PROPERTIES AND IMPLICATIONS OF DYNAMIC RUPTURE ALONG A MATERIAL INTERFACE

We perform two-dimensional plane-strain finite-difference calculations of dynamic rupture along an interface separating different elastic me dia. The calculations extend earlier results of Andrews and Ben-Zion ( 1997) who found a self-sustaining narrow slip pulse associated with dy namic reduction of normal stress along a material interface governed b y constant friction, in agreement with Weertman (1980). The pulse prop agates in a wrinklelike mode having remarkable dynamic properties that may be relevant to many geophysical phenomena. Here we examine the ra nge of values of elastic parameters, friction coefficient, and strengt h heterogeneities allowing for the existence of the wrinklelike pulse. Rupture is initiated in the simulations by imposed slip in a limited space-time domain. Outside the region of the imposed slip, the pulse b ecomes narrower and higher with propagation distance along the interfa ce. The strength of the wrinklelike pulse increases with S-wave veloci ty contrast up to a maximum at about 35% contrast. Beyond such a veloc ity contrast, there is no solution for a generalized Rayleigh wave alo ng a material interface, and the strength of the pulse decreases. Howe ver, the wrinklelike pulse can still propagate in a self-sustaining ma nner for larger velocity contrasts. For a fixed S-wave velocity contra st, the strength has little dependence on density contrast or Poisson' s ratio, but the pulse strength increases rapidly with increasing coef ficient of friction. Stress and strength heterogeneities with small co rrelation length have little effect on the pulse, while long wavelengt h heterogeneities reduce the strength of the pulse. The high mechanica l efficiency of the wrinklelike pulse suggests that earthquake rupture s may favor such mode of failure when possible.