 7.00 0.14 0.06 0.07 0.03 7.50 0.12 0.05 0.06 0.03 10.00 0.11 0.05 0.06 0.03
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 9-7 PSHA for Generic Site Conditions (Section 5)
Site Response Analysis (Section 7)
975-yr UHS at 225-yr UHS at Ground Surface Ground Surface (Geomean) (Geomean)
Apply Maximum Direction Factors Apply Maximum Direction Factors
975-yr UHS at 225-yr UHS at Ground Surface Site-Specific Ground Surface Site-Specific (Maximum Direction) BSE-2N (Maximum Direction) BSE-1N = Site-Specific = Site-Specific
MCER DRSR (computed per ASCE 7-10) (computed per ASCE 7-10)
Minimum of 975-year UHS Minimum of 225-year UHS at Ground Surface at Ground Surface (Maximum Direction) (Maximum Direction) and BSE-2N and BSE-2N
80% General Code 80% General Code BSE-2E for site class BSE-1E for site class (2008 USGS maps (2008 USGS maps use NGA-West1 use NGA-West1 ground motion models) ground motion models)
Site-Specific BSE-2E Site-Specific BSE-1E = maximum of 975-year UHS (capped by BSE-2N) = maximum of 225-year UHS (capped by BSE-1N) and 80% of General Code BSE-2E and 80% of General Code BSE-1E
Project No. 26818815 METHODOLOGY TO DETERMINE Figure Stanford Univeristy SITE-SPECIFIC GROUND MOTIONS (BSE-2E AND BSE-1E) 9-1 Palo Alto, California ACCORDING TO ASCE 41-13 2.5 Zone 1 5% Damping 2
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BSE-2N (MCER) Spectral Acceleration0.5 (g) 80% general BSE-2E,Class C and D Site-Specific BSE-2E 0 0.01 0.1Period (s) 1 10
Project No. 26818815 Figure SITE-SPECIFIC BSE-2E FOR ZONES 1,2 AND 3 Stanford Univeristy 9-2 Palo Alto, California 1.5 Zone 1 5% Damping
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BSE-1N (DRSR) Spectral Acceleration (g) 80% general BSE-1E,Class C and D Site-Specific BSE-1E 0 0.01 0.1Period (s) 1 10
Project No. 26818815 Figure SITE-SPECIFIC BSE-1E FOR ZONES 1,2 AND 3 Stanford Univeristy 9-3 Palo Alto, California 2
5% Damping 1.8
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ASCE 41-13 Site-Specific BSE-2E - Zone 1 ASCE 41-13 Site-Specific BSE-1E - Zone 1 ASCE 41-13 Site-Specific BSE-2E - Zone 2 ASCE 41-13 Site-Specific BSE-1E - Zone 2 ASCE 41-13 Site-Specific BSE-2E - Zone 3 ASCE 41-13 Site-Specific BSE-1E - Zone 3
Project No. 26818815 SITE-SPECIFIC BSE-2E AND BSE-1E Figure Stanford Univeristy FOR ZONES 1, 2, AND 3 9-4 Palo Alto, California 3
2 Spectral Acceleration (g) 1
5% Damping
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Site-Specific Spectra Horizontal ASCE 41-13 Site-Specific BSE-2E - Zone 1 Vertical ASCE 41-13 Site-Specific BSE-2E - Zone 1 Horizontal ASCE 41-13 Site-Specific BSE-2E - Zone 2 Vertical ASCE 41-13 Site-Specific BSE-2E - Zone 2 Horizontal ASCE 41-13 Site-Specific BSE-2E - Zone 3 Vertical ASCE 41-13 Site-Specific BSE-2E - Zone 3
Project No. 26818815 HORIZONTAL AND VERTICAL Figure Stanford Univeristy SITE-SPECIFIC BSE-2E 9-5 Palo Alto, California FOR ZONES 1, 2 AND 3 2
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Site-Specific Spectra Horizontal ASCE 41-13 Site-Specific BSE-1E - Zone 1 Vertical ASCE 41-13 Site-Specific BSE-1E - Zone 1 Horizontal ASCE 41-13 Site-Specific BSE-1E - Zone 2 Vertical ASCE 41-13 Site-Specific BSE-1E - Zone 2 Horizontal ASCE 41-13 Site-Specific BSE-1E - Zone 3 Vertical ASCE 41-13 Site-Specific BSE-1E - Zone 3
Project No. 26818815 HORIZONTAL AND VERTICAL Figure Stanford Univeristy SITE-SPECIFIC BSE-1E 9-6 Palo Alto, California FOR ZONES 1, 2 AND 3 5 Bedrock Depth < 300 ft
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5% Damping 0 0.01 0.1 1 10 Period (s) 975-year UHS - maximum direction
BSE-2N (MCER) 80% general ASCE 41 BSE-2E,Class C 80% general ASCE 41 BSE-2E,Class D Site-Specific BSE-2E
Project No. 26818815 Figure SITE-SPECIFIC BSE-2E FOR ZONE 0 Stanford Univeristy 9-7 Palo Alto, California 2.5
Bedrock Depth < 300 ft
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225-year UHS - maximum direction rds BSE-1N (2/3 MCER) 80% general ASCE 41 BSE-1E,Class C 80% general ASCE 41 BSE-1E,Class D Site-Specific BSE-1E
Project No. 26818815 Figure SITE-SPECIFIC BSE-1E FOR ZONE 0 Stanford Univeristy 9-8 Palo Alto, California 4
3
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5% Damping
0 0.01 0.1 1 10 Period (s)
Site-Specific Spectra Horizontal ASCE 41-13 Site-Specific BSE-2E - Zone 0, Bedrock < 300 ft Vertical ASCE 41-13 Site-Specific BSE-2E - Zone 0, Bedrock < 300 ft Horizontal ASCE 41-13 Site-Specific BSE-2E - Zone 0, Bedrock >= 300 ft Vertical ASCE 41-13 Site-Specific BSE-2E - Zone 0, Bedrock >= 300 ft
Project No. 26818815 HORIZONTAL AND VERTICAL Figure Stanford Univeristy SITE-SPECIFIC BSE-2E 9-9 Palo Alto, California FOR ZONE 0 2
1.6
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5% Damping
0 0.01 0.1 1 10 Period (s)
Site-Specific Spectra Horizontal ASCE 41-13 Site-Specific BSE-1E - Zone 0, Bedrock < 300 ft Vertical ASCE 41-13 Site-Specific BSE-1E - Zone 0, Bedrock < 300 ft Horizontal ASCE 41-13 Site-Specific BSE-1E - Zone 0, Bedrock >= 300 ft Vertical ASCE 41-13 Site-Specific BSE-1E - Zone 0, Bedrock >= 300 ft
Project No. 26818815 HORIZONTAL AND VERTICAL Figure Stanford Univeristy SITE-SPECIFIC BSE-1E 9-10 Palo Alto, California FOR ZONE 0 SECTIONTEN Comparison With 2010 Spectra and General Code Spectra
10. Section 10 TEN Comparison With 2010 Spectra and General Code Spectra This section compares the site-specific design spectra for both new and existing buildings to general code spectra and to the 2010 site-specific spectra. First, the differences between the site- specific MCER and DRSR and the general code MCER and DRSR are discussed (Section 10.1.1). Next, the site-specific BSE-2E and BSE-2E spectra are compared to the ASCE 41-13 general code spectra (Section 10.1.2). Finally, the site-specific design spectra are compared to the 2010 site-specific spectra, both for new buildings (Section 10.2.1) and existing buildings (Section 10.2.2).
10.1 COMPARISON OF SITE-SPECIFIC AND GENERAL CODE DESIGN SPECTRA The building codes provide methodology for developing general code design spectra for a site based on a NEHRP site class. The NEHRP site class (A through E) groups sites within a range of near surface material properties (hard rock, rock, very dense soil and soft rock, stiff soil, and soft clay). The classification is made based on shear wave velocities or standard penetration blowcounts in the top 30 m. As discussed in Section 3, the site classification for the Stanford campus varies from C (very dense soil and soft rock) to D (stiff soil). Based on the NEHRP site class, site factors are used to develop general design spectra according to the building codes. These site factors have been shown to be inconsistent with the NGA ground motion models (Stewart and Seyhan, 2013) and do not account for the amplification due to bedrock at shallow depths.
10.1.1 Design Spectra for New Buildings
Figures 10-1 and 10-2 compare the site-specific MCER and DRSR and general MCER and DRSR for zones 1, 2 and 3. Response spectra are shown log-linear and linear-linear to highlight different period ranges. The site-specific spectra are generally larger than the code-based spectra for periods larger than 1.0 sec due to the site amplification from the relatively thick deposits of unconsolidated sediments and weathered rock underlying the campus and overlying hard crystalline rock. In addition to site amplification, the mapped ground motion values used in the general MCER and DRSR are based on the NGA-West1 ground motion models, while the site- specific spectra were developed using the NGA-West2 ground motion models. NGA-West2, which will be incorporated in the next versions of the USGS Seismic Hazard maps and building codes, predict larger ground motions for near fault, strike-slip large events contributing to the hazard at Stanford (Section 6, Figures 6-2 and 6-3).
For zone 0, the site-specific and general MCER and DRSR are compared on Figures 10-3 and 10- 4. For the case of bedrock depth less than 300 ft, the site-specific MCER and DRSR exceed the general code spectra for periods between approximately 0.1 and 5.0 sec. For the case of bedrock depths greater or equal to 300 ft, the site-specific DRSR are less than the general code for periods less than 0.8 sec.
10.1.2 Design Spectra for Existing Buildings Figure 10-5 compares the site-specific BSE-2E spectra to the general code spectra for site classes C and D for zones 1, 2 and 3. The site-specific BSE-2E spectra are generally lower than the code spectra for short periods and larger than the code spectra at periods greater than 1.0 seconds due to the same reasons discussed above for the MCER spectra. Figure 10-6 shows a similar comparison of site-specific and general code spectra for the BSE-1E hazard level for all zones.
