Near-surface mapping using SH-wave and P-wave seismic land-streamer data acquisition in Illinois, U.S.

Abstract

Human activities have considerable impact on the upper 300 m of sediments of the earth. Conflicting activities in highly populated areas involving groundwater exploitation, aggregate extraction, and hazardous chemical-related production and storage induce stress on the environment. Nearly half the population living around the Great Lakes depends on shallow groundwater aquifers. A coalition of four Great Lakes states (Illinois, Indiana, Michigan, and Ohio), in conjunction with the U. S. Geological Survey, has initiated a program to map this sensitive upper 300-m layer. As part of this effort, the Illinois State Geological Survey (ISGS) has undertaken the task of preparing 3D quadrangle maps of the upper 100 m of the entire state at a scale of 1:24 000. Although large-scale maps indicating potential aquifer contamination already exist (Figure 1), very little is known about the groundwater pathways through the upper sedimentary column, which mainly consists of deposits from the Quaternary continental glaciers that once covered most of Illinois. Due to strong shearing at the base of the glacial ice sheets associated with subglacial meltwater flow, the shallow sedimentary architecture is very difficult to predict using conventional geologic approaches. Along with a substantial borehole database, geophysics has the potential to provide crucial data to enhance the quality of subsurface geologic maps. Another important societal concern for a state geological survey is the elastic properties of the near-surface sediments (e.g., shear strength) that govern localized ground acceleration during an earthquake.