Validation of physics-based ground motion earthquake simulations using a velocity model improved by tomographic inversion results 1 Ricardo Taborda, 1 En-Jui Lee, 2 David Gill, 3 Po Chen, 4 Philip Maechling, 3 Thomas H. Jordan 2,3 1 Center for Earthquake Research and Information, and Department of Civil Engineering, University of Memphis 2 Department of Earth Sciences, University of Southern California 3 Southern California Earthquake Center, University of Southern California 4 Department of Geology and Geophysics, University of Wyoming

2 southern California models CVM-H+GTLCVM-S4.26 CVM-HCVM-S Alternative velocity models for southern California Magistrale et al. (1996, 200) Kohler et al. (2003) (…) + Chen et al. (2011) Lee et al. (2011, 2013) Gil et al. (2013, 2014) Süss and Shaw (2003) Süss et al. (2005) Plesch et al. (2007, 2009) (…) + Ely et al. (2010)

3 Crustal structure basin depths at fixed values of Vs

4 Basins geometry depth to Vs = 1 km/s CVM-S CVM-H

5 Taborda and Bielak (2014) BSSA, 104(4): in press Recent work using different velocity models case study: 2008 Chino Hills earthquake Taborda and Bielak (2013) BSSA, 103(1): 131–156

6 southern California models CVM-H+GTLCVM-S4.26 CVM-H CVM-S Alternative velocity models for southern California Magistrale et al. (1996, 200) Kohler et al. (2003) (…) + Chen et al. (2011) Lee et al. (2011, 2013) Gil et al. (2013, 2014)

7 The latest CVM-S4.26 velocity model tomographic inversion results and merge into CVM-S CVM-S4.26 (Final Model) CVM-S (Base Model) Magistrale et al. (1996, 200) Kohler et al. (2003) Built as a model with “arbitrary” resolution (…) + Chen et al. (2011) Lee et al. (2011, 2013) Starting model discrete version of the model with fixed resolution: regular grid every 500 m and minimum Vs = 1000 m/s 3D tomographic inversion yields perturbations to starting model inversion process included 26 iterations Po Chen and En-Jui Lee Recovering and merging process various scheme(s) devised to recover model features truncated by the starting model and merge the pertur- bations back into the model for “arbitrary” querying resolution Distributed via SCEC’s UCVM (…) + Gil et al. (2013, 2014)

8 The CVM-S4.26 velocity model merging alternatives Option 1 Base Vs < 1 km/s Use Starting Props. + Perturbation Negative Perturbation Final Model NO YES Use Base Props. + Perturbation Use Base Props. NO YES checks whether base model is softer than starting model —inside a basin?— if the base model is softer checks whether the perturbation will make it even softer prevents the perturbation from making softer than the base model —preserves floor base props.— otherwise it hardens the base model otherwise it hardens the starting model

9 The CVM-S4.26 velocity model merging alternatives Option 2 Base Props. < Starting Use Base Props. Negative Perturbation Final Model NO YES Starting Values + Perturbation Use Base Props. NO YES Positive Perturbation YES checks whether base model is softer than starting model —inside a basin?— if the base model is softer, checks whether the perturbation will make it even softer prevents the perturbation from making softer than the base model prevents the perturbation from making stiffer than the base model if the base model is stiffer, checks whether the perturbation will make it even stiffer

10 The CVM-S4.26 velocity model merging alternatives Option 3 Base Props. < Starting Use Starting Props. + Perturbation Final Model NO YES Use Base Props. checks whether base model is softer than starting model —inside a basin?— the base model is preserved everywhere it is softer than the starting model the inversion results are used everywhere else

11 Comparison between base and merged models CVM-S CVM-S4.26 Option 1 CVM-S4.26 Option 2CVM-S4.26 Option 3 Surface shear wave velocity (Vs) in m/s

12 Largest earthquake in the L.A. region since the 1994 Northridge earthquake. Combination of thrust and strike-slip faulting between the Whittier and Chino faults. No significant damages, no fatalities. Excellent opportunity for testing assumptions and methodologies. Recorded in over 450 strong motion station from different seismic networks. 336 surface stations within simulation domain. The 2008 chino hills earthquake and region of interest

13 Low-frequency (0–0.5 Hz) ground motion selected locations Data Starting model Inverted model

14 “High”-frequency (0–4 Hz) ground motion selected locations Data Base model Merge Option 1 Merge Option 2 Merge Option 3

6 – 8 Good 4 – 6 Fair 4 – 6 Fair 0 – 4 Poor 8 – 10 Excellent 15 »Anderson (2004) 13 th World Conf. Earthq. Eng. »as modified in Taborda and Bielak (2013) Bull. Seismol. Soc. Am. 103(1):131–156 Arias Intensity Energy Integral Duration PGA PGV PGD Fourier Spectrum Response Spectrum Cross Correlation Validation criteria goodness of fit

16 CVM-S CVM-S4.26 Option 1 CVM-S4.26 Option 2CVM-S4.26 Option 3 GOF scores comparison (0–0.25 Hz)

17 CVM-S4.26 Option 1 CVM-S4.26 Option 2CVM-S4.26 Option 3 GOF scores improvement with respect to the base model (0–0.25 Hz) Scale corresponds to change in the GOF score with respect to the values obtained for the simulation using the base CVM-S model

18 CVM-S CVM-S4.26 (Option 1) GOF scores improvement with respect to the base model (0–0.25 Hz)

19 CVM-S CVM-S4.26 (Option 1) GOF scores improvement with respect to the base model (0–0.25 Hz)

20 Improvements beyond inversion f max with respect to the base model (0–4 Hz) CVM-S CVM-S4.26 (Option 1)

21 Improvements beyond inversion f max with respect to the base model (0–4 Hz) GOF score change w.r.t. base model validation

22 »general improvements in the synthetics are obtained but some areas will need further attention »changes in GOF scores are of the order of 1 to 4 points maximum »additional improvements are unlike to come from marginal changes to the velocity models at this point, therefore other aspects (like frequency dependent attenuation and coherency in the source model) will need to be considered Closing remarks and future work

Validation of physics-based ground motion earthquake simulations using a velocity model improved by tomographic inversion results 23 Ricardo Taborda, 1 En-Jui Lee, 2 David Gill, 3 Po Chen, 4 Philip Maechling, 3 Thomas H. Jordan 2,3 1 Center for Earthquake Research and Information, and Department of Civil Engineering, University of Memphis 2 Department of Earth Sciences, University of Southern California 3 Southern California Earthquake Center, University of Southern California 4 Department of Geology and Geophysics, University of Wyoming