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Detailed Investigation of the Foreshock Sequence of the 2010 Mw 7.2 El Mayor-Cucapah Earthquake

Dongdong Yao, Yihe Huang, Zhigang Peng, & Raul R. Castro

Published June 3, 2020, SCEC Contribution #10030

Foreshocks can provide valuable information about possible nucleation process of a mainshock. However, their physical mechanisms are still under debate. In this study, we present a comprehensive analysis of the earthquake sequence preceding the 2010 Mw 7.2 El Mayor-Cucapah mainshock, including waveform detection of missing smaller events, relative relocation and source parameter analysis. Based on a template matching method, we find a tenfold increase in the number of earthquakes than reported in the Southern California Seismic Network (SCSN) catalog. The entire sequence exhibits nearly continuous episodes of foreshocks that can be loosely separated into two active clusters. Relocated foreshocks show several seismicity streaks at depth, with a consistently active cluster at depths between 14-16 km where the mainshock was nucleated. Stress drop measurements from a spectral ratio approach based on empirical Green’s functions show a range between 3.8 MPa and 41.7 MPa with a median of 13.0 MPa, and no clear temporal variations. The relocation results, together with the source patches estimated from the corner frequencies, revealed a migration front towards the mainshock hypocenter within last 8 hours and a chain of active burst immediately 6 minutes prior to the mainshock. Our results support combined effects of aseismic slip and cascading failure on the evolution of foreshocks.

Yao, D., Huang, Y., Peng, Z., & Castro, R. R. (2020). Detailed Investigation of the Foreshock Sequence of the 2010 Mw 7.2 El Mayor-Cucapah Earthquake. Journal of Geophysical Research: Solid Earth, 125(6). doi: 10.1029/2019JB019076.