Three-dimensional seismic imaging of a dynamic Earth

Seismic imaging is the most important tool for investigating the interior o f the solid Earth. Over the last 20 years, a major advance has been the rap id development and application of three-dimensional seismic reflection tech nology. Routinely used by the hydrocarbon industry to aid exploration for, and extraction of, oil and gas, this three-dimensional imaging technique is now ripe for exploitation on a global scale. Seismic reflection surveying uses acoustic or sound energy, which is easily transmitted through solid ro ck. Where rock properties change at depth, some of this energy is reflected back towards the surface and recorded. Seismic data are most easily collec ted at sea, where a vessel tows a long streamer of hydrophones in a series of parallel traverses. Acoustic waves are generated by large airguns suspen ded in the water; reflections, which return from depths of up to 100 km, ar e recorded by the streamer. Since the 1960s, many important scientific brea kthroughs have been made using two-dimensional seismic imagery. More recent ly, three-dimensional seismic surveying has become cheaper and coverage has rapidly increased. A typical three-dimensional survey generates around 300 billion bytes of information, which, after sophisticated signal processing , yields a cube-shaped image of the subsurface. With this unique probing ab ility, we can map the three-dimensional subsurface architecture of continen tal margins where repositories of sedimentary rock contain an important rec ord of how our planet has behaved over millions of years. We can also image the detailed pattern of deformation within these rocks. Seismic imaging is especially powerful because it contains a record of the fourth dimension: time. Other time-dependent processes, such as the movement of magmas, hydro carbons and water through the pores of rocks, can be monitored by repeated three-dimensional surveying. Seismic imaging is the key to unravelling elus ive yet fundamental processes that keep our convecting planet alive.