Synthetic Seismogram Calculations for Two-Dimensional Velocity Models.

Abstract : A variety of synthetic seismogram methods for laterally heterogeneous earth models have been developed and tested. Explicit finite difference methods for elastic wave propagation generally display high accuracy, but are limited in their application due to extensive computer time and storage requirements. Implicit finite difference methods may be able to realize a factor of eight improvement in computer time and factor of four improvement in computer storage requirements as compared to explicit methods. The implicit methods of synthetic seismogram calculation are less well developed and are more difficult in the application of absorbing boundary conditions. Approximate methods using the scalar wave equation may also be useful for preliminary modeling of seismic data. A ray-theoretical method using ray tracing and disk ray theory (DRT) synthetic seismogram synthesis has been developed and compared to calculations using reflectivity (for 1-D) and finite difference (for 2-D) methods. The DRT method is fast and reasonably accurate making it very useful for routine modeling of 2-D seismic data. Its principal problem is the difficulty in tracing rays in certain complex geologic models. Various calculations of synthetic seismograms in laterally heterogeneous model sand comparison with homogeneous models indicate the importance of including lateral heterogeneity, elastic wave propagation, proper source design and absorption in seismic modeling. (Author)