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

Yang Lu, & Yehuda Ben-Zion

Submitted July 23, 2020, SCEC Contribution #10188, 2020 SCEC Annual Meeting Poster #TBD

Crustal seismic velocity models provide essential information for many applications, including earthquake source properties, simulations of ground-motion and related derivative products. It is therefore important to validate velocity models by assessing their ability to explain new observations not used for their derivation. In this study, we evaluate several seismic velocity models derived for the southern California region, including CVMS-4.26, CVM-S4.26.M01, CVMH (see summary in Small et al., SRL, 2017), the model of Berg et al. JGR, 2018) and a new model under development (Fang et al., 2020). For each model, we perform 3D viscoelastic simulations of ground motion (up to 1Hz generally and 4Hz for selected models and events) generated by 36 moderate-magnitude earthquakes in various locations, and compare the simulated waveforms to those recorded by the seismic network. We measure and analyze phase delays and waveform similarities between the synthetics and observed waveforms in different sub-regions at multiple-frequency bands. All examined models show good phase and waveform agreements for body waves below 0.5Hz and surface waves below 0.2 Hz. For surface waves, the small remaining misfits mainly appear in basin areas and around fault zones. Inaccuracies generated by the shallow soft layers and damaged fault zone regions may affect tomography and model simulation results at other regions. At frequencies above 0.5 Hz, the synthetics and observations start to show significant mismatches, reflecting poorly constrained small-scale heterogeneities and near-surface structures. The results clearly indicate the need for an accurate structural representation of the shallow crust to improve the current crustal models of southern California. The methodology applied in the study can be used to assess quantitatively seismic velocity models of other regions.

[1] Berg, E., Lin, F.-C., Allam, A., Qiu, H., Shen, W., & Ben-Zion, Y., 2018. Tomography of Southern California via Bayesian joint inversion of Rayleigh wave ellipticity and phase velocity from ambient noise cross-correlations, J. Geophys. Res. Solid Earth, 123, 99339949.
[2] Small, P., Gill, D., Maechling, P. J., Taborda, R., Callaghan, S., Jordan, T. H., Ely, G. P., Olsen, K. B., & Goulet, C. A., 2017. The SCEC Unified Community Velocity Model Software Framework, Seism. Research. Lett., 88, 1539-1552.

Lu, Y., & Ben-Zion, Y. (2020, 07). Validation of seismic velocity models in southern California with full-waveform simulations. Poster Presentation at 2020 SCEC Annual Meeting.

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