HR: 1340h
AN: S43A-1057    [Abstracts]
TI: Thermo-hydraulic effects on anti-plane dynamic shear rupture in porous media
AU: * Suzuki, T
EM: suzutake@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Yamashita, T
EM: tyama@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: We theoretically study thermo-hydraulic effects on dynamic earthquake rupture. We consider one-dimensional (1D) and two-dimensional (2D) anti-plane shear fracture models. The treatment of a porous medium is based on the work of Pride et al. [1992]. Heat generated by friction is assumed to be distributed over a certain zone which has a constant width. Two types of non-linear feedback among changes in temperature, fluid pressure and fault slip are shown to play important roles in the rupture dynamics; the fault slip behavior is significantly dependent on which feedback is more predominant. It is also shown that one of the feedbacks is sometimes transformed into the other because the feedback mechanism is non-linear. This nonlinearity causes the system behavior of our model largely different from the expectation from the Griffith crack model. The slip-weakening behavior and gradual slip onset observed in our model are clearly related to the feedback mechanism. We derive the approximate solution for the slip-weakening distance in a simple form in 1D model, and find that its value is comparable to seismological estimates. We assume that the crack tip growth is bilateral with a constant velocity and is arrested abruptly when the crack length exceeds a certain length in 2D model. We find that the fault slip duration is, in general, longer than expected from the classical Griffith crack model. It is also found that smaller-size ruptures tend to have smaller static stress drop averaged over the crack surface, which is consistent with some seismological observations. These two findings are closely associated with the increase in the stress drop due to the fluid-pressure build-up with ongoing fault slip. Our simulations suggest that scaling relation between small- and large-size earthquakes are rather complicated because of thermo-hydraulic effects. Our simulation also shows that the temperature rise is rather below the melting temperature of rocks if the rate of fluid outflow from the heated fault zone is relatively low; this was also found by Lachenbruch [1980] and Mase and Smith [1987]. This finding suggests that field observation of few pseudotachylytes is the consequence of relatively low permeability in a porous fault zone.
DE: 5114 Permeability and porosity
DE: 5134 Thermal properties
DE: 7209 Earthquake dynamics (1242)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: Fall Meeting 2005