An aerial photo shows the locations of two earthquakes and five aftershocks in and near Monroe, which rattled the Puget Sound region on July 12. The first was the magnitude 4.6 quake at upper right, 13 miles under the intersection of U.S. 2 and Fryelands Boulevard SE at 2:51 a.m. The second, magnitude 3.5, occurred 18 miles under the Old Snohomish-Monroe Road at 2:53 a.m. The aftershocks followed during the ensuing two hours. This image depicts an area about 3 miles wide. (Herald staff and the Pacific Northwest Seismic Network)

An aerial photo shows the locations of two earthquakes and five aftershocks in and near Monroe, which rattled the Puget Sound region on July 12. The first was the magnitude 4.6 quake at upper right, 13 miles under the intersection of U.S. 2 and Fryelands Boulevard SE at 2:51 a.m. The second, magnitude 3.5, occurred 18 miles under the Old Snohomish-Monroe Road at 2:53 a.m. The aftershocks followed during the ensuing two hours. This image depicts an area about 3 miles wide. (Herald staff and the Pacific Northwest Seismic Network)

July’s Monroe earthquake is informing plans for future danger

Gathered by lucky accident, data from the 4.6-magnitude quake could help assess bigger hazards.

MONROE — The magnitude 4.6 Monroe earthquake felt by thousands of Puget Sound-area residents in July is helping scientists assess how future quakes will impact the region.

The relatively tame event was serendipitous for a group of scientists from Harvard, the University of Washington and the Pacific Northwest Seismic Network.

Just over a week before the earthquake hit, the group placed seismometers throughout the Seattle-Tacoma area to record how background noises like traffic or swaying trees interacted with the area’s geology.

The scientists planned to study the Seattle and Tacoma sedimentary basins — depressions filled with soft sediment, rather than rock — to learn more about how they’re shaped.

But when the Monroe earthquake hit, they got more data than they bargained for.

Seattle, Tacoma and Everett all lie within some of Puget Sound’s largest basins. These areas magnify how much the ground shakes in an earthquake.

“You can think of a basin as a bowl of Jello-O,” said Alex Hutko, a project lead with the Seismic Network.

If the bowl is shaking, the stack of Jell-O inside it shakes even more.

Seattle, Tacoma, Everett and Mukilteo all lie within some of Puget Sound’s largest basins. These areas magnify how much the ground shakes in an earthquake. (Erin Wirth)

Seattle, Tacoma, Everett and Mukilteo all lie within some of Puget Sound’s largest basins. These areas magnify how much the ground shakes in an earthquake. (Erin Wirth)

Everett’s basin is centered under Hat Island in Possession Sound and extends north to Marysville, east to Granite Falls and west past Whidbey Island.

With the data retrieved during the Monroe earthquake, U.S. Geological Survey geophysicist Erin Wirth said scientists are now able to study just how much basins amplify ground shaking.

The amount a basin increases shaking is the same regardless of an earthquake’s magnitude, so the data will help them determine how future, bigger quakes will impact Puget Sound’s urban areas, Wirth said.

But each basin is unique. The Seattle Basin won’t magnify shaking the same way Everett’s will.

Scientists are still combing through the data, and results won’t be published for months to a year. In the meantime, Wirth said, they’re learning just how crucial it is to know how urban basins will respond to larger-magnitude earthquakes.

The amplification will affect tall structures the most, she said, so the research could inform how buildings are built to withstand shaking.

“This has driven home the need to have these (instruments) in these basins permanently,” Wirth said.

Julia-Grace Sanders: 425-339-3439; jgsanders@heraldnet.com.

Talk to us

More in Local News

Keith Wagoner
Senator becomes first GOP candidate for secretary of state

Sen. Keith Wagoner will challenge Democrat Steve Hobbs, who was appointed to the statewide post in November

Madison is one of three aging elementary schools that would be torn down and replaced if the Everett schools bond is passed next year. (Sue Misao / Herald file)
Everett school leaders have 2 big levies on February ballot

The district is asking voters to renew a levy for programs and operations, and to pass a $325 million capital and tech levy.

Reagan Dunn to take on U.S. Rep. Kim Schrier in 8th District

The Republican is challenging incumbent Democrat Kim Schrier in a district which could include a slice of Snohomish County.

Charges: Arlington-area shooting suspect had gun stash, bomb lab

A bomb squad spent two days detonating explosive material. Detectives also discovered an underground bunker full of guns.

A fatal crash prompted closure of West Mukilteo Boulevard between Forest Park and Dogwood Drive Friday afternoon. (Everett Police Department) 20211126
2 identified in deadly T-bone crash in Everett

Otila Retel Azanedo de Jones, 67, and William Jones, 85, died at the scene.

Two brother bear cubs, burned in a fire last summer, were recently reunited at PAWS in Lynnwood. (PAWS) 20211129
Bear cubs, burned in wildfires, reunited in viral video in Lynnwood

The brother cubs are being treated at PAWS Wildlife Center. They were injured in a wildfire near Lake Chelan.

A car breaks and waits for traffic to pass before turning onto 123rd Avenue on Monday, Nov. 22, 2021 in Lake Stevens, Wa. (Olivia Vanni / The Herald)
Can roundabouts, lower speed limit make 84th Street NE safer?

Maybe, but transportation and disability advocates want design features to make crossing safe.

Everett officials have questions about a 125-room hotel shelter

City Council members say they weren’t aware of the county’s proposal until it made headlines.

A banner outside the door of Goodies in Mountlake Terrace says, “$795,000 Hit 5 ticket sold here.” (Andrea Brown / The Herald) 20211201
Who has the $795,000 Hit 5 ticket sold in Mountlake Terrace?

The winner has until Dec. 8 to claim the prize from a lottery ticket sold June 11 at Goodies Food.

Most Read