The New 2008 USGS National Seismic Hazard Maps

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Raymond Houston
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1 NEHRP The New 2008 USGS National Seismic Hazard Maps Mark Petersen September 10, 2008 Building Seismic Safety Council

2 Seismic hazard map for PGA firm rock: 2% probability of exceedance in 50 years Yellowstone Charlevoix Ottawa- Adirondacks Meers Alaska Walker San Andreas Cascadia Rio Grande New Madrid Wasatch Hawaii Wabash Valley Charleston Eastern Tennessee

3 Attenuation Aug 2005 Oct 2005 CA Oct 2006 PacNW Mar 2006 InterMtn West June 2006 CEUS May 2006 National User-Needs Workshop DEC 2006 Process for 2008 Maps Draft maps (Project 07) Feb 15, 2007 External Review Panel on NGA Sep, 2006 Comments From Outside Community June-July 2007 Update of California Update of NGA Sep-Dec 2007 External Review Panel on Maps May 2007 Draft maps May 2007 Final Maps January 2008 Released April 2008 Quality Assurance

4 Central and Eastern United States

5 New Central and Eastern U.S. Source Models New analysis of magnitude distribution for earthquakes in the central and eastern U.S. New Madrid seismic zone: revised rates, added temporal cluster model New Charleston, SC zones: include offshore structures New CEUS attenuation relations (one of the new ground motion relations falls off faster with distance from earthquake than previous models}. Damage from 1886 Charleston, SC earthquake

6 Evidence of prehistoric earthquake sequences from sandblows

7 Amplitudes decay faster than 1/R at R<70 km. This has important implications for ENA ground motion relations. By G.Atkinson

8 New Attenuation relations for the Central and Eastern U.S.

9 Western United States Crustal Attenuation relations

10 NGA Project Database NGA strong-motion database: 172 worldwide earthquakes 1,400 recording stations 3,500 multicomponent strongmotion recordings Over 100 parameters describing source, path, and site conditions Published Earthquake Spectra, Feb 2008 Magnitude Distance (km) Previous Data New Data Provided by Ken Campbell

13 Western U.S.

14 PACIFIC NW REGION New Cascadia subduction zone magnitude-frequency distribution and weights Added Portland, OR deep zone New subduction zone attenuation relations Added 2 new crustal faults

15 CASCADIA SUBDUCTION ZONE

16 The January 27, 1700 Cascadia Earthquake/Tsunami

17 Subduction zone attenuation relations ( 1 s Spectral Acceleration)

19 Intermountain West Region Western States Seismic Policy Council Recommendations 1. Account for uncertainty in dip 2. Apply magnitude-freq distributions as in CA 3. Account for geodetic data Working Groups in Utah and Nevada 1. Use new slip rates 2. Account for M 7.5 multi-segment rupture Next Generation Attenuation Relations

20 GEODETIC DATA FOR WUS

21 Geodesy Indicates Higher Strain Rate than Geology Entire Great Basin Ratio of Geodetic to Geologic Moment by Sub-Region Pancha et al., 2006

22 California Working Group on California Earthquake Probabilities Report released on April 14, 2008 Next Generation Attenuation Relations

23 California Working Group on California Earthquake Probabilities (2007) Statewide Uniform California Earthquake Rate Model New fault models for San Andreas fault System New analysis of gps strain data Scientific Review Panel

24 WORKING GROUP ON CALIFORNIA EARTHQUAKE PROBABILITIES

25 Changes in Hazard

26 Western U.S. Uniform Hazard Spectra

27 Central and Eastern U.S. Uniform Hazard Spectra

28 Ratio of 5 hz 2008 maps and 2002 maps

29 Ratio of 1 hz 2008 maps and 2002 maps

30 5hz SA: Ratio 2008 to 2002 maps

31 1 hz SA: Ratio 2008 to 2002 maps

32 10 hz 2 second period

33 Deterministic Calculations

34 Deterministic Calculations Selected files based on weight in logic tree Ran deterministic hazard code using same attenuation relations and weights as applied in probabilistic maps, did not include additional uncertainty on magnitude Used GIS to compare ground motions from each scenario and select maximum ground motion

35 Deterministic Calculations Did not include Charleston Zone (difficult to apply since it covers a very broad area) Applied 2005 Alaska maps with older attenuation relations (used in 2005 maps)

37 Conclusions

CONCLUSIONS New attenuation relations causing significant differences at 1 s SA in western U.S. New models for Cascadia, Wasatch, New Madrid also cause changes to hazard Ground motions have decreased in several areas in 2007 maps of CEUS and WUS.

38 CONCLUSIONS New attenuation relations causing significant differences at 1 s SA in western U.S. New models for Cascadia, Wasatch, New Madrid also cause changes to hazard Ground motions have decreased in several areas in 2007 maps of CEUS and WUS. This will influence insurance rates and future building design standards.

EARTHQUAKE MAGNITUDE

EARTHQUAKE MAGNITUDE Earliest measure of earthquake size Dimensionless number measured various ways, including M L local magnitude m b body wave magnitude M s surface wave magnitude M w moment magnitude