Geologic research is a blast

Scientists use dynamite to probe earth's crust in Nevada, California region

Published September 16, 2004
in the Klamath Falls Herald and News

By JEAN BILODEAUX

CEDARVILLE - Scientists detonated tons of dynamite buried deep in the earth early this morning as part of a test to learn more about the structure of the earth's crust in northeastern California and northern Nevada.

The explosions set off at 1 and 3 a.m. went unnoticed by most residents of the area, alleviating fears the experiment would touch off earthquakes.

The study is being conducted by geologists, geophysicists, and graduate and undergraduate students from Stanford University.

The dynamite charges were placed in up to six holes located along a line extending from near Winnemucca, Nev., across Surprise Valley to the plateau region along Highway 139 northwest of Canby, Calif.

Dynamite was placed at the bottom of the 200- to 400-foot-deep, 10-inch diameter wells by an explosives expert from the U.S. Geological Survey in Menlo Park, Calif.

There were 4,000 pounds of explosives in the two end holes and 2,500 pounds of explosives in the other holes. Once the dynamite was placed, the holes were filled with gravel and capped with concrete.

The charges were detonated at night so truck traffic and other and other extraneous noise wouldn't generate false data on the seismographs.

"They will be more like mining explosions, no big craters, just a blast of sound into the earth," explained Anne Egger, of Stanford University's Geology Department.

Egger said there was absolutely no chance of the explosions triggering an earthquake.

"Earthquakes come from deep in the earth's crust. We are much too shallow with our blasts to generate any big earthquake," Egger said.

The sound waves generated from the explosions travel through the earth's crust, which is rocks and other material with the density of granite. Below the earth's crust is the mantle, which is much more dense.

"We are sending the sound waves down and they will bounce off the more dense mantle and return. The time the waves take to return will be recorded and that will tell us how think the earth's crust is in this locale," Egger said. "Usually it is about nine miles thick."

To measure the sound waves, the group has placed 1,300 geophones along the line approximately 300 meters apart. The geophones are in 10-inch cylinders with a 3-inch diameter, with red sensors attached. Inside each cylinder is a small seismograph and computer.

The geophones are owned and remotely operated by a team from the Program for the Array Seismic Studies of the Continental Lithosphere of Socorro, N.M. The team set up its headquarters at the Modoc County Fairgrounds in Cedarville. Another team set up in Winnemucca and a small team is working out of Soldier Meadows. They are running the eastern part of the project.

On Wednesday afternoon the geophone team activated all 1,300 units. They will remain activated until Friday, when they will be collected by the Stanford group. Each geophone holds 32 to 64 megabytes of data, which will be transmitted to the fairgrounds. The data will be processed at Stanford and may take up to two years to be made public.

The experiment will tell some of the earth's history and processes, and why it looks like it does.

After the geophones are collected and downloaded, they will be redistributed in an area a few miles north of Cedarville for a more intense study of the Surprise Valley area.

Correspondent Jean Bilodeaux covers Surprise Valley. She can be reached at (530) 279-2031, or at P.O. Box 5, Cedarville, CA 96104, or by sending an e-mail to jeanb@hdo.net