Whole Lot Of Shaking Going On
Pastor Dale Morgan
Whole Lot Of Shaking Going On*
B.C. enters window of increased quake risk
Updated Fri. Feb. 2 2007 11:20 PM ET
CTV News Staff
CANADA - Experts warn that British Columbia's south coast has entered a
two-week window of increased probability in which a major earthquake
could occur.
While the chances of that happening are still very slim, such an event
could trigger a tsunami equal to the size and the strength of what hit
the Sumatra-Andaman Islands in 2004.
Seismologists with B.C.'s Geological Survey of Canada made the
announcement after measuring a series of minor tremors deep below the
Earth's surface and along the Cascadia Subduction Zone -- a long,
sloping fault that stretches from northern California to Vancouver Island.
The zone, which separates the Juan de Fuca Plate and the North American
Plate, has a very large fault area which can produce large earthquakes
with a magnitude of 9.0 or greater if a rupture were to occur.
"Where the Juan de Fuca plate is subducting beneath the North American
plate, and where those plates are touching, it's locked," earthquake
seismologist Alison Bird told CTV.ca.
"To the east of that, every 14 months we see low frequency tremor
activity ... sliding along that zone, which is almost directly beneath
us," Bird told CTV.ca in a phone interview from the Geological Survey of
Canada headquarters in Sidney, B.C., near Victoria.
"When that happens, we believe what it's doing is loading additional
stress onto the locked zone. So if that locked zone happens to be close
to critical, it could theoretically trigger a mega earthquake."
Bird and her colleagues noticed a phenomenon, called Episodic Tremor and
Slip (ETS), occurs in the area about every 14 months -- each time adding
stress to the fault line and increasing the likelihood of a major
earthquake.
The seismologists started detecting strong ETS movement last Friday.
If a major quake should occur, said seismologist Garry Rogers: "You're
looking at a big tsunami happening at the same time. The west coast of
Vancouver Island, the Washington and Oregon coasts, are all vulnerable
to a force powerful enough to certainly bring down buildings.
Rogers told CTV.ca that the area of the Cascadia Subduction Zone is
comparable in size to the rupture zone of the Dec. 26, 2004 earthquake
in the Pacific Ocean that triggered a devastating tsunami in the
Sumatra-Andaman Islands.
Another comparable scenario, said Roberts, is the 1964 earthquake that
struck Alaska.
"Most of the bigger, taller buildings and structures like bridges
suffered some damage, whereas most of the small structures such as
houses suffered hardly any damage. So there's an analogy which is
probably what is going to happen in Vancouver, Seattle and Victoria."
While larger structures that were built a number of years ago are most
vulnerable, continued Roberts, recently-built structures are better off,
"because what we do is put this type of knowledge into building codes.
Older, bigger structures are more vulnerable because they don't have the
present day knowledge built into their design."
The last known great earthquake in the Pacific Northwest -- the Cascadia
Earthquake -- struck in January, 1700. While such phenomena are
infrequent, with a cycle of every few hundred years, the region is due
for a big one.
The Geological Survey of Canada added for an average week, the chances
of a mega thrust earthquake occurring is 0.0005 per cent (or one in
200,000); during a week of Episodic Tremor and Slip this increases to
0.026 per cent (or one in 4,000) -- a 50-fold increase.
"We are at a time when (a mega thrust quake) could occur, but it could
also be 100 years from now," Bird told CTV.ca.
Rogers compared the heightened risk to driving in rush hour as opposed
to driving in less crowded road conditions.
"We all go out and drive every day and we take the chance of getting
into a traffic accident. It's a low probability but we know it probably
could happen, so we take the step to put our seatbelt on," he told CTV.ca.
"Now we know that the probability is much higher in rush hour and we
still drive. What we are doing in Vancouver Island right now, we're
driving in rush hour. We have been over the last week and we probably
will be for another week. And then we turn to a lower probability."
Bird added this period of higher earthquake risk is a time to get
organized and take precautions.
"What I encourage people to do is whenever we're about to have an ETS,
it's a good time to use that as a trigger to go over your emergency plan
with your family to make sure that your earthquake kit is full stocked,"
Bird said.
"Sometimes things get taken from earthquake kits to use for other
things. So replenish the food and water and other equipment. It's just a
good practice, a good reminder, like when the clocks change you check
the battery in your smoke detector. For the west coast, you check your
earthquake kit every 14 months."
* Click here for advice from Natural Resources Canada on how to
prepare for an earthquake
Should B.C. escape the big one this time, the next window of higher
earthquake risk will occur around April 2008.
Rogers said seismologists haven't figured out why the ETS phenomenon
happens every 14 months in the Pacific Northwest.
"And interestingly enough it's 14 months fairly regularly here for the
last decade as we looked back at our old records," he said. "But in
Japan, it seems to be about one year; in New Zealand it appears to be
about every few years; and Alaska every 18 months. We don't know if it's
because of different subduction zones, or it's about where we are in the
earthquake cycle."