Body and Surface Wave Modeling of Observed Seismic Events

Coupling of surface waves in laterally inhomogeneous source regions to teleseismic propagation paths was studied. Dimensions of the cylindrical source region and its linear gradient transition zone were varied in order to determine their effect on generation teleseismic Rayleigh waves. By comparing amplitudes from a source region with sharp boundaries at the sides and bottom with those from a region bounded by various combinations of sharp and transition boundaries, it was determined that, for these source dimensions at the periods of interest, the more the body wave energy that leaves the source region as downgoing waves, the larger the fundamental mode Rayleigh wave. A review on the theory and application of synthetic seismograms was conducted. Emphasis was on body phase wave forms at teleseismic, regional, and local epicentral distances. At teleseismic distances, it was shown that long period body phases from shallow earthquakes are coherent at neighboring stations and that the observed waveform could be decomposed in a manner that allows determination of faulting parameters. By modeling both long and short period body waveforms using distributed point sources it is found that most earthquakes are indeed complex and that high frequency strong motions appear to be more strongly controlled by the jumps in the source time history than by the overall duration.