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Authors: Bizzarri, A.* 
Cocco, M.* 
Title: A thermal pressurization model for the spontaneous dynamic rupture propagation on a 3–D fault: Part II – Traction evolution and dynamic parameters
Issue Date: 3-Jun-2005
Keywords: Thermal pressurization
Frictional heating
Subject Classification04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics 
Abstract: We investigate the dynamic traction evolution within the cohesive zone during the spontaneous propagation of a 3–D earthquake rupture governed by slip weakening or rate- and state-dependent constitutive laws and accounting for thermal pressurization effects. The analytical solutions as well as temperature and pore pressure evolutions are discussed in a companion paper (Bizzarri and Cocco, 2005b). Our numerical experiments reveal that frictional heating and thermal pressurization modifies traction evolution. The breakdown stress drop, the characteristic slip weakening distance and the breakdown work (i.e., fracture energy) depend on the slipping zone thickness (w) and hydraulic diffusivity ( ω). Thermally activated pore pressure changes caused by frictional heating yield temporal variations of the effective normal stress acting on the fault plane. In the framework of rate- and state-dependent friction, these thermal perturbations modify both the effective normal stress and the friction coefficient. Breakdown stress drop, slip weakening distance and specific breakdown work (J/m 2 ) increases for decreasing values of hydraulic diffusivity and slipping zone thickness. We propose scaling relations to evaluate the effect of w and ω on these physical parameters. We have also investigated the effects of choosing different evolution laws for the state variable as well as the porosity evolution during the breakdown time. Our simulations point out that thermal pressurization modifies the shape of the traction evolution as a function of slip. For particular configurations, the traction versus slip curves display a gradual and continuum weakening for increasing slip: in these cases, the definition of a minimum residual stress and the slip weakening distance become meaningless.
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