Strain localization driven by thermal decomposition during seismic shear

John D. Platt, N. Brantut, & James R. Rice

Submitted 2014, SCEC Contribution #1965

Field and laboratory observations show that at seismic slip rates shear deformation is often extremely localized, with a typical deforming zone width on the order of a few tens of microns. This extreme localization can be easily understood in terms of thermally driven weakening mechanisms such as thermal pressurization and thermal decomposition. A zone of initially high strain rate will experience more shear heating and thus weaken faster, making it more likely to accommodate future deformation. Rice et al. [2014] and Platt et al. [2014] showed how a combination of analytic and numerical methods could be used to predict the localized zone thickness when dynamic weakening is controlled by thermal pressurization, finding localized zone thicknesses between 4 and 44 microns for representative fault gouge parameters. In this paper we extend that work to account for thermal decomposition. A linear stability analysis predicts a localized zone thickness that is tested using numerical simulations. We investigate how the onset of thermal decomposition drives additional strain localization, how the endothermic thermal decomposition reaction and thermal diffusion combine to limit the maximum temperature, and how the pore fluid released by the reaction accelerates dynamic weakening.

Citation
Platt, J. D., Brantut, N., & Rice, J. R. (2014). Strain localization driven by thermal decomposition during seismic shear. Journal of Geophysical Research: Solid Earth, (submitted).