GEOLOGIC GROUND PENETRATING RADAR (GPR) APPLICATIONS IN SOUTHWESTERN INDIANA

Ground penetrating radar (GPR) is a powerful noninvasive tool to image the shallow subsurface. In southern Indiana, GPR has been employed to: 1) detect man-made void spaces such as mines, natural caves, and other karst features; 2) locate paleoliquifaction features; 3) examine archaeological features; 4) show bedding or other features in sediments or rock; 5) estimate ground-water levels; and 6) locate hidden infrastructure; among other studies.

Underground voids from coal mining are seen by GPR only in special conditions because most coal mines are surrounded by clay-rich rocks that absorb radar energy. Most mines also exceed depths viewable by GPR. Depending on wavelengths used and geologic details, radar can “see” features to a depth of 60 feet, although GPR is usually limited to much shallower (less than 25 feet) depths.

Caves and other karst features directly affect mining activities and, consequently, mining companies need to know cave locations and extents. GPR has detected caves in several circumstances at quarries and has been used to locate wild caves. Fractures or grikes in carbonate rocks can also be tracked by GPR.

Paleoliquefaction features have been observed as have fractures, faults, dipping beds, rotated blocks, and other structural details. Bedding planes, cross beds, and other sedimentary discontinuities can sometimes be viewed. Archaeological features such as graves, structures, and fortifications can often be viewed prior to excavation. Modern features such as buried pipes or electric lines are readily viewable. Conglomerates in sand deposits, cross beds and erosion surfaces, and other sedimentary structures have been imaged in unconsolidated sediments. GPR is a rapid and relatively inexpensive method to peer into the Earth and can be used extensively in geologic studies.