Seismic survey:

An exploration method in which strong low-frequency sound waves are generated on the surface or in the water to find subsurface rock structures that may contain hydrocarbons.

The sound waves travel through the layers of the earth’s crust; however, at formation boundaries some of the waves are reflected back to the surface where sensitive detectors pick them up.

Reflections from shallow formations arrive at the surface sooner than reflections from deep formations, and since the reflections are recorded, a record of the depth and configuration of the various formations can be generated.

Interpretation of the record can reveal possible hydrocarbon-bearing formations.