May 12 2021
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Previous story Small Quake Shakes Off Oregon Coast This Weekend As Another Rattles Alaska Next story

Story By Oregon Coast Beach Connection staff - Story Source
Published on Sunday February 28, 2021 - 8:38 PM

(Bandon, Oregon) – A small earthquake shook off the southern Oregon coast early Saturday morning, clocking in at a minor 4.0 in magnitude. Meanwhile, a larger quake rattled parts of southern Alaska a bit later in the day, reminding some Oregonians of the quake there that caused a tsunami here in the '60s. (Graphic courtesy Pacific Northwest Seismic Network. Other recent tremblors are in yellow)

The undersea quake took place about 250 miles off the south coast, this time in more of a straight line westward from Dunes City instead of the usual Coos Bay or Reedsport. At a magnitude 4.0 it was not strong enough to generate a tsunami; it takes at least a 7.0 to do that. The quake shook at 5:33 a.m. Saturday at a depth of about six miles.

According to the U.S. Geological Survey (USGS), three people reported feeling the quake.

This quake follows a set of two minor quakes that shook a bit east of this spot last week on February 20 – one a magnitude 5.1 and the other a 4.9.

The southern Oregon coast is an area with many active faultlines, although not all of them directly related to the larger Cascadia Subduction Zone. While that faultline is where the two continental plates meet, the Blanco Fracture intersects with other sections of these boundaries, creating more seismically-active areas. The Blanco Fracture portion of the plate boundaries zone hosts a number of areas where the two sections are locked against each other in a vertical manner, and when the plate moves these locked sections can release and generate an earthquake.

The Blanco Fracture generates more than 20 quakes a year on average, so this is nothing unusual. 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.