'Slightly nervous' about small earthquakes? We should be
Recent earthquakes don't raise the risk of a devastating quake in southwestern B.C., but that doesn't mean we shouldn't be worried
If recent seismic activity in California and coastal B.C. has your spidey senses tingling, you can relax.
But not too much.
“People should be slightly nervous,” said Simon Fraser University geologist Brent Ward. “There are three different kinds of earthquakes, and southwestern B.C. is at risk for all of them.”
A 6.2-magnitude earthquake was recorded between Vancouver Island and Haida Gwaii on Wednesday followed by a 4.0 aftershock.
On Friday, three more aftershocks were recorded, according to Earthquakes Canada.
The tremors were barely 10 minutes apart and struck at around 6 a.m. The 5.1 quake hit 220 kilometres west-southwest of Bella Bella on B.C.’s central coast at 5:58 a.m. Two smaller quakes were also recorded, one measuring 4.9 near Port Hardy at 5:51 a.m. and one measuring 4.7 near the village of Queen Charlotte at 6:02 a.m.
But such is life in the Cascadia subduction zone.
“There’s constantly quakes in the 6 to 7 range,” said Ward. “In the past 30 days there have been at least a dozen around the world, but you don’t hear about them because they are in remote locations.”
But when a 6.4-magnitude earthquake caused property damage in California on Thursday, people desperately wanted to put two and two together.
“People get a little nervous when there are reports of quakes coming back to back to back, but they really aren’t related to each other at all,” he said.
Earthquakes recorded in the past 30 days.
That doesn’t mean you shouldn’t worry.
“It’s good to have these little (quakes) so it gets people thinking they should put together an earthquake kit and have a plan,” he said.
The local Juan de Fuca plate is a smallish collection of plates between the behemoth Pacific and continental plates that is trying to burrow under the North American Plate.
“The fault zone is stuck, so there is energy building up along that zone that starts off the coast of Vancouver Island and extends underneath the Island,” Ward said. “The west coast of Vancouver Island is slowly rising because of these forces.”
When a large subduction quake hits, the west coast of the Island could drop by a metre or two in one fell swoop.
“A huge amount of energy will be released, probably in the high 8’s to low 9’s in magnitude, the flexure release will trigger a tsunami and that will inundate the coastal zones of Vancouver Island,” he explained. “It will change the coast of the Island.”
Southwestern B.C. is also prone to crustal quakes much closer to the surface, which cause high-frequency shaking that can result in severe damage to low-rise structures, especially brick buildings and chimneys.
“We get one of these crustal quakes every 40 or 50 years, so we are due for one,” said Ward.
A 1946 earthquake on Vancouver Island triggered massive landslides, including one mass of rock that displaced the contents of what is now know as Landslide Lake, creating a massive fresh-water tsunami that wiped out everything in its path for three kilometres.
A third kind of quake occurs due to the bending of the subducting plates around 40 to 60 kilometres deep in the earth. The 2001 Nisqually earthquake in Washington state caused $2 billion in property damage, according to a report to the U.S. Department of Commerce.
Similar active faults have been detected on Vancouver Island, close to Victoria, Ward said.
PreparedBC recommends everyone assemble an emergency preparedness kit, including drinking water, shelf-stable food, a battery-powered radio and a flashlight. You can find the entire list plus instruction on how to create an emergency plan for your family at gov.bc.ca/preparedbc.
With a file from The Canadian Press
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