Vancouver Island Magnitude 4.9 Is 3rd Strong Earthquake In Region This Week

SEATTLE, WA — A magnitude 4.9 earthquake struck off the coast of Vancouver Island early Friday morning, which is the third strong quake in the region this week.

On Wednesday, a magnitude 4.2 quake struck about 34 miles west of Seattle along the western edge of the Kitsap Peninsula. That same night, a magnitude 4.4 struck off the coast of Vancouver Island.

Friday's quake happened about 275 miles west of Victoria, British Columbia, far enough out in the Pacific Ocean that no damage was reported. But seismologists say that relatively strong quakes in the magnitude 4 range can foreshadow larger quakes to come.

On Thursday, the Pacific Northwest Seismic Center's Bill Steele told Patch.com that the 48 hours following a relatively strong quake are sensitive.

"In the 48 hours after, there's an increase in probability [of a larger quake], then it drops down to background probability. It's a curve that drops off rapidly," he said.

The three recent earthquakes have happened during the periodic "slow-slip" event that affects the Pacific Northwest every 14 months. During slow-slip, the region experiences what is essentially a long, slow earthquake deep underground over the course of about two weeks.

Deep under the Pacific Ocean, the Juan de Fuca tectonic plate is subducting under the North American plate; at some point, enough pressure will build up that the two plates will come apart, causing a Cascadia subduction zone megathrust earthquake. There's a slightly higher risk of a Cascadia event during the periodic slow-slip event.

The key word there is "slight," Steele said.

"I want to remind folks there is a slight increase chance in a [Cascadia event], but it's so small from the background daily risk," he said.

Still, it's a good time to review your earthquake preparedness; seismologists say there's about a 37 percent chance of a Cascadia event occurring within the next 50 years.

Image via Patch.com