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Seismic sail through the Andes.

Seismic sail through the Andes

Dragging a 2-mile-long streamer that holds thousands of underwater microphones, seismologists aboard the research vessel Robert D. Conrad are cruising in the waterways that weave through the extreme southern portion of the Andes Mountains. They are attempting to use underwater explosions to get at the roots of a longstanding puzzle about the origin of the southern mountains in that range.

Every 20 seconds, air guns towed behind the ship will go off, sending sound waves through the water and down into the earth's crust. The microphones on the streamer will detect waves that reflect off irregularities in the crust, thereby producing a sonic picture of the Andes' innards, says chief investigator John C. Mutter of the Lamont-Doherty Geologic Observatory in Palisades, N.Y. This underwater seismic technique is often used out in the open ocean, but scientists are only beginning to bring the technology into enclosed waterways. These surveys will help geologists understand why the mountains are as large as they are, says Mutter.

Seismic techniques conducted on land are a common geological tool for probing into the earth. But marine techniques can be cheaper and easier than land-based studies, especially in a remote and rugged area like the Andes. In one day, marine seismologists can map the same amount of area that it would take a land crew three months to cover.
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Title Annotation:seismological research in Andes Mountains
Publication:Science News
Date:Feb 20, 1988
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