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Stress-Strain Characterization of Seismic Sequences in Southern California Using Moment Measures of Mechanism Complexity

Session: Crustal Stress and Strain and Implications for Fault Interaction and Slip II

Type: Oral

Date: 4/22/2021

Presentation Time: 02:30 PM Pacific

Description: 

We develop a probabilistic model for characterizing stress and strain fields using mechanism complexity measures derived from moment tensor fields. Distributions of source mechanisms in seismic sequences and earthquake ruptures are used to estimate the ratio of the Aki moment to the total moment and the moment partitioning of the moment tensor field over an orthonormal basis of five deviatoric mechanisms. These complexity measures are then used to estimate the principal-stress directions, a differential stress ratio (R), and a strain-sensitivity parameter (κ). Larger values of κ indicate higher sensitivity to stress magnitude and thus lower complexity. We apply the model to characterize the stress and strain fields of seismic sequences in Southern California. Temporal monitoring of San Jacinto Fault seismicity from 1981-2019 does not reveal any significant changes in the principal stress orientation; during this period, R=0.42±0.1, and κ=5.5±2. The seismicity associated with El Mayor-Cucapah earthquake of 2010 shows a relatively low complexity before the mainshock (κ=10.5±4.6) and higher complexity during the aftershock sequence (κ=5±2.5), suggesting that the stress change during the mainshock promoted fault ruptures with more diverse orientations. In contrast, the seismicity before the Ridgecrest earthquake of 2019 shows a relatively high complexity (κ=3.5±2), while the aftershocks show less complexity (κ=6±2), indicating that the aftershocks are more aligned with the mainshock mechanisms and have less complexity than the background seismicity.

Presenting Author: Alan Juarez

Student Presenter: Yes

Authors