Cluster of Seven Quakes Off Oregon Coast, Some Within Minutes

Published 04/29/21 at 5:55 PM PDT
By Oregon Coast Beach Connection staff

(Bandon, Oregon) – A rather large cluster of underwater quakes hit off the Oregon coast Thursday morning, with four of them within minutes of each other. A total of six occurred between 3 a.m. and 6:30 a.m., while a seventh happened mid afternoon on Wednesday. (Graphic courtesy USGS)

All of them were about 180 miles west by northwest of Bandon, concentrated in a radius of several miles. Each happened along the Blanco Fracture Zone – which is physically connected to the greater Cascadia Subduction Zone but not directly related to it.

No tsunami alerts were issued. It takes at least a 7.0 magnitude quake to generate a tsunami.

The first was a magnitude 4.4 about 2:30 p.m. on Wednesday, approximately six miles deep.

The first of the major cluster was a M4.3 quake at 3:25 a.m.

The second took place at 3:30 a.m. and was the largest at M 5.4. The U.S. Geological Survey (USGS) said it received eight responses from the “Did You Feel It” report section of its website.

Third in the cluster was a M5.2 at quake at 3:35 a.m.

20 minutes later, a 5.3 magnitude quake happened at 3:58 a.m., with two reports of it being felt in the south Oregon coast region.

The sixth in the entire series happened at 6:25 a.m., clocking in at M 4.1. At 6:33 a.m., the final undersea shaker happened with a magnitude 3.9.

Earthquake magnitude measurements are extremely wide although the increments may appear small. A 7.0 is 1,000 times bigger than a 4.0, according to the USGS. But it is 31,622 times stronger in its release of energy.

See Oregon, Coast Earthquake Updates - Live Data Oregon, Washington, California, Tsunamis

Around 20 quakes a year are generated by the Blanco Fracture, which makes this essentially business as usual for the hotspot. It's the greater Cascadia fault that is the worrisome section, which will someday release a magnitude 9.0 megathrust and create havoc along the Oregon and Washington coastlines.

Contrary to some popular rumors these days, the Cascadia Subduction Zone is not releasing pressure with these smaller quakes. The big one will come no matter what the smaller faultlines do.

MORE PHOTOS BELOW

Crissey Field, Brookings - courtesy Bonnie Morela

Bandon, courtesy Manuela Durson

Otter Point, Gold Beach

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