High Definition Earthquake Modeling - How Technology is Changing our Understanding of Earthquake Risk

Transcription

1 High Definition Earthquake Modeling - How Technology is Changing our Understanding of Earthquake Risk Morgan Moschetti U.S. Geological Survey Geologic Hazards Science Center, Golden, GO

2 Representative 3D-simulation efforts, U.S. Seattle San Francisco Bay Area Salt Lake City Los Angeles (SCEC CyberShake) Las Vegas Mississippi embayment Past and on-going 3D-simulation-based efforts to characterize earthquake ground motions within the U.S.

3 Overview Ground motion simulations: What are they? How do they differ from traditional ground motion models? What can they add to our understanding of earthquake hazard and risk? Use in engineering design: How are ground motion simulations being used for seismic hazard Process to using simulations in engineering design Future directions in earthquake simulations: Testing the effects of simulations in the U.S. National Seismic Hazard Model What should we expect from ground motion simulations in the next 5+ years?

4 Empirical Ground Motion Models

5 Abrahamson et al. (2014) Empirical Ground Motion Models

6 Abrahamson et al. (2014) Empirical Ground Motion Models

7 Empirical Ground Motion Models Day et al. (2008)

8 Displacements from Landers M7.3 Earthquake - Wave-structure interactions (amplification structure deeper than 30 m, incidence at basin edge, surface waves, focusing, trapping, scattering) - Wave-wave interactions (wave interference and resonance) Day et al. (2008) Wald and Graves (1998)

9 Seismological studies of earthquake sources and earth structure and understanding of wave propagation Shapiro et al. (2004)

10 Earth properties Model of earthquake rupture on fault Shi and Day (2013) Roten et al. (2014) Supercomputing calculations Physics of the problem Meshing for numerical calculations

11 Natural features of ground motion simulations Source effects the way that earthquake faults radiate seismic waves and how this affects ground-shaking (directivity) Path-dependent effects how the direction of incoming seismic waves affects ground shaking Site effects Regional variations in geologic structure

12 Source effects: Directivity Radiation of seismic waves from earthquake fault similar to effect of a moving source Directivity affects the frequency and amplitude of seismic waves and groundshaking Enhance ground shaking in forward direction of earthquake rupture

13 Directivity effects on ground motions Directivity results in large ground motion pulses Directivity pulses observed in many earthquakes and depend on epicenter location

14 Directivity: visualized through moving sources Radiation of seismic waves from earthquake fault similar to effect of a moving source Directivity affects the frequency and amplitude of seismic waves and groundshaking Enhance ground shaking in forward direction of earthquake rupture

15 Directivity: visualized through moving sources Radiation of seismic waves from earthquake fault similar to effect of a moving source Directivity affects the frequency and amplitude of seismic waves and groundshaking Enhance ground shaking in forward direction of earthquake rupture

16 Directivity: visualized through moving sources Radiation of seismic waves from earthquake fault similar to effect of a moving source Directivity affects the frequency and amplitude of seismic waves and groundshaking Enhance ground shaking in forward direction of earthquake rupture

17 Path effects: not (currently or ever?) captured by empirical ground motion models Hyogo-ken Nambu, 1995, Kobe Northridge, 1994 Seattle basin 1-Hz amplification Kawase (1996) Graves et al. (1998) Frankel et al. (2009)

18 Path effects: not (currently or ever?) captured by empirical ground motion models Hyogo-ken Nambu, 1995, Kobe Northridge, 1994 Seattle basin 1-Hz amplification Kawase (1996) Graves et al. (1998) Frankel et al. (2009)

19 Path effects: not (currently or ever?) captured by empirical ground motion models Hyogo-ken Nambu, 1995, Kobe Northridge, 1994 Seattle basin 1-Hz amplification Kawase (1996) Graves et al. (1998) Frankel et al. (2009)

20 Site effects: Regional differences in sedimentary basins Marafi et al. (2017)

21 Site effects: Regional differences in sedimentary basins Region Max. Depth, Z2.5 Los Angeles Seattle SF Bay Area Salt Lake City 8.7 km 6.7 km 3.6 km 3.1 km

22 Site effects: Regional differences in sedimentary basins Region Max. Depth, Z2.5 Los Angeles Seattle SF Bay Area Salt Lake City 8.7 km 6.7 km 3.6 km 3.1 km

23 Simulation example: San Andreas Fault

24 Differences between empirical and simulationbased ground motion models Empirical ground motion model 3D Simulation Wang and Jordan (2014)

