Swarm of Ten Quakes Off S. Oregon Coast, 7 Within Minutes - Update

Updated 3/28/24 at 4:35 p.m.
By Andre' Hagestedt / Oregon Coast Beach Connection

(Port Orford, Oregon) – UPDATES FROM GEOLOGISTS. A wide-ranging swarm of underwater quakes hit off the south Oregon coast starting Monday night, totaling ten small to medium quakes so far. The bulk of them happened in a small area around the Gorda Ridge, about 100 miles offshore from Port Orford and Gold Beach. Two happened a short distance from Bandon, only about 24 miles offshore. (Graphic courtesy USGS)

The U.S. Geological Survey (USGS) recorded the data, and also collected some input from the public who said they felt some of them.

No tsunami alert was issued for any of these, which ranged from a magnitude 2.1 to a M 5.7, although some quake apps did go off for at least one shaker. No damage occurred and no danger is expected.

The first lit up data centers on Monday at 5:30 p.m., with a M 3.7 130 miles west of Bandon. All ten were about six miles deep.

Tuesday's (March 26) quakes:

1:15 p.m.: M 3.0 about 146 miles west of Port Orford.

8:22 p.m. M 4.4 at 109 miles WSW of Port Orford.
8:14 p.m. M 3.9 103 miles WSW of Port Orford.

8:23 p.m.: M 5.7 a little more than 100 miles WSW of Port Orford. This one set off some quake alert apps and caused NOAA to state there was no tsunami threat. This is considered a moderate quake, the USGS said.

Several people reported feeling this quake, including around Brookings and Bandon. Some as far south as Crescent City, California, into Eugene, Blogdett and even Portland reported to the USGS they had felt it.

8:25 p.m.: M 4.8 a little more than 100 miles WSW of Port Orford.
8:34 p.m.: M 3.5 at 105 miles WSW of Port Orford.
8:49 p.m. M 4.1 around 100 miles WSW of Port Orford.
10:14 p.m.: M 1.8 a little more than 20 miles WNW of Port Orford.
1:40 a.m. on Wednesday morning: M 2.1 a little more than 20 miles west of Bandon.

It requires at least a magnitude 7.0 to initiate a tsunami.

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

The two close to shore at Bandon are an interesting curiosity as normally these quakes happen out there by the Blanco Fracture Zone. The two near Bandon are in an area that doesn't appear to have a name, sitting just outside the boundaries of the main faultlines.

PSU geologist Dr. Scott Burns and Seaside geologist Tom Horning agree that it's likely still part of the Gorda Ridge and Blanco Fracture in some way.

"It aligns with Cape Blanco and the Gorda Transform Fault, so it is my guess that the two faults moved due to strain release along the spreading center farther to the south. It may not be as active as the Gorda Ridge, but it is lifting Cape Blanco fast enough to create the cape in the first place," Horning told Oregon Coast Beach Connection.

These fracture lines are separate from the bigger Cascadia Subduction zone fault off the Oregon coast, though they are close in the region. The Blanco Ridge area is where two plates are rubbing up against each other and occasionally release pressure.

They do not affect the larger fault offshore. Contrary to popular belief, they do not relieve pressure in the main Cascadia Subduction Zone.

In December of 2021, an astounding 70 small quakes rattled in this area around the southern Oregon coast for about 36 hours, although much of it a bit farther north of the usual area.

These swarms came on the 60th anniversary of the massive Alaska Quake of 1964, which devastated that region and created a tsunami that hit the Oregon coast from Warrenton down through at least Florence. It killed four children camping in Newport.

See 1964 Tsunami Part 1: Its Impact on S. Oregon Coast
-- 1964 Tsunami Part 2: Tragedy, Destruction Hits Central Oregon Coast
-- 1964 Tsunami Part 3: Tearing Up Bridges, Homes on the N. Oregon Coast

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Andre' GW Hagestedt is editor, owner and primary photographer / videographer of Oregon Coast Beach Connection, an online publication that sees over 1 million pageviews per month. He is also author of several books about the coast.

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