After the Chile quake, is ‘the big one’ around the corner for B.C.?

Around 8:45 p.m. Wednesday, residents on Chile’s coast were jolted from where they stood or sat when the earth began to shake violently. Items tumbled off shelves, landslides were triggered, power was knocked out to thousands, and several fires destroyed businesses. Though tragic, it was miraculous that only six people lost their lives in the magnitude-8.2 quake.

A similar situation — or worse — could lie in store for residents along the coast of British Columbia, though seismologists aren’t concerned about the Chilean earthquake being the catalyst to a major earthquake here at home.

“We don’t expect any impacts in B.C. in terms of triggering [an] earthquake,” John Cassidy, a seismologist with Earthquakes Canada told Global News. “Looking back at previous events over time, we don’t see any direct link between these very distant earthquakes triggering very large, very distant earthquakes.”

However, that doesn’t rule out smaller ones being triggered.

Cassidy explained that when large earthquakes — magnitude 8 or 9 — occur any place on Earth, it can trigger smaller earthquakes around the globe.

“The [seismic] waves from that earthquake will circle the globe,” he said. “And as those waves, sort of a rolling motion, pass through certain areas, they will trigger small earthquakes. So you’ll see micro-seismic, or very tiny earthquakes, that people don’t feel.”

Generally, the this type of repercussion is limited to volcanic areas, which also includes Yellowstone National Park. That area received a magnitude-4.8 earthquake on March 30. It was the strongest in the area since 1980.

“It’s an interesting phenomena that was discovered, but we don’t see these waves triggering large earthquakes,” Cassidy said. “But it’s a young science and we can’t say absolutely not, but our experience so far is that we’re not seeing large earthquakes being triggered by these waves.”

The Chilean earthquake is actually similar to the type of earthquakes B.C. receives, called subduction earthquakes. This occurs when a part of one tectonic plate slides beneath another.

“It’s a very important earthquake, in that we can learn from this earthquake, because we have exactly the same kind of earthquakes off of our coast.”

The plate that subducted, or moved beneath another plate, off the coast of Chile is called the Nazca Plate. The plate moves toward Chile about 6 cm a year. Off the coast of B.C., the Juan de Fuca plate moves in the same manner at 5 cm a year.

In the case of the Juan de Fuca plate, seismologists know that a large earthquake occurs roughly between 200 to 850 years apart. And by ‘big one,’ seismologists mean a magnitude-9. The last one was in 1700, which means that, statistically, B.C. could expect one.

“We’re right in that window, where certainly we should be prepared for one of those earthquakes.”
If such a major earthquake were to occur, the effects could be enormous. For one, the shaking would last for about four to five minutes. For those on the west coast of Vancouver Island, they would have less than an hour to make it to higher land before a major tsunami washed ashore. As well, parts of the west coast of the island could drop as much as a metre.

“You’d see damage. You’d see landslides and liquifaction effects through the lower mainland and certainly all across Vancouver Island,” Cassidy said.

Not only that, but places as far as Toronto could feel the shaking. People in highrises would feel their buildings sway as the shockwave reached the city.

Trying to predict earthquakes

The difficulty with earthquakes is that there is, for now, no way to predict them. Though “swarms” of quakes — a cluster of localized earthquakes — have been linked to predicting a bigger earthquake, it’s not an exact science.

“It’s something that certainly people will be looking at really carefully now, because that’s one of the big questions,” Cassidy said. “Before one these giant earthquakes, is there any indication, any signal, any change in land level, or in seismicity that might tell us that one of these giant earthquakes is about to occur?”

But looking back at earthquake history, these swarms predict a larger one only 1 out of 20 times. That means 19 out of 20, there is no major quake that follows, making it an imperfect way to forecast larger earthquakes.

The good news for B.C. residents is that the Chile earthquake isn’t a portent of disaster. But the big one could be around the corner.

Source: http://globalnews.ca/news/1246076/after-the-chile-earthquake-is-the-big-one-around-the-corner-for-b-c/

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