Comparison of Recorded and Simulated Ground Motions

1. Comparison of Recorded and Simulated Ground Motions • Presented by: • EmelSeyhan, PhD Student • University of California, Los Angeles • Collaborators: • Lisa M. Star, PhD Candidate, University of California, Los Angeles • Robert W. Graves, PhD, USGS • Jonathan P. Stewart, PhD, PE, University of California, Los Angeles

2. Outline • Motivation • Hybrid Simulation Procedure • Validation Analysis & Results • Distance scaling • Standard deviation • Calibration of Hybrid Simulation Procedure • Distance attenuation • Standard deviation • Conclusions

3. Motivation • Broadband motions for response history analysis • Some (M, R) ranges poorly sampled by recordings • Motions needed with specific attributes, e.g. • Basin effect • Near fault effects

4. Motivation • Broadband motions for response history analysis • Some (M, R) ranges poorly sampled by recordings • Motions needed with specific attributes, e.g. • Basin effect • Near fault effects Simulations hold potential to provide useful ground motions for engineering application in these situations

5. ShakeOut Scenario Description Hughes Lake SanGorgonioPass Bombay Beach • Moment magnitude 7.8 earthquake • 150 yr return period (last events 1857 & 1680) • Evaluated for three different possible hypocenters

6. Puente Hills Scenario • Directly under down town Los Angeles • 7.15 Mw Earthquake • Buried reverse fault

7. Simulation Procedure • Hybrid procedure • f<1 Hz: physics based Physics-based

8. Simulation Procedure • Hybrid procedure • f<1 Hz: physics based • f>1 Hz: stochastic Reference: Graves et al, 2004 Stochastic

9. Simulation Procedure • Hybrid procedure • f<1 Hz: physics based • f>1 Hz: stochastic Reference: Graves et al, 2004

10. Simulation Procedure • Hybrid procedure • Source function • Kinematically prescribed source model • Slip distribution • Rupture velocity ShakeOut, Mw 7.8

11. Simulation Procedure • Hybrid procedure • Source function • Semi-empirical site term (fn of Vs30)

12. Distance Attenuation

13. Calibration Analysis Approach • Calculate residuals • 4 GMPEs: AS, BA, CB, CY • Random effect analysis: Separate event term (hi) from within-event residual (ei,j) • Distance-scaling evaluated from (ei,j)

14. Calibration Analysis ei,j = Ri,j - hi General Model

15. Intra-event Residuals

16. Intra-event Standard Deviation • too low for T < 1.0 s • Large transition at T=1.0 s s=stdev(e)

17. Calibration of Hybrid Simulation Procedure • Focus on high frequency stochastic model • Controlling parameters • Source parameters: Stress drop, slip function, rise time, rupture velocity • Path parameters: Distance, crustal velocity & damping (Q) • Site parameters: Near surface crustal velocity, shallow site term (Vs30) • Parameter selected for remove distance attenuation bias • Procedure to increase intra-event standard deviation

18. Scope • Distance attenuation calibration • Strike slip fault M5, 6.5, 7.25 and 8 • Distributed arrays M5 M6.5 M7.25 M8

19. M6.5 M5 • Slip models • For M5, 6.5, 7.25 and 8 • Random slips

20. M7.25 M8

21. Various levels of crustal damping, Q • Low Qo (a=25) • Mid Qo (a=41) • High Qo (a=57) Q (f) = Qo*fn (n = 0.6) ShakeOut Qo= a + b*Vs (b = 34)

22. Verification of Hybrid Trends Using Stochastic Part Only • Using same level of Q (Low Qo) • Original ShakeOut • This study (M8) similar trend with previous work esp. beyond about 10 km

23. Removing Distance Attenuation Bias • Comparing different level of Q (M7.25) • Using low Qo • Using high Qo

24. Removing Distance Attenuation Bias • Residuals for different level of Q (M7.25) • Using low Qo • Using high Qo

25. Removing Distance Attenuation Bias • Fit semi-log line to residuals of average ground motions • For different level of Q • Using low Qo • Using high Qo • Repeat for all M, GMPEs, IMs Y = c*ln(X) + d

26. Removing Distance Attenuation Bias PGA • Slope of residuals of average ground motions • Scatter based on all gmpes • Using low Qo • Using high Qo

27. Removing Distance Attenuation Bias • Slope of residuals of average responses • Using low Qo • Using high Qo

28. Intra-event scatter calibration • Increasing intra-event standard deviation • Randomized velocity • Randomized Fourier Amplitude • Randomized Q

29. Intra-event scatter calibration Approach • Modify parameters e.g. • Velocity profile Rand Case NonRand Case BA08

30. Intra-event scatter calibration Approach • Randomization of Fourier Amplitude • Adding variation

31. Intra-event scatter calibration Approach • Randomization of Fourier Amplitude • Adding variation Rand Case NonRand Case BA08

32. Concluding Remarks • Calibrated simulation procedures needed for engineering practice • Validation process reveals: • Faster distance attenuation at shorter periods • Low intra-event standard deviation T<1s

33. Cont’d • Calibration process reveals: • Possible to get slower distance attenuation by using higher Q • Randomization of Fourier Spectrum gives better results than randomization of velocity

34. More? • Implementation fully hybrid simulation with revised Q and Vs

35. Thank you