abstract

We compare displacements, due to incident SH waves, on the surface of a polyurethane foam model of a two-dimensional semi-cylindrical basin with theoretical results based upon an analytic solution by Trifunac (1971) and obtain excellent agreement. Observations indicate that the SV response is similar to the SH response, except that the SV-induced resonances are of somewhat shorter period. Further measurements are made on a foam model of an idealized alluvial fan. SH responses observed in cross profiles across the mouth and head of the fan indicate that the resonance observed on the deeper foam, at the mouth of the fan, is of longer period than the resonance observed at the head on shallower foam. Finally, the amplitudes on the fan are observed to be somewhat larger for SH and SV waves traveling downdip, than for such waves traveling updip, given the same source-receiver distance and source amplitude.

The agreement between theory and experiment for the two-dimensional semicylindrical basin geometry indicates that polyurethane foam with different densities and rigidities can successfully model the seismic responses of piecewise homogeneous linear elastic media in configurations with arbitrarily complicated three-dimensional geometries. Once constructed, such models provide inexpensively the response to various kinds of input motion incident at arbitrary angles. The applicability of foam models to real-earth structures depends upon the validity of assuming linear elastic behavior and piecewise homogeneity.

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