Revisiting Evidence for Widespread Seismicity in the Upper Mantle under Los Angeles

Lei Yang, Xin Liu, & Gregory C. Beroza

Accepted November 12, 2020, SCEC Contribution #10871

We revisit the finding of widespread deep seismicity in the upper mantle imaged with a dense, temporary nodal seismic array in Long Beach, California using back-projection to detect candidate events, and trace randomization to develop a reliable imaging threshold for candidate detections. We find that nearly all detections of small events at depths greater than 20 km in the upper mantle fall below the reliability threshold. We find a modest number of small, shallower events in the crust that appear to align with the active Newport-Inglewood Fault. These events occur primarily at 15-20 km depth near the base of the seismogenic zone. Localized seismicity under fault zones is consistent with the notion that the deep extensions of active faults are localized and deforming, with stress concentration leading to a concentration of small events, near the seismic-aseismic transition.

Citation
Yang, L., Liu, X., & Beroza, G. C. (2020). Revisiting Evidence for Widespread Seismicity in the Upper Mantle under Los Angeles. Science Advances, (accepted).