Two Quakes Off South Oregon Coast - No Tsunami Alert

Published 12/29/20 at 6:45 PM PDT
By Oregon Coast Beach Connection staff

(Bandon, Oregon) – Two earthquakes shook off the southern Oregon coast in the last day, with the first one large enough to cause Oregon officials to clarify there would be no threat of a tsunami. (Graphic courtesy USGS)

The first occurred at 11:10 p.m. Monday night, at a magnitude 5.7 about 125 miles west of Bandon. It was logged at a depth of 10 kilometers deep, about six miles.

5.7 is considered a bit large for many of the underwater quakes that happen off the south coast, but there is no damage reported. However, the US Geological Survey (USGS) website is showing some 141 people reported having felt the quake. Reports came in mostly from the southern and central Oregon coast, but there were many in the Willamette Valley, some on the north coast, and even Portland. There were a few reports as far south as California and as far north as southern Washington.

The second quake occurred at 3:21 a.m. with a magnitude 3.2. That one was recorded about 100 miles west of Langlois, also at a depth of just over six miles.

It takes a magnitude 7.0 or higher to create a tsunami.

Most of these quakes off the southern Oregon coast take place on or around the Blanco Fracture, especially what is called the Blanco Ridge. All are connected to the larger Cascadia fault. In turn, these are all in the vicinity of the volcanic hot spot known as the Cascadia Subduction Zone, where the Juan de Fuca plate is slowly separating from the Pacific Plate. But it is the Blanco Fracture generally causing small quakes to happen with regularity.

The Blanco fracture isn’t a subduction zone in itself, like the larger Cascadia zone - which will someday produce a massive quake off the Oregon coast. Hence, the Blanco fracture can’t set off such a massive rattler on its own, but it could produce something around a magnitude 7 quake. Some studies suggest if this spot produces a quake that size it could trigger something larger from the Cascadia Subduction Zone.

Keep an eye on Oregon coast quakes: Oregon, Coast Earthquake Updates - Live Data Oregon, Washington, California, Tsunamis

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