Seismic waves

From Wikimarcellus

Seismic waves are emitted by thumper trucks. These vehicles are specially equipped with impact devices that generate ground waves. They are driven down rural highways in areas where gas is suspected and have electronic equipment on board to record the returns when sound waves bounce back from underground features. These recordings can be used to map out the locations of the features.

The noise and vibrations from thumper trucks can be heard from a considerable distance. The trucks usually work in groups of three or four, one right behind the other, and the impacts they generate are synchronized.

Information from seismic studies has occasionally been used for leverage in land negotiations between gas companies and landowners.