HR: 0830h
AN: NG41B-0064    [PDF]
TI: Model of Dynamical Slip Events and the Generation of Propagating Slip Pulses
AU: * El Khoury, J E
EM: elkhoury@ess.ucla.edu
AF: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095 United States
AU: Knopoff, L
EM: knopoff@physics.ucla.edu
AF: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095 United States
AB: We describe a new model for the simulation of extended dynamical slip events and for the rapid calculation of the Statistical properties of repeated model seismicity events. The fault model generates 2-D in-plane dynamical ruptures. The discretization involves first- and second-nearest neighbors, is of Burridge-Knopoff type and is isotropic in both compression and shear properties. All rupture events are causal and numerical oscillations in slip velocity at crack tips due to discretization are minimized. The computational speed is fast in comparison with 3-D models; in sample tests of statistical compilations, $10^5$ events can be simulated in about 1.5 hours on a contemporary PC. We use the model to study growth and healing of individual faults in an effort to understand the formation of propagating slip pulses. We consider an elongated rectangular model fault in which the upper surface is free and the lower boundary is rigid. The rupture velocities of fractures with homogeneous stress drop equal to the strength, are the P-wave velocity in the direction of the prestress and the S-wave velocity in the perpendicular direction. Two mechanisms for generation of isolated rupture pulses have been proposed, which are 1) an increase in the dynamical friction with decelerating slip and 2) encounter with elongated regions of large difference between the threshold fracture stress and the prestress. We have identified a third mechanism which is that of a velocity dependent friction that operates equally on the phases of increasing and decreasing slip velocities and has a characteristic length scale. This frictional mechanism is a parameterization of the absorption of near-fault fracture energy in large earthquakes during the formation of aftershock zones. Pulses develop due to the influence of stress waves reflected from the rigid bottom boundary of the seismogenic slab. In general, crack fracture speeds are controlled by excess of strength over stress drop; if it is too large, the crack stops. For given boundary conditions, slip velocities are higher where prestresses are higher. Isolated slip pulses have small static slips and rise times for small thicknesses of the seismogenic zone and for large values of the near-fault absorption.
DE: 3210 Modeling
DE: 3220 Nonlinear dynamics
DE: 3230 Numerical solutions
DE: 7209 Earthquake dynamics and mechanics
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting