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.

More in News

Two Renton officers involved in shooting

Suspect allegedly had a shotgun and a knife

Despite concerns, homelessness authority moves toward final Seattle vote

Seattle’s homelessness committee aligned the city’s plan with King County’s.

King County’s current climate action plan was adopted in 2015 and has provided a blueprint for reducing emissions and preparing for climate change. File photo
King County approves environmental justice provision

An update to the King County climate action plan should include an… Continue reading

Homelessness authority approved by King County, awaits Seattle vote

The agreement would consolidate emergency services for people experiencing homelessness.

The King County Courthouse is located at 516 Third Ave. in downtown Seattle. Photo courtesy of King County
Council approves $600,000 to increase security at King County Courthouse

The funding will be split evenly between increasing deputies, security and social services.

Luck be Renton’s lady

Chamber of commerce ends the year in style

Photo courtesy of city of Renton. New Councilmember Valerie O’Halloran and her husband, Michael.
O’Halloran takes her seat

Councilmember sworn in before the new year

Photo by Haley Ausbun. Evergreen City Ballet dancers rehearsing at the Meydenbauer Center Theatre in Bellevue, Dec. 4.
From Evergreen’s Cavalier to Broadway and back home again

Artistic Director Bennyroyce Royon introduces himself with “The Nutcracker”

Victims, law enforcement speak about King County Courthouse conditions

An entrance to the courthouse was closed after an assault.

Most Read