HR: 16:30h
AN: S14B-03    [Abstracts]
TI: Asymmetric pulse-like rupture at bimaterial interface with slip-weakening friction model
AU: * Dalguer, L A
EM: ldalguer@moho.sdsu.edu
AF: Geological Sciences, SDSU, 5500 Campanile Dr, San diego, CA 92182, United States
AU: Day, S M
EM: day@moho.sdsu.edu
AF: Geological Sciences, SDSU, 5500 Campanile Dr, San diego, CA 92182, United States
AB: Under some circumstances, pulse-like rupture propagation at a bimaterial interface becomes strongly asymmetric, and can be characterized as unilateral in the sense that slip diminishes and eventually dies out in one direction while growing unstably in the other. Pulse-like ruptures capable of this mode of evolution can sometimes be induced for inplane (2D) models with strongly velocity-weakened friction (Ampuero and Ben-Zion, 2007), but have not been seen for 2D slip-dependent friction models (e.g., Harris and Day, 1997). However, we have found that 3D effects (leading to pulse-like rupture) can induce the strongly asymmetric rupture mode even with purely slip-weakening friction. In the slip-weakening case, rupture of faults much longer than their down-dip width initially develops in a crack-like, bilateral mode, and subsequently (due to stopping phases from the top and bottom edges) evolves into two separate slip pulses traveling in opposite directions (e.g., Day, 1982). Under a restricted range of initial conditions, when the fault is at a bimaterial interface (we have so far investigated wavespeed contrasts of ~20%), the slip pulse in the preferred direction propagates indefinitely, while the one in the non-preferred direction dies out. This mode only occurs when the rupture initiates from a localized stress concentration and then propagates into a lower-stress background for which the critical dimension for unstable rupture is tuned closely to the fault width. When initial conditions permit this mechanism to originate, the subsequent propagation distance in the non-preferred direction depends on the value of the quotient (1 + phis)/(1-phid), where phis and phid are, respectively, the static and dynamic friction coefficients (with the die-out distance reducing for high values of this quotient and increasing or transitioning to bilateral rupture for low values). For a surface-rupturing fault, similar relations govern the transition of the rupture mode, provided one interprets the width of the fault as the half-width of an equivalent embedded fault. Both free surface effects and initial normal stress also have some effect on the die-out distance of the non-preferred pulse. If there is no tensile limit imposed on the fault stresses, the preferred-direction slip velocity grows indefinitely with propagation distance, but when fault opening (mode I displacement) is permitted in order to enforce a tensile limit, pulse slip- velocity approaches a steady state value. Whether this 3D mechanism is important in real earthquakes may depend upon a number of phenomena that we have yet to explore, including its sensitivity to natural heterogeneities in initial and frictional stresses, the extent to which it may be amplified by velocity-dependent friction, and the effect of stress limits imposed by off-fault material damage.
DE: 0545 Modeling (4255)
DE: 7209 Earthquake dynamics (1242)
DE: 7290 Computational seismology
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: 2007 Fall Meeting