
A so-called "ghost forest" along the coast of Washington state with the remains of trees inundated by seawater from a tsunami that occurred following the last major Cascadia "mega-quake" in January 1700.
The message isn't exactly "breathe easy, B.C."
But a new study of the historical earthquake and tsunami record along the Pacific Coast of southern Canada and the northern U.S. has found that the British Columbia stretch of the 1,200-kilometre-long seismic hazard zone - including Vancouver and Vancouver Island - is significantly less likely than California and Oregon to experience the next 9.0 "mega-quake" that's expected to hit the region some day.
A sleuthing team of Canadian geologists, after examining coastal tsunami deposits and other evidence to reconstruct the 6,500-year history of earthquakes in the volatile offshore area known as the Cascadia subduction zone, has concluded that major "megathrust" quakes - the last of which occurred there in January 1700 - happen about every 230 years along the southern part of the fault line but only every 480 years, on average, in the north.
The hitch, however, is that even if the epicentre of the next monster Pacific quake lies off the coast of California, the wall of sea water triggered by the event could well reach Canada, the study's lead author Lucinda Leonard, a researcher with the Geological Survey of Canada, told Postmedia News.
"It's fair to say that the probability of a major subduction earthquake is higher in the southern area, but we cannot be complacent in the north," she said. "Even if the next one ruptures only the southern part of the margin, the resultant tsunami will likely be hazardous to the B.C. coast."
There's also, of course, the difficulty of precisely predicting when, where and how the grinding of the Juan de Fuca and North America tectonic plates will produce the next "Big One" in the region. Despite an average historical frequency of 480 years between major ruptures in the northern part of the hot zone, Leonard points out that successive mega-quakes have occasionally occurred there within gaps as short as 200 years and as long as 700 years.












