Double-Couple Earthquake Source: Symmetry and Rotation

TL;DR

This paper analyzes the symmetry and rotational properties of double-couple earthquake sources, applying statistical distributions and geometric representations to better understand their orientation patterns in seismic data.

Contribution

It introduces a comprehensive statistical framework for analyzing DC earthquake focal mechanisms, incorporating symmetry considerations and rotation distributions.

Findings

Different symmetry cases lead to varying numbers of rotation transformations.

The paper discusses how to estimate rotation parameters from seismic data.

Focal mechanisms can be effectively visualized in Rodrigues vector space.

Abstract

We consider statistical analysis of double couple (DC) earthquake focal mechanism orientation. The symmetry of DC changes with its geometrical properties, and the number of 3-D rotations one DC source can be transformed into another depends on its symmetry. Four rotations exist in a general case of DC with the nodal-plane ambiguity, two transformations if the fault plane is known, and one rotation if the sides of the fault plane are known. The symmetry of rotated objects is extensively analyzed in statistical material texture studies, and we apply their results to analyzing DC orientation. We consider theoretical probability distributions which can be used to approximate observational patterns of focal mechanisms. Uniform random rotation distributions for various DC sources are discussed, as well as two non-uniform distributions: the rotational Cauchy and von Mises-Fisher. We discuss how parameters of these rotations can be estimated by a statistical analysis of earthquake source properties in global seismicity. We also show how earthquake focal mechanism orientations can be displayed on the Rodrigues vector space.