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 10-1 SECTIONTEN Comparison With 2010 Spectra and General Code Spectra
The site-specific BSE-2E and BSE-1E spectra for Zone 0 are compared to the general code spectra for site classes C and D on Figures 10-7 and 10-8. The site-specific BSE-2E spectrum for bedrock at depths less than 300 ft is generally larger than the code spectra, especially in the period range of 0.1 to 2.0 sec (Figure 10-7). The site-specific BSE-2E spectrum for bedrock at depths greater than or equal to 300 ft is greater than the general code spectra only for periods between 0.75 and 4.0 sec. The site-specific BSE-1E spectra are generally larger or equal to than the general code spectra (Figure 10-8).
10.2 COMPARISON WITH 2010 SPECTRA Differences between current design spectra and those in the 2010 study are the result of several factors. There have been revisions to the building codes for both new and existing buildings. These changes include the use of risk-targeted, maximum direction ground motions and updates to the mapped ground motions. In addition, an update to the NGA ground motion models has been made since the publishing of the latest building codes.
10.2.1 Design Spectra for New Buildings
Figures 10-9 to 10-11 compare the MCER and DRSR for Zones 1, 2, and 3 to the 2010 study MCE and DRS. The current DRSR are 30 to 76% larger than the 2010 DRS in the 1.0 to 5.0 sec period range. The current MCER and DRSR are controlled by the site-specific deterministic spectra for most periods greater than 0.2 sec. In the 2010 study, the site-specific spectra were based on a M 7.9 San Andreas event using the NGA-West1 models (geometric mean). The current study uses a M 8.0 San Andreas event and the NGA-West2 models. Following the requirements of ASCE 7-10, the deterministic ground motions are adjusted to maximum direction. Both the use of the NGA-West2 models and maximum direction cause an increase in the site-specific deterministic ground motions over the 2010 deterministic ground motions. Table 10-1 provides the ratio of the geomean 84th percentile deterministic spectra for Zone 1 using NGA-West2 and NGA-West1. The NGA-West2 models are 26 to 34% larger in the 1.0 to 5.0 period range. Also shown are the maximum direction scaling factors, which are 30 to 40% larger in this period range. The total increase is 64 to 88%. The ratios of the 2014 to 2010 spectra, however, are not as large as these combined increases due to changes in the general code spectra (reduction in mapped values) and resulting code minimums. In 2010 the MCE and DRS were controlled at most periods (except between 1.0 and 4.0 sec) by the code minimums. The code minimums at that time (ASCE 7-05) were based on the 2002 USGS National Seismic Hazard Maps, which used 1997 ground motion models. The current code minimums (ASCE 7-10) are based on the 2008 risk-targeted maps, which use the NGA- West1 models converted to maximum direction. While the use of maximum direction increases the ground motions, the NGA-West1 models predict lower ground motions than the 1997 models for this site. Thus, the code spectra for the Stanford Campus are lower following ASCE 7-10 compared to ASCE 7-05.
10.2.2 Design Spectra for Existing Buildings Figures 10-12 to 10-14 compare the BSE-2E and BSE-1E spectra to those developed in the 2010 study. The current BSE-2E and BSE-1E spectra are generally larger than the 2010 spectra. The BSE-2E spectra are 10 to 40% larger than the 2010 BSE-2E spectra for periods between 0.1 and
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 10-2 SECTIONTEN Comparison With 2010 Spectra and General Code Spectra
4.0 sec. The BSE-1E are 5 to 22% larger for this same period range. The increase in the current spectra is due to the reasons discussed in Section 10.2.1 for the MCER and DRSR. The 2010 spectra were based on ASCE41-06, which did not require the use of maximum direction spectra, and the NGA-West1 ground motion models. Note that Stanford has elected to use BSE-2N and BSE-1N (equal to MCER and DRSR for new buildings, respectively) for existing buildings. BSE-2N and BSE-1N are also larger than the 2010 spectra for existing buildings due to the same reasons discussed above for design spectra for new buildings.
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 10-3 SECTIONTEN Comparison With 2010 Spectra and General Code Spectra
Table 10-1 Factors Impacting 84th Percentile Deterministic Spectra for Zone 1 (M 8.0 at 6.0 km)
Period (sec) NGA-West2 / Maximum Direction Total Increase NGA-West1 Scale Factors 0.2 1.18 1.10 1.30 0.3 1.33 1.10 1.46 0.4 1.37 1.15 1.58 0.5 1.42 1.20 1.70 0.75 1.32 1.25 1.65 1.0 1.29 1.30 1.68 2.0 1.26 1.30 1.64 3.0 1.30 1.35 1.76 4.0 1.34 1.40 1.88 5.0 1.30 1.40 1.82 10.0 0.98 1.40 1.37
W:\X_WCFS\PROJECTS\STANFORD UNIV\2013 UPDATE GM\STANFORD PSHA 2013 UPDATE_FINAL.DOCX\28-APR-14\\OAK 10-4 2.5
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ASCE 7-10 Site-Specific MCER -Zone1 ASCE 7-10 MCER ,SiteClassCandD-Zone1
ASCE 7-10 Site-Specific MCER -Zone2 ASCE 7-10 MCER ,SiteClassCandD-Zone2
ASCE 7-10 Site-Specific MCER -Zone3 ASCE 7-10 MCER ,SiteClassCandD-Zone3
Project No. 26818815 SITE-SPECIFIC MCE FOR R Figure Stanford Univeristy ZONES 1, 2 AND 3 COMPARED TO 10-1 Palo Alto, California ASCE 7-10 GENERAL MCER SPECTRA 1.50
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ASCE 7-10 Site-Specific DRSR - Zone 1 ASCE 7-10 DRSR , Site Class C and D - Zone 1
ASCE 7-10 Site-Specific DRSR - Zone 2 ASCE 7-10 DRSR , Site Class C and D - Zone 2
ASCE 7-10 Site-Specific DRSR - Zone 3 ASCE 7-10 DRSR , Site Class C and D - Zone 3
Project No. 26818815 SITE-SPECIFIC DRS FOR R Figure Stanford Univeristy ZONES 1, 2 AND 3 COMPARED TO 10-2 Palo Alto, California ASCE 7-10 GENERAL DRSR SPECTRA 2.75
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ASCE 7-10 Site-Specific MCER - Zone 0, Bedrock < 300 ft
ASCE 7-10 Site-Specific MCER - Zone 0, Bedrock >= 300 ft General Code Spectra
ASCE 7-10 MCER ,SiteClassCandD-Zone0
Project No. 26818815 SITE-SPECIFIC MCE FOR R Figure Stanford Univeristy ZONE 0 COMPARED TO 10-3 Palo Alto, California ASCE 7-10 GENERAL MCER SPECTRA 2 5% Damping 1.75
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ASCE 7-10 Site-Specific DRSR - Zone 0, Bedrock < 300 ft
ASCE 7-10 Site-Specific DRSR - Zone 0, Bedrock >= 300 ft General Code Spectra
ASCE 7-10 DRSR , Site Class C and D - Zone 0
Project No. 26818815 SITE-SPECIFIC DRS FOR R Figure Stanford Univeristy ZONE 0 COMPARED TO 10-4 Palo Alto, California ASCE 7-10 GENERAL DRSR SPECTRA 2 5% Damping
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0 0246810 Period (s) Site-Specific Spectra General Code Spectra ASCE 41-13 Site-Specific BSE-2E - Zone 1 ASCE 41-13 BSE-2E, Site Class D - Zone 1 ASCE 41-13 Site-Specific BSE-2E - Zone 2 ASCE 41-13 BSE-2E, Site Class D - Zone 2 ASCE 41-13 Site-Specific BSE-2E - Zone 3 ASCE 41-13 BSE-2E, Site Class D - Zone 3
Project No. 26818815 SITE-SPECIFIC BSE-2E FOR Figure Stanford Univeristy ZONES 1, 2 AND 3 COMPARED TO 10-5 Palo Alto, California ASCE 41-13 GENERAL BSE-2E SPECTRA 1.5 5% Damping
1
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0 0246810 Period (s) Site-Specific Spectra General Code Spectra ASCE 41-13 Site-Specific BSE-1E - Zone 1 ASCE 41-13 BSE-1E, Site Class D - Zone 1 ASCE 41-13 Site-Specific BSE-1E - Zone 2 ASCE 41-13 BSE-1E, Site Class D - Zone 2 ASCE 41-13 Site-Specific BSE-1E - Zone 3 ASCE 41-13 BSE-1E, Site Class D - Zone 3
Project No. 26818815 SITE-SPECIFIC BSE-1E FOR Figure Stanford Univeristy ZONES 1, 2 AND 3 COMPARED TO 10-6 Palo Alto, California ASCE 41-13 GENERAL BSE-1E SPECTRA 2.5 5% Damping
2
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Project No. 26818815 SITE-SPECIFIC BSE-2E FOR Figure Stanford Univeristy ZONE 0 COMPARED TO 10-7 Palo Alto, California ASCE 41-13 GENERAL BSE-2E SPECTRA 2 5% Damping
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0 0246810 Period (s) Site-Specific Spectra ASCE 41-13 Site-Specific BSE-1E - Zone 0, Bedrock < 300 ft ASCE 41-13 Site-Specific BSE-1E - Zone 0, Bedrock >= 300 ft General Code Spectra ASCE 41-13 BSE-1E, Site Class C and D - Zone 0
Project No. 26818815 SITE-SPECIFIC BSE-1E FOR Figure Stanford Univeristy ZONE 0 COMPARED TO 10-8 Palo Alto, California ASCE 41-13 GENERAL BSE-1E SPECTRA 2
Zone 1 5% Damping
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ASCE 7-10 Site-Specific DRSR 2010 ASCE 7-05 Site-Specific MCE 2010 ASCE 7-05 Site-Specific DRS Project No. 26818815 SITE-SPECIFIC MCE SPECTRA AND DRS R R Figure Stanford Univeristy FOR ZONE 1 COMPARED TO 10-9 Palo Alto, California 2010 SITE-SPECIFIC MCE SPECTRA AND DRS 2
Zone 2 5% Damping
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ASCE 7-10 Site-Specific DRSR 2010 ASCE 7-05 Site-Specific MCE 2010 ASCE 7-05 Site-Specific DRS Project No. 26818815 SITE-SPECIFIC MCE SPECTRA AND DRS R R Figure Stanford Univeristy FOR ZONE 2 COMPARED TO 10-10 Palo Alto, California 2010 SITE-SPECIFIC MCE SPECTRA AND DRS 2
Zone 3 5% Damping
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ASCE 7-10 Site-Specific DRSR 2010 ASCE 7-05 Site-Specific MCE 2010 ASCE 7-05 Site-Specific DRS Project No. 26818815 SITE-SPECIFIC MCE SPECTRA AND DRS R R Figure Stanford Univeristy FOR ZONE 3 COMPARED TO 10-11 Palo Alto, California 2010 SITE-SPECIFIC MCE SPECTRA AND DRS 2
5% Damping Zone 1
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Project No. 26818815 SITE-SPECIFIC BSE-2E AND BSE-1E Figure Stanford Univeristy FOR ZONE 1 COMPARED TO 10-12 Palo Alto, California 2010 SITE-SPECIFIC BSE-2 AND BSE-1 2
Zone 2 5% Damping
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Project No. 26818815 SITE-SPECIFIC BSE-2E AND BSE-1E Figure Stanford Univeristy FOR ZONE 2 COMPARED TO 10-13 Palo Alto, California 2010 SITE-SPECIFIC BSE-2 AND BSE-1 2
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Project No. 26818815 SITE-SPECIFIC BSE-2E AND BSE-1E Figure Stanford Univeristy FOR ZONE 3 COMPARED TO 10-14 Palo Alto, California 2010 SITE-SPECIFIC BSE-2 AND BSE-1 SECTIONELEVEN Conditional Mean Spectra
