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Poster #009, SCEC Community Models (CXM)

The USGS San Francisco Bay region 3D seismic velocity model (SF-CVM) version 21.1.0: Updates for the East and North Bay and a new storage scheme for 3D Earth models

Brad T. Aagaard, & Evan T. Hirakawa
Poster Image: 

Poster Presentation

2021 SCEC Annual Meeting, Poster #009, SCEC Contribution #11252 VIEW PDF
Version 21.1.0 of the USGS San Francisco Bay Region 3D Seismic Velocity Model (SF-CVM) updates regions east and north of the San Francisco Bay and uses an improved storage scheme and query interface. This latest version revises version 08.3.0 (Aagaard et al., 2010) by assigning more appropriate velocity–depth relations to the 3D geologic model on which the seismic velocity model is based. We quantify model improvements by simulating 20 moderate earthquakes (Mw 3.7 - 4.5) using the SW4 finite-difference seismic wave propagation code. We compare synthetic ground-motions with observed motions using a set of metrics that measure waveform shape, arrival time, and cumulative energy (Hirakawa and A...agaard, in review) and attribute differences to errors in the seismic velocities along the propagation path. These metrics facilitate updating velocity-depth rule assignments because the quantities are directly related to the seismic velocities. The primary changes involve (1) assigning correct rules with corresponding corrections to the seismic velocities where geologic units appear to be mislabeled in the 3D geologic model (East Bay Hills), (2) reducing surface velocities to better fit arrival times (Livermore Basin), and (3) subdividing zones into regions with different velocity-depth rules (North Bay). The improvements in ground-motion fits are greatest in the East Bay Hills and the Livermore Basin. SF-CVM version 21.1.0 also uses a novel HDF5 storage scheme (https://geomodelgrids.readthedocs.io), which provides efficient, flexible storage and querying of 3D grid-based Earth models. The new storage scheme builds on the IRIS EMC format for seismic velocity models while supporting other types of models, a wide variety of georeferenced coordinate systems, and greater flexibility in how a model is discretized.