Science

Researchers Explain Recent Coastal Earthquake Swarms

OPB | Oct. 26, 2009 9:04 a.m. | Updated: July 17, 2012 1:09 a.m. | Bend, OR

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By Ethan Lindsey

Oregon State University researchers announced Monday they solved the mystery of the unexplained earthquake swarms of 2008. Ethan Lindsey reports.


On March 30, 2008, the earthquakes began — and for 10 days, more than 1000 tremors shook the sea floor, sometimes reaching a magnitude of 5.0 — a dangerous level.

Then, just as suddenly as they started, they stopped for a short period. Scientists were baffled.

Bob Dziak is an Oregon State University marine geologist.

His team now says the culprit was an undiscovered series of fault lines, about 140 miles off the coast.

Bob Dziak: “Going out and investigating the site, we found faults in the area with really big slip, along them. So that was probably the source of the earthquake swarms, so that was a bit of a surprise.”

Dziak says they don’t know if the fault lines were brand-new, or just unseen until now – but either way, the data suggest the sea floor off the Oregon coast is actively changing.

He says the discovery doesn't increase the state's onshore earthquake risk.

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