Swarm of Over 40 Earthquakes in One Day Rattle Oregon

by Jennifer Shea

More than 40 earthquakes shook northwest Oregon on Tuesday, worrying residents and intriguing geologists. The quakes, with magnitudes varying from 3.5 to 5.8, hit off the coast of Oregon, and so only a few people reported feeling some shaking.

Most of the earthquakes struck about 200 to 250 miles off the coast of Newport, Oregon, KGW 8 reports. The National Weather Service said the geological activity posed no tsunami threat.

A U.S. Geological Service (USGS) earthquake map showed roughly 50 minor earthquakes and aftershocks in the area between Tuesday and Wednesday. Roughly a dozen had magnitudes above 5.0.  

Blanco Fracture Zone Very Active with Earthquakes

The area where the earthquakes hit is known as the Blanco Fracture Zone. It’s a high-activity area, with 49 earthquakes above a 4.5 magnitude striking there over just the last five years.

Because Oregon is close to moving fault lines, earthquakes happen frequently off the state’s coast. There’s also the nearby Cascadia Subduction Zone, where the Juan de Fuca plate sits beneath the North American plate, ratcheting up pressure and then releasing it.

Geologists say there’s a 37 percent chance of a 7.1 or higher magnitude earthquake in the Cascadia Subduction Zone over the next 50 years. Such a quake would set off a huge tsunami that could wreak havoc on Northern California, Oregon, and Washington state.

Blanco Is Unlikely to Give Rise to a Tsunami

While Oregonians have cause to worry about the Cascadia Subduction Zone, the Blanco Fracture Zone, where Tuesday’s earthquakes emanated from, is no cause for alarm, geologists say.

Geology researcher Dana Hunter once compared Blanco to a fresh-baked cookie, according to NPR, saying it has a “young, warm crust” that tends more to crumble than to send seismic waves crashing through Oregon and California. Fortunately for residents of the area, earthquakes along the Blanco Fracture Zone don’t create enough vertical displacement to cause a tsunami.

But as for the Cascadia Subduction Zone? Watch out, Oregon. The Oregon Office of Emergency estimates that the zone has the potential to generate a 9.0-plus magnitude earthquake, which could cause a tsunami of up to 100 feet in height.

Local residents can only hope that doesn’t come to pass. It would mean widespread destruction for much of the Pacific Northwest. And there’s no sign that authorities in the area have undertaken any preparations to brace for such a disaster.

In the meantime, the little tremors and shakes from the neighboring Blanco Fracture Zone are apparently nothing to stress about.