Over the past 24 hours there have been 5 medium magnitude earthquakes a little over 300 miles off of the Central Oregon Coast. Three of those quakes have registered at least 5.5 magnitude, and they are all shallow quakes.
1 Day, Magnitude 2.5+ Worldwide
Moderate quakes continue to shake off Oregon coast
The earthquakes were shallow, at 6 miles deep, often a signal of a dangerous quake.
It usually takes an earthquake of magnitude 7 or better to trigger a tsunami, said geophysicist Paul Caruso of the U.S. Geological Survey.
The quakes were clustered in an area about 300 miles west of Coos Bay, Oregon, along what's known as the Blanco Fracture Zone.
"It's a well-known place for earthquakes," said another agency geophysicist, Julie Dutton. "They're frequent throughout the year."
A 2008 agency report said the zone had produced about 70 of magnitude 5 or greater in the previous 28 years, as many as eight some years. Also in 2008, scientists detected a swarm of hundreds of smaller quakes.
In the Blanco faults, blocks of crust slide horizontally past each other, Dutton said. Faults that feature blocks rising and falling violently in relation to each other are the kind that can generate the energy for tsunamis, she said.
When you live in a tsunami zone like I do in the Pacific Northwest we have to be mindful of offshore quakes. One could eventually be
a monster magnitude 9 quake that could generate catastrophic tsunamis in nearby coastal regions and all around the rim of the north Pacific.
Its interesting to note all five quakes were at the exact same shallow depth.
UPDATE Two more earthquakes occurred overnight at exactly the same depth. One was a 3.9 and the most recent a 4.2.