Earthquake rattles much of Southwest Washington Thursday night

A magnitude 3.5 earthquake was felt by many in Southwest Washington Thursday night, with residents from Longview to Centralia to East Lewis County reporting they felt the quake.

According to the Pacific Northwest Seismic Network (PNSN), the earthquake epicenter was along the border between Cowlitz and Lewis Counties just south of Morton and north of Mount St. Helens. The earthquake was reported at a depth of 8.5 miles at 11:16 p.m. Thursday.

According to Britannica, a 3.5 earthquake is considered “minor” and while it may be “felt by many people,” it is unlikely to cause damage. Between 12,000 and 100,000 earthquakes of this magnitude occur each year, according to Britannica.

Earlier Thursday, the PNSN reported a magnitude 6.4 earthquake off the coast of Vancouver Island. In a Facebook post, the PNSN said a cluster of fireworks off the coast of Washington was “notable for their size & number” but did not “represent a threat.”

The earthquakes off the Washington coast occurred on the Juan de Fuca ridge and the oceanic Nootka fault zone, not the Cascadia Subduction Zone.

“These types of earthquakes are very unlikely to cause tsunamis, and also very unlikely to affect the subduction fault,’ the PNSN wrote.

Scientists closely monitor the Cascadia subduction zone for signs of the “Big One.”

The last megathrust that occurred in the Cascadia Subduction Zone took place in 1700 and was an estimated 9.0 earthquake. Scientists estimate these quakes occur every 300 to 500 years along the fault line, which runs 600 miles along the Pacific coast.

According to the U.S. Geological Survey, “approximately 350 earthquakes have been located at Mount St. Helens” since mid-February,” which represents “the largest short-term increase in earthquake rates since the last eruption ended in 2008.”

While the activity is labeled “recharging,” the USGS does not consider an eruption imminent.