SH AND P-WAVE SEISMIC REFLECTION USING LANDSTREAMERS TO MAP SHALLOW FEATURES AND POROSITY CHARACTERISTICS IN ILLINOIS

Abstract

With increasing urbanization, the need for detecting unknown hazards, like hidden cavities or gas venues in populated areas, is of significant importance. The acoustic geophysical methods present a great potential to map such underground anomalies. At the Illinois State Geological Survey (ISGS), we have developed SH-wave and P-wave landstreamers to map large areas. More than one-hundred kilometers of data acquired in 2004-2005 have shown the extreme diversification of the shallow geology in the Midwest (< 100 m). Features such as buried channels, shallow thrusts and high-angle faults, and karst commonly are detected using landstreamers. The detection of gas venue from natural gas storage facilities using seismic reflection is the object of intense research at the ISGS. The P-wave is well known for its strong response to the presence of gas within pore spaces characterized by a high reflectivity and absorption of the acoustic energy. Our new results detect the presence of gas in the upper 100 meters of the Paleozoic bedrock. Whereas gas is mainly mapped using P-wave reflection, S-wave sections show the lithological layering and the location of bedrock fractures. The integrated P-wave and SH-wave reflection analysis of the sections demonstrates that the gas migrates in the most fractured areas.