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.


In consideration of how we voice our opinions in the modern world, we’ve closed comments on our websites. We value the opinions of our readers and we encourage you to keep the conversation going.

Please feel free to share your story tips by emailing editor@bellevuereporter.com.

To share your opinion for publication, submit a letter through our website https://www.bellevuereporter.com/submit-letter/. Include your name, address and daytime phone number. (We’ll only publish your name and hometown.) We reserve the right to edit letters, but if you keep yours to 300 words or less, we won’t ask you to shorten it.

More in News

Bellevue Chamber CEO: Volunteers help with downtown cleanup

Update: They are not seeking additional volunteers at this time. Cleanup comes after a few stores in Bellevue faced property damage from looters.

Bellevue City Hall. Photo courtesy city of Bellevue
How is COVID-19 impacting Bellevue?

New King County data dashboard breaks down case rates, number of unemployment filings and more.

Kabal Gill, owner of East India Grill in Federal Way, wears gloves to hand over take-out orders at his restaurant on March 23. File photo
New guidelines for Phase 2 reopenings in King County

All workers will need to wear masks as restaurants, retail shops and other businesses reopen.

This undated file photo provided by U.S. Centers for Disease Control and Prevention shows CDC’s laboratory test kit for the new coronavirus. Courtesy photo
Inslee wants nursing home residents and staff tested by June 12

Governor says state will pay for test kits and personal protective equipment.

Bellevue College selects Gary Locke as interim president

Locke formerly served as governor of Washington State

Stock image
Campgrounds to reopen in 22 Washington counties

Campgrounds in counties actively in Phase 2 of the reopening plan will begin to welcome visitors June 1, state says.

King County Sheriff Mitzi Johanknecht. FILE PHOTO
King County sheriff releases message about Minneapolis Police officer

Mitzi Johanknecht calls video of officer kneeling on neck of George Floyd ‘heartbreaking and disturbing’

File photo of construction near North Bend on Aug. 16. Sound Publishing file photo
                                File photo of construction near North Bend on Aug. 16. Sound Publishing file photo
Rural King County mayors want state to let them enter Phase 2

Mayors cite heavy economic damage from prolonged shutdown.

New dashboard shows how far along King County is to meeting Phase II metrics

The county has met more than half its goals, but the ones it hasn’t met are critical in determining how many people are still being infected, and how quickly people are being tested.

Most Read