Even if a major earthquake misses Victoria by hundreds of kilometres, the city could still be at increased risk of a major followup shake, a new report suggests.
An article in the journal Science says researchers found the megaquake that struck Japan in 2011 sparked a spike in aftershocks 400 km away in Tokyo.
A similar phenomenon was recorded in Santiago in 2010, after a major quake hit Chile’s coast 400 km from the capital.
“Immediately after both megaquakes, the rate of small shocks beneath each city jumped by a factor of about 10,” said the article’s authors, Ross Stein of the U.S. Geological Survey and Shinji Toda of Tohoku University in Japan.
The rate of aftershocks in Santiago is still twice as high today as it was before the earthquake. The rate in Tokyo is three times as high.
The researchers say the heightened rate of aftershocks means that the cities may be twice as likely to experience a large quake.
The findings point to the need for cities in earthquake zones to put good seismic monitoring systems in place and prepare for possible disasters, the researchers say.
The type of quake that hit Japan is similar to the one that could occur off the coast of Vancouver Island, said Kate Moran, president of the University of Victoria’s Ocean Networks Canada.
“It is well known that we will have one of those earthquakes some time in the future, and the answer could be sooner than later.”
Moran said the same things that researchers found in Japan and Chile could also happen here, with a megaquake transmitting stress to fault systems hundreds of kilometres away beneath Victoria or Vancouver.
She said one of the advantages in B.C. is that the NEPTUNE fibre-optic cable observatory network has sensors placed near where mega-thrust earthquakes occur in the ocean.
Moran said a team of government and university researchers is working on a five-year project to modify the sensors to detect the first wave of energy seconds before shaking begins.
“We want to detect that primary wave, and we’ll be able to then send a 30- to 50-second warning to major centres like Victoria and Vancouver,” she said. “And with that information, we’ll be able to shut down elevators and potentially shut off gas lines — things that could save lives and save money.”
Sharlie Huffman, a senior seismic and structural health engineer with B.C.’s Transportation Ministry, said the Science article underlines how well-prepared people and governments need to be.
“After you have a major earthquake, it’s not time to take your eyes off the instruments,” she said. “You want to keep tracking them.
“I think it’s difficult for people who haven’t been through an earthquake to quite comprehend how overwhelming the impact’s going to be.”
Huffman said people and agencies need to have emergency plans in place and need to practise them. “We need to have earthquake drills just like you have fire drills,” she said.