Learning how to use resistivity soundings for interpretation of subsurface stratigraphy

Remke Van Dam

Michigan State University

This project is used in a 400-level applied geophysics course, with an enrollment of upper level undergraduate students (75%) and graduate students (25%). For most students in the class it is their first exposure to geophysics.
Designed for a geophysics course

Students will need a basic understanding of current flow in layered media. Besides working with numbers and plotting in excel, the required basic skills that must be in place are quiet minimal. Most skills will be developed during the activity (these skills include proper laboratory and field procedures, a.o.).

The activity is a sequence of potentially stand-alone projects that are integrated so that students learn all steps towards a successful application of geophysical methods; that is planning, execution and analysis.

- Understand how soil texture and water saturation influences bulk resistivity.
- Learn to work with basic software for forward modeling and inversion of resistivity soundings.
- Plan a resistivity sounding based on available information from well logs, lab data and forward modeling exercise.

Students need to integrate data from a several (inconclusive) sources to interpret a field site in terms of stratigraphy and hydrology.

The activity requires that students work efficiently and careful with geophysical and laboratory equipment. Students work in groups, where each student is responsible for the write-up of a section of the report.

Students will be presented with a problem; that is to determine the general characteristics (stratigraphy, water table depth) of a heterogeneous deposit (glacial till south of the MSU campus or proglacial sediments south of Ludington, MI) using electrical resistivity methods. The project consists of three separate activities: 1) use laboratory experiments to measure the relationship between soil water content and electrical resistivity for different soil samples obtained from the sites (2-3 samples per group), 2) use simple modeling software to calculate the resistivity response for simple geological models, based on information from well logs and the results of the laboratory measurements, and 3) design (min-max a-spacing and stepsize, based on the forward modeling results), execute, and analyze a field sounding experiment. Results will be summarized in a report and presented in class.

Uses geophysics to solve problems in other fields