25 Differences in ground motions from 3D simulations Frankel et al. (2018) Wang and Jordan (2014) Graves et al. (2010) Moschetti et al. (2017)

26 Validation of simulated ground motions Distance (km) Frankel (2009) Graves et al. (1998) Moschetti et al. (2017)

27 Validation of simulated ground motions

28 Room for improvements in 3D simulations For seismic hazard applications, simulations need to move from explaining features to predicting features Simulations are only as good as our knowledge of the physics and the underlying properties of the earth Require high-quality geologic models Frequency limitations (spatial and computational) (~ 1 Hz) Details of earthquake source and expected variations Nonlinearity Roten et al. (2014) Without elastoplastic effects With elastoplastic effects

29 Example use of simulations in engineering design Seattle 2013 report Los Angeles 2018 report

30 Seismic hazard from 3D simulations

31 Multidisciplinary panels developed recommendations for engineering design Los Angeles Seattle Geotechnical Consultants Doug Lindquist and Michael Chamberlain (Hart Crowser) Hamilton Puangnak and Melanie Walling (GeoEngineers) Ali Shahbazian and Matt Gibson (Shannon & Wilson) Reda Mikhail and Feng Li (Golder) Organizational Representatives Kevin Aswegan (MKA/ASCE 7 Seismic Committee) Andy Taylor (KPFF/SEAW EEC) Douglas Beck (City of Bellevue) Peer Reviewers C.B. Crouse (AECOM Seattle) Steve Dickenson (New Albion) Ivan Wong (Lettis Consultants) GMM Developers and Seismologists Norm Abrahamson (UC Berkeley) Ken Campbell (CoreLogic) Andreas Skarlatoudis (AECOM LA) USGS/M9 Art Frankel and Erin Wirth (USGS/M9) Marc Eberhard and Steve Kramer (UW/M9) SDCI Susan Chang Scott Pawling Courtesy S. Chang

32 Example use of simulations in engineering design, Seattle Subduction interface sources (based on recorded motions and simulations) MCE R spectrum multiplied by basin amplification factor Modification of empirical GMMs at longer periods BAF = 1 for T= 0 sec; BAF = 2 at T > 2 sec Wirth et al. (2018)

33 Example use of simulations in engineering design, Los Angeles Weighted Averaging of MCE R Response Spectra Increasing weighting of simulations at longer (T>2 s) periods

34 Looking forward: Incorporating simulations into U.S. National Seismic Hazard Model (NSHM) Convened panel of ~15 scientists and engineers within USGS ( ) National-scale hazard model: Incorporate studies from different regions to produce national-scale model Role of NSHM in developing seismic provisions of U.S. building codes and for many other users. Historically have required outreach and buy-in from user communities. Only incorporating those features of 3D simulations that are widely supported Initial focus on basin amplification not using absolute ground motions or path effects

35 Looking forward: Incorporating simulations into U.S. National Seismic Hazard Model (NSHM) Modify empirical ground motion models with (spatially varying basin amplifications from 3D simulations Validation of 3-D-simulation-derived amplification factors comparison with small-m earthquake data Incorporation of this model into NSHM will (likely) rely on weightings between simulated and empirically based GMPEs (period-dependent, similar to SCEC-UGMS recommendations?)

36 Validating the Incorporation of 3D Simulations into NSHM

37 Validating the Incorporation of 3D Simulations into NSHM

38 LA effect of 3D simulations, 3 s Likely Effects of Incorporating 3D Simulations into U.S. NSHM Seattle basin amplification Effects from simulations will initially be limited to a few regions Los Angeles, Seattle, (later) San Francisco Bay Area, Salt Lake City Simulated data affect longer periods (T>1 s) Region-dependent amplification of earthquake ground motions Many cases, simulations indicate higher-thancurrent predictions within deepest parts of basins Effects will initially be introduced only within basins (deeper sediments)

39 Summary Benefits of the use of ground motion simulations for seismic hazard Naturally model source, path, and site effects (different earthquake and fault types, by region) Increasingly subjected to quantitative and multidisciplinary testing Increasingly widely supported by earth science and engineering communities Use in local engineering design and potential use in national building codes Results from 3D simulations being used for engineering design in Los Angeles and Seattle Independent processes for developing standards for incorporating simulations: Long-period (T>1, 2 s) results Combined multiple types of ground motion predictions Incorporation into U.S. National Seismic Hazard Model following guidance and using features of local efforts In the next 5+ years, seismic hazard and risk products will increasingly incorporate ground motion simulations