Minor Undersea Earthquake Off South Oregon Coast: 4.0 Magnitude, No Tsunami Threat

Published 03/28/23 at 8:30 PM
By Oregon Coast Beach Connection staff

(Bandon, Oregon) – The southern Oregon coast got a wee jolt in the early evening on Sunday, as a magnitude 4.0 undersea quake erupted offshore some 120 or miles away. The small rattler was about six miles below the ocean and did no damage on land. (Graphic USGS)

U.S. Geological Survey (USGS) reported the earthquake shook at 9:53 p.m., at 130 miles west of Coos Bay and 124 miles west of Bandon.

No tsunami threat occurred because of the small quake, as it takes a 7.0 magnitude shaker or stronger to initiate a tsunami.

The USGS said two people reported that they had felt the quake. One was in Langlois, right outside of Bandon. The other was in Rockaway Beach, which is well over 100 miles away.

Courtesy USGS

USGS' “Shake Alert” was not activated as it was too far from shore to trigger the app alert, although a 4.5 magnitude would create a quake alert if closer to this part of the south Oregon coast.

This quake – as in most others from the south Oregon coast – fired off from what is known as the Blanco Fracture Zone. You can see from the USGS graphic at the stop of this story there is a kind of diagonal line of locales that other undersea earthquakes have emanated from.

This area is part of the Blanco Fracture Zone, a south Oregon coast faultine that is separate from the larger Cascadia Subduction zone fault. In this area, two plates are rubbing up against each other and occasionally releasing that pressure. The two faultlines are not directly connected, and the Blanco Fracture cannot trigger the 9.0 quake from the Cascadia Subduction Zone that is expected some day along the Oregon coast.

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

Contrary to popular belief, these small but regular quakes in the Blanco area are not releasing pressure from the greater faultline.

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.

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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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Keywords: south Oregon coast earthquake, tsunami alert, Blanco Fracture Zone, Oregon Coast Beach Connection