Seismic Reflection Attribute Analysis and Inversion Techniques to Map Stratigraphic Interfaces and Thin Beds

We demonstrate, using data from two different sites, that seismic attribute analysis and constrained seismic inversion applied to high-resolution seismic reflection data can increase the resolution of the data to delineate shallow (< 35 m depth) thin (< 1 m) beds and stratigraphic interfaces that might not otherwise be identified. During site characterization, delineating these features is important because contaminants such as DNAPLs tend to accumulate at stratigraphic interfaces (buried channels) and in fine-grained beds. The traditional method for characterizing these features is drilling numerous boreholes and correlating the interfaces between holes. Noninvasive shallow high-resolution seismic reflection surveys can provide a near continuous record of vertical and spatial geologic/lithologic changes between boreholes. Unfortunately the seismic section is a smoothed version of the subsurface representing differences in reflectivity at a resolution far lower than provided by geophysical logs. Seismic attribute analysis and constrained seismic inversion techniques use the properties of borehole data (fine resolution) and seismic data (coarser resolution) in combination to produce a seismic properties model with a vertical resolution close to that found in borehole logs, but with added horizontal dimension. At United States Department of Energy's Hanford Site in Washington seismic impedance stacks were used to map thin silt layers, not evident on the standard amplitude stacks, where carbon tetrachloride was accumulating. Also buried channels and other stratigraphic features that are potential contaminant pathways at this site were better defined. At Marine Corps Air Station Beaufort, South Carolina seismic impedance stacks were used to map the continuity of a clay confining unit.