On the importance of 3D stress state in 2D earthquake rupture simulations with off-fault deformation

TL;DR

This paper demonstrates that accurately modeling the 3D stress state is crucial in 2D earthquake rupture simulations, as it significantly affects damage zone estimation and rupture dynamics, highlighting the limitations of traditional assumptions.

Contribution

The study reveals the importance of incorporating the correct 3D stress field in 2D seismic models, showing that simplified assumptions can lead to substantial inaccuracies.

Findings

Incorrect initial stress assumptions underestimate damage zone width by up to six times.

Initial stress field affects rupture propagation and off-fault deformation.

Proper 3D stress modeling is essential even in 2D earthquake simulations.

Abstract

During the last decades, many numerical models have been developed to investigate the conditions for seismic and aseismic slip. Those models explore the behavior of frictional faults, embedded in either elastic or inelastic media, and submitted to a far field loading (seismic cycle models), or initial stresses (single dynamic rupture models). Those initial conditions impact both on-fault and off-fault dynamics. Because of the sparsity of direct measurements of fault stresses, modelers have to make assumptions about these initial conditions. To this day, Anderson's theory is the only framework that can be used to link fault generation and reactivation to the three-dimensional stress field. In this work we look at the role of the three dimensional stress field in modelling a 2D strike-slip fault under plane-strain conditions. We show that setting up an incorrect initial stress field, based on Anderson's theory, can lead to underestimation of the damage zone width by up to a factor of six, for the studied cases. Moreover, because of the interactions between fault slip and off-fault deformation, initial stress field influences the rupture propagation. Our study emphasizes the need to set up the correct initial 3D stress field, even in 2D numerical simulations.