Seismic and aseismic fault growth lead to different fault orientations

Abstract

Orientations of natural fault systems are subject to large variations. They often contradict classical Andersonian faulting theory as they are misoriented relative to the prevailing regional stress field. This is ascribed to local effects of structural or stress heterogeneities and reorientations of structures or stresses on the long-term. To better understand the relation between fault orientation and regional stresses, we simulate spontaneous fault growth and its effect on the stress field. Our approach incorporates earthquake rupture dynamics, visco-elasto-plastic brittle deformation and a rate-and state- dependent friction formulation in a continuum mechanics framework. We investigate how strike slip faults orient according to local and far-field stresses during their growth. We identify two modes of fault growth, seismic and aseismic, distinguished by different fault angles and slip velocities. Seismic fault growth causes a significant elevation of dynamic stresses and friction values ahead of the propagating fault tip. These elevated quantities result in a greater strike angle relative to the maximum principal regional stress than that of a fault segment formed aseismically. When compared to the near-tip time-dependent stress field the fault orientations produced by both growth modes follow Anderson’s classical faulting theory. We demonstrate how the two types of fault growth may be distinguished in natural faults by comparing their angles relative to the original regional max- imum principal stress. A stress field analysis of the Landers-Mojave fault suggests thatan angle greater than approximately 25° between two faults indicates seismic fault growth.

Seismic and Aseismic Fault Growth Lead to Different Fault Orientations

“…It takes ∼5 s from the nucleation of the event in the center until two rupture fronts reach the fault tips that were formed in stage S1. During this process, V max increases approximately by a factor of 5 (from 0.012 to 0.058 m/s), which results in the generation of shear and pressure waves as shown in the video in the supporting information and in the repository for this publication (Preuss et al, ). As the rupture reaches the old fault tip of stage S1, the fault starts to bend and the fault angle β increases.…”

“…Red star indicates the 1992 Landers earthquake (section 4.1.1). Here we assume a static friction of 0.6. supporting information and in the repository for this publication (Preuss et al, 2019). As the rupture reaches the old fault tip of stage S1, the fault starts to bend and the fault angle increases.…”

“…The repository cited in the references (Preuss et al, 2019) contains an executable, with which the reference model can be rerun. Figures 2-10 of this paper can thus be reproduced.…”

“…A video showing the temporal evolution of the fault and also the generation of shear and pressure waves is in the repository of this paper (Preuss et al, 2019) and can be found under this link.…”

Deep Ductile Shear Zone Facilitates Near‐Orthogonal Strike‐Slip Faulting in a Thin Brittle Lithosphere

“…In particular, Preuss et al. (2019) show that the fault angle grows differently during quasi‐static nucleation and dynamic rupture.…”