A Numerical Study on the Effects of Heterogeneity, Anisotropy, and Station Coverage on the Compensated Linear Vector Dipole Component of Deep Earthquake Moment Tensors

TL;DR

This study uses 3D elastic modeling and inversion to evaluate whether heterogeneity, anisotropy, or station coverage can explain non-double-couple components in deep earthquake moment tensors, concluding that near-source anisotropy is the primary cause.

Contribution

The paper demonstrates through modeling that near-source anisotropy, not heterogeneity or station coverage, explains the non-DC components in deep earthquake radiation patterns.

Findings

Heterogeneity and station coverage do not cause non-DC components.

Strong near-source S-wave anisotropy explains observed non-DC patterns.

Modeling supports anisotropy as the primary factor in deep earthquake radiation.

Abstract

The moment tensors of a large portion of deep earthquakes show apparent non-double-couple (non-DC) components. Previously, the observed apparent non-DC values in deep earthquakes have been attributed to different mechanisms such as complex source processes or complicated source medium structures. In this paper, we focused on evaluating the second mechanism. We investigated the effect of slab heterogeneity, supra-slab anisotropic structure, intra-slab weakly anisotropic structure (e.g., the purported existence of the metastable olivine wedge), and non-uniform station coverage, on the non-DC radiation patterns of deep earthquakes using our 3-dimensional elastic finite-difference modeling and full-waveform inversion of moment tensors. We found that these investigated issues cannot cause the observed non-double-couple radiation patterns and the in-situ structure with strong S-wave anisotropy near to the earthquake focus is the simplest way to account for the apparent non-DC components in the radiation patterns of deep earthquakes.