HR: 1340h
AN: G13A-0784    [Abstracts]
TI: Temporal Clustering of Earthquakes due to Stress Transfer in Viscoelastic Layers
AU: * DiCaprio, C J
EM: dicaprio@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., MS 252-21, Pasadena, CA 91125 United States
AU: Simons, M
EM: simons@caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., MS 252-21, Pasadena, CA 91125 United States
AU: Kenner, S J
EM: skenner@uky.edu
AF: University of Kentucky, 101 Slone Building, Lexington, KY 40506 United States
AU: Williams, C A
EM: willic3@rpi.edu
AF: Rensselaer Polytechnic Institute, 110 8th St., JSC 1W19, Troy, NY 12180 United States
AB: Postseismic processes can have a significant effect on the reloading rate of the seismogenic portion of active faults. As a result, the rheology of the non-seismogenic lower crust and mantle lithosphere may play a role in determining earthquake recurrence times. Previously, \emph{Kenner and Simons} (2004) used a one dimensional spring-dashpot-slider analogue model to investigate fault reloading due to viscous relaxation. They found that the system's behavior was controlled by a non dimensional number called the Wallace number, \emph{W}. \emph{W} is equal to the average earthquake stress drop divided by the product of the applied geologic strain rate and the effective viscosity of the system. In the presence of a small amount of normally distributed environmental noise, temporal clustering of earthquakes was observed when \emph{W} was high. To study a more physical system we expand the model beyond a one-dimensional analogue. When more than one viscoelastic layer is present, the effective viscosity of the entire system is a function of both the thicknesses and the viscosities of the viscoelastic layers. We use a two-dimensional, out-of-plane finite element model of an infinite strike slip fault. The model consists of an elastic layer over one or more Maxwell viscoelastic layers. A far-field, constant velocity boundary condition drives the interseismic strain accumulation. The seismogenic portion of the fault is allowed to slip freely and instantaneously when its yield stress is exceeded. When this occurs, stress accumulated on the seismogenic fault is shed to the viscoelastic layers below; in this way, the relaxation time of the viscoelastic layers effects the stress reloading rate of the seismogenic fault. This stress is then recycled back to the seismogenic fault as the lower layers relax. The two-dimensional finite element model exhibits the same clustering behavior and dependence on \emph{W} as the spring-dashpot-slider analogue model. We determine the dependence of the effective viscosity on the thicknesses of the viscoelastic layers. \section*{References} Kenner, S.J. and Simons, M., 2004. Temporal cluster of major earthquakes along individual faults due to postseismic reloading, \emph{Geophysical Journal International}, submitted.
DE: 8123 Dynamics, seismotectonics
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
DE: 3210 Modeling
DE: 3230 Numerical solutions
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting