A 4.2-magnitude earthquake in Washington state has prompted a warning that further tremors are possible after more than 9,200 people reported feeling the shaking across the Puget Sound region.
The earthquake struck at about 2.05pm on Tuesday, September 29, near Wauna in Kitsap County, around 6km west-north-west of the community. It was initially recorded as magnitude 4.3 before being revised following further analysis.
Residents on the Kitsap Peninsula, as well as in Seattle, Tacoma, Bremerton and Bainbridge Island, reported weak shaking. The US Geological Survey said reports extended as far as Salem and Union in Oregon, and Nanaimo and Vancouver in British Columbia.
There were no immediate reports of injuries or significant damage. Some residents described hearing a boom before windows rattled and buildings shook, while a school seismograph in nearby Gig Harbor captured the event as it happened.
Aftershock forecast for Washington earthquake
The latest USGS forecast gives a 34 per cent chance of at least one aftershock measuring magnitude 3 or higher in the affected area during the week following the main earthquake. The probability of a magnitude 4 or higher aftershock over the same period is estimated at 7 per cent. ([earthquake.usgs.gov](https://earthquake.usgs.gov/earthquakes/eventpage/uw714111952/oaf/overview?utm_source=openai))
Scientists stress that the forecast describes probabilities rather than predicting the exact time or location of another earthquake. They also warn that aftershock activity generally declines over time but can remain above normal levels for months.
The earthquake came amid a period of increased seismic activity in the wider Pacific North-west, including several tremors west of Vancouver Island and a smaller earthquake near Mount Adams over the previous two days.
People who felt the shaking have been encouraged to submit reports to the USGS, which uses public accounts to help map the earthquake’s intensity and reach. ([fox13seattle.com](https://www.fox13seattle.com/news/earthquake-kitsap-county))
Seismologists at the Pacific Northwest Seismic Network said the experience of the earthquake varied according to distance from the epicentre, local ground conditions and the type of building people were in. They urged residents to remain prepared for future earthquakes in a region where seismic activity is common. ([fox13seattle.com](https://www.fox13seattle.com/news/earthquake-shakes-puget-sound))
