HR: 08:45h
AN: S41B-03    [PDF]
TI: Rupture Dynamics With Energy Loss Outside the Slip Zone
AU: * Andrews, D J
EM: jandrews@usgs.gov
AF: U.S. Geological Survey, Mail Stop 977 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: Energy loss in a damage zone outside the slip zone contributes to fracture energy. Because the thickness of the damage zone increases with rupture propagation distance, fracture energy increases with earthquake size. A rupture front propagating near its limiting velocity has a stress concentration with large shear components at orientations different from that of the slip zone. These components can become large enough to induce non-elastic response (such as micro-cracking). The thickness in which stress reaches a threshold value for damage is proportional to rupture propagation distance in the case of constant stress drop. If non-elastic response in the damage zone can be represented as plastic yielding, then energy loss per unit area of rupture is proportional to the damage zone thickness and therefore to rupture propagation distance. I have performed numerical calculations of rupture on a slip plane with relatively low friction with stress drop occurring as abruptly as can be adequately resolved with the grid spacing. Material off the slip plane is subject to a Coulomb yield condition with a larger coefficient of friction. As rupture on the slip plane grows with constant stress drop, both peak slip velocity and off-fault stress components increase until stress in elements next to the fault reaches the Coulomb yield condition. As the rupture continues to grow, the thickness of the yielded material increases while peak stress and peak slip velocity remain constant. Rupture velocity is somewhat less than its limiting value, consistent with the increasing total fracture energy. Although stress on the slip plane is prescribed to drop quickly, slip velocity remains near its limiting value for a longer time while off-fault material is yielding. Slip velocity behaves as if the slip plane were subject to slip-weakening friction with larger $D_C$, corresponding to fracture energy that includes the off-fault energy loss. In a mode-2 rupture, confining stress changes in opposite senses on opposite sides of the slip plane, so the Coulomb yielding is not symmetric. Non-elastic extension in the direction of rupture is enhanced on one side of the slip plane, so that there is a net compressive change of normal stress on the slip plane, which has a slight stabilizing effect. These complications do not change the conclusions listed above.
DE: 5104 Fracture and flow
DE: 7209 Earthquake dynamics and mechanics
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting