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Mysterious Swarm of Earthquakes Detected Off Oregon Coast

Thursday, May 08, 2008 by: Barbara L. Minton
Tags: earthquakes, health news, Natural News

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(NewsTarget) An unusual swarm of earthquakes off the coast of central Oregon has been detected by scientists listening to underwater microphones called hydrophones. More than 600 earthquakes were recorded during the first ten days in April by Oregon State University's Hatfield Marine Science Center. The earthquakes are in an area not typically known for a high degree of seismic activity.

This swarm is unique because it is occurring within the middle of the Juan de Fuca plate, away from the major regional tectonic boundaries, according to OSU marine geologist Robert Dziak. "In the 17 years we've been monitoring the ocean though hydrophone recording, we've never seen a swarm of earthquakes in an area such as this," Dziak says. "We're not certain what it means."

Scientists hope to send out the OSU research ship, Wecoma, to take water samples looking for evidence that sediment on the ocean bottom has been stirred up, and chemicals in the water that would indicate whether the process causing the earthquakes is tectonic or hydrothermal.

"It looks like what happens before a volcanic eruption, except there are no volcanoes in the area," Dziak said.

The crust of the Earth is made up of plates that rest on molten rock, often called magma, which are rubbing together up and down and side to side. When the magma erupts through the crust it creates volcanoes. This can happen in the middle of a plate. When the plates bump against each other, they create earthquakes along the edges of the plates.

The earthquakes occurred in a basin 150 nautical miles southwest of Newport. At least three of the earthquakes have been of a magnitude of 5.0 or higher, which is unusual according to Dziak. They have not followed the typical pattern of a major shock followed by a series of diminishing aftershocks. Because they originated offshore and deep within the ocean, few of these earthquakes could be felt on shore.

Looking at the decreasing intensity of the tremors as they radiate outward suggests that the earthquakes are not the usual sequence of a primary event followed by a series of aftershocks. "Some process going on down there is sustaining a high stress rate in the crust," Dziak pointed out.

The system of hydrophones used by Dziak and colleagues for monitoring the quakes is located on the ocean floor. The network, called the Sound Surveillance System, was used during the decades of the Cold War to monitor submarine activity in the northern Pacific Ocean. When the Cold War ended, these assets were offered to civilian researchers.

To those listening on the hydrophones, the quakes sound like low rumbling thunder and are unlike anything scientists have heard since they have been in possession of the instruments, Dziak says. Some of the quakes have also been detected by earthquake instruments on land.

The earthquake swarm has captured the attention of the scientists who are puzzled by the fact that it is taking place in the middle of the plate and not at a boundary. "It's something worth keeping an eye on" admitted Dziak.


Science Daily, April 14, 2008.

Barnard, Jeff, Associated Press, April 11, 2008.

About the author

Barbara is a school psychologist, a published author in the area of personal finance, a breast cancer survivor using "alternative" treatments, a born existentialist, and a student of nature and all things natural.

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