Underground Explosions Shed New Light on the Inner Earth
This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts.From Southern New Mexico to the Great Slave Lake of Canada, scientists recently detonated ten underground chemical explosions to generate a clearer picture of the Earth's crust and upper mantle.
Sponsored by the National Science Foundation (NSF), the United States Air Force, and Canada's National Science and Engineering Research Council, scientists in the U.S. and Canada participated in this joint experiment, called Project Deep Probe, designed to see through the crust and into the upper mantle to a depth of 300 miles.
Earth scientists from Rice University, Purdue University, and the University of Oregon received funding from NSF's continental dynamics program to conduct the research over a four-year period.
"Researchers hope to get a picture of the upper mantle beneath the Rocky Mountains and the Colorado Plateau, to understand the role the mantle played in their formation and uplift," says geophysicist Alan Levander of Rice University in Houston, Texas.
To help with enhancing this picture, 750 portable seismographs -- instruments that record vibrations in the Earth - were placed along a roughly north-south line extending from Crownpoint, New Mexico to Edmonton, Alberta to record the seismic waves from the explosions. The seismic recordings will be used to enhance weak seismic waves which penetrated the upper mantle. (Seismic waves are affected by the density and seismic velocity structure of the rocks they pass through). Many of the seismographs were provided and maintained by the Incorporated Research Institutions for Seismology (IRIS), headquartered in Arlington, Virginia.
To detonate the ten shots, explosives were placed in drill holes about 150 feet deep. Two shots occurred in New Mexico using 36,000 to 38,000 pounds of explosives, two in Wyoming using 12,000 to 15,000 pounds, one shot in Canada with 9,000 pounds, and one shot along the Canadian border, which used 4,500 pounds.
The explosion field experiment and a pilot earthquake recording experiment, which took place this summer, made up the first part of the three-phase project. The second phase, which recently began, entails analysis of the explosion data and will continue through May 1997. The third phase begins in the summer of 1997, and involves recording seismic waves from earthquakes around the world using many portable seismographs located in the Rockies.
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