Effect of Near-fault Terrain upon Dislocation Modeling

Coseismic surface deformation provides important information needed to determine source rupture geometry and slip distribution as well as to estimate seismic moment. In this study, numerical experiments were designed to analyze and classify how free-surface topography affects surface deformation. The investigation was performed by 3-D finite element modeling. Results of this study show that crustal deformation induced by near-fault terrain is significant and can be measured with present geodetic survey techniques. The characteristics of the terrain effects show that a hill structure produces more crustal deformation than a half-space model, and that the crustal deformation of a basin structure is less than that of the half-space model. The topographic correction is in the order of five percent of the fault dislocation. On the basis of the relationship between fault offset and earthquake magnitude, it is suggested that the terrain effects on the coseismic crustal deformation of shallow earthquakes with a magnitude greater than 5.6 should be considered as one of the major errors in coseismic deformation modeling which ignored the surface topography on the order of 300 meters.