Aftershock Moment Tensor Scattering

Abstract

Coseismic rotations of principal stress axes can provide insights into the strength of the crust, but it is unclear how common this phenomenon is. We use a nearest-neighbor clustering algorithm to identify earthquake sequences in the global ISC-GEM catalog and the regional Southern California catalog. Using an inner-product-based pairwise measure of moment tensor similarity, we demonstrate that, in both catalogs, aftershocks are less similar to their respective mainshocks than foreshocks are. We interpret this effect, which we call moment tensor scattering, as evidence for widespread coseismic stress rotations. Moment tensor scattering is observable for a broad range of mainshock magnitudes in both catalogs. We further demonstrate that mainshock-aftershock similarity recovers logarithmically to pre-mainshock levels on decadal timescales. We conclude that moment tensor scattering is a generally observable feature of seismic sequences which may be useful in future work to discriminate between models of crustal strength.

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