People who explore for oil and gas traps are called Exploration geologists and geophysicists. Their main job is to find subsurface traps that could contain hydrocarbons.One of the sciences that geophysicists use in their search for traps is seismology. Seismology is the study of vibrations in the earth. The vibrations take the form of sound waves. For instance, an earthquake creates sound vibrations that can be studied by seismology. Sound vibrations can also be made and studied on the surface of the earth. Man - made sounds can help geophysicists find traps.
To understand these special sounds and how they are used to find tarps, lets look at a simple comparison. Most of us have experienced the sound of our voices coming back to us from the face of a cliff or building. The sound travels through air, bounces off the cliff or wall, and returns back to us as an echo. The use of seismology to explore for petroleum traps is based on the same principal, but it is somewhat different.
In seismic exploration, geophysicists are looking for traps buried deep beneath the surface. So, the sound has to travel not through air but through rock. Also, the sound has to have the right characteristics to go through thousands of feet of rock and back up to the surface. Further, the seismic work of a geophysicist usually covers many miles of surface area in order to increase the chances of finding a potential reservoir.
**Source: Fossil Oil Company: http://www.fossiloil.com/3d-seismic-technology/ **