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Probing the Digital Depths of Earth




COURTESY OF RICHARD DAVIES
Scientists interested in examining the deep layers of the earth's rocky guts are finally getting their hands on expensive, often confidential image data intended for petroleum companies in search of fossil fuel sources. The data, collected with a technology called seismic reflection, produces three-dimensional images of geologic features buried under hundreds and thousands of meters of terrestrial and marine sediment. Not only are the images aesthetically stunning, but they are shedding light on fundamental processes including the formation of structures on the earth's surface, the chemical changes that occur in deeply buried rocks, the intrusion of magma into continental crusts and the flow of sediments along ocean basins.

Obtaining the images usually requires a strong bond between individuals at a university and in industry to persuade to companies to release the data for scientific purposes, observes senior exploration geologist Richard Davies of the 3DLab at Cardiff University in Cardiff, U.K. "Individuals that are presently spearheading it in academia have usually worked in the oil and gas industry in a previous life," says Davies, who worked for ExxonMobil for eight years.

With the aid of powerful computers and sophisticated software at Cardiff¿s 3DLab--one of the first to specifically use 3D seismic data as a primary research tool--scientists can rotate, slice, dice and practically julienne rock formations to gain important glimpses into the planet's geologic past. "We can completely strip off a few thousand meters of earth and reveal long-ancient landscapes," remarks Henry W. Posamentier, chief geologist at Calgary, Alberta-based Anadarko Canada Corp., which uses the images to search for hydrocarbons. Posamentier and Davies presented some of their images in the recent issue of GSA Today.

Seismic reflection technology uses artificially generated seismic waves to produce the three-dimensional images. On land, the waves are created with a large pad that thumps the surface, sending a vibration hundreds or thousands of meters underground. The waves reflect and refract off underground features and travel back to the surface, where they are sensed by receivers. In the ocean, ships use an air gun that sends a shock wave through the water and into the seafloor.

Certain characteristics of the reflection of the waves, such as their angle and how long they take to return to the surface, are collected as three-dimensional cubes of seismic reflection data, which can be interpreted and visualized with specialized software. In both cases, the seismic waves are generated every 12.5 to 25 meters and entire data sets can cost millions of dollars.

The best resolution of underground features occurs at depths between zero and 1,000 meters--a range that appeals to academic geologists. But petroleum geologists are more concerned with older sedimentary layers located at depths between 1,000 and 6,000 meters, where the resolution is poorer. As a result, they must extrapolate deep rock clues from shallow region data.

Involving university geologists in the process benefits both parties. Academics gain access to expensive data that ultimately improves their understanding of geological processes. And based on those improvements, industrial geologists can refine their models for exploring deep layers.

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