Finding faults: Using ground roll reflections to image lateral discontinuities

Craig Hyslop, Robert R. Stewart, and Minyu Zhang

ABSTRACT

Determining lateral change in the subsurface is important for many scales of geophysical investigation: It is helpful in constraining models for tectonic behavior, structural mapping on a regional scale, characterizing reservoirs, and identifying faults for engineering applications. Surface-seismic survey geometries and reflection processing methods are well suited for imaging horizontal layers in the subsurface; however, illuminating and analyzing near-vertical features and lateral discontinuities may be more difficult. Processing surface waves directly can provide additional information about lateral change in the sub-surface. We have developed a processing flow for imaging faults using reflected surface waves. The method relies on VSP-type procedures as well as the undoing of dispersive effects. It provides a way to locate lateral change and the discontinuity depth using extracted surface-wave reflectivity. We apply the method to synthetic datasets generated from a buried fault model and find interpretable images of the fault. Next, we use surface-wave reflectivity for interpreting a near-surface fault in field data from the Hockley Fault system near Houston Texas. We note that a major fault breaks the surface (pavement) at 400m which is identified in the ground-roll image.

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