Magnitude 3.7 earthquake wakes residents in southwest Washington
A tremor was recorded in the region, triggering alerts and reports of impact.
A magnitude 3.7 earthquake struck southwest Washington, United States, in the early hours of Saturday, September 5, waking residents across several communities and activating alert systems. The seismic event, which generated hundreds of reports and information about tremors in the area, quickly became a top‑of‑mind news item.
The tremor in southwest Washington
The quake was recorded at 4:09:28 a.m. local time, with its epicenter located 16.22 miles east‑northeast of Longview and 49.21 miles north of Portland. The depth was 10.95 miles, shallow enough for the shaking to be felt well beyond the immediate epicenter area.
Location and characteristics of the epicenter
The epicentral area lies in a forested region between Castle Rock and the Mount St. Helens National Volcanic Monument, a few miles west of the volcano and roughly parallel to State Highway 504, which connects Interstate 5 to Johnston Ridge.
Details of the seismic event
The Pacific Northwest Seismic Network (PNWS) was responsible for recording the quake. Initially posted with a preliminary magnitude of 3.8, the magnitude was later revised to a final 3.7 after analysts reviewed the data.
PNWS classified the magnitude as "minor" and estimated the shaking intensity at IV on the Modified Mercalli scale, described as "light." At this level, it is common for people inside buildings to feel dishes and windows rattle and for parked cars to shake, but structural damage is not expected.
Alerts and public information
The tremor awakened residents throughout Cowlitz County, and ShakeAlert system notifications were sent to phones from Longview to the Portland metropolitan area. ShakeAlert is a West Coast early‑warning system operated by the U.S. Geological Survey.
Monitoring and public reports
By mid‑morning, more than 730 personal reports of feeling the quake had been submitted, with the shake map extending north toward Olympia and south into the Portland area. The full event page remains available on the PNWS website, where residents can continue to submit their "Did You Feel It?" reports.
PNWS’s Facebook post about the earthquake generated over 500 reactions and 150 comments within a few hours, with many locals sharing what woke them up. Users interested in tracking regional seismic activity can follow updates via the MyNorthwest earthquake tracker, which uses live U.S. Geological Survey data for the Puget Sound region and southwest Washington.
With information from Seattle Red.
Source: Seattle Red