HR: 1340h
AN: T23A-0570    [Abstracts]
TI: A numerical simulation of the interaction between seismic slip and frictional melting
AU: * Matsuzawa, T
EM: tmatsu@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Takeo, M
EM: takeo@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: Frictional heat generated in the faulting process causes melting of the fault rocks. This may also drastically change the mechanical property of the fault. It is often suggested that the melt plays a role of lubricant in such case. However, after the result of Tsutsumi and Shimamoto (1997), some researchers point out the possibility that the melt behaves like a brake to decelerate the slip due to the high viscosity at the beginning of melting (e.g. Fialko, 2004). We simulate the interaction between seismic slip and viscous friction of melting layer in 2-D elastic medium, numerically. We aim to simulate an earthquake from the beginning of rupture. Thus, to treat the frictional behavior as a constitutive law of friction on the fault surface, we introduce following three friction regimes. At the initial stage of rupture, frictional stress obeys a slip weakening friction law (slip weakening friction regime). We assume the boundary between moving fault surfaces is filled by fault gouge and the frictional work heats the gouge layer. Then friction regime changes into a transitional stage from slip weakening to viscous friction (transitional friction regime). In this stage, the fault surface is not fully covered by viscous material though the melting started partially in the gouge layer. Finally, when the melt fraction becomes large, the viscosity of the viscous layer (hereafter, melt layer) controls friction on the fault (viscous friction regime). For the slip weakening friction regime, we assume a slip-dependent friction law with a critical slip distance. We assume heat is generated homogeneously in the fault gouge layer, and calculate the thermal field around the fault zone. For the viscous friction regime, we estimate the frictional stress from the thickness of the melt layer, slip velocity, and melt viscosity, assuming laminar flow in the melt layer. We calculate the evolution of thickness of the melt layer and the thermal field solving Stefan problem. In this regime we assume melt viscosity is temperature dependent (Vogel equation type). For the transitional friction regime, we gradually change the frictional behavior between slip weakening and viscous friction regime as linear function of averaged temperature in the gouge layer. We simulate rupture process of an earthquake in 2-D elastic medium regarding the above regimes as a constitutive relationship of friction. In this study, 2-D anti-plane rupture is simulated by finite difference method, and rupture starts when the shear stress exceeds the peak strength. In our typical result of simulation, after the shear stress decreases at the slip weakening regime, the frictional stress increases at the transient friction regime in the case of high slip velocity. This corresponds to viscous braking stage. If the elastic medium continues to supply energy into the gouge layer, the frictional regime changes to a viscous friction, then the melt layer is heated to high temperature, and large stress drop occurs. This is a viscous lubrication stage. For example, when the gouge thickness is 2 mm, the initial stress level is 25 MPa, and the frictional stress level drops to 20 MPa at slip weakening regime, frictional stress level increases to 23 MPa at viscous braking stage. Then the seismic slip continues and finally the frictional stress level drops to 5 MPa. On the other hand, melt lubrication doesn't occur in the case of low frictional stress level. Available energy supplied from the surrounding elastic medium determines whether the subsequent viscous lubrication arises or not. This is characteristic behavior in 2- (or 3-) dimensional elastic medium.
DE: 7260 Theory and modeling
DE: 8159 Rheology--crust and lithosphere
DE: 7209 Earthquake dynamics and mechanics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting