3-D versus 2-D finite-difference seismic synthetics including real surface topography

Abstract

We have pursued and compared two-dimensional (2-D) and three-dimensional (3-D) finite-difference (F-D) modeling of scattering from free surface topography. A velocity–stress formulation of the full elastic wave equations are combined with exact boundary conditions for the surface topography and numerically discretized by an eighth-order F-D method on a staggered grid. We have simulated scattering in 2-D and 3-D from teleseismic P-waves using a plane, vertically incident P-wave and real topography from a 60×60 km 2 area including the NORESS array in southeastern Norway. Many field observations that are not easily explained by simpler 2-D cases are shown to better match qualitative effects from 3-D surface topography modeling. These include 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 original software, possibilities have been opened for modeling with higher resolution and/or larger areas than before.