Science/Medicine : Rolling Thunder : Scientists Shake Earth Across Ohio for Geologic ‘Snapshots’

At a leisurely four miles per day, a curious caravan of earthshaking trucks is wending through the rolling farmlands of western Ohio, helping scientists probe miles below the surface where ancient continents may have collided.

If underground mountains can be found, scientists say, they could be loaded with valuable minerals and provide a picture of what Earth was like a billion years ago.

“This is the beginning of the effort to understand the large-scale architecture, and ultimately the history of Earth is wrapped up in the architecture of the crust,” says Doug Nelson, a senior researcher at Cornell University in Ithaca, N.Y.

Nelson is with the Consortium of Continental Reflection Profiling, COCORP, at Cornell, which is funded by the National Science Foundation at a cost of about $3 million a year. Scientists hope to build a model geologic cross-section of the crust under the United States by 1990, based on the work in Ohio and other states.

The journey by a crew from Seismograph Services Corp. of Houston began in August at the Ohio-Indiana line in Mercer County and is to conclude this month at a point along the Ohio River across from West Virginia.

In between, the trucks will have shaken the path along back roads and state highways, sending vibrations up to 30 miles deep which are reflected back to a constantly changing 7 1/2-mile string of geophones--instruments designed to pick up the smallest tremors--spaced about 14 feet apart.

Minute changes in the vibrations tell scientists what kinds of rocks are underground.

The sophisticated underground mapping technology was developed by the petroleum industry, not to search for oil or minerals, but to aid in the understanding of the formation of the Earth’s crust.

“We’re able to understand the history of the Earth,” says Larry Brown, another Cornell geophysicist who is one of the co-directors of the project.

Work in the Appalachians has revealed, for example, that those peaks were not pushed up from underneath, as some had theorized, but rather were created when a thin layer of rock from the east was pushed westward, up and over existing rock layers.

That discovery, as it happens, had immediate practical consequences. It turned out that the rocks on the surface of the mountains were masking rocks below that might be likely to contain petroleum deposits. Oil companies have already begun searching for deposits there, Brown says.

This is the first time researchers have ever conducted this type of exploration of the deep crust, Brown says.

In Ohio, the scientists are searching for what some believe is an ancient fault line where two continents collided a billion years ago, forming a mountain range that may be similar to the Himalayas, which were produced by the collision of India and Asia.

Ricky Vuittonet, 27, of Kress, Tex., as the senior observer, sits in a tiny trailer twisting dials and punching buttons for 12 1/2 hours a day, four days a week. His caravan draws a lot of onlookers.

The five trucks alone are guaranteed to draw a crowd. Like ungainly 22-ton ballerinas, they slowly push themselves up on legs attached to a pad that for 28 seconds vibrates the ground from 10 to 45 times per second.

The vibrations penetrate the soles of your shoes and seem to shake every bone.

The trucks wait 15 seconds for the vibrations to come back, then they move 20 feet and repeat the process.

Michael C. Hansen of the Ohio Geological Survey is excited by the prospect of discovering the mineral-rich Grenville Front, one reason the state was proposed for inclusion in the COCORP project in 1983.

Rocks of the Grenville Front surface in Canada, then dip under the Great Lakes. Geologists theorize the front runs under western Ohio near Anna and Sidney, areas of earthquake activity.

One theory is that the front was formed by two land masses “that collided and sutured to each other, stuck together,” Hansen says.

Hansen says that if the front can be found, “this will give us some idea of the continental drift that was taking place in the 1-billion-year range.”

COCORP’s interest goes beyond the Grenville Front to “basement rocks” that generally begin at about 6,000 feet down, Nelson says.

Unlike rocks closer to the surface, which formed from deposits of sediment, basement rocks are thought to have been formed when the Earth was hot, often from volcanic activity.

Already the COCORP scientists are discovering what appears to be unexpected layering in those rocks, Nelson says.

“This could mean there is a whole new package of sedimentary rocks we haven’t explored,” he says. Or, it could be traced to “a long layer of volcanic rocks that also would tell us what was going on at the time.

“I think we’re making quantum leaps forward on understanding the basement geology, although we’re not very far along,” he says.