Stability and localization of rapid shear in fluid‐saturated fault gouge: 1. Linearized stability analysis

Abstract

Field observations of major earthquake fault zones show that shear deformation is often confined to principal slipping zones that may be of order 1–100 μm wide, located within a broader gouge layer of order 10–100 mm wide. This paper examines the possibility that the extreme strain localization observed may be due to the coupling of shear heating, thermal pressurization, and diffusion. In the absence of a stabilizing mechanism shear deformation in a continuum analysis will collapse to an infinitesimally thin zone. Two possible stabilizing mechanisms, studied in this paper, are rate‐strengthening friction and dilatancy. For rate‐strengthening friction alone, a linear stability analysis shows that uniform shear of a gouge layer is unstable for perturbations exceeding a critical wavelength. Using this critical wavelength we predict a width for the localized zone as a function of the gouge properties. Taking representative parameters for fault gouge at typical centroidal depths of crustal seismogenic zones, we predict localized zones of order 5–40 μm wide, roughly consistent with field and experimental observations. For dilatancy alone, linearized strain rate perturbations with a sufficiently large wavelength will undergo transient exponential growth before decaying back to uniform shear. The total perturbation strain accumulated during this transient strain rate localization is shown to be largely controlled by a single dimensionless parameter E, which is a measure of the dilatancy of the gouge material due to an increase in strain rate.

The importance of Thermo-Hydro-Mechanical couplings and microstructure to strain localization in 3D continua with application to seismic faults. Part II: Numerical implementation and post-bifurcation analysis

“…In this paper, a quasi-static analysis is conducted and therefore, no 550 maximum in the LSA is observed in this case. Therefore, in the following, the shear band thickness obtained in the LSA is evaluated as in Rice et al (2014).…”

Frictional heating lubrication for submarine landslide

“…Thermopressurization weakening (TPW) mechanism has been studied for years in fault mechanics, particularly the gouge friction in the shear zone of faults (Segall and Rice 1995;Garagash and Rudnicki 2003;Rempel and Rice 2006;Rice 2006;Urata et al 2013;Rice et al 2014;Suzuki and Yamashita 2014). Such a highly localized shear layer has a thickness often on the order of centimeters, millimeters, or smaller, nested within the fault core (Rice 2006;Rice et al 2014).…”

“…Such a highly localized shear layer has a thickness often on the order of centimeters, millimeters, or smaller, nested within the fault core (Rice 2006;Rice et al 2014). It has been widely accepted that during the rapid shear of a fluid-saturated fault, the friction in the shear zone can cause an increase of temperature (called as "frictional heating"), which can induce a rise of excess pore pressure there.…”

Thermal and chemical effects in shear and compaction bands

“…Although strain localization in the form of shear band formation can occur with negative or positive rate of strain hardening, softening behaviour definitely favours shear banding (Rudnicki & Rice, 1975, Vardoulakis & Sulem, 1995. This softening behaviour may correspond to a mechanical degradation of the rock properties (microcracking, grain crushing and grain size reduction…), but various other physical processes can be responsible for it (Das et al, 2011).…”

“…As emphasized by Rice et al (2014) the width of the deforming zone is a key parameter, as narrow deforming zones concentrate the frictional heating, which leads to large temperature rises and thus to more rapid weakening. The width of the deforming zone is determined by the various physical processes involved in the above weakening mechanisms but it also controls the multi-physics couplings which occur during dynamic slip.…”