Swarm of Oregon Coast Quakes Slightly Unusual But Not Doomsday Sign

Published 07/31/2018 at 2:41 PM PDT
By Oregon Coast Beach Connection Staff

(Florence, Oregon) – A sizable swarm of about 11 small quakes shook off the Oregon coast last week, and then another minute one rattles the waters on Sunday morning. No tsunami alerts were issued, no one was injured and in fact it appears as if they weren’t even felt by humans.

Still, it begged the question for some: is this the precursor to the big one?

No, say U.S. Geological Survey scientists. While it is slightly unusual, it is also a reminder of what lurks off these shores.

The USGS said a magnitude 5.3 quake occurred shortly after 7 a.m., approximately 280 miles west of Florence, Oregon. The quake was about seven miles beneath the sea floor.

It requires at least a 7.0 magnitude quake to generate a tsunami.

A string of 10 quakes happened Tuesday morning, mostly about 125 miles west of Gold Beach. The largest was a 5.6 magnitude. Although the region will at some point produce a massive subduction quake and tsunami, USGS scientists say this isn’t the sign of the big one. Small quakes like this are common along the fault lines off the Oregon coast.

A network of them runs parallel to the coast, stretching some 600 miles long along the western U.S., called the Cascadia Subduction Zone.

Measurements of earthquake magnitudes 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. Stay up-to-date with Oregon, Coast Earthquake Updates - Live Data Oregon, Washington, California, Tsunamis.

Other Oregon coast earthquake information from this year:

4.0 Quake Off the Southern Oregon Coast Sunday, No Alerts A 4.0 earthquake shook up the ocean floor off the southern Oregon coast in April. The small quake was centered about 120 miles west of Bandon, happening at 7:20 p.m. It happened about six miles beneath the bottom.

Small 3.8 Quake Off Southern Oregon Coast A small quake struck off the southern Oregon coast early Thursday morning (April), about 70 miles west of Charleston. The submarine quake caused no damage but there reports it was felt as far away as Eugene.

The earthquake was a magnitude 3.8, which hit at 1:44 a.m. The USGS is listing the quake as 67 miles west of an incorporated town called Barview, which is immediately north of Charleston. This is not to be confused with the town of Barview on the north Oregon coast, next to Garibaldi.

The quake was centered about six miles deep. That location is 98 miles SW of Newport.

For a time, the USGS had two earthquakes listed around that location at the same time of 1:44 a.m., but about three seconds apart. A scientist with the USGS office in Seattle told Oregon Coast Beach Connection it took some time to verify the and unify two different sensor readings.

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