HIGH RESOLUTION SEISMIC MAPPING OF THE MAHOMET VALLEY AQUIFER

High-resolution reflection seismic mapping technique was used to collect S-wave, P-wave and VSP data from Robert Allerton Park, Piatt County, Illinois. Eavesdropper (by Kansas Geological Survey), Kingdom Suite+ (Seismic Micro-Technology, Houston, Texas), and other ISGS processing modules were used in combination to process and interpret digital seismic data. Better S-wave reflection signals are obtained in areas with poor P-wave signals. Poor P- wave signals are attributed to the presence of methane. This interpretation is based on the following: the velocity of P waves is lowered considerably in the presence of gas, methane was present in one of the boreholes drilled for this project, and methane present elsewhere in the Mahomet Valley Aquifer System is used for heating. Channels in the valley are clearly shown by the S-wave sections. It is recommended that VSP, S-wave and P-wave surveys should be used in conjunction for an accurate and detailed interpretation of geologic conditions. The aims of this study are to update existing data on the aquifer in order to revise existing literatures, to clearly define the valley wall shape of the Mahomet Valley Aquifer System, to define vertical and horizontal heterogeneity of the lithologic units and to clearly distinguish between sand and gravel units because these factors constrain hydrogeologic modeling. Another objective of the project was to determine the whether P-wave or S-wave seismic data best depict sedimentary structure or geometry. This collaborative project between the Illinois State Geologic Survey and Illinois State University was supported by the Illinois Board of Higher Education.