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People stand outside the Main Street Skytrain station after the commuter train system was shut down to check for any possible damage to elevated guideways in Vancouver, B.C., in the early morning hours of Wednesday, Dec. 30, 2015, after an earthquake struck off the west coast late Tuesday night.DARRYL DYCK/The Canadian Press

Kent Johansen knew Tuesday night's earthquake was coming about 13 seconds before it momentarily shook his Burnaby home.

That is because the University of B.C. research associate had installed an alarm connected to the institution's network of sensors spread across the southern coast of the province to detect the faster, less disruptive tremors that travel through the earth's crust before an earthquake's shaking begins.

When the alarm sounded, Dr. Johansen's wife asked him if he was testing the system, to which he replied: "This is a real one, we've got to get under the table."

The 4.7 magnitude earthquake northwest of Victoria caused no damage or injuries, but experts say it is a warning to prepare for a much-larger megathrust earthquake that could hit the region any time. The Cascadia coastal subduction zone – which stretches from the northern tip of Vancouver Island to northern California – has averaged one of these massive earthquakes about every 500 years, he said.

Seismologists have yet to find a reliable way of predicting when an earthquake will occur. But in recent years, sensor systems helped give Japanese authorities crucial seconds to protect critical infrastructure during 2011's megathrust earthquake, and alarms like the one run by UBC's civil engineering department could give vulnerable citizens time to shield themselves from possible damage.

The province has not yet made such a system mandatory.

The sensors pick up the P – or primary – shock waves that travel through the earth's crust from the epicentre of a quake. These P-waves precede the slower, more destructive S – or secondary – waves that radiate outward and produce the shaking that can damage buildings.

So far, the sensors have been buried at 25 sites across Vancouver Island and the Lower Mainland, and the early warning system has been connected to alarms that ring at 61 private Catholic and public schools in the region, Dr. Johansen said.

If classes had been in session during Tuesday's earthquake – which happened at 11:39 p.m. – sirens would have given students about six seconds' warning in Victoria and about double that for those in Lower Mainland classrooms, he added. (The difference is because of the distance from the epicentre.)

The epicentre of "the Big One" is expected to be offshore of the west coast of Vancouver Island, which could give those schools on the southern end of the island or in Metro Vancouver up to a minute or more warning once the alarm is triggered, he said.

In 2013, the Roman Catholic Archdiocese of Vancouver announced it would install the sensors as part of its program to upgrade most of its schools and parishes, which were constructed before B.C. added seismic standards to its building code in 1992. Public schools in the Fraser Valley are contemplating installing the alarms, he said. Dr. Johansen said he does not know if other public school boards will bring on the systems, but a company selling ocean and land-based sensors told the Victoria Times Colonist in 2014 it was in talks with the provincial education ministry to test such sensors at public schools.

The sensors are relatively inexpensive to build and install and have a very high success rate, Dr. Johansen said. Their readings are relayed instantly to UBC's Earthquake Engineering Research Facility, where the data are pooled and an alert is issued and alarms triggered if multiple sensors meet the threshold of a light-to-moderate earthquake. This pooling of data means a falling tree or a building being demolished do not trigger the warning, he said.

Honn Kao, an earthquake seismologist with the Geological Survey of Canada, said the early warning systems are also very important for critical infrastructure, noting that sensors were installed at both ends of the George Massey Tunnel in 2006 to shut it down to traffic if a large earthquake hits.

Power plants, hospitals, bridges and transit could benefit from similar alarms, he said, noting the Japanese bullet train system can slow or stop trains depending on the severity of an oncoming earthquake.

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