| BY DAVID COGLON
Freelance Writer
Remember the line from the Carole King song reminding us
what it’s like to “feel the earth move” under
our feet? It’s hard to forget these words as you listen
to Garry Rogers talk about his lifelong passion — earthquakes.
No one can tell exactly where or when earthquakes will occur.
The earth under our feet is not really as firm and stable
as it appears: it is constantly moving. But if anyone can
predict the next earthquake, it’s Dr. Rogers, an earthquake
seismologist with the Geological Survey of Canada and head
of the National Earthquake Hazards Program for Western Canada.
At his GSC office in Sidney, B.C., Dr. Rogers keeps a close
watch on earthquakes across Western Canada. Each day he and
his team of analysts meticulously sort through data from
a network of seismographs and monitoring instruments across
the country.
“We go through what’s happened in the last 24
hours, sort out the seismic ‘noise,’ save data
for analysis and locate the earthquakes that have happened
in Western Canada,” says Dr. Rogers, who was a guest
speaker at the Honorary Address in Calgary in October. “If
the earthquake is big enough, we calculate the faulting and
stress mechanisms that caused the event.”
Each year the team locates and records about 1,500 earthquakes
across the region.
“One of the most recent earthquakes occurred at about
8:42 p.m. on Oct. 11 just east of Victoria,” says Dr.
Rogers. “It was a magnitude of 2.6 — so a fairly
small earthquake — but a lot of people felt it across
the greater Victoria area. We received e-mails from about
100 people about this quake.”
Plenty of Public Contact
Each year the team also fields hundreds of calls from the
public, often from residents reporting tremors in their homes
and buildings.
“In November 2002, for example, we received many
calls from people across Western Canada reporting they felt
a large earthquake. The earthquake actually occurred more
than a 1,000 kilometres away in Alaska, but it was such a
large event — magnitude 7.9 — that it caused
buildings in Edmonton, Calgary, Vancouver and Victoria to
gently sway back and forth.”
An earthquake measuring between two and three on the Richter
scale is the lowest normally felt by people. And because
many of the earthquakes in Western Canada measure between
1 and 2, we hardly notice them. But as Dr. Rogers warns,
there’s always the potential of larger earthquakes,
especially on the West Coast.
The area just west of Vancouver is considered one of the
most vulnerable in the country. It’s here in the Juan
de Fuca Strait that two tectonic plates — the North
American Plate and the Juan de Fuca Plate — rub against
each other. The North American Plate is gradually sliding
underneath its neighbour. And as it does, pressures build
along the plate boundary.
Eventually, scientists say, this will unleash a “subduction
earthquake” – an incredibly powerful quake that
can measure nine on the Richter scale.
Dr. Rogers says the Geological Survey of Canada has found
evidence of a large subduction earthquake that destroyed
an Aboriginal village near Victoria more than 300 years ago.
In their oral traditions, First Nations people on the island
talk about a big earthquake that occurred in the winter in
the middle of the night. The earthquake probably began just
offshore, and then minutes later the water of the bay rose
into a tsunami, a massive surge of water several metres high,
that pushed its way ashore, tearing trees from the ground
and pounding wooden buildings to pieces.
Thanks to Japanese records from that time that describe
a tsunami damaging that country’s east cost, it’s
possible to date the earthquake to around 9 p.m. on Jan.
26, 1700. By examining trees submerged centuries ago in a
peaty bog, scientists have also been able to count tree rings
back to this destructive event.
Could such a killer quake happen again?
“Mother nature doesn’t go like clockwork. Sometimes
we’ve had two or three major earthquakes in a year
on the coast. The last one was in 1946,” Dr. Roger
says, referring to a 7.3 quake that damaged school buildings
near Courtenay, Vancouver Island. “Since then, there’s
been an absence of big earthquakes on the coast.”
The Next Big One
Hunting for ways to anticipate the “next big one” has
become a quest for Dr. Rogers. Last year he came closer to
this goal, as he and his colleague, Herb Dragert, announced
a scientific breakthrough.
By studying narrow frequency bands from seismographs, the
two scientists have discovered a way to “listen” to
tectonic plates slipping under Vancouver Island.
“We’ve found that about every 14 months the
Juan de Fuca and North American plates put out pulsating
vibrations that signal they are going to slip against each
other. These stresses are building up in the earth like a
staircase.
“Every time this happens we’re moving up the
staircase to the next big one. We don’t know exactly
where we are in the staircase. But this gives us an important
clue.”
Should we be concerned about a serious earthquake in Western
Canada? And how well prepared are we?
This is a question that is top of mind for Dr. Rogers, who,
as a member of the Canadian National Committee on Earthquake
Engineering, regularly meets with engineers and academics
to review and recommend earthquake design requirements for
Canada’s National Building Code.
“If engineers understand the ground-shaking forces
of earthquakes, they can design structures that can successfully
resist these events. To help them do that, we look at recent
earthquake events from around the world to determine what
structures fail — or don’t fail. If there are
important lessons from these events, we incorporate these
into the building code.”
After studying recent earthquakes in Japan and the U.S.,
the committee plans to introduce new, expanded earthquake
design requirements in 2004.
“The new code will provide more information for designing
earth-resistant structures of all sizes,” says Dr.
Rogers. “Also, we’re incorporating changes for
the first time to address ground-shaking from very large
subduction earthquakes.”
The Real Impact
Indeed, earthquakes should not be underestimated. Dr. Roger
says he never ceases to be impressed by their power.
“In 1989 there was a fairly large earthquake south
of San Francisco. One of the hotels that I’ve stayed
in was severely damaged, with big cracks going up it. When
you see that impact in a building, where you’ve been
and walked in, it makes it all very real.”
Dr. Roger’s fascination with earthquakes goes back
to his days as a 10-year-old growing up in Vancouver. “As
a kid, I was always really impressed by the world of big
interesting geologic events – earthquakes, tsunamis
and volcanoes,” says the 58-year-old scientist.
Today, after decades of study, his fascination continues
to deepen.
“In the last decade especially, the whole field of
earthquake science has really accelerated, with new computers,
with better monitoring instruments. And this is encouraging
because it means that someday we’ll get to the bottom
of some of the fundamental forces that we don’t understand.
“ Like any scientist, I’m fascinated with how
the earth works and want to contribute to that understanding.
But I also get a double benefit, knowing that the results
of my work are going to directly help make people safer — and
for me, that’s very satisfying.”
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