3D COHESIVE END-ZONE MODEL FOR SOURCE SCALING OF STRIKE-SLIP INTERPLATE EARTHQUAKES

Abstract

A 3D, static fracture mechanics model of earthquake rupture that incorporates cohesive end zones (CEZs), or zones of increased frictional strength, is tested to determine whether it helps to understand the observed scaling behavior of average slip with rupture dimensions for shallow (<20 km), continental, interplate strike-slip earthquakes. our new compilation of average source parameters suggests that (1) slip increases with aspect ratio (along-strike length down-dipwidth), although in decreasing proportions for progressively larger ruptures, and (2) a gradual scaling change exists at an ~6. these general trends match the functional form predicted by cez model. despite trends, significant scatter is apparent among similarly sized ruptures. we test hypothesis cezs represent strength heterogeneities along rupture surface result from velocity-strengthening frictional behavior; this heterogeneity behavior fault primary reason failure universal (constant stress drop) law. lengths are measured drop distributions determined published inversions geophysical data 1984 morgan hill, 1992 landers, 1999 hector mine, izmit earthquakes, range ~15 to 40% segment lengths. order magnitude than inferred characteristics high-frequency seismic radiation (i.e., fmax). These data indicate that the ratio of average coseismic slip to rupture length decreases in the presence of large CEZs. Measured CEZ lengths, rupture dimensions, and average slip are used to calculate average resolved shear-driving stresses and CEZ shear-yield strengths on the order of ~ 10-30 MPa. In our new model of earthquake rupture, stress drop is predicted to be a small fraction of fault strength and thus supports a partial stress drop model of earthquake rupture for strike-slip interplate events.