Validation of seismic velocity models in southern California with full-waveform simulations

Yang Lu, & Yehuda Ben-Zion

Under Review 2021, SCEC Contribution #11023

Crustal seismic velocity models provide essential information for many applications including earthquake source properties, simulations of ground-motion and related derivative products. We present a systematic workflow for assessing the accuracy of velocity models with full-waveform simulations. The framework is applied to four regional seismic velocity models for southern California: CVM-H15.11 (Shaw et al., 2015), CVM-S4.26 (Lee et al, 2014), CVM-S4.26.M01 that includes a shallow geotechnical layer, and the model of Berg et al. (2018). For each model, we perform 3D viscoelastic wave propagation simulations for 48 virtual seismic noise sources (down to 2 s) and 44 moderate-magnitude earthquakes (down to 2 s generally and 0.5 s for some cases). The synthetic waveforms are compared with observations associated with both earthquake records and noise cross-correlation datasets. We measure, at multiple period bands for well-isolated seismic phases, traveltime delays and normalized zero-lag cross-correlation coefficients between the synthetic and observed data. The obtained measurements are summarized using the mean absolute derivation of time delay and the mean correlation coefficient. These two metrics provide reliable statistical representations of model quality with consistent results in all datasets. In addition to assessing the overall (average) performance of different models in the entire study area, we examine spatial variations of the models’ quality. All examined models show good phase and waveform agreements for surface waves at periods longer than 5 s, and discrepancies at shorter periods reflecting small-scale heterogeneities and near-surface structures. The model performing best overall is CVM-S4.26.M01. The largest misfits for both body and surface waves are in basin structures and around large fault zones. Inaccuracies generated in these areas may affect tomography and model simulation results at other regions. The seismic velocity models for southern California can be most improved by adding accurate structural representations of the shallow crust and volumes around the main faults.

Lu, Y., & Ben-Zion, Y. (2021). Validation of seismic velocity models in southern California with full-waveform simulations. Geophysical Journal International, (under review).