Improved stress drop estimates for M 1.5 to 4 earthquakes in Southern California from 1996 to 2019

Peter M. Shearer, Rachel E. Abercrombie, & Daniel T. Trugman

Published August 15, 2021, SCEC Contribution #11455, 2021 SCEC Annual Meeting Poster #218

We estimate stress drops for over 70,000 southern California earthquakes from 1996 to 2019 using a P-wave spectral decomposition approach. Based on our recent work documenting hard-to-resolve tradeoffs between absolute stress drop, stress-drop scaling with moment, high-frequency fall-off rate, and empirical corrections for path and attenuation terms, we adopt a new approach in which the corner frequencies of the smallest earthquakes in each region are fixed to a constant value. This removes any true coherent spatial variations in stress drops among the smallest events but ensures that any spatial variations seen in larger event stress drops are real and not an artifact of inaccurate path corrections. Applying this approach across southern California, we document spatial variations in stress drop that agree with previous work, such as lower-than-average stress drops in the Salton Trough, as well as small-scale stress-drop variations along many faults and aftershock sequences. These results provide new insights into many longstanding questions, such as: (1) Does median stress drop scale with moment? (2) Does median stress drop increase with depth? (3) Are small-event stress drops predictive of nearby larger earthquake stress drops? (4) Do aftershock sequences typically have lower median stress drops than their mainshocks? (5) Do earthquake stress drops vary systematically with distance from major faults?

Key Words
earthquake stress drop, P-wave spectra

Shearer, P. M., Abercrombie, R. E., & Trugman, D. T. (2021, 08). Improved stress drop estimates for M 1.5 to 4 earthquakes in Southern California from 1996 to 2019. Poster Presentation at 2021 SCEC Annual Meeting.

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