Subsurface detection involves determining the characteristics of subsurface materials indirectly, that is without direct physical contact. Surveys can be run on land, at sea, or from the air. Seismic reflection and refraction studies using seismographs have allowed scientists to explore the geology of the interior of the Earth. Shallow seismic studies are usually done with an explosion or air blast, especially at sea, or in some cases, a special truck that makes the ground vibrate. Deep seismology surveys make use of earthquakes or nuclear explosions to explore the deepest interior of the Earth.

Seismic reflection involves interpretation of rock or sediment depth and character based upon the amount of time required for a seismic wave to travel from the Earth's surface down to a reflective layer and back again to the surface. The waves are generally created by a small concussion below ground or, if at...