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NGA-East: National Seismic Hazard Mapping Perspective

NGA-East: National Seismic Hazard Mapping Perspective. Mark Petersen USGS Golden, CO. New Madrid Ground Motions. Tennessee: Lowered building codes

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NGA-East: National Seismic Hazard Mapping Perspective

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  1. NGA-East: National Seismic Hazard Mapping Perspective Mark Petersen USGS Golden, CO

  2. New Madrid Ground Motions • Tennessee: Lowered building codes • Arkansas: Legislative hearing to lower building codes (Have these ground motions occurred historically?, How do they compare to California earthquake ground motions?) • Kentucky: Ground motion equations are conservative, uncertainties high, PSHA not valid- mixing temporal • Building code community: Can these ground motions occur? Are there physical limits that can be applied? Have we adequately accounted for the distribution of ground motions and truncation levels?

  3. New Hazard Maps

  4. Ratio of new hazard maps with 2002 maps

  5. Figure 9: CEUS 0.2 s SA attenuation relations for M 7 earthquake on Vs30 760 m/s site conditions: AB95 AB05 (Atkinson and Boore, 1995, 2005; F96 (Frankel et al., 1996); T97 T02m (Toro, 1997, 2002); C03 (Campbell, 2003); S01 (Somerville 2001); SV02 (Silva et al., 2002); TP05 (Tavakoli And Pezeshk, 2005) From Chris Cramer

  6. From Chris Cramer Figure 10: CEUS 1 s SA attenuation relations for M 7 earthquake on Vs30 760 m/s site conditions: AB95 AB05 (Atkinson and Boore, 1995, 2005; F96 (Frankel et al., 1996); T97 T02m (Toro, 1997, 2002); C03 (Campbell, 2003); S01 (Somerville 2001); SV02 (Silva et al., 2002); TP05 (Tavakoli And Pezeshk, 2005)

  7. From Atkinson and Boore (2006; updated 2007) Does this contradict Intensity data from CEUS and WUS Earthquakes?

  8. Geometrical spreading (r-1.3 vs r-1.0) Stress drop Site kappa (0.01 vs 0.02) Differences

  9. Amplitudes decay faster than 1/R at R<70 km. This has important implications for ENA ground motion relations. From Gail Atkinson

  10. Average Stress Drop Determinations 570 bars ≥410 bars 110 bars 290 bars From Art Frankel

  11. Slide and caption from Gail Atkinson Some intriguing ground motion information from MMI, based on the USGS “Did You Feel It?” website database.Higher ENA MMI appears to persist to near-source, suggesting higher stress drops From Art Frankel

  12. From Frankel et al. (1990)

  13. Conclusions • Need more information on geometric spreading, stress drop, kappa • Need to resolve the discrepancy between new attenuation relations and MMI data • Need to determine whether high values over New Madrid are reasonable • Need to involve CEUS ground motion modelers (Hermann, Chapman, Ebel, others)

  14. kappa= 0.01 kappa= 0.02 Acceleration Spectral Amp. Vs30= 705 m/sec Vs30= 470 m/sec Corrected for Atkinson Q model and B-C boundary site amplification Frequency (Hz) We used kappa=0.01 for CEUS B-C sites

  15. From Art Frankel Stress Drop Determinations from Spectral Ratios * Determined from comparison of spectral levels with 5/1/05 event

  16. What is kappa (high-frequency spectral falloff) for CEUS B-C sites? Vs30= 760 m/sec OLIL Vs30= 470 m/sec USIN Vs30= 705 m/sec

  17. 5/1/05 earthquake, NE Arkansas, M4.2, fc= 2 Hz (at OLIL) Acceleration spectral Amp. Corrected for Atkinson Q model and B-C boundary site amplification Frequency (Hz)

  18. Western Kentucky 6/20/05 12:21 UTC, d= 21 km Mw= 3.6 (Herrmann), fc= 8-12 Hz, stress drop=270-880 bars OLIL OLIL USIN USIL Spectral Ratio fc= 12 Hz fc= 12 Hz red: fc= 12 Hz blue: fc= 8 Hz red: fc= 12 Hz blue: fc= 8 Hz UTMT PVMO Spectral Ratio fc= 9 Hz fc= 8 Hz All spectral ratios wrt Md 2.7 foreshock 8 8 Frequency (Hz) Frequency (Hz)

  19. uncorrected spectra (proportional to velocity 1-10 Hz) 6/20/05 W. Kentucky Station USIN Dist= 167 km From Art Frankel

  20. Brune spectra for earthquakes whose moments differ by factor of 125 and have equal stress drops Ratio of spectrum of larger event divided by spectrum of smaller event fc= 5 Hz fc= 5 Hz fc= 25 Hz fc= 25 Hz Taking spectral ratio of collocated earthquakes removes path and site effects (and instrument response) and provides estimate of corner frequency of large event (and the small event if you have sufficient bandwidth) From Art Frankel

  21. Red stars show earthquakes studied here, Mw 3.6-4.6 Triangles are broadband stations of the New Madrid seismic network and other ANSS stations used in this study From Art Frankel

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