"British Columbia and West Coast of USA Placed on High Alert for Huge Earthquake" - but relax, its all off?

VANCOUVER ? Scientists have alerted British Columbia's emergency-planning department to the possibility of a catastrophic earthquake striking the province's southwest coast next week.

Garry Rogers, a seismologist at the centre, compared the current earthquake odds to the dangers of driving a car.

?Everyone drives their car every day, and the probability of getting in a car accident is small,? Dr. Rogers said. But during rush hour, the probability of getting into an accident is much higher. ?Well, Vancouver Island is now driving in rush hour.?

What prompted the alert was a series of imperceptible tremors emanating from deep beneath the ocean, which scientists now recognize as ominous warnings that the earth is on the move again off Vancouver Island.

The tremors occurred on what is known as the Cascadia subduction zone, which lies beneath the Pacific Ocean off the West Coast and runs from Vancouver Island to Northern California. The rumblings began last week near Puget Sound near Seattle and made their way north to Vancouver Island in recent days.

The tremors ? known in earthquake-speak as an episodic tremor and slip ? monitor the ongoing strain between the solid earth on the West Coast and the offshore Juan de Fuca Plate.

The two plates are rubbing against one another, with the offshore plate continually pushing against and under the North American Plate.

The recent tremors mean that even more stress is building between the two, which scientists believe will one day rupture into a major earthquake the size of the one off the coast of Indonesia on Dec. 26, 2004, which killed thousands.

Dr. Rogers said the chances of a major earthquake striking southwestern B.C. spike during the tremor events. The current tremor session is expected to last for another week.

Reference:

http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20070202/bc_quake_070202/20070202

LATEST
Earthquake risk lowered
Episode of subterranean tremors stops
Vancouver Islanders, stocking up on emergency supplies after warnings of increased chances of a major earthquake, can relax ? a little.

The latest episode of subterranean tremors has ended earlier than expected, seismologists at the Pacific Geoscience Centre in Sidney said Saturday.

?Things have quietened down very quickly. We don?t know why,? said Natural Resources Canada seismologist John Cassidy.

The tremors, measured by sensitive instruments, are caused by the slipping of the bottom plate in the Cascadia fault, which runs off the west coast of Vancouver Island, and beneath the Island.

Scientists at the Pacific Geoscience Centre discovered the episodes occur about every 14 months and add stress to the shallow, locked part of the plate, bringing it closer to giving way, which would result in a major earthquake. When the plate fails, it is expected the earthquake will measure about nine on the Richter scale

The next expected episode of tremor and slip will be about April 2008.

Usually, the rupture travels across Juan de Fuca Strait, up-Island through Lake Cowichan and on to the Alberni Inlet, but, this time, it appeared to stop north of Duncan, Cassidy said.

?This one has been a little bit different.?

Seismographs show the tremors have stopped, but data from other instruments does not yet show whether Vancouver Island is still being pulled towards Japan or if it is again moving in its usual direction towards Ottawa, Cassidy said.

Although the immediate possibility of a major earthquake along the Cascadia subduction zone has subsided, there are other faults which cause earthquakes, and all Vancouver Islanders should remember they live in an active quake zone, Cassidy said.

The 1946 Vancouver Island quake and the 2001 Seattle quake had different causes.

The last massive Cascadia quake was Jan. 26, 1700. Information about it came largely from Japan, where a tsunami was documented, and from oral records of Vancouver Island First Nations.

jlavoie@tc.canwest.com