Finite-difference seismograms for SH waves

The accuracy of the finite-difference method for generating synthetic seismograms of SH wave propagation in cylindrically symmetric media is discussed. The finite-difference method has the advantage that arbitrary density and velocity fields in the medium may be specified. A point source is generated by a simple transformation of a line source. The accuracy of the finite-difference seismograms in flat- and dipping-layered media is confirmed by comparison with the generalized ray method. A source radiation pattern is inserted by introducing a “near-field” which has permanent displacement near the source. \nStrong motion synthetics are constructed with this new method for the 1968 Borrego Mountain earthquake as recorded at El Centro. Good fits to the data are achieved using the laterally varying model determined by a detailed refraction survey and the source parameters determined by teleseismic waveform modeling. Shallow faulting is no longer necessary to explain the long-period surface-wave development.