Scientists baffled by hundreds of earthquakes off Oregon coast

www.chinapost.com.tw/print/151683.htm

seattletimes.nwsource.com/html/localnews/20043447 28_webearthquakes12.html

Sunday, April 13, 2008
AP

GRANTS PASS, Oregon -- Scientists listening to underwater microphones have detected an unusual swarm of earthquakes off central Oregon, something that often happens before a volcanic eruption -- except there are no volcanoes in the area.

Scientists don't know exactly what the earthquakes mean, but they could be the result of molten rock rumbling away from the recognized earthquake faults off Oregon, said Robert Dziak, a geophysicist for the National Oceanic and Atmospheric Administration and Oregon State University.

There have been more than 600 quakes over the past 10 days in a basin 150 miles (240 kilometers) southwest of Newport. The biggest was magnitude 5.4, and two others were more than magnitude 5.0, OSU reported.

On the hydrophones, the quakes sound like low thunder and are unlike anything scientists have heard in 17 years of listening, Dziak said. Some of the quakes have also been detected by earthquake instruments on land.

The hydrophones are left over from a network the Navy used to listen for submarines during the Cold War.

They routinely detect passing ships, earthquakes on the ocean bottom and whales calling to one another.

Scientists hope to send out an OSU research ship to take water samples, looking for evidence that sediment has been stirred up and chemicals that would indicate magma is moving up through the Juan de Fuca Plate, Dziak said.

The quakes have not followed the typical pattern of a major shock followed by a series of diminishing aftershocks, and few have been strong enough to be felt on shore.

The Earth's crust is made up of plates that rest on molten rock, which are rubbing together. When the molten rock, or magma, erupts through the crust, it creates volcanoes.

That can happen in the middle of a plate. When the plates lurch against each other, they create earthquakes along the edges.

In this case, the Juan de Fuca Plate is a small piece of crust being crushed between the Pacific Plate and North America, Dziak said. 

Not to mention the quake in China. The death toll is getting up there. As devestating as Northridge and San Francisco quakes were, the death toll doesn't even approach the horrific figures of other countries. Our strict building codes have much to do with it. Yet, with a quake the magnitude of 7, there's not a whole that can be done about it.

The Pacific Plate and the North American Plate collided millions of years ago. The Pacific Plate, over geological time, subducted under the North American Plate, causing an uplift of what are now the western states. Oceanic fossils can be found in Wyoming and the Grand Canyon. This process of subduction is still occurring off the coast of Washington and Oregon.

A thousand years ago the quake may not have killed anyone. 

More people, more buildings, more congestion, and they're startled at the increase in lives lost.  

No mention of the quakes around Reno increasing?

The Newfoundland Hurricane of 1775 killed over 4,000 people, Pointe-A-Pitre lost over 6,000 lives to a hurricane in 1776 and 4 years later The Great Hurricane of 1780 killed over 27,000 people.  Going back in time there were rashes of natural disasters.  The deadliest earthquake to hit China was in 1556.

About the same time as those hurricanes (from our vantage point) the Lisbon Earthquake killed 60-100,000 people.  Folks said God was mad because Ben Franklin invented the lightning rod.

And wasn't there a famous war during that time as well ;)