Calculation of 3-dimensional synthetic seismograms on the connection machine

Abstract

Abstract : A three dimensional, second order finite difference method was used to create synthetic seismograms for elastic wave propagation in heterogeneous media. These synthetic seismograms are used to model rough seafloor, the shallow crust, or complex structural and stratigraphic settings with strong lateral heterogeneities. The finite difference method is preferred because it allows models of any complexity to be generated and includes all multiple scattering, wave conversion and diffraction effects. The method uses a fully staggered grid as developed by Virieux (1986). Wavefront snapshots and time series output allow the scattering and focussing of different wave modes with direction to be visualized. The extensive calculations required for realistic size models stretches the resources of serial computers like the VAX 8800. On the Connection Machine, a massively parallel computer, the finite difference grid can be directly mapped onto the virtual processors, reducing the nested time and space loops in the serial code to a single time loop. As a result, the computation time is reduced dramatically. (kt)