The hydrophone system called the Sound Surveillance System, or SOSUS was used during the decades of the Cold War to monitor submarine activity in the northern Pacific Ocean. As the Cold War ebbed, these and other unique military assets were offered to civilian researchers performing environmental studies, Dziak said.
SOSUS also pointed the researchers to the activities leading to the "anti-plume" discovery outlined in Nature.
The number of earthquakes offshore initially stunned researchers because they weren't being detected on land even by the most sensitive seismometers. The scientists also discovered that these quakes occurred daily, but every so often there would be a "swarm" of as many as a thousand quakes in a three-week period.
"In the last 10 years, I've seen seven of these swarms," Dziak said. "The plate doesn't move in a continuous manner and some parts move faster than others. Every four years or so, a section of the Juan de Fuca Ridge exhibits a large earthquake swarm and lava breaks through onto the seafloor.
"Usually, the plate moves at about the rate a fingernail might grow say three centimeters a year. But when these swarms take place, the movement may be more like a meter in a two-week period."
On Monday, July 12, the region was jolted by a 4.9 magnitude quake just offshore from Dziak's Newport lab one that was felt more than 50 miles inland at the main OSU campus.
"There's a lot of activity going on out there," Dziak said of the offshore quakes. "That was one of the few that did show up on conventional seismic equipment and drew the attention of the public. There are hundreds, even thousands more that do not."
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Contact: Robert Dziak
robert.dziak@oregonstate.edu
541-867-0175
Oregon State University
14-Jul-2004