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Site-Specific Seismic-Hazard Maps and Deaggregation in the Western United States Using the NGA Models for Ground-Motion Prediction

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Site-Specific Seismic-Hazard Maps and Deaggregation in the Western United States Using the NGA Models for Ground-Motion Prediction By Stephen Harmsen Open-File Report 2011–1218 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2011 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1–888–ASK–USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1–888–ASK–USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Harmsen, Stephen, 2011, Site-specific seismic-hazard maps and deaggregation in the western United States using the NGA models for ground-motion prediction: U.S. Geological Survey Open-File Report 2011–1218, 67 p. ii Contents Abstract ...................................................................................................................................................................... 1 Introduction ................................................................................................................................................................. 1 Site Response in GMPEs ........................................................................................................................................... 3 Rock versus Soil in the Hazard Integral ...................................................................................................................... 4 Regional Scale Uniform Soil Hazard Maps ................................................................................................................. 6 Methods for Estimating Vs30 over Broad Regions ..................................................................................................... 9 Regional Scale Site-Specific Hazard Maps ................................................................................................................ 9 Regional Scale Site-Specific Vs30 Maps for Central California .............................................................................. 9 Regional Scale Site-Specific Hazard Maps for Central California ......................................................................... 15 Regional Scale Site-Specific Vs30 Maps for Southern California.......................................................................... 27 Regional Scale Site-Specific Hazard Maps for Southern California ...................................................................... 31 Deaggregation of Seismic Hazard at Specific Sites .................................................................................................. 44 Case I. Soil Mode Same as Rock Mode................................................................................................................ 45 Case 2. Soil Mode Different from Rock Mode ....................................................................................................... 49 Caveats and Model Limits ........................................................................................................................................ 59 Discussion and Conclusions ..................................................................................................................................... 63 Acknowledgments .................................................................................................................................................... 64 References ............................................................................................................................................................... 64 Figures Figure 1. Schematic diagram of spectral acceleration distribution from two types of sources recorded on two types of sites .................................................................................................................................................. 5 Figure 2. Spectral acceleration ratio for sites in the western United States, using the new Next Generation of Attenuation ground-motion prediction equations ........................................................................... 7 Figure 3. Regional scale site-specific Vs30 maps for central California using three methods to determine Vs30 .................................................................................................................................................. 10 Figure 4. Regional scale site-specific hazard maps for central California, 5-hertz spectral acceleration ............. 16 Figure 5. Regional scale site-specific hazard maps for central California, 3-second spectral acceleration .......... 22 Figure 6. Regional scale site-specific Vs30 maps for southern California using three methods to determine Vs30 .................................................................................................................................................. 28 Figure 7. Regional scale site-specific hazard maps for southern California, 5-hertz spectral acceleration .......... 32 Figure 8. Regional scale site-specific hazard maps for central California, 3-second spectral acceleration .......... 38 Figure 9. Map showing principal faults in the vicinity of the Los Angeles site over a base map showing the site-specific 1-second spectral acceleration at 2 percent in 50 years probability of exceedance, using method 1 to estimate Vs30 ....................................................................................................................... 46 Figure 10. Map showing principal faults in the vicinity of a site in San Jose, California, over a contour map showing site-specific 1-second spectral acceleration with 2 percent in 50 years probability of exceedance using method 1 to estimate Vs30 ................................................................................................... 48 Figure 11. Rock-site hazard near San Rafael: 5-hertz spectral acceleration with 2 percent in 50 years probability of exceedance for a site with Vs30 of 760 meters per second .......................................................... 51 Figure 12. Soil-site hazard near San Rafael: 5-hertz spectral acceleration with 2 percent in 50 years probability of exceedance for a site with Vs30 of 180 meters per second .......................................................... 52 Figure 13. Harbor Island 5-hertz hazard deaggregation assuming rock site condition ....................................... 54 iii Figure 14. Harbor Island 5-hertz hazard deaggregation assuming soil site condition ........................................ 55 Figure 15. Harbor Island 1-second spectral acceleration assuming rock site condition ..................................... 57 Figure 16. Harbor Island 1-second spectral acceleration assuming soil site condition ...................................... 58 Figure 17. Scattergram of Vs100 versus Vs30 at or near 50 southern California strong-motion sites ............... 62 Tables Table 1. Important future earthquake sources in Los Angeles, California. .......................................................... 45 Table 2. Seismic hazard at San Jose, California. ............................................................................................... 49 Table 3. Comparison of Vs30 values measured by one of three methods (borehole, spectral analysis of surface waves, or refraction microtremor) and Vs30 values from three regional model values. ......................... 60 List of Abbreviations Used in This Report μ and σ median and logarithmic standard deviation, respectively, of ground-motion prediction equation g gravitational acceleration at Earth surface, approximately equal to 9.8 m/s2 GMPE ground-motion prediction equation, also known as attenuation equation Hz hertz (frequency in cycles per second of seismic waves or building oscillations) IMW Intermountain West; a boundary that separates the central and western United States based on differences in attenuation of seismic waves in the Earth’s continental crust IP Intermediate-period; generally in the range 0.5 to 2.0 seconds km kilometer LP long-period; generally in the range 2.5 seconds or greater m meter NEHRP National Earthquake Hazard Reduction Program NGA Next Generation of Attenuation models (developed for tectonically active regions) NSHMP National Seismic Hazards Mapping Project (Golden, Colorado) PE probability of exceedence; probability that a specified ground acceleration or other intensity measure will be exceeded in a specified time, such as 50 years. Typically, PE values like 2% in 50 years or 10% in 50 years are considered. (Term coined for use in PSHA.) PGA peak (horizontal) ground acceleration; generally, PGA is the geometric mean of the two horizontal components PGV peak (horizontal) ground velocity PSHA probabilistic seismic hazard analysis SA 5% damped pseudo spectral acceleration SASW spectral analysis of surface waves SP short-period; generally in the range 0.01 to 0.4 seconds Vs30 average shear-wave velocity in upper 30 meters of the soil column iv Site-Specific Seismic-Hazard Maps and Deaggregation in the Western United States Using
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