Seismic testing of the ground around Fife High School
An earthquake strikes without warning and can take lives within seconds. Being ready for one is the only defense.
That’s why 48 geophones were plunged into the baseball field of Fife High School on Thursday, listening for a sledgehammer.
The geophones — devices that detect ground movement — were set up by researchers with the state’s Washington Geologic Survey, a branch of the Department of Natural Resources.
Along with the Office of Superintendent of Public Instruction, the geologists are studying 220 public school buildings across the state to determine if they can withstand the intense shaking of a major earthquake.
Determining whether school buildings are structurally sound is part of the School Seismic Safety Assessment. But on Thursday, scientists were looking underground.
Travis West, a geophysicist with the Geologic Survey, was wielding the sledge hammer, outfitted with a electronic sensor. Every few seconds he would slam it into a 9-inch square plate laid on the field.
To his right, the geophones were spaced along a 94-meter-long line. They were picking up the pulse from the hammer.
“You can’t get too close to the school,” West said of the geophone placement. “There’s different ambient noises, AC (air conditioning units). Even people walking near the sensors can affect the readings.”
How and when the wave from the hammer strike reached each sensor can tell geologists what kind of soil is underlying the field — down to 100 feet. In an earthquake, soil makes a huge difference to the buildings above it.
“If you have a softer soil, you’ll have stronger ground shaking in the event of an earthquake,” said Corina Forson, chief hazards geologist.
Sand and soft soils can liquefy in an earthquake. The process happens within seconds of an earthquake strike. The soil takes on a liquid-like nature, leading to building collapse.
In the United States, the most recent example of the liquefaction process was the heavy damage done to San Francisco’s Marina district in the 1989 Loma Prieta earthquake that killed 63 people.
“In the event of shaking, if you don’t have the right fill or the right pilings, then the building could fall,” Forson said.
The gold standard for quake-resistant ground is bedrock.
Since May, the team has been traveling from Neah Bay to Ilwaco, from Aberdeen to Spokane as it visits the 220 schools.
While drilling and core sampling would give researchers specific samples, the sound wave study is much cheaper and quicker, Forson said.
“You get more schools done in a day, and it’s more cost effective,” she said.
Washington earthquake country
Some 72 percent of Washington’s schools are in very high- to high-risk locations for seismic activity, the Geologic Survey states.
The $1.2 million program — the first of its kind in the state — was approved in February by the state Legislature and field work started in late May.
The geologists should wrap up their field work in September, but engineering inspections will continue through the winter.
Each building’s structural components will be assessed to determine if they need retrofitting for seismic safety.
For 20 of the schools, retrofit designs and cost estimates will be prepared. Those plans will be used as guides for other buildings in need of retrofitting.
“We’re trying to get a representative sample from across the state,” Forson said. “From the early 1900s to a little more modern. From wood frame to concrete and different geologic settings.”
Commissioner of Public Lands Hilary Franz, who swung the hammer a few times on Thursday, noted that Washington ranks just below California on the list of most earthquake prone states but ranks far below other Western states in preparedness.
“We are far behind our West Coast states in being able to assess our critical facilities: our schools, our hospitals, fire and police for the ability to withstand an earthquake,” Franz said.
The final reports are not just for school districts but also for communities and the legislature, Franz said.
“What are the steps that need to be taken to secure the funding to make those retrofits happen,” she said.
The study will wrap up in June 2019.