HR: 10:35h
AN: S12B-02 INVITED    [Abstracts]
TI: Thermal Pressurization is Significant During Earthquake Nucleation, Before Seismic Slip
AU: * Schmitt, S V
EM: schmitt@stanford.edu
AF: Department of Geophysics Stanford University, 397 Panama Mall, Stanford, CA 94305, United States
AU: Segall, P
EM: segall@stanford.edu
AF: Department of Geophysics Stanford University, 397 Panama Mall, Stanford, CA 94305, United States
AU: Matsuzawa, T
EM: tkmatsu@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, 305-0006, Japan
AB: Shear heating-induced thermal pressurization has long been invoked as a potential weakening mechanism during earthquakes. It is often assumed that thermal pressurization does not become important until earthquakes have reached a critical size. Segall and Rice [2006], however, suggested that thermal effects may become dominant during the quasi-static nucleation phase, well before inertial effects are significant. By neglecting the feedback between pore-pressure change and slip rate, they estimated that thermal pressurization dominates weakening at slip rates in excess of 10^-5 to 10^-3 m/s. We further explore this problem numerically assuming a planar fault in a 2D elastic medium and accounting for full thermo-mechanical coupling. We include one-dimensional thermal and pore pressure diffusion normal to a fault governed by rate-state friction. Stress rate and fault slip rate are related through a Hilbert transform in the Fourier domain, and the thermal diffusion is computed with an explicit finite difference formulation. For uniform thermal and hydraulic properties, the pore pressure and temperature on the fault are uniquely related [Rice, 2006, JGR], so only one finite difference grid is required in this limit. As the slip rate increases, the temperature gradient adjacent to the fault increases dramatically. We refine the finite difference grid when the error in the spatial derivative exceeds a specified threshold. The radiation damping approximation is used to simulate inertial effects. For a hydraulic diffusivity of 10^-6 m²/s---consistent with permeability inferred for some active fault zones-- -we find that results with and without thermal coupling diverge at slip rates substantially less than those estimated by Segall and Rice [2006]. This reinforces the conclusion that thermal pressurization cannot be ignored in earthquake nucleation. For calculations with the aging form of the state evolution equation and a/b = 1/3, the nucleation zone contracts to a smaller size than Dieterich's [1992] result, which ignored thermal effects.
DE: 0545 Modeling (4255)
DE: 7209 Earthquake dynamics (1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Seismology [S]
MN: 2007 Fall Meeting