A LANDSTREAMER TO NAVIGATE ON MIDWEST ROADS

Seismic reflection is a proven, reliable geophysical method for subsurface exploration. It is a primary tool for oil exploration and management. More recently, High-Resolution Seismic Reflection (HRSR) technology has been used to map shallow aquifers. However, the relatively high operational cost for HRSR has limited its use in water and environmental management applications. When it is used, it is typically limited to small surveys less than a kilometer in length.

Geological mapping requires regional scale measurements of the upper 50 to 100 m of sediments. In theory, HRSR is an appropriate tool to make those measurements if the cost can be reduced. We have developed new HRSR acquisition methodologies that dramatically increase the acquisition rate and reduce the personnel costs. The most labor-intensive part of the traditional HRSR field operation involves deploying and retrieving the geophones. We eliminated this part of the operation by mounting geophones on sleds that are towed behind the acquisition vehicle. Borrowing a term from marine work, the array of sleds is called a landstreamer. Using the traditional methods, we were able to acquire 1.6 km/day of 48-channel reflection data using an eight person field crew. Presently, we can deploy a 24-channel landstreamer that requires a crew of four and can acquire up to 3.2 km/day of reflection data without significantly decreasing the data quality.

To demonstrate the efficiency of the landstreamer on the side-roads of Illinois, we present examples of HRSR sections through the buried Teays-Mahomet Valley. In Illinois, this buried valley is about 200 km long, up to 32 km wide and 120 m deep and contains a major aquifer. During May and June 2003 our landstreamer crew acquired 29 km of HRSR profiles. We found that the valley fill of various fluvial sand and glacial till bodies can be mapped at necessary large scale. Using pseudo-3D representations of the sections we were able to map sand channels cutting into tills. We believe this plays a major role in the hydraulic interactions between lower and upper aquifers and surface waters.

This project was conducted in collaboration with the Illinois State University, Bloomington, IL and funded by the Illinois Board of Higher Education.