Poster #114, Stress and Deformation Over Time (SDOT)

A Refined Comprehensive Earthquake Focal Mechanism Catalog for Southern California Derived with Deep Learning Algorithms

Yifang Cheng, Zachary E. Ross, Egill Hauksson, & Yehuda Ben-Zion
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Poster Presentation

2021 SCEC Annual Meeting, Poster #114, SCEC Contribution #11306 VIEW PDF
Earthquake focal mechanisms are primary data for analyzing fault zone geometry, sense of slip, and the crustal stress field. Solving for the focal mechanisms of small earthquakes is challenging because phase arrivals and first-motions are hard to separate from noise. To overcome this challenge, we implement CNN algorithms (Ross et al., 2018a, b) to detect additional phases and polarities for the focal mechanism calculations. Using both existing and these new data we build a high-quality focal mechanism catalog for 696,568 events that occurred from 1981 to 2019 in southern California with the HASH method of Hardebeck and Shearer (2002, 2003). The new focal mechanism catalog is overall consist...ent with the standard catalog (Yang et al., 2012) but with 42% more solutions and is more consistent with the moment tensor solutions derived using waveform-fitting methods. The new catalog makes it possible to identify a strong stress rotation in the Sierra Cucapah after the 2010 Mw7.2 El Mayor Cucapah earthquake, a significant positive correlation between the net production rate and the percentage of reverse faulting events in the Salton Sea Geothermal Field, as well as more near-vertical active faults near the southern San Andreas fault zone. Furthermore, the high-resolution catalog will contribute to future detailed studies of the crustal stress field, earthquake triggering mechanisms, and fault zone geometry and sense of slip in southern California.