Comparison of Strong Ground Motion from Several Dislocation Models*

To examine the effects of different earthquake sources, ground motion near the rupture for several dislocation models has been calculated. Quite different dislocation models of the rupture can give very similar displacements at stations located only one fault dimension from the fault in an infinite homogeneous elastic space. In particular: (1) models with fault motions and rupture geometry quite different from Haskell's propagating ramp can often have near-field motions very similar to those from a ramp model; and (2) quite similar near-field motions are found, for different ramp models in which the rupture velocity and rise time are varied together over rather large ranges (e.g. a factor of three in rise time). We infer that there is considerable ambiguity in interpreting near-field displacement data in terms of a model of fault motion. The ambiguity may be reduced by using acceleration data, although this entails a considerable increase in computer time for solving forward problems.