Evaluation and Adjustments of the USGS San Francisco Bay Area Velocity Model: Special Focus on the East Bay

Evan T. Hirakawa, & Brad T. Aagaard

Submitted August 15, 2019, SCEC Contribution #9775, 2019 SCEC Annual Meeting Poster #313

The current version of the USGS Bay Area Velocity Model is a 3D representation of the seismic velocity structure in the San Francisco Bay region. The model has been shown to successfully reproduce many aspects of ground motion and wave propagation from local earthquakes. Still, some users have noted that there are regions in the model that should be investigated for improvement. Here, we present an exercise to evaluate and adjust the model in a subregion centered around the East Bay. Our final model significantly improves arrival times and cumulative kinetic energy of the synthetic waveforms in comparison with synthetic waveforms generated with the current version of the velocity model.
We use SW4, a fourth order finite-difference code, to simulate wave propagation from eight Mw 3.6-4.2 earthquakes in the East Bay. The synthetic seismograms obtained are compared with observed motions at 50-100 strong motion stations located within about 40 km of the earthquake epicenters. We judge similarity between synthetic and observed motions by measures of arrival time difference and energy mismatch. Special attention is paid to the velocity structure in the area immediately east of the Hayward Fault in the Berkeley Hills. First, some questionable features in the current version of the model are addressed and modified. Then, several variations of the model are generated by adjusting velocities assigned to particular geologic units. The evaluation procedure indicates which variation best represents the true velocity structure by the chosen metrics.

Key Words
velocity model, San Francisco Bay Area

Citation
Hirakawa, E. T., & Aagaard, B. T. (2019, 08). Evaluation and Adjustments of the USGS San Francisco Bay Area Velocity Model: Special Focus on the East Bay. Poster Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
SCEC Community Models (CXM)