FINITE-DIFFERENCE MODELING OF NEAR SURFACE SEISMICS TO EVALUATE SEISMIC FIELD DATA

Abstract

Shallow reflection seismics utilizing P-waves as well as shear waves has become a useful tool for different near-surface issues, e.g., in geohazard analysis or hydrogeology. However, data we have acquired show large variations in terms of quality for both wave types. To verify our data and resultant models we therefore additionally use Finite-Difference (FD) modeling. That method is able to simulate wavefield propagation even for complicated layering in the subsurface. As a side effect we can study the influence of our processing scheme on the resulting models. The seismic FD modeling code we are currently using was introduced by Bohlen (2002). As part of a hydrogeological survey, we have acquired ca. 8 km of high resolution P-wave reflection seismics as well as 2.8 km of shear wave (SH) reflection seismics on the German North Sea island of Föhr. Detailed seismic velocities were determined from Vertical Seismic Profiles and assigned to lithological layers. After processing, the seismic depth section alone did not provide an unambiguous structural interpretation, but finally a hydrogeological model was compiled using the reflection seismic data in combination with airborne electromagnetic and borehole logging data (Burschil et al., 2012). It was used as input for FD modeling. P-wave modeling resolves the internal structure of the input model but shows differences compared with the field data, even with respect to some of the main reflections. A modification of the input model resulted in a better consistency. We now reproduce the main reflections and thereby validate our modified model. This model will be used for following signal absorption analysis and SH-wave modeling.