Surface displacements and energy release rates for constant stress drop slip zones in joined elastic quarter spaces

A three-dimensional quasi-static model of faulting in an elastic half-space with a horizontal change of material properties (i.e., joined elastic quar ter spaces) is considered. A boundary element method is used with a stress drop slip zone approach so that the fault surface relative displacements as well as the free surface displacements are approximated in elements over t heir respective domains. Stress intensity factors and free surface displace ments are calculated for a variety of cases to show the phenomenological be havior of faulting in such a medium. These calculations showed that the beh avior could be distinguished from a uniform half-space. Slip in a stiffer m aterial increases, while slip in a softer material decreases the energy rel ease rate and the free surface displacements. Also, the 1989 Kalapana earth quake was located on the basis of a series of forward searches using this m ethod and leveling data. The located depth is 8 km, which is the closer to the seismically inferred depth than that determined from other models. Fina lly, the energy release rate, which can be used as a fracture criterion for fracture at this depth, is calculated to be 11.1 x 10(6) J m(-2).