HR: 08:40h
AN: T21D-03 INVITED     [Abstracts]
TI: Numerical simulation of frictional melting: dependence of shear stress on viscosity
AU: * Sirono, S
EM: sirono@eps.nagoya-u.ac.jp
AF: Earth and Environmental Sciences, Nagoya University, Building E, Tikusa-ku, Nagoya, 464-8602 Japan
AU: Satomi, K
EM: satomi@dipro.co.jp
AF: Earth and Environmental Sciences, Nagoya University, Building E, Tikusa-ku, Nagoya, 464-8602 Japan
AB: Frictional melting might lead to stress drop during slippage of a fault. McKenzie and Brune (1972) investigated frictional melting as a one dimensional heat conduction problem. They concluded that if the driving stress are of the order of 1 kbar, melting could occur for fault slips as small as 1 mm. Formation of a melting layer is also observed in laboratory experiments (Tsutsumi and Shimamoto 1997, Spray 1995). Once a melting layer is formed, the thickness of the layer increases or decreases (melting or solidification, respectively) according to a heat generation rate in the layer, and shear stress is determined by the thickness and viscosity of the layer. On the other hand, the heat generation rate depends on the viscosity, which strongly depends on temperature. Therefore, we have to solve a heat conduction problem with moving boundary condition (Stefan problem). In this study, we numerically solved this problem and determined shear stress evolution after a melting layer formed. A melting layer is sandwiched between two blocks moving at a constant sliding velocity. Viscosity of a melting layer is given by $\eta(T)=\eta_0\exp(E/T)$, where $E$ is an activation energy and $\eta_0$ is a temperature independent constant. The main results are summarized as follows: 1) dependence of the shear stress on both $\eta_0$ and $E$ is small. The stress increases only by a factor of three even if $\eta_0$ is increased by five orders of magnitude. The shear stress decreases as $1/\sqrt{t}$, and an approximate formula of shear stress evolution is derived. 2) the thickness of a melting layer increases as $\sqrt{t}$ and weakly depends on the viscosity parameters. For parameters simulating gabbro, the thickness is 1 mm after 1 s slippage. Comparison with an experiment reveals importance of escaping of a melt layer. Possible effect due to fracturing is discussed. References McKenzie, D. and Brune, J. N., Melting on fault planes during large earthquakes. {\it Roy. Astron. Soc. Geophys. J.}, {\bf 29}, 65--78, 1972. Spray, J. G., Pseudotachylyte controversy: Fact or friction? {\it Geology}, {\bf 23}, 1119--1122, 1995. Tsutsumi, A., and Shimamoto, T., High-velocity frictional properties of gabbro, {\it Geophys. Res. Lett.}, {\bf 24}, 699--702, 1997.
DE: 7260 Theory and modeling
DE: 5104 Fracture and flow
DE: 5134 Thermal properties
DE: 7209 Earthquake dynamics and mechanics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting