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

Abstract

Abstract. A three-dimensional quasi-static model of faulting in an elastic half-space with a horizontal change of material properties (i.e., joined elastic quarter 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 their respective domains. Stress intensity factors and free surface displacements are calculated for a variety of cases to show the phenomenological behavior of faulting in such a medium. These calculations showed that the behavior could be distinguished from a uniform half-space. Slip in a stiffer material increases, while slip in a softer material decreases the energy release rate and the free surface displacements. Also, the 1989 Kalapana earthquake was located on the basis of a series of forward searches using this method and leveling data. The located depth is 8 km, which is the closer to the seismically inferred depth than that determined from other models. Finally, the energy release rate, which can be used as a fracture criterion for fracture at this depth, is calculated to be 11.1 x 106 J m -2. IntroductionSeismic velocity studies have found horizontal as well as vertical variations in the mechanical properties of the Earth's crust. These variations are not usually considered, though, when earthquakes are located using quasi-static elasticity dislocation models and geodetic data. The results from these earthquake location calculations are usually quite good, but sometimes the location of the earthquake is considered to be too far away from and/or not aligned with the seismically inferred locations of the main shock and aftershocks. Also, sometimes the calculated free surface displacements do not adequately match the leveling data in some region. These problems and the seismic velocity studies suggest that the dis- A model of faulting in an elastic half-space with a horizontal change of material properties (i.e., joined elastic quarter spaces) is considered. The stress drop slip zone approach is used with a boundary element method so that the fault surface relative displacements as well as the free surface displacements are approximated in elements over their respective domains. A parameter study is performed, and the calculated energy release rates and free surface displacements are compared to those for a uniform half-space. Finally, the 1989 Kalapana earthquake is revisited to show how the current model can be used. Owing to the computational intensity of the current model, a series of forward searches (rather than an inversion) are made to compare the calculated vertical surface displacements to leveling data. In this way, the 1989 Kalapana earthquake is located and the energy release rate is determined. Method of AnalysisEnergy release rates and free surface displacements are calculated in a simulation of faulting in joined elastic quarter spaces using stress drop slip zones and the boundary element method. The geometry co...

Finite element model predictions of static deformation from dislocation sources in a subduction zone: Sensitivities to homogeneous, isotropic, Poisson‐solid, and half‐space assumptions

“…Solutions are available for static displacement predictions in the special cases of either a vertically [ Savage , 1998] or horizontally [ Rodgers et al , 2000] layered half‐space. Others have gone to great lengths to precisely estimate the geometry of a dislocation source [ Harris and Segall , 1987; Cervelli et al , 2001; Hutton et al , 2001] in an HIPSHS problem domain.…”