Full Waveform Inversion Tomography of Central and Northern California

Arthur J. Rodgers, & Claire D. Doody

Published September 8, 2024, SCEC Contribution #13880, 2024 SCEC Annual Meeting Poster #042

We present work-in-progress toward a new tomographic model of the seismic wavespeeds of Central and Northern California derived from full waveform inversion (FWI). Our domain spans the Pacific-North America plate boundary from the creeping section of the San Andreas Fault in central California along the northern San Andreas Fault, north of the Mendocino Triple Junction to Oregon and the Pacific Ocean to the western Nevada (Walker Lane). We selected moderate earthquakes (moment magnitude MW 4.5 – 6.0) and openly available broadband waveforms from various networks. We started with a simple 1D model that honors low shear wavespeeds in the upper crust and the laterally variable Moho. Using a multiscale inversion approach, we started inversions with long periods and reduced the minimum period in several stages, each with fixed period band, data windows and smoothing parameters. The resulting model reveals strong lateral heterogeneity of shear and compressional wavespeeds, Vs and Vp, respectively, across the region. Low wavespeeds are seen in the upper crust of Central Valley with strongest low Vs in the Sacramento-San Joachim Delta, corresponding with sedimentary deposits. The Sierra Nevada reveals higher Vs in the upper and middle crust corresponding with Nevada Orogeny. Mid-crustal and uppermost mantle structure reveals low Vs in the Clear Lake Volcanic Field corresponding to the Gorda slab window. The new model with its large domain will be useful for earthquake source characterization (e.g., moment tensor inversions; finite fault inversions) and large magnitude scenario earthquake ground motion simulations.

Key Words
Full Waveform Tomography, Ground Motion Simulation

Citation
Rodgers, A. J., & Doody, C. D. (2024, 09). Full Waveform Inversion Tomography of Central and Northern California. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology