NSF PR 95-63 - September 22, 1995
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Underground Explosions Shed New Light on the Inner
Earth
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 fouryear 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 drillholes 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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