Scientists say a group of previously unknown faults was behind an odd swarm of earthquakes last year off the Oregon Coast. But just what set them off remains unknown.
Oregon State University marine geologist Robert Dziak (ZEE-ack) says the discovery about 140 miles off Newport suggests the Juan de Fuca Plate is still actively converging with North America in the Cascadia Subduction Zone.
He adds that they do not know what triggered the quakes, and it is not clear if they represent a normal release of stress within the plate, or something else.
Using a network of underwater microphones, scientists recorded some 1,600 quakes over two months. Most were between magnitude 3.0 and 4.0, but a few exceeded magnitude 5.0.
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