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

Yang Lu, & Yehuda Ben-Zion

Submitted August 15, 2021, SCEC Contribution #11433, 2021 SCEC Annual Meeting Poster #212

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., EPSL, 2015), CVM-S4.26 (Lee et al, JGR, 2014), CVM-S4.26.M01 that includes a shallow geotechnical layer (as summarized in Small et al., SRL, 2017), and the model of Berg et al. (JGR, 2018). Synthetic waveforms obtained from viscoelastic wave simulations (down to 2 s generally and 0.5 s for some cases) are compared with observations associated with both earthquake records and noise cross-correlation datasets. 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 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 locations. The seismic velocity models for southern California can be improved by adding accurate structural representations of the shallow crust and volumes around the main faults.

The significance of the study involves mainly the following aspects. First, comparisons among tested models provide an objective way for selecting an optimal velocity model for relevant applications. Second, the analyses help to identify the main limitations of current models, which is needed for future model improvements. Third, the spatial analysis of model quality provides a basis for merging tested velocity models. Although CVMS and CVMS.M01 show better overall model performance, CVMH and B2018 could be superior in certain sub-regions. Merging the best performing portions of different models can yield a regional framework that outperforms any individual model. As subsequent steps, merging multi-scale local velocity models into the combined regional model will provide a multi-scale platform that benefits from the various available velocity models.

Lu, Y., & Ben-Zion, Y. (2021, 08). Validation of seismic velocity models in southern California with full-waveform simulations. Poster Presentation at 2021 SCEC Annual Meeting.

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