Fault orientation in damage failure under compression

TL;DR

This study challenges the traditional use of the Mohr-Coulomb criterion for predicting fault orientations in geosciences, showing that actual fault angles are governed by the most unstable damage mode and are influenced by microstructural disorder.

Contribution

It introduces a damage model that reveals fault orientations are not dictated by Mohr-Coulomb but by the most unstable damage mode, considering microstructural disorder.

Findings

Fault orientation differs from Mohr-Coulomb predictions.

Microstructural disorder influences fault angles.

Most unstable damage mode determines fault orientation.

Abstract

The Mohr-Coulomb criterion is widely used in geosciences to relate the state of stress at failure to the observed orientation of the resulting faults. This relation is based on the assumption that the fault occurs along a plane that maximizes the Coulomb stress. Here, we test this hypothesis using an elastic, progressive damage model that implements the Mohr-Coulomb criterion at the local scale. We find that the orientation of the fault is not given by the Mohr-Coulomb criterion. Instead, for minimal disorder, it corresponds to the most unstable mode of damage in the model, which we determine through a linear stability analysis of the homogeneously damaged state. Our simulations show that microstructural disorder significantly affects the orientation of the fault, which, however, remains always far from the Mohr-Coulomb prediction.