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

Suspect with violent history killed by officers outside Enumclaw

It’s unclear why Anthony Chilcott was not being held after a late October arrest for resisting arrest and damaging a patrol car before this most recent incident, which resulted in his death.

Father charged with assault after giving step daughter chloroform

Though initially put on life support, the girl has recovered enough to talk to police.

Black Diamond police blotter | Nov. 18 – 24

A juvenile with a knife and trespassers.

Mountain View Fire moves to end contract with Black Diamond

Three years remain on the current contract, but this move highlights the financial tensions between the city and fire department.

Fire along Twisp River Road in the Okanogan Wenatchee National Forest in 2018. Courtesy photo
Wildfire response: State unveils funding legislation proposal

Last year, Department of Natural Resources responded to record number of wildfires.

A new report, complete with recommendations to the Legislature, has been released by a statewide task force that was formed to address a lack of child care in Washington. File photo
Report outlines lack of child care in Washington

In King County, supply doesn’t meet demand for child care.

Students work to bring holiday cheer to Buckley

It’s the second annual Merry on Main, brought to you by the White River High School DECA club.

St. Elizabeth practices chemical emergency

Staff were able to handle a high-volume number of patients and were able to “decontaminate” them quickly, but they did find some holes in their procedures.

Demonstrators from La Resistencia protest Amazon’s involvement with ICE. Photo courtesy of La Resistencia
How will the U.S. respond to climate refugees?

Business as usual has been harder borders, are there other ways to address climate migration?

Most Read