Stability and Localization of Rapid Shear in Fluid-Saturated Fault Gouge, 1. Linearized stability analysis

James R. Rice, John Rudnicki, & John D. Platt

Published 2014, SCEC Contribution #1825

Field observations of major earthquake fault zones show that
the majority of shear deformation is confined to principal slipping zones that may be of order 10 - 100 microns 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. As noted in Rice [2006], in the absence of a stabilizing mechanism shear deformation in a continuum analysis will collapse to an infinitesimally thin zone. Two such 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 microns wide, roughly con-
sistent with field and experimental observations. For dilatancy alone, linearized strain rate perturbations with a suciently 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 parameter dimensionless parameter E, which is a measure of the dilatancy of the gouge material
due to an increase in strain rate.

Citation
Rice, J. R., Rudnicki, J., & Platt, J. D. (2014). Stability and Localization of Rapid Shear in Fluid-Saturated Fault Gouge, 1. Linearized stability analysis. Journal of Geophysical Research: Solid Earth, 119. doi: 10.1002/2013JB010710.