Figure 14.6(a) The Geco Topaz, a vessel operated by WesternGeco Inc., towing hydrophones, conducting a three-dimensional seismic survey. The bubbles behind the ship are compressed-air explosions that send out compressional waves; the reflections of those waves from the rocks below are recorded by seismographs pulled on cables behind the ship to produce an image of the subsurface structure. (b) A three-dimensional image produced by a seismic survey. The colors represent layers of sediment beneath the seafloor, some of which may trap oil and natural gas.