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Stress-Strain Characterization of Seismic Source Fields 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: 02:15 PM Pacific

Description: 

Earthquake ruptures and seismic sequences can be very complex, involving slip in various directions on surfaces of variable orientation. How is this geometrical complexity in seismic energy release, here called mechanism complexity, governed by tectonic stress? We address this question by formulating a probabilistic model for the distribution of double couples consistent with three assumptions commonly used in regional stress inversions: the tectonic stress is constant, slip vectors are aligned with the maximum shear traction in the plane of slip, and higher shear stress promotes more seismic energy release. We characterize the moment-tensor field of a stress-aligned source process by an ordered set of principal-stress directions, a differential stress ratio R, and a strain-sensitivity parameter κ. The latter governs the dependence of the seismic moment density on the shear-traction magnitude and therefore parameterizes the seismic strain response to stress. The stress-strain characterization (SSC) parameters are determined by moment measures of mechanism complexity that can be observed in large earthquakes and seismic sequences. These moment measures are the ratio of the Aki moment to the total moment and the total-moment fractions partitioned by the projection of the moment-tensor field onto an orthonormal basis of five deviatoric source mechanisms. We construct this basis to be stress-oriented by choosing its leading member to be the centroid moment tensor (CMT) mechanism and three others to represent orthogonal rotations of the CMT mechanism about its principal axes. From the projections of the stress-aligned field onto this stress-oriented basis, we derive explicit expressions for the moment-fraction integrals as functions of R and κ. The SSC model provides a theoretical foundation for the stress-strain characterization of any moment-tensor field, including earthquake stress gluts, fault-zone seismicity, and seismic sequences (Juarez & Jordan, this meeting).

Presenting Author: Thomas H. Jordan

Student Presenter: No

Authors