Seismic testing

From Wikimarcellus

Seismic testing is a technology used to search for pockets of natural gas. High tech trucks that hunt along rural roads of Appalachia can shoot seismic waves into the surrounding ground in order to discover geologic formations under fields, farms and homes.

A typical survey in a forest preserve was described this way:

Workers clear the vegetation and mulch down 4 ft. wide paths in a grid pattern throughout woods being surveyed. Microphones are then connected to bright orange cables along the paths. Vibrator units mounted on buggies emit sound waves that go approximately five miles down into the ground. These waves reflect back off of underground rock formations, and are picked up by the microphones.