Hakai Magazine

Coastal science and societies

a large earthquake recorded on a seismograph
The Cascadia region is long overdue for an earthquake. Photo by Jim Phillips/Alamy Stock Photo

New Underwater Sensors to Watch for the Big One

Canada’s west coast is getting a new earthquake early-warning system.

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by Erica Gies

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It’s an ordinary Tuesday morning in Vancouver, British Columbia, and people are heading to work on the SkyTrain. The train pulls up to the station … and waits. Down the street, the doors of a firehall clang open automatically. At the hospital, a surgeon gets an alert and pulls her scalpel away from her patient. On the street, cellphones begin to squeal and display a message: “Earthquake! Earthquake! Drop, cover, hold on. Expect strong shaking.” Sirens sound across the city.

This scenario hasn’t happened yet, but within the next few years, it could, says Teron Moore, an earthquake and tsunami emergency planning expert at the University of Victoria’s Ocean Networks Canada (ONC). In 2016, motivated by the destruction wrought by the 2011 Tōhoku earthquake and tsunami in Japan, the BC government earmarked nearly CAD $5-million for ONC to develop an earthquake early-warning system for Canada’s West Coast. The prototype system, expected to be deployed by spring 2019, will give people up to 90 seconds of warning for an earthquake and several minutes for a tsunami.

Ninety seconds may not sound like much, says Kate Moran, president and chief executive officer of ONC, but “you can do a lot in a few seconds.”

Deploying an effective earthquake early-warning system is something of a race against time. The Cascadia subduction zone, off the coast of southern British Columbia and northwestern United States, is well overdue for a massive earthquake. Garry Rogers, a seismologist who has worked for Natural Resources Canada (NRC) and with ONC, says the Cascadia subduction gets stuck for centuries and then “breaks loose in these giant earthquakes, which cause a lot of shaking and tsunamis. We know where those earthquakes are going to happen, and we know they will have societally significant consequences.”

Earthquake early-warning systems exist, but there’s plenty of room for improvement. Mexico built the first one in the 1990s in response to the magnitude 8.0 Michoacan earthquake that killed more than 9,500 people in 1985, says Moore, and the idea has spread since. This year, on the 32nd anniversary of that devastating quake, sensors along Mexico’s Pacific coast detected a magnitude 7.1 earthquake, giving many people across the region 12 to 48 seconds’ notice.

On the other side of the Pacific, Japan also has a warning system. It did alert people to the 2011 earthquake and tsunami, but not accurately, says Rogers. That quake was a magnitude 9, but the system initially flagged it as magnitude 7—1,000 times weaker.

The ONC team and international researchers are studying why Japan’s system made this error, and are working to build a more accurate system, Rogers says.

Generally speaking, earthquakes cause the earth to shake mainly in two ways: a rippling motion, and a larger sideways movement. The ripples, known as primary waves (P waves), spread out from the earthquake’s epicenter more quickly than those that cause the rolling sideways motions, known as secondary waves (S waves). In an earthquake, the bulk of the destruction is caused by the larger S waves.

Existing early-warning systems work by monitoring P waves, which arrive at sensors first. The amount of warning a system can give, then, depends on the time between when the P waves are detected and when the S waves hit. Some of this crucial time will be lost interpreting the signal and getting the message out.

For Canada’s early-warning system, ONC is working on a few specific upgrades to improve on existing designs. For one, ONC is adding new accelerometers to existing underwater ocean observatories they operate off the coast. These accelerometers are seismographs that are less sensitive than usual. This lowered sensitivity prevents the measurements from going off the scale during a big earthquake, something that can happen to more sensitive equipment. These new sensors will be linked with land-based accelerometers and GPS sensors run by NRC on northern Vancouver Island.

The GPS tracks where seismic waves happen and the actual movement of the land. As the two tectonic plates of the Cascadia subduction zone push against each other, they deform Vancouver Island, says Rogers. “Rocks store elastic strain, kind of like squeezing a sponge.” When the earthquake happens, the pressure is released and the land shifts suddenly. “These jumps are going to be more than a meter.”

The GPS measurements are key to avoiding an incorrect magnitude estimate, Rogers says. The different streams of data can give a better assessment of the earthquake than any one type of sensor alone.

“We’re going to have the most advanced system in the world here in Canada,” says Moran.

ONC is also partnering with universities and federal agencies in the United States to possibly give even more warning time. The Cascadia subduction zone spans 1,000 kilometers from British Columbia to Northern California, and historically ruptures have started at one end of the fault and moved to the other. Rogers says the earthquake rupture will spread down the fault line at around three kilometers a second.

“If the earthquake rupture started off of Northern California and then went north, that would mean we would have minutes of early warning up here, and vice versa,” says Moran.

With the detection technology in the process of being deployed, Moore says the next challenge is finding the best way to get the warnings to the people who need them most urgently, such as public broadcasters, and those in schools, factories, and firehalls. For industry and infrastructure, responses could be simple, or even automated—doors can spring open, trains shut down, equipment powers off.

For the public, cellphone alerts are a likely approach. But even this will take some research. In Japan, social scientists studied a range of sounds to decide on one that cannot be ignored. “They found a sound that was horrible to everybody, so they would pay attention,” says Moran. “It was the sound of Godzilla.”

Social scientists might need to come up with a different sound to command Canadians’ attention. The call of a loon? A hockey goal horn? Bagpipes?