Spontaneous dynamic rupture propagation with thermal pressurization: Phase transitions of pore fluid
Abstract
In 3-D numerical simulations of spontaneous dynamic ruptures with thermal pressurization (TP), we considered changes in physical properties of pore water owing to its phase transitions, and investigated the effects. Our preliminary numerical simulations without processes of the phase transitions predicted that frictional heating and TP are likely to change liquid pore water into supercritical pore water (Urata et al., ASC 2010). If the phase transition occurs, viscosity, compressibility, and thermal expansion of water can change by a few orders of magnitude, which can affect strength of TP itself. In this study, we performed numerical simulations of dynamic ruptures with TP, taking into account changes in the physical properties owing to the phase transitions. Our numerical algorithm is based on the finite-difference method by Kase and Kuge (2001). Pore pressure and temperature are calculated by the 1-D diffusion equations including frictional heating. The physical properties of water, which vary with pore pressure and temperature, are calculated by using PROPATH*). These affect the diffusion process of pore fluid. We put a square fault with the length of 2 km in an infinite medium. Initial values of stresses, pore pressure, and temperature are uniform, corresponding to conditions at a depth of 3 km (Case 1) and 6 km (Case 2). We examined the shear zone thickness w of 1, 2, 5, and 20 cm. When w=1 cm in Case 1 and w≤5 cm in Case 2, the pore water changes to supercritical water. The changes in the physical properties owing to the phase transition have two opposite effects on TP. One of the effects is suppression of a rise in pore pressure from temperature increase, and the other is decrease in hydraulic diffusivity. Except Case 2 with w of 1 cm, the two effects cancel out each other, and thus the changes in the physical properties have almost no effect on dynamic rupture propagation. In Case 2 with w of 1 cm, on the other hand, the changes in the physical properties suppress total slip amount, although the changes hardly affect time evolution of rupture front. *)PROPATH Group, PROPATH: A Program Package for Thermophysical Properties, version 13.1, 2008.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.T13A2351U
- Keywords:
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- 7209 SEISMOLOGY / Earthquake dynamics