11. Section 11 ELEVEN Conditional Mean Spectra The UHS represents the spectral accelerations at each period based on the rates of occurrence of all nearby sources, the ground motion prediction models and the uncertainties in these models. It is a broader spectrum than is expected for any single event. This uniform hazard can be represented by a suite of spectra that individually more closely represent the spectral shape of expected events contributing to the hazard. At a given period, a spectrum can be computed based on the deaggregated magnitude, distance and epsilon at that period. Depending on the epsilon required to match the spectrum to the UHS, the expected shape of this spectrum is not necessarily the median predicted spectral shape. Given the epsilon at a target period, epsilon at all other periods can be determined using a correlation function. Thus, a CMS represents a more realistic shape of an event likely to cause the target spectral acceleration at the target period. The CMS approach was developed for the purpose of using the results of a PSHA to develop input to the seismic evaluation of structures (i.e., performing dynamic response calculations). The approach provides a method for defining the ground motion response spectrum input to a structural response analysis, where the estimated response is linked to the PSHA result (the hazard curve for a spectral acceleration at a given period), and where the estimate of structural response is mean-centered (i.e., non-conservative). The CMS response spectrum is associated with a SA level for a single-structure period or narrow period range (e.g. the fundamental period of the structure to be analyzed), at a specified annual frequency of exceedance or return period. By linking a response spectrum suited to input to structure response analyses to the PSHA results, makes it possible to make statements about the likelihood of observing levels of structural response and potential damage. When design spectra are controlled by 84th percentile deterministic spectra, CMS may also be advantageous if the period of the structure is known. An event with 84th percentile (one sigma) ground motion at one period will likely have less than one sigma ground motions at other periods. Thus the CMS conditioned to 84th percentile deterministic spectra represents a more realistic shape of an event likely to cause the 84th percentile ground motion at the target period.
11.1 CMS IMPLEMENTATION The procedure to implement the CMS approach is described in Baker (2011) and is summarized here. The steps in the process as defined by Baker (2011) are:
Step 1: Determine the Target Sa at a Given Period, and the Associated M, R and ε For a specified annual frequency of exceedance (AFE), determine the target Sa from the mean hazard curve for Sa for the fundamental period of the structure to be analyzed. This period is denoted T*. For this ground motion, obtain the mean magnitude (M), distance (R), and from the PSHA deaggregation results. Depending upon the response characteristics of the structure or structures to be analyzed, CMS may need to be developed for several values of T*. Step 2: Compute the Mean and Standard Deviation of the Response Spectrum, Given M and R For the mean M and R determined in Step 1, compute the mean and standard deviation of logarithmic spectral acceleration at all periods for a the mean magnitude and distance. These are provided by standard ground motion prediction (attenuation) models. The predicted mean and standard deviation, given magnitude, distance, period, etc., are denoted lnSa ( M , R , T ) and
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ln Sa ()T , respectively. The mean and standard deviation of the log spectral acceleration can be computed using the ground motion prediction models that were used in the PSHA itself. Since multiple ground motion models were used in the PSHA, a weighted estimate of the mean log Sa and the standard deviation can be used. Alternatively, a CMS can be developed for each GMPE and a weighted average taken to produce the final CMS.
Step 3: Compute at Other Periods, Given (T*) Compute the “conditional mean” at other periods. The conditional mean at (T*) was determined in Step 1. The conditional mean at other periods, Ti, is determined by,
Ti T* (6-1)
* * where ρ(Ti,T ) is the correlation coefficient between for periods Ti and T . This correlation coefficient, which is applicable to periods in the range 0.05 – 5 sec, is (Baker and Cornell 2006),
T T min min (Tmin ,Tmax ) 1 cos 0.359 0.163I ln( ) ln( ) 2 (T 0.189) 0.189 T min max (6-2)
where I is an indicator function equal to 1 if Tmin < 0.189 and 0 otherwise. Tmin and (Tmin 0.189) Tmax are the smaller and larger of the periods of interest, respectively. Step 4: Compute the Conditional Mean Spectrum The CMS is computed using the estimated log mean and standard deviation from Step 2 and the conditional mean (Ti) values determined in Step 3. The CMS is estimated according to:
* * * ln S (M , R,Ti ) (Ti ,T ) (T ) ln S (Ti ) (6-3) ln Sa (Ti )|ln(Sa (T ) a a The CMS is,
Sa,CMS (T ) exp(ln( S (T )|ln(S (T * ) ) a i a (6-4)
11.2 EXAMPLE CMS AT STANFORD For illustrative purposes, a short-period (0.2 sec) and long-period (1.0 sec) CMS have been computed for Zone 1 for the DRSR spectrum (Figure 11-1). Note the CMS that is conditioned at 0.2 sec contains significantly lower moderate and long period motion. The CMS that is conditioned at 1.0 seconds also has lower long period motion (2 sec and longer). Depending on the period of a specific facility on campus, the use of CMS may be advantageous. When a structure is sensitive to a single or a few period ranges, a broad UHS may be overly conservative for design ground motions. In application, individual CMS may need to be broadened to cover the period range of interest to a structure. Current building codes do not specifically address the use of CMS in building design. However, CMS can currently be useful in a time history analysis. In this application, a
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CMS can be broadened to match the target (DRSR) spectra in the period range 0.2 T to 1.5 T, where T is the fundamental period of the building. ASCE 7-10 requires that the input time histories are spectrally-matched to the target spectra such that the square root of the sum of the squares (SRSS) spectrum does not fall below the target. The CMS instead of the broad DRSR can be used to select input time histories, as it represents a more realistic response spectrum shape. The time histories are then scaled or spectrally-matched to match the CMS that has been broadened in the required 0.2 T to 1.5 T period range. Figure 11-2 illustrates an example for a building with a natural period of 1.0 sec. The CMS conditioned at 1.0 sec has been broadened to match the DRSR from 0.2 to 1.5 sec. The potential savings is the difference between the DRSR (black line) and the CMS (purple line).
The DRSR spectra for all Stanford zones are controlled by the 84th percentile deterministic event for all period ranges. Unlike a UHS, which can be very broad due to the contribution of many types of sources (small, nearby and distant, large events), the savings obtained using the CMS approach is due only to the reduction in sigma at periods other the conditioning period. An event with an 84th percentile 1.0 sec ground motion is not expected to have 84th percentile ground motions at all other periods. Individual building projects which require time history analyses may use the CMS approach illustrated on Figure 11-2.
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Site-Specific Horizontal DRSR Spectrum CMS conditioned at 0.2 sec CMS conditioned at 1.0 sec
Project No. 26818815 CONDITIONAL MEAN SPECTRA CONDITIONED Figure TO SITE-SPECIFIC DRS SPECTRUM Stanford Univeristy R 11-1 Palo Alto, California AT 0.2 AND 1.0 SEC 2.00
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CMS conditioned at 1.0 sec and broadened to match DRSR in the 0.2 to 1.5 second period range
Project No. 26818815 EXAMPLE CMS CONDITIONED TO Figure SITE-SPECIFIC DRS AT 1.0 SEC AND Stanford Univeristy R 11-2 Palo Alto, California BROADENED IN REQUIRED PERIOD RANGE SECTIONTWELVE Final Remarks
12. Section 12 TWELVE Final Remarks The 2010 site-specific seismic design ground motions have been updated for the Stanford University campus following ASCE 7-10, the CBC, and ASCE 41-13. A PSHA and DSHA were performed to compute the design ground motions. The campus has been microzoned into four zones with each zone having its own set of horizontal and vertical design ground motions i.e., MCER, DRSR, BSE-2E and BSE-1E. In this update, Zone 0 design ground motions have been added and Zones 1 to 3 have been revised. The use of ASCE 7-10 particularly its adoption of maximum direction and the recently released NGA-West2 ground motion prediction models have resulted in higher design ground motions than in 2010. It should be noted that the NGA-West2 ground motion models have just been incorporated into the draft 2014 National Seismic Hazard Maps and thus have not been incorporated into the current version of the CBC or ASCE 7-10. A significant factor in both the 2010 and current design ground motions are site effects which were addressed in both studies by performing site response analysis. The relatively thick unconsolidated sediments and weathered rock overlying crystalline basement has resulted in site amplification particularly at periods greater than 1 sec. The soil in Zone 0 ranges in thickness from 100 to 500 ft. There is a significant difference between ground motions as the soil thickness is varied due to the effects of site amplification. We have developed design ground motions for two ranges of soil thickness: less than 300 ft and 300 ft and greater. The design ground motions are higher for the former except at periods longer than 1 sec. The depth to rock should be confirmed to select the appropriate set of design ground motions to use in design. In general, the site-specific design ground motions computed in this study exceed code-based ground motions. The code-based ground motions are based on the NEHRP design maps in the CBC which are based on the 2008 National Seismic Hazard Maps. The 2008 maps are derived using the NGA-West1 rather than the current NGA-West2 ground motion prediction models. The code-based ground motions do not adequately address site amplification at the Stanford campus but simply rely on generic NEHRP site categories and their associated site factors which have been shown to be inconsistent with the NGA-West ground motion models. Hence it is recommended that the site-specific design ground motions be used in lieu of code-based ground motions unless the building/structure poses a low hazard to human life in the event of failure or is a non-essential facility. For buildings requiring dynamic analyses, use of CMS may have some value. Current building codes do not specifically address the use of CMS. However, the requirements of ASCE 7-10 for matched time histories can be met using a CMS conditioned at the fundamental period of the building (T) and broadened to match the target in the required period range of 0.2T to 1.5T. An example has been provided (Section 11) to provide an illustration for a building with a fundamental period of 1.0 sec. The benefits in using CMS for computing design ground motions depends on the natural period of the structure. Because design ground motions are controlled by the deterministic spectrum rather than the broad-banded UHS, the use of CMS may be of limited value for many structures.
