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Poster #014, SCEC Community Models (CXM)

Parsimonious velocity inversion applied to the Los Angeles Basin, CA

Jack B. Muir, Robert W. Clayton, Victor C. Tsai, & Quentin BRISSAUD
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Poster Presentation

2021 SCEC Annual Meeting, Poster #014, SCEC Contribution #11625 VIEW PDF
Effectively combining local high-resolution tomographic results with existing regional models presents an ongoing challenge. We have recently developed a framework based on the Tikhonov-regularized level-set method that provides a simple means to infer where local data provides meaningful constraints on seismic observables beyond those found in larger scale regional models --- for example the Community Velocity Models (CVMs) of southern California. This technique defines a volume within which updates are made to a reference CVM, with the boundary of the volume being part of the inversion rather than explicitly defined. By appropriately penalizing the complexity of the boundary, a minimal upd...ate which best explains the data is achieved.

To test this framework, we utilize the high-resolution data from the Community Seismic Network, a large 400-station permanent urban deployment. We inverted Love wave dispersion, derived from eikonal tomography of two-station cross-correlation travel-time delays, and relative amplification data from the Mw 6.4 July 3 and Mw 7.1 July 5 2019 Ridgecrest earthquakes. We invert for an update to CVM-S4.26 using the Tikhonov Ensemble Sampling scheme, a highly efficient derivative-free approximate Bayesian method. We find that the Ridgecrest Earthquake data is best explained by a deepening of the Los Angeles Basin (compared to the CVM-S4.26 reference model) with its deepest part just south of downtown Los Angeles, along with a substantially steeper northeastern wall of the basin. This result offers new progress towards the parsimonious incorporation of detailed local basin models within regional reference models utilizing an objective inverse-problem framework, and highlights the importance of accurate basin geometry models when accounting for the potentially significant amplification of surface waves from regional earthquakes in the high-rise building response band.