ABSTRACT

High-resolution seismic reflections have been used effecttively to investigate sinkholes resulting from the dissolution of a bedded salt unit found throughout most of central Kansas. A seismic reflection survey was conducted to investigate the shallow subsurface between a sinkhole that formed catastrophically within a few tens of meters of a main east/west rail line. Data quality was significantly below expectations and not equivalent to other seismic data from this area where acquisition parameters, equipment, and target intervals were similar. Near-surface tomographic and MASW analyses revealed a highly irregular bedrock surface characterized by what appear to be a high concentration of short wavelength dissolution features. These bedrock features are below about 20 m of unconsolidated sediments with physical dimensions several meters deep and several meters wide. Data quality is quite good on other seismic reflection surveys from this general area where these bedrock features are not present. Pronounced static shifts and degradation in spectral characteristics of reflections where these bedrock features are present seems to be isolated to an area suspected to be the crest of a relatively broad anticlinal structure where surface fractures could have provided a conduit for fresh water to access shallow, thin evaporite layers within the thick shale sequence in the upper 200 m. Broadband high-resolution compressional-wave energy suffered significantly from this highly irregular bedrock topography.

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