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13. Section 13 THIRTEEN References Abrahamson, N.A. and Silva, W.J., 1997, Empirical response spectral attenuation relations for shallow crustal earthquakes: Seismological Research Letters, v. 68, p. 94-127. Abrahamson, N.A., Silva, W.J., and Kamai, R., 2013, Update of the AS08 ground-motion prediction equations based on the NGA-West2 data set. PEER Report 2013/04 Pacific Earthquake Engineering Research Center. Aki, K., 1983, Seismological evidence in support of the existence of “Characteristic Earthquakes”: Earthquake Notes, v. 54, p. 60-61. Anderson, J.G., 1979, Estimating the seismicity from geological structure for seismic risk studies: Bulletin of the Seismological Society of America, v. 69, p. 135-158. Anderson, L.W. and Piety, L.A., 2001, Geologic seismic source characterization of the San Luis- O'Neill area, eastern Diablo Range, California for B.F. Sisk and O'Neill Forebay dams, San Luis Unit, Central Valley Project, California: U.S. Bureau of Reclamation, Seismotectonic Report 2001-2, 76 p. Angell, M., Hanson, K., and Crampton, T., 1997, Characterization of Quaternary contractional deformation adjacent to the San Andreas fault, Palo Alto, California: Final Technical Report, National Earthquake Hazard Reduction Program, Award No. 1434-95-G- 2586. Angell, M.A., Hanson, K.L., and Crampton, T., 1998, Characterization of Quaternary contractional deformation adjacent to the San Andreas fault, Palo Alto, California: Final Report submitted to the U.S. Geological Survey, National Earthquake Hazards Reduction Program, Award No. 1434-95-G-2586. Aydin, A., 1982, The East Bay hills, a compressional domain resulting from interaction between the Calaveras and Hayward-Rogers Creek faults, in Hart, E.W., Hirschfeld, S.E., and Schulz, S.S. (eds.), Proceedings, Conference on Earthquake Hazards in the Eastern San Francisco Bay Area: California Division of Mines and Geology Special Publication 62, p. 11-21. Baker, J.W., 2011, The conditional mean spectrum: A tool for ground motion selection, American Society of Civil Engineers, Journal of Structural Engineering, v. 137, p. 322-331. Baker J.W. and Cornell C.A., 2006, Correlation of response spectral values for multi-component ground motions: Bulletin of the Seismological Society of America, v. 96, p. 215-227. Boore, D.M., Stewart, J.P., Seyhan, E., Atkinson, G.M., 2013, NGA-West2 equations for predicting response spectral accelerations for shallow crustal earthquakes. PEER Report 2013/05 Pacific Earthquake Engineering Research Center. Bryant, W.A., and Cluett, S.E., compilers, 1999, Fault number 60a, San Gregorio fault zone, San Gregorio section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/regional/qfaults, accessed 01/03/2008 09:16 AM. Bullard, T.F., Hanson, K.L., and Abramson-Ward, H.F., 2004, Quaternary Investigations to Evaluate Seismic Source Characteristics of the Frontal Thrust Belt, Palo Alto region, California: Final Report to U.S. Geological Survey, National Earthquake Hazards Reduction Program, Awards 01HQGR0015 and 01HQCR0016.
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Bürgmann, R., Arrowsmith, R., Dumitru, T., and McLaughlin, R., 1994, Rise and fall of the Southern Santa Cruz Mountains, California, from fission tracks, geomorphology, and geodesy: Journal of Geophysical Research, v. 99, p. 20181-20202. Campbell, K.W. and Bozorgnia, Y., 2013, NGA-West2 Campbell-Bozorgnia ground motion model for the horizontal components of PGA, PGV, and 5%-damped elastic pseudo- acceleration response spectra for periods ranging from 0.01 to 10 sec. PEER Report 2013/06 Pacific Earthquake Engineering Research Center. Cao, T.C., Bryant, W.A., Rowshandel, B., Branum, D., and Wills, C.J., 2003, The revised 2002 California probabilistic seismic hazard maps, June 2003: California Geological Survey website. Carpenter, D.W., Ramirez, A.L., and Wagoner, J., 1980, Status report on the geology of the Lawrence Livermore Laboratory site and adjacent areas: Lawrence Livermore National Laboratories, UCLR-53065, v. 2. Carpenter, D.W., Sweeney, J.J., Kasameyer, P.W., Burkhard, N.R., Knauss, K.G., and Shlemon, R.J., 1984, Geology of the Lawrence Livermore National Laboratory site and adjacent areas: Lawrence Livermore National Laboratory UCRL-53316, 150 p. CDWR, 1979, Re-evaluation of seismic hazards for Clifton Court Forebay, Bethany Dams and Reservoir, Patterson Reservoir, Del Valle Dam and Lake Del Valle: State of California, Department of Water Resources, Sacramento, CA. Chiou, B.S.J. and Youngs, R.R., 2013, Update of the Chiou and Youngs NGA Ground Motion Model for Average Horizontal Component of Peak Ground Motion and Response Spectra. PEER Report 2013/07 Pacific Earthquake Engineering Research Center. Clahan, K.B., 1996, Paleoseismic characteristics of the San Andreas Fault, Woodside, California: M.S. Thesis, San Jose State University, California, 96 p, plus plates. Clahan, K.B., Wagner, D., Bezore, S., Saucedo, G., and Gutierrex, C., 2005, New geologic mapping of the northern San Francisco Bay region: Implications and findings for Quaternary faulting: U.S. Geological Survey National Earthquake Research Program, Northern California Earthquake Hazards, Research Summaries, FY2005, 2p. Cornell, C.A., 1968, Engineering seismic risk analysis: Bulletin of the Seismological Society of America, v. 58, p. 1583-1606. d’Allesio, M.A., Johanson, I.A., Bürgmann, R., Schmidt, D.A., and Murray, M.H., 2005, Slicing up the San Francisco Bay Area: Block kinematics and fault slip rates from GPS-derived surface velocities: Journal of Geophysical Research 110, doi:10.1029/2004JB003496, 19 p. dePolo, C.M., 1994, The maximum background earthquake for the Basin and Range Province, western North America: Bulletin of the Seismological Society of America, v. 84, p. 466-472. Dibblee, T.W., 1980, A preliminary geologic map of the Livermore Quadrangle, Alameda and Contra Costa counties, California: U.S. Geological Survey Open-File Report 80-533b, scale 1:24,000. Dibblee, T.W., Jr., 1981, A preliminary map of the Mendenhall Springs Quadrangle, Alameda County, California: U.S. Geological Survey Open-File Report 81-235, scale 1:24,000.
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Electric Power Research Institute (EPRI), 1993, Guidelines for determining design basic ground motions, v. 1: Method and guidelines for estimating earthquakes ground motion in eastern North America: EPRI Report TR-102293. Fenton, C. H., and Hitchcock, C.S, 2001, Recent Geomorphic and Paleoseismic Investigations of Thrust Faults in Santa Clara Valley, California in Engineering Geology Practice in Northern California, Association of Engineering Geologists Special Publication 12, Edited by H. Ferriz and R. Anderson, pp. 239 – 257. Gülerce, Z. and Abrahamson, N., 2011, Site-specific design spectra for vertical ground motion: Earthquake Spectra, v. 27, p. 1023-1047. Graymer, R.W., Bryant, W., McCabe, C.A., Hecker, S., and Prentice, C.S., 2006, Map of Quaternary-active faults in the San Francisco Bay region: U. S. Geological Survey Scientific Investigations Map 2919, one sheet, scale 1:275,000. Hall, N.T., 1984, Holocene History of the San Andreas fault between Crystal Springs Reservoir and San Andreas Dam, San Mateo County, California: Bulletin of the Seismological Society of America, vol. 74, no., 1, p. 281-300. Hall, N.T., Wright, R.H. and Clahan, K.B., 1999, Paleoseismic studies of the San Francisco Peninsula segment of the San Andreas fault Zone near Woodside, California: Journal of Geophysical Research, v. 104, p. 23,215-23,236. Hanks, T.C. and Kanamori, H. 1979, A moment magnitude scale: Journal of Geophysical Research, v. 84, p. 2348-2350. Hanson, K.L. and Wesling, J.R., 2006, Mapping of the West Napa fault zone for input into the Northern California Quaternary fault database: USGS NEHRP Northern California Earthquake Hazards Research Summaries FY2005: 3rd Annual Northern California Earthquake Hazards Workshop, January 18-19, 2006, Workshop Report, p. 38-39. Hanson, K.L. and Wesling, J.R., 2007, Mapping of the West Napa fault zone for input into the Northern California Quaternary fault database: USGS NEHRP Northern California Earthquake Hazards Research Summaries FY2006: 3rd Annual Northern California Earthquake Hazards Workshop, January 18-19, 2007, Workshop Report, 2 p. Harland Tait & Associates, 1994, Fault and limited geotechnical investigation North Fairfield Site, Fairfield, California: unpublished report submitted to the City of Fairfield. Hart, E.W., 1980, Calaveras and Verona faults (Dublin Quadrangle): California Division of Mines and Geology Fault Evaluation Report FER-108. Hart, E.W., 1981a, Las Positas fault, south branch: California Division of Mines and Geology Fault Evaluation Report FER-112. Hart, E.W., 1981b, Pleasanton and related faults (Dublin Quadrangle vicinity): California Division of Mines and Geology Fault Evaluation Report FER-109. Haugerud, R.A. and Ellen, S.D., 1990, Coseismic ground deformation along the northeast margin of the Santa Cruz Mountains, in Schwartz, D.P. and Ponti, D.J. (eds.), Field guide to neotectonics of the San Andreas fault system, Santa Cruz Mountains, in light of the 1989 Loma Prieta earthquake: U.S. Geological Survey Open File Report 90-274, p. 32-38.
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Hazelwood, R.M., 1976, Contour map and interpretive cross sections showing depth and configuration of bedrock surface, South San Francisco Bay Region, California: U.S. Geological Survey Miscellaneous Field Study Map, MF-796. Herd, D.G. and Brabb, E.E., 1980, Faults at the General Electric test reactor site, Vallecitos Nuclear Center, Pleasanton, California: A summary review of their geometry, age of last movement, recurrence, origin, and tectonic setting and the age of the Livermore Gravels: U. S. Geological Survey Administrative Report, 77 p. Hitchcock, C. and Kelson, K., 1999, Growth of late Quaternary folds in southwest Santa Clara Valley, San Francisco Bay area, California: Implications of triggered slip for seismic hazard and earthquake recurrence: Geology, v. 27, p. 391–394. Idriss, I.M., 2013, NGA-West2 model for estimating average horizontal values of pseudo- absolute spectral accelerations generated by crustal earthquakes: PEER Report 2013/08, Pacific Earthquake Engineering Research Center, College of Engineering, University of California, Berkeley, 15 p. Irwin, W.P., 1990, Geology and plate tectonic development, in The San Andreas Fault System, California, Wallace, R.E. (ed.), U.S. Geological Survey Professional Paper 1515, p. 61-80. Jahns, R.H. and Harding, R.C., 1982, Evaluation of the inferred Verona fault in the Vallecitos Valley, California (abs.), in Proceedings, Conference on Earthquake Hazards in the Eastern San Francisco Bay Area, California, E.W. Hart, S.E. Hirschfeld, and S.S. Schulz (eds.): California Division of Mines Geological Special Publication 62, 185 p. Jennings, C.W. 1994. Fault activity map of California and adjacent areas: California Division of Mines and Geology, California Geologic Data Map Series, Map No. 6. 1:750,000 scale. Keefer, D.I. and Bodily, S.E., 1983, Three-point approximations for continuous random variables: Management Science, v. 26, p. 595-609. Kennedy, D.G., Caskey, J., Hitchcock, C.S., Kelson, K.I., Thompson, S.C., Rubin, R.S., Connelly, S.F., Borchardt, G., Bullard, T.F., Hanson, K.L., AbramsonWard, H., Angell, M.M., and Wesling, J. R., 2005, Seismic Hazard of the Front Range Thrust Faults, Santa Cruz Mountains, Field trip guidebook and volume prepared for the Joint Meeting of the Cordilleran Section, GSA and Pacific Section, AAPG, April 29-May 1, 2005, San Jose, California. Koehler, R.D., Simpson, G.D., Witter, R.C., Hemphill-Haley, E., and Lettis, W.R., 2004 Paleoseismic investigation of the northern San Gregorio fault at Pillar Point Marsh near Half Moon Bay, California: final technical report, U.S. Geological Survey National Earthquake Hazards Reduction Program, Award # 02HQGR0071. Koehler, R.D., Simpson, G.D., Witter, R.C., Hemphill-Haley, E., and Lettis, W.R., 2005 Paleoseismic investigation of the northern San Gregorio Fault, Half Moon Bay, California: final technical report, U.S. Geological Survey National Earthquake Hazards Reduction Program, Award #02HQGR0045. Lienkaemper, J.J., 1992, Map of recently active traces of the Hayward fault, Alameda and Contra Costa counties, California: U.S. Geological Survey Miscellaneous Field Studies Map MF- 2196, 1:24,000.
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Lienkaemper, J.J., 2006, Digital database of recently active traces of the Hayward fault, California: U.S. Geological Survey DS-177, available at http://pubs.usgs.gov/ds/2006/177/ index_viewers.html. Lienkaemper, J.J. and Galehouse, J.S., 1997, Revised long-term creep rates on the Hayward fault, Alameda and Contra Costa Counties: California, U.S. Geological Survey Open-File Report 97-690, 18 p. Lienkaemper, J.J. Schwartz, D.P., Kelson, K.I., Lettis, W.R., Simpson, G.D., Southon, J.R. Wanket, J.A., Williams, P.L., 1999, Timing of paleoearthquakes on the northern Hayward fault – preliminary evidence in El Cerrito, California: U.S. Geological Survey Open-File Report 99-318, p. 34. Lienkaemper, J.J. and Williams, P.L., 2007, A 1650-year record of large earthquake on the southern Hayward fault: Bulletin of the Seismological Society of America, in press. McNally, K. and Ward, S.N., 1990, The Loma Prieta earthquake of October 17, 1989: Introduction to the special issue: Geophysical Research Letters, v. 17:8, p. 1177-1177. Molnar, P., 1979, Earthquake recurrence intervals and plate tectonics: Bulletin of the Seismological Society of America, v. 69, p. 115-133. Niemi, T.M., 2002, Determination of high resolution paleoearthquake chronology for the northern San Andreas fault at the Vedanta Marsh site, Marin County, CA, Annual Summary Report prepared for U.S. Geological Survey National Earthquake Hazards Reduction Program Award 01-HQ-GR-0194 http://erp-web.er.usgs.gov/reports/annsum/vol43/nc/ 01HQGR0194.htm. Niemi, T. and Hall, N.T., 1992, Late Holocene slip rate and recurrence of great earthquakes on the San Andreas fault in northern California: Geology, v. 20, p. 195-198. Oppenheimer, D.H. and Macgregor-Scott, N., 1992, The seismotectonics of the eastern San Francisco Bay region, in Proceedings of the Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area, Borchardt, G., Hirschfeld, S.E., Lienkaemper, J.J., McClellan, P., Williams, P.L. and Wong, I.G. (eds.), California Division of Mines and Geology Special Publication 113, p. 11-16. Prescott, W.H. and Burford, R.O., 1976, Slip on the Sargent fault: Bulletin of the Seismological Society of America, v. 66, p. 1013-1016. Roering, J.J., Arrowsmith, J.R., and Pollard, D.D., 1996, Characterizing the deformation and seismic hazard of a blind thrust fault near Stanford, California: coseismic elastic modeling, in Jayko, A.S. and Lewis, D.D. (eds.), Towards assessing the seismic risk associated with blind faults, San Francisco Bay Regions: U.S. Geological Survey Open-File Report 96-267, p. 41- 44. Savy, J.B. and Foxall, W., 2002, Lawrence Livermore National Laboratory site seismic safety program: Summary of findings: UCRL-LR-53674 Rev. 2. Sawyer, T.L., 1998, Assessment of contractile deformation rates of the Mt. Diablo Fold and Thrust Belt, eastern San Francisco Bay Region, northern California: Tech. Rep. National Earthquake Hazards Reduction Program Award 98-HQ-GR-1006, U.S. Geological Survey, 7 p.
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Sawyer, T.L. and Unruh, J.R., 2002, Holocene Slip Rate Constraints for the Northern Greenville Fault, Eastern San Francisco Bay Area, California: Implications for the Mt. Diablo Restraining Stepover Model: Eos Transactions AGU 83(47), Fall Meeting. Supplement. Schwartz, D.P. and Coppersmith, K.J., 1984, Fault behavior and characteristic earthquakes-- examples from the Wasatch and San Andreas fault zones: Journal of Geophysical Research, v. 89, p. 5681-5698. Schwartz, D.P., Pantosti, D., Hecker, S., Okomura, K., Budding, K.E. and Powers, T., 1992, Late Holocene behavior and seismogenic potential of the Rodgers Creek fault zone, Sonoma County, California, in Proceedings of the Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area, Borchardt, G., Hirschfeld, S.E., Lienkaemper, J.J., McClellan, P., Williams, P.L. and Wong, I.G. (eds.), California Division of Mines and Geology Special Publication 113, p. 393-398. Silva, W.J., Abrahamson, N.A., Toro, G., and Constantino, C., 1997, Description and validation of the stochastic ground motion model: unpublished report prepared for the Brookhaven National Laboratory. Silva, W.J. and Lee, K., 1987, WES RASCAL code for synthesizing earthquake ground motions, State-of-the-Art for Assessing Earthquake Hazards in the United States, Report 24, U.S. Corps of Engineers Waterways Experiment Station, Miscellaneous Paper S-73-1, 120 p. Simpson, G.D. and Knudsen, K.L., 2000, Paleoseismic investigation of the northern San Gregorio Fault at the Pillar Point Marsh near Half Moon Bay, California: report to U.S. Geological Survey Western Region, Bay Area Pale Seismological Experiment (BAPEX). Simpson, G.D., Lettis, W.R., and Randolph, C.E., 1998, Slip rate and earthquake history of the northern San Gregorio fault zone, near Seal Cove, California: final technical report, U.S. Geological Survey, National Earthquake Hazards Reduction Program. Simpson, G.D., Thompson, S.C., Noller, J.S., and Lettis, W.R., 1997, The northern San Gregorio Fault Zone: evidence for the timing of late Holocene earthquakes near Seal Cove, California: Bulletin of the Seismological Society of America, v. 87, p. 1158-1170. Sojourner, A.C., Prentice, C.S., Catchings, R.D., and Harden, DR, 2000, Fluvial geomorphology and late Quaternary history of the San Gregorio fault Zone between San Gregorio and Pescadero, California: Eos Trans. AGU, v. 81, Fall Meeting Supplement, Abstract S62B-08. Sowers, J.M., Noller, J.S., and Unruh, J.R., 1992, Quaternary deformation and blind-thrust faulting on the east flank of the Diablo Range near Tracy, California, in Borchardt, Glenn, and others (eds.), Proceedings of the Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area: California Department of Conservation, Division of Mines and Geology Special Publication 113, p. 377-383. Stewart and Seyhan 2013 Thomas, P.A., Wong, I.G., and Abrahamson, N., 2010, Verification of probabilistic seismic hazard analysis software programs: PEER Report 2010/106, Pacific Earthquake Engineering Research Center, College of Engineering, University of California, Berkeley, 173 p.
