A preliminary magnitude 4.2 earthquake struck the Puget Sound region in Washington on Tuesday afternoon, sending sudden jolts across nearby communities and prompting brief disruptions as far away as Seattle. According to initial reports recorded by the U.S. Geological Survey (USGS) and the Pacific Northwest Seismic Network, the seismic event occurred at 2:05 p.m. local time.
- Details on Shaking and Regional Impact
- Why Did the Earthquake Happen?
- Alert Systems and Aftershock Probabilities
- Frequently Asked Questions
- What was the magnitude of the Wauna earthquake?
- When did the earthquake strike?
- Where was the epicenter located?
- Were there any injuries or structural damages?
- Did emergency cell phone alerts go out?
The epicenter was centered approximately 3.4 miles west-northwest of Wauna, Washington, along the Pierce and Kitsap County lines. Seismologists noted the depth of the quake reached approximately 16 to 17 miles (27 to 27.9 kilometers). Initial assessments from NOAA’s Tsunami Warning System confirmed there was no immediate threat of a tsunami following the tremor.
Details on Shaking and Regional Impact
Residents across Seattle, Tacoma, Olympia, Bremerton, and Port Orchard reported feeling weak to moderate shaking indoors. Many took to social media to describe the sudden movement. Stephanie Holloway shared online that the tremor “shook the whole house and the chandelier in the living room,” while Courtney Clark Childers noted feeling shaken back and forth.
The shaking was forceful enough to temporarily interrupt public proceedings. In Seattle, city councilmembers paused their scheduled 2 p.m. meeting as the room shuddered. Once normal operations resumed, officials moved swiftly through the agenda out of an abundance of caution.
The preliminary location of the quake was calculated roughly 8.3 miles north-northwest of Artondale, nearly 10 miles south-southwest of Port Orchard, about 12 miles south-southwest of Bremerton, and around 27 miles north-northeast of Olympia.
Why Did the Earthquake Happen?
Earthquakes of this magnitude are a normal part of the active seismicity in the Puget Sound region. The area faces ongoing tectonic risks from faults located directly beneath Puget Sound and the offshore Cascadia subduction zone, where the oceanic Juan de Fuca plate pushes beneath the North American plate.
Because the quake was relatively shallow, residents widely felt it indoors across multiple counties. Intensity models categorized the overall expected surface impact as “light” under the Modified Mercalli scale. USGS representatives encouraged anyone who experienced the shaking to submit a “Felt Report” to assist researchers in mapping local intensity data.
Alert Systems and Aftershock Probabilities
The ShakeAlert Earthquake Warning System successfully detected the seismic wave. However, the magnitude fell below the threshold required to trigger automated wireless emergency alerts or FEMA cell phone notifications. For reference, the ShakeAlert system triggers FEMA Wireless Emergency Alerts at magnitude 5.0+, app notifications at 4.5+, and automated public systems at 4.0+.
According to USGS statistical models following the event, there is a moderate 37% chance of a magnitude 3 or greater aftershock occurring within the week, and an 8% probability of a magnitude 4 aftershock. The probability of an even larger magnitude earthquake following this event remains under 1%.
Emergency management agencies remind Pacific Northwest residents to maintain standard earthquake readiness. This includes securing heavy indoor furniture, establishing family communication plans, and stocking emergency supplies.
Frequently Asked Questions
What was the magnitude of the Wauna earthquake?
The earthquake was measured at a preliminary magnitude of 4.2 by both the U.S. Geological Survey and the Pacific Northwest Seismic Network.
When did the earthquake strike?
The seismic event occurred at precisely 2:05 p.m. PT on Tuesday, September 29.
Where was the epicenter located?
The epicenter was located approximately 3.4 miles west-northwest of Wauna, Washington, at a depth of about 17 miles, along the border of Pierce and Kitsap counties.
Were there any injuries or structural damages?
As of initial reports from local authorities and the USGS, there have been no injuries or major structural damages reported across the Puget Sound region.
Did emergency cell phone alerts go out?
No cell phone alerts were triggered because the 4.2 magnitude fell below the 4.5 threshold required for ShakeAlert app notifications and the 5.0 threshold for FEMA Wireless Emergency Alerts.
