A tool used to “see” beneath the earth’s surface. It involves sending acoustic vibrations into the ground and measuring the length of time it takes to rebound off the subsurface rocks back to the surface, or more precisely to record the amplitude of reflected energy from the sub-surface formations. High-tech supercomputers are used to process billions of data samples and generate a detailed, 3-D image of underground structures. Geophysicists interpret the data to make estimates as to the depth of the reservoir, its porosity, fluid content and other information valuable in determining where oil and gas deposits are most likely to be found