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Thornburg, J. and Weber, G.E., 1998, Paleoseismic study of the San Gregorio fault zone, San Mateo County, California: final technical report, U.S. Geological Survey, National Earthquake Hazards Reduction Program (award # 1434-95-G-2593). Toppozada, T.R., Real, C.R., and Parke, D.L., 1981, Preparation of isoseismal maps and summaries of reported effects for pre-1900 California earthquakes: California Division of Mines and Geology Open File Report 81-11, 181 p. Unruh, J.R. and Hector, S.T., 1999, Subsurface characterization of the Potrero-Ryer Island thrust system, western Sacramento-San Joaquin Delta, northern California, William Lettis and Associates, Inc., Final Technical Report, U.S. Geological Survey, National Earthquake hazards Reduction Program Award No. 1434-HQ-96-GR-02724, 32 p. Unruh, J.R. and Kelson, K.I., 2002, Critical evaluation of the northern termination of the Calaveras fault, eastern San Francisco Bay area, California, U.S. Geological Survey National Earthquake Hazard Reduction Program: Final Technical Report Award No. 00-HQ-GR- 0082, 77 p. Unruh, J.R. and Sawyer, T.L., 1997, Assessment of blind seismogenic sources, Livermore Valley, eastern San Francisco Bay region, William Lettis and Associates, Inc., Final Report to U.S. Geological Survey National Earthquake Hazards Reduction Program Award No. 1434-95-G-2611, 95 p. URS Corporation/Jack R. Benjamin & Associates, Inc., 2007, Technical memorandum topical area: seismic hazard, Delta Risk Management Study (DRMS) Phase 1, unpublished report submitted to California Department of Water Resources. Wagner, D.L. and Bortugno, E.J., 1982, Geologic map of the Santa Rosa quadrangle: California Division of Mines and Geology, Regional Geologic Map Series No. 2A, 1:250,000. Wallace, R.E., 1990, The San Andreas fault system, California: U.S. Geological Survey, Professional Paper 1515, 283 p. Weber, G.E., 1994, Late Pleistocene slip rates on the San Gregorio fault Zone at Point Año Nuevo, San Mateo County, California: in Field Trip Guidebook to Transpressional Deformation in the San Francisco Bay Region, W.R. Lettis (eds.), Friends of the Pleistocene, Pacific Southwest Cell. Weber, G.E. and Cotton, W.R., 1981, Geologic investigation of recurrence intervals and recency of faulting along the San Gregorio fault zone, San Mateo County, California: U.S. Geological Survey Open-File Report OF-81-263. 131 pp. Weber, G.E., Nolan, J.M., and Zinn, E.N., 1995, Determination of late Pleistocene-Holocene slip rates along the San Gregorio fault zone, San Mateo County, California: final technical report for U.S. Geological Survey National Earthquake Hazard Reduction Program, 52 p. Wells, D.L. and Coppersmith, K.J., 1994, New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement: Bulletin of the Seismological Society of America, v. 84, p. 974-1002. Wesnousky, S.G., 1986, Earthquakes, Quaternary faults, and seismic hazard in California: Journal of Geophysical Research, v. 91, p. 12,587-12,631.
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WGCEP (Working Group on California Earthquake Probabilities), 2003, Earthquake probabilities in the San Francisco Bay region: 2002–2031: U.S. Geological Survey. Open- File Report 03-214. WGCEP (Working Group for California Earthquake Probabilities), 2008, The uniform earthquake rupture forecast, version 2 (UCERF2): U.S. Geological Survey Open-File Report 2007-1437. WGNCEP (Working Group On Northern California Earthquake Potential), 1996, Database of potential sources for earthquakes larger than magnitude 6 in Northern California: U.S. Geological Survey Open-File Report 96-705. Willis, B. 1924, Earthquake risk in California: Bulletin of the Seismological Society of America, v. 14, p.150 - 164. Witter, R.C., Kundsen, K.L., Sowers, J.M., Wentworth, C.M., Koehler, R.D., and Randolph, C.E., 2006, Maps of Quaternary deposits and liquefaction susceptibility in the central San Francisco Bay region, California, Part 3: Description of Mapping and Liquefaction Interpretation: U.S. Geological Survey Open-File Report 2006-1037. Wong, I.G., 1991, Contemporary seismicity, active faulting and seismic hazards of the Coast Ranges between San Francisco Bay and Healdsburg, California: Journal of Geophysical Research, v. 96, p. 19891-19904. Wong, I., Thomas, P., Hanson, L., Silva, W., Gregor, N., Stokoe, K., and Yuan, J., 2010, Update to the site-specific seismic hazard analyses and development of seismic design ground motions, Stanford University, California: unpublished report submitted to Stanford University. Wong, I., Thomas, P., Upadhyaya, S., Silva, W., Zachariasen, J., Terra, F., and Salah-Mars, S., 2008, Site-specific probabilistic and deterministic seismic hazard analyses of Stanford University, California: unpublished report prepared for Stanford University. Woodward-Clyde Consultants (WCC), 1990, Geotechnical engineering study for proposed medical clinic, Stanford F.P.O. project no. 3428: unpublished technical report prepared for Stanford University. Woodward-Clyde Consultants (WCC), 1991, Site specific seismic study, Veterans Administration Replacement Hospital, Palo Alto, California: unpublished technical report prepared for Stanford University. Woodward-Clyde Consultants (WCC), 1995, Evaluation of site response and design earthquake motions, Stanford University, Palo Alto, California: unpublished technical report prepared for Stanford University. Woodward-Lundgred & Associates, 1973, Ground response studies, Stanford Medical Center expansion – Phase I. Youngs, R.R. and Coppersmith, K.J., 1985, Implications of fault slip rates and earthquake recurrence models to probabilistic seismic hazard estimates: Bulletin of the Seismological Society of America, v. 75, p. 939-964.
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Youngs, R.R, Coppersmith, K.J., Taylor, C.L., Power, M.S., Di Silvestro, L.A., Angell, M.L., Hall, N.T., Wesling, J.R., and Mualchin, L.,1992, A comprehensive seismic hazard model for the San Francisco Bay Region, in Proceedings of the Second Conference on Earthquake Hazards in the Eastern San Francisco Bay Area, Borchardt, G., Hirschfeld, S.E., Lienkaemper, J.J., McClellan, P., Williams, P.L. and Wong, I.G. (eds.), California Division of Mines and Geology Special Publication 113, p. 431-441.
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Probability Rupture Direction of Sense of Fault Name of Activity1 Rupture Scenario2 Segment Name Length3 Width4 Dip5 Dip6 Slip7 Magnitude8 Slip Rate9 Notes San Andreas 1.0 Unsegmented (0.5) 1906 473 13 ± 3 90 N/A SS 7.9 24 ± 3 Characterization based on WGCEP (2003). Unsegmented rupture (Northern and Two Segments Offshore + North 326 11 ± 2 90 N/A SS 7.7 24 ± 3 scenario is a repeat of the 1906 M 7.9 San Francisco earthquake. Central) (0.2) Coast Peninsula + Santa 147 13 ± 2 90 N/A SS 7.4 17 ± 4 Cruz Mountains Three Segments Offshore + North 326 11 ± 2 90 N/A SS 7.7 24 ± 3 (0.1) Coast Peninsula 85 13 ± 2 90 N/A SS 7.15 17 ± 4 Santa Cruz 62 15 ± 2 90 N/A SS 7.0 17 ± 4 Mountains Floating N/A N/A 13 ± 3 90 N/A SS 6.9 24 ± 3 Earthquake (0.2) Calaveras 1.0 Unsegmented Northern + Central + 123 11 ± 2 90 N/A SS 6.9 4 (0.2) Characterization of WGCEP (2003) modified by recent (0.05) Southern Calaveras 6 (0.4) paleoseismic data of Kelson (written communication, 2006). 15 (0.3) 20 (0.1) Two Segments Northern Calaveras 45 13 ± 2 90 N/A SS 6.8 6 ± 2 (0.05) South + Central 78 11 ± 2 90 N/A SS 6.4 15 ± 3 Calaveras Three Segments Northern Calaveras 45 13 ± 2 90 N/A SS 6.8 6 ± 2 (0.3) Central Calaveras 59 11 ± 2 90 N/A SS 6.2 15 ± 3 Southern Calaveras 19 11 ± 2 90 N/A SS 5.8 15 ± 3 Segment + Floating Northern Calaveras 45 13 ± 2 90 N/A SS 6.8 6 ± 2 Earthquake (0.5) Floating Earthquake N/A 11 ± 2 90 N/A SS 6.2 15 ± 3 on Central + South Calaveras Floating N/A N/A 11 ± 2 90 N/A SS 6.2 4 (0.2) Earthquake (0.1) 6 (0.4) 15 (0.3) 20 (0.1) Concord – Green 1.0 Unsegmented N/A 56 14 ± 2 90 N/A SS 6.7 5 ± 3 Characterization based on WGCEP (2003). Valley (0.35) Three Segments Concord 20 16 ± 2 90 N/A SS 6.25 4 ± 2 (0.1) Southern Green 22 14 ± 2 90 N/A SS 6.25 5 ± 3 Valley Northern Green 14 14 ± 2 90 N/A SS 6.0 5 ± 3 Valley Two Segments Concord 20 16 ± 2 90 N/A SS 6.25 4 ± 2 (0.15) Green Valley 36 14 ± 2 90 N/A SS 6.5 5 ± 3 Two Segments Concord + Southern 42 14 ± 2 90 N/A SS 6.6 5 ± 3 (0.15) Green Valley Northern Green 14 14 ± 2 90 N/A SS 6.0 5 ± 3 Valley Floating N/A N/A 14 ± 2 90 N/A SS 6.2 5 ± 3 Earthquake (0.25)
