3-D versus 2-D finite-difference seismic synthetics including real surfacetopography

We have pursued and compared two-dimensional (2-D) and three-dimensional (3 -D) finite-difference (F-D) modeling of scattering from free surface topogr aphy. A velocity-stress formulation of the full elastic wave equations are combined with exact boundary conditions for the surface topography and nume rically discretized by an eighth-order F-D method on a staggered grid. We h ave simulated scattering in 2-D and 3-D from teleseismic P-waves using a pl ane, vertically incident P-wave and real topography from a 60 x 60 km(2) ar ea including the NORESS array in southeastern Norway. Many field observatio ns that are not easily explained by simpler 2-D cases are shown to better m atch qualitative effects from 3-D surface topography modeling. These includ e strong amplifications at hills, complex wave pattern caused by scattering , and directivity of scattered waves. Snapshots and seismograms show clear conversion from P- to Rg- (short period fundamental mode Rayleigh) waves in an area of rough topography in the vicinity of the array site. All results are consistent with numerous observations. By parallellization of the orig inal software, possibilities have been opened for modeling with higher reso lution and/or larger areas than before. (C) 1999 Elsevier Science B.V. All rights reserved.