The earth shook on a cold winter night Jan. 26, 1700. More precisely at 9 p.m., according to radiocarbon-dated sediment extracted from the sea floor of Effingham Inlet in Barkley Sound on the west coast of Vancouver Island.
The research released last week by scientists at Royal Roads University corroborates oral history from the Cowichan Tribes, which relates that it was dark and cold.
Coastal villages such as the site of the Huu-ay-aht First Nation at Pachena Bay were washed away by the subsequent tsunami, which was recorded in Japan.
In Tofino, you can still see the grey stumps of coastal trees that were suddenly immersed in salt water that cold night 313 years ago.
North of Seattle the earth sawed up and down, creating today's coastal cliffs.
The west coast of Vancouver Island and other parts of B.C. sunk, so that if you stand in the water up to your waist off Long Beach, you're standing on the old shoreline.
That was the last megath-rust earthquake, magnitude 8 and higher on the Richter scale, recorded in the Pacific Northwest.
According to the U.S. Geological Survey, it's the only remaining area on the Pacific Ring of Fire to not have a megathrust quake in the last 50 years.
The Royal Roads team reported that the area from the northern tip of Vancouver Island to northern California has had 22 such major earthquakes over the past 11,000 years and is due for another "either tomorrow or 700 years from now."
And that of course is the problem. If it's tomorrow, we all buy bottled water and earthquake insurance today. But the year 2713 is someone else's problem.
Nanoose Bay geologist Tony Ransom is figuring sooner than later.
It's true that if you divide 11,000 by 22 you get an average interval of 500 years but the actual intervals have been as short as 200 years.
Besides the activity elsewhere on the Ring of Fire, which includes magnitude 9 and higher quakes in Alaska and Chile, Ransom, along with geologists from the USGS and Natural Resources Canada, sees a worrisome set of circumstances, particularly in relation to Vancouver Island.
Firstly, he told a meeting of the Nanoose Naturalists last week, the plates in the area are locked. The crust of the Pacific Northwest is a series of small plates, including the Juan de Fuca plate, being crushed between the Pacific plate and the North American plate.
From west to east, these plates are being pushed under one another, or subducted.
Usually these plates glide by each other or crunch along releasing smaller earthquakes, 400-500 a year around the Island and about 1.4 million a year globally.
But that's not happening so much in this area anymore, Ransom says. "We're in a locked subduction zone," from north of Vancouver Island to northern California.
Secondly, the area to the west of Vancouver Island is moving toward the mainland at a rate of 42 millimetres per year.
Victoria, however, is only moving toward the mainland at a rate of seven millimetres a year. Something's gotta give and research by the School of Earth and Ocean Sciences at the University of Victoria shows that parts of Vancouver Island are rotating (counterclockwise), bending and buckling and the west coast of the Island is rising. "Everything happening is consistent with an active subduc-tion zone," federal seismologist John Cassidy told the Times Colonist last January. "It's the kind of observation seen in Japan and Chile before their big earthquakes."
Chile's Big One, May 22, 1960, at magnitude 9.5 was the largest ever recorded.
Japan's most recent Big One, March 11, 2011 and magnitude 9, moved Honshu, the main island of Japan, 2.4 metres (eight feet) to the east and shifted the Earth's axis by 10-25 centimetres (4-10 inches).
But a lesson from the Japan quake, Ransom says, is that despite the total collapse of buildings (almost 130,000 of them) "the biggest life-threatening risk" is the tsunami afterward.
He acknowledges that the risk of that on the east coast of Vancouver Island is much diminished from that of the exposed coasts but he advises against complacency.
If you're near the water when an earthquake occurs, he says, "you've got only minutes to get to higher ground."
Everyone should have an emergency kit in their homes and in their vehicles, he says, because if the Big One hits, "the cavalry isn't coming."
More information on emergency preparedness is available at www.rdn.ca.
/ This map from the U.S. Geological Survey shows where major earthquakes have occurred on the Ring of Fire in the past 50 years. Note that there are no blue stars between Mexico and Alaska.; / Nanoose Bay geologist Tony Ransom, like most geologists, is expecting the Big One sooner than later. Everyone, he says, should have an emergency kit ready.; / This map from Natural Resources Canada shows the plates directly affecting Vancouver Island. Of course they, in turn, are being crunched by other plates, such as the giant Pacific plate to the west.; / Okay, so if the outside is moving at 42mm a year and the inside at 7mm a year, that's a problem, right?;
© Copyright 2013