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Probability Rupture Direction of Sense of Fault Name of Activity1 Rupture Scenario2 Segment Name Length3 Width4 Dip5 Dip6 Slip7 Magnitude8 Slip Rate9 Notes Greenville 1.0 Unsegmented (0.4) N/A 58 15 ± 3 90 N/A SS 6.9 2 (0.2) Characterization based on paleoseismic data from Sawyer and 4 (0.6) Unruh (2002) and T.L. Sawyer (personal communication, 2006). 6 (0.2) Floating (0.6) N/A N/A 15 ± 3 90 N/A SS 6.5 2 (0.2) 4 (0.6) 6 (0.2) Hayward – 1.0 Unsegmented Hayward + Rodgers 151 12 ± 2 90 N/A SS 7.3 9 ± 2 Characterization based on WGCEP (2003) model. Rodgers Creek (0.05) Creek Two Segment (A) North Hayward + 98 12 ± 2 90 N/A SS 7.1 9 ± 2 (0.1) Rodgers Creek Southern Hayward 53 12 ± 2 90 N/A SS 6.7 9 ± 2 Two Segment (B) Rodgers Creek 63 12 ± 2 90 N/A SS 7.0 9 ± 2 (0.3) Hayward 88 12 ± 2 90 N/A SS 6.9 9 ± 2 Three Segment Rodgers Creek 63 12 ± 2 90 N/A SS 7.0 9 ± 2 (0.5) North Hayward 35 12 ± 2 90 N/A SS 6.5 9 ± 2 Southern Hayward 53 12 ± 2 90 N/A SS 6.7 9 ± 2 Floating N/A N/A 12 ± 2 90 N/A SS 6.9 9 ± 2 Earthquake (0.05) Mt Diablo 1.0 Unsegmented (0.5) N/A 31 17 ± 2 30 (0.2) NE R 6.7 1 (0.2) Characterization from Unruh (personal communication, 2006). 45 (0.6) 3 (0.6) Fault tip inferred to approach within 5 km (0.5) to 1 km (0.5) of the 50 (0.2) 5 (0.2) surface based on restorable cross section, and on map-scale relationships between surface faults and fold axis. Segmented (0.5) Mt. Diablo North 12 17 2 30 (0.2) NE R 6.3 1 (0.2) North: Fault tip inferred to approach within 4 km (0.5) to 2 km 45 (0.6) 3 (0.6) (0.5) of the surface based on model in restorable cross section. 50 (0.2) 5 (0.2) Mt. Diablo South 19 17 2 30 (0.2) NE R 6.6 1 (0.2) South: Fault tip inferred to approach within 5 km (0.5) to 1 km 45 (0.6) 3 (0.6) (0.5) of the surface based on model in restorable cross section, and 50 (0.2) 5 (0.2) map-scale relationships between surface faults and fold axis. San Gregorio 1.0 Unsegmented Northern + Southern 176 13 ± 2 90 N/A SS 7.5 1 (01) Characterization based on WGCEP (2003) model. (0.35) San Gregorio 3 (0.4) 7 (0.4) 10 (0.1) Segmented (0.35) Northern San 110 13 ± 2 90 N/A SS 7.2 7 ± 3 Gregorio Southern San 66 12 ± 2 90 N/A SS 7.0 3 ± 2 Gregorio Floating N/A N/A 13 ± 2 90 N/A SS 6.9 1 (0.1) Earthquake (0.3) 3 (0.4) 7 (0.4) 10 (0.1) Briones (zone) 1.0 N/A N/A 23 15 3 90 N/A SS 6.5 0.5 (0.2) Characterization from Unruh (personal communication, 2006). 1.0 (0.6) 2.0 (0.2) Cordelia 1.0 Unsegmented (1.0) N/A 19 15 ± 3 90 N/A SS 6.6 0.05 (0.4) Characterization based on paleoseismic data from Harlan Tait & 0.6 (0.5) Associates (1994). 1.0 (0.1)
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Probability Rupture Direction of Sense of Fault Name of Activity1 Rupture Scenario2 Segment Name Length3 Width4 Dip5 Dip6 Slip7 Magnitude8 Slip Rate9 Notes Cull Canyon- 1.0 Unsegmented (1.0) N/A 25 12 3 90 N/A SS 6.6 0.5 (0.2) Characterization from Unruh and Kelson (2002) and Unruh Lafayette-Reliz 1.0 (0.6) (personal communication, 2006). Valley 3.0 (0.2) Foothill Thrust 0.6 Floating N/A N/A 15 3 60 SW R 6.25 (0.3) 0.2 (0.2) Simplified characterization based on WGCEP (2003) subgroup and System Earthquake (1.0) 6.5 (0.3) 0.5 (0.6) recent studies as summarized in Kennedy et al. (2005).. 6.75 (0.3) 0.8 (0.2) Incorporates Berrocal, Shannon-MonteVista, and Cascade faults. 7.0 (0.1) Although there is clear evidence of Holocene and latest Pleistocene fold deformation along this fault zone (Hitchcock and Kelson, 1999; Bullard et al., 2004), the fault is assigned a Probability of Activity of 0.6 to address the uncertainty as to whether the fault is an independent seismic source capable of generating moderate to large magnitude earthquakes. The seismogenic potential of the range front thrust faults is not well known. Aseismic slip (Bürgmann et al., 1994) and coseismic slip during large magnitude events on the San Andreas fault system fault, such as occurred during the 1989 Loma Prieta earthquake (Haugerud and Ellen, 1990) may account for some or all of the local San Andreas fault- normal contraction, precluding the need for independent large magnitude events on the compressive structures. (Angell et al., 1997; Hitchcock and Kelson, 1999). Stanford 0.7 Unsegmented N/A 16 (0.5) 12 2 45 (0.2) SW R 6.3 0.4 (0.2) Fault width and dip are constrained by spatial relations with San 18 (0.5) 60 (0.6) 0.7 (0.6) Andreas fault. Slip rate is from Angell et al., 1998 and Bullard et al. 75 (0.2) 1.0 (0.2) (2004). Length estimates are from Graymer et al., 2006 and Fenton and Hitchcock, 2001. Las Trampas 0.5 Unsegmented N/A 12 14 3 45 SW R 6.2 0.5 (0.2) Characterization from Unruh and Kelson (2002) and Unruh 60 1.0 (0.6) (personal communication, 2006). 75 3.0 (0.2) Los Medanos 1.0 Unsegmented (0.2) N/A 15 17 ± 2 30 (0.2) NE R 6.5 0.3 (0.3) Characterization based on Unruh and Hector (1999) and the Thrust Fold and Thrust 45 (0.2) 0.5 (0.4) Fault Subgroup of the 1999 Working Group. Roe thrust: fault tip Belt 60 (0.6) 0.7 (0.3) inferred to lie between 0 km and 1 km depth based on analysis of gas well data. Segmented (0.8) Roe Island 5 5 ± 2 30 (0.2) NE R 5.8 0.3 (0.3) Roe thrust: fault tip inferred to lie between 0 km and 1 km depth 45 (0.2) 0.5 (0.4) based on analysis of gas well data. 60 (0.6) 0.7 (0.3) Los Medanos 10 10 ± 2 30 (0.2) NE R 6.0 0.3 (0.3) Los Medanos thrust: fault tip inferred to lie between 1 km and 2 45 (0.6) 0.5 (0.4) km depth based on analysis of gas well data and construction of 60 (0.2) 0.7 (0.3) geologic cross sections. Midway/ Black 1.0 Floating N/A 31 15 3 70 10 W RO 6.25 (0.2) 0.1 (0.3) The Black Butte fault is a documented late Quaternary-active Butte Earthquake (1.0) 6.5 (0.4) 0.5 (0.4) reverse (oblique?) fault (Sowers et al., 1992) that appears to be 6.75 (0.4) 1.0 (0.3) related to the late Cenozoic dextral Midway fault by a short left- restraining bend. Limited data are available on slip rate and rupture behavior. The slip rate estimate is based on uplift of middle to early Pleistocene pediment surface across the Black Butte fault (Sowers et al., 1992) and an inferred H:V ratio for the components of slip of 3:1. Monterey Bay- 1.0 Unsegmented (1.0) N/A 84 14 90 N/A SS 7.1 0.5 0.4 Cao et al. (2003) Tularcitos
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Probability Rupture Direction of Sense of Fault Name of Activity1 Rupture Scenario2 Segment Name Length3 Width4 Dip5 Dip6 Slip7 Magnitude8 Slip Rate9 Notes Mt Oso 0.7 Unsegmented N/A 25 15 ± 2 30 (0.3) NE R 6.9 0.5 (0.2) Inferred thrust fault occupying the contractional stepover between (1.0) 45 (0.4) 1.5 (0.6) the Ortigalita and Greenville faults. NE-dipping rupture geometry 60 (0.3) 2.5 (0.2) inferred from the SW-vergence of the Mt. Oso anticline and analogy to Mt. Diablo thrust (J. Unruh, Wm. Lettis and Associates, Pers. Comm., 2006). Activity based on slip transfer from the northern Ortigalita to the southern Greenville. Fault tip at 5 km depth. Ortigalita 1.0 Segmented (0.3) Northern Ortigalita 40 15 ± 3 90 N/A SS 6.9 0.5 (0.15) Characterization revised from Cao et al. (2003) using recent 1.0 (0.35) mapping and paleoseismic data from Anderson and Piety (2001) to 2.0 (0.35) modify the lengths and slip rates for the north and south segments 2.5 (0.15) of the fault. They estimate a slip rate of 1.0-2.0 mm/yr for the Southern Ortigalita 60 15 ± 3 90 N/A SS 7.1 0.2 (0.2) northern section based on abundant geomorphic evidence for 0.6 (0.6) probable latest Pleistocene and Holocene displacement and, 1.0 (0.2) paleoseismic trench investigations that indicate that Quaternary Segmented + Northern Ortigalita 40 15 ± 3 90 N/A SS 6.9 0.5 (0.15) deposits estimated to be between 10 ka and 25 ka, are right Floating 1.0 (0.35) laterally offset between about 13 and 25 m by the Cottonwood Earthquake (0.7) 2.0 (0.35) Arm segment of the Ortigalita fault. They note the southern 2.5 (0.15) segment appears much less active and accordingly, they assign a Floating Earthquake 60 15 ± 3 90 N/A SS 6.6 0.2 (0.2) lower slip rate of 0.2 to 1.0 mm/yr to this segment. on Southern 0.6 (0.6) Ortigalita 1.0 (0.2) Pittsburgh-Kirby 1.0 Unsegmented (0.4) N/A 24 20 ± 5 90 N/A SS 6.7 0.3 (0.4) Characterization from the Thrust Fault Subgroup of the 1999 Hills 0.5 (0.4) Working Group. 0.7 (0.2) Floating N/A N/A 20 ± 5 90 N/A SS 6.3 0.3 (0.4) Earthquake (0.6) 0.5 (0.4) 0.7 (0.2) Potrero Hills 0.7 Unsegmented (1.0) N/A 9 9 ± 2 40 ± 10 SW R 5.75 (0.3) 0.1 (0.2) Characterization based on Unruh and Hector (1999). Fault tip 6.0 (0.6) 0.3 (0.6) inferred to lie between 0 km and 1 km depth based on analysis of 6.25 (0.1) 0.6 (0.2) gas well data and construction of geologic cross sections. The fault is assigned a Probability of Activity of (0.7) based on geomorphic and physiographic evidence that slip is being transferred from the active Pittsburg Kirby Hills fault to Wragg Canyon and Hunting Creek-Berryessa fault zones to the north via the Potrero Hills fault. Pt. Reyes 0.8 Unsegmented N/A 47 12 3 40 (0.2) NE R 7.0 0.05 (0.2) Cao et al. (2003) 50 (0.6) 0.3 (0.6) 60 (0.2) 0.5 (0.2) San Andreas 1.0 Unsegmented (1.0) N/A 312 12 2 90 N/A SS 7.8 28 (0.2) Characterization from URS. (Southern) 33 (0.6) 38 (0.2)
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Probability Rupture Direction of Sense of Fault Name of Activity1 Rupture Scenario2 Segment Name Length3 Width4 Dip5 Dip6 Slip7 Magnitude8 Slip Rate9 Notes Sargent 0.8 Unsegmented (1.0) Sargent 52 15 ± 3 80 10 SW RO 6.9 1.5 (0.3) Characterization based on WGNCEP (1996). Geodetic 3.0 (0.4) measurements indicative of right slip across the southern Sargent 4.5 (0.3) fault (Prescott and Burford, 1976), evidence for creep of about 3-4 mm/yr, as well as associated historical microseismicity suggest that the Sargent fault is an independent seismic source. The Sargent
fault experienced triggered slip during the 1989 MW 6.9 Loma Prieta earthquake (Aydin, 1982). A Probability of Activity of less than 1.0 (0.9) considers that fault slip may occur coseismically as creep or during large magnitude events on the San Andreas fault. Southeast 0.95 Unsegmented (1.0) N/A 26 10 80 10 N/A SS/RO 6.4 1.0 (0.2) Characterization based on WGNCEP (1996), Graymer et al. Extension of (SS) 3.0 (0.6) (2006), and Fenton and Hitchcock (2001). Hayward (zone) 50 10 5.0 (0.2) (RO) Verona/Williams 1.0 Unsegmented (0.6) N/A 22 21 2 30 (0.1) NE R 6.7 0.1 (0.2) In this model, the Verona/Williams fault is the near surface Thrust System 45 (0.6) 0.7 (0.5) expression of a deeper east-to northeast-dipping blind thrust fault 60 (0.3) 1.4 (0.3) that underlies the Livermore Valley (Unruh and Sawyer, 1997; Sawyer, 1998). This model explains fault and fold deformation in the Livermore Valley (including the Los Positas fault, Livermore thrust and Springtown anticline) as secondary structures that either root into the deeper structure or are secondary structures in the hanging wall of the Verona/Williams thrust. These secondary structures are non-seismogenic and are not treated as independent seismic sources. The slip rate distribution is from Savy and Foxall (2002). Fault tip is estimated to be at a depth of 3 km (0.5) or 5 km (0.5). Segmented (0.4) Verona 10 10 30 (0.2) NE R 6.2 0.1 (0.2) Characterization of the fault is based on information summarized 45 (0.4) 0.7 (0.5) in Herd and Brabb (1980), Hart (1980, 1981a,b), Jahns and 60 (0.4) 1.4 (0.3) Harding (1982), and source parameters developed by the Thrust Fault Subgroup of Working Group 1999 (WGCEP (2003) subgroup). The total length of the fault is approximately 7-9 km. Field observations and trenching described by Herd and Brabb (1980) provide evidence for late Quaternary surface-rupturing events on the fault. A 5.65-km-long-segment of the fault is included in an Alquist-Priolo zone (Hart, 1980, 1981a,b). The slip rate distribution is from Savy and Foxall (2002). Fault tip is estimated to be at a depth of 3 km (0.5) or 5 km (0.5). Williams 13 13 30 (0.1) NE R 6.3 0.1 (0.2) Characterization of the fault is based on the following. The total 45 (0.6) 0.3 (0.6) length of the fault is based on mapping by Dibblee (1980,1981). 60 (0.3) 1.0 (0.2) Carpenter et al. (1984) show the fault as a southwest-vergent thrust fault. The CDWR (1979) suggested the fault was active based on displacements observed in Plio-Pleistocene Livermore gravels in the Hetch-Hetchy tunnel and the occurrence of moderate seismicity adjacent to its trace. In the absence of any reported slip rate estimates, a rate of slip comparable to Verona fault is used. Fault tip is estimated to be at a depth of 3 km (0.5) or 5 km (0.5).
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Probability Rupture Direction of Sense of Fault Name of Activity1 Rupture Scenario2 Segment Name Length3 Width4 Dip5 Dip6 Slip7 Magnitude8 Slip Rate9 Notes Las Positas 17.5 15 ± 3 90 N/A SS 6.5 0.1 (0.2) Characterization is based on information summarized by Carpenter P(a) = 0.7 0.3 (0.6) et al. (1980,1984) as follows. The total length of ~17.5 km is 1.0 (0.2) based on geologic mapping and air photo interpretation. Movement on both southern and northern fault traces extends up into Holocene deposits: faulting may have occurred as recently as 500 to 1,000 years ago. The average slip rate for the north branch of the Las Positas fault zone is 0.4 mm/yr; the range of rates obtained from observed vertical offset and inferred horizontal-to-vertical ratios and age estimates is 0.02 to 0.9 mm/yr. West Napa 1.0 Unsegmented St. Helena/Dry Creek 52 15 ± 3 90 N/A SS 6.9 1.0 (0.3) Characterization is based on recent compilation and mapping of the (0.15) + West Napa 2.0 (0.3) West Napa fault by Hanson and Wesling (2006 and 2007) and 3.0 (0.3) Clahan et al. (2005) conducted in support of the USGS Quaternary 4.0 (0.1) fault database for Northern California (Graymer et al., 2006). The slip rate for the West Napa is not well constrained, but was previously considered to be on the order of 1 mm/yr (1 ± 1 mm/yr, Cao et al., 2003). Several recent studies and observations suggest Floating N/A N/A 15 ± 3 90 N/A SS 6.5 0.5 (0.1) the slip rate is higher. These include: 1) more detailed mapping of Earthquake (0.35) 1.0 (0.3) the fault zone (Hanson and Wesling, 2006, 2007) that shows that 2.0 (0.3) the fault is better expressed geomorphically than had been 3.0 (0.2) recognized previously with evidence for recent (< 600 to 700 years 4/0 (0.1) B. P.) displacement; 2) comparison of slip budgets between the Segmented (0.15) St. Helena/Dry Creek 24 15 ± 3 90 N/A SS 6.6 1.0 (0.5) regions north and south of Carquinez Strait suggests that a 2.0 (0.2) significant amount of slip is being transferred from the North 3.0 (0.1) Calaveras fault to the West Napa fault via the Cull West Napa 38 15 ± 3 90 N/A SS 6.8 1.0 (0.5) Canyon/Laffette/Reliz Valley fault zone; and 3) a recent analysis 2.0 (0.2) of GPS data with the preferred model indicating a rate of 4 ± 3 3.0 (0.1) mm/yr (d’Alessio et al., 2005). Segmented + Floating Earthquake N/A 15 3 90 N/A SS 6.4 1.0 (0.5) Floating on West Napa 2.0 (0.2) Earthquake (0.35) 3.0 (0.1) St. Helena/Dry Creek N/A 15 3 90 N/A SS 6.4 1.0 (0.5) 2.0 (0.2) 3.0 (0.1) Zayente-Vergeles 1.0 Unsegmented (1.0) N/A 58 12 70 10 SW R 6.9 0.1 0.1 Cao et al. (2003); Dip information from USGS Quaternary Database
1 Probability of Activity: Independent seismic source (M 6.0) and repeated displacements in late-Quaternary or historical activity (1.0); Late Pleistocene or inferred association with historical seismicity (0.7); activity inferred from fault geometry considered likely to move under current tectonic regime (0.5). 2 Weight assigned according to likelihood of occurrence of rupture scenario. 3 Rupture length in kilometers. 4 Down-dip width of fault rupture. Unless otherwise stated, weights are 0.4 for the best estimate and 0.3 for the upper and lower bound estimates. 5 Inclination of fault plane, measured from the horizontal. Dips are not varied unless otherwise stated. Weights are 0.4 for the best estimate and 0.3 for the upper and lower bound estimates. 6 Direction of inclination of the fault plane. N/A infers a vertical fault plane. 7 SS – strike-slip; R – reverse; OR – oblique-reverse. 8 Unless otherwise stated, uncertainties in the best estimate magnitude are 0.3 magnitude unit. Weights are 0.2, 0.6, and 0.2 unless otherwise stated. A single magnitude value is weighted 1.0. 9 Slip rate based on paleoseismic data. Unless otherwise stated, weights are 0.2, 0.6, and 0.2.
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