Is it time to worry after the third major quake in two week in British Columbia?

A strong earthquake, measuring 6.3 on the Richter scale, struck off the coast of Vancouver Island at just after 5 p.m. Pacific Standard Time on Wednesday night. It was followed by a magnitude 4.5 aftershock just after noon PST on Thursday. There were no reports of damage or injuries, but with last week's magnitude 7.7 quake and the accompanying aftershocks, is there reason to worry?

Regardless of anyone's belief or perception about earthquake prediction, there is no way to accurately predict earthquakes. We can speak of how many earthquakes have happened in the past. We can look at patterns that may have emerged in the frequency and location of earthquakes. We can even search for reliable 'precursors' to quakes. It may be possible to forecast quakes in the future as we learn more about them, but right now, any serious attempts to forecast them is likely based purely on statistics.

Still, experts have said that a 'big one' may be lurking for southwestern British Columbia. It's not all hype. The Geological Survey of Canada has put some significant research into the geophysical and geological evidence that supports the idea that the Vancouver area is not only a high-risk area, but also vulnerable to powerful earthquakes. Looking at the earthquake seismic hazard maps at this link, you can see that southwestern British Columbia has some of the highest seismic hazard values in the country, and possibly the highest values for stronger earthquakes (some background on these maps can be found here).

Needless to say, a major earthquake hitting the populated areas of southwestern B.C .would be devastating. If the earthquakes experienced over the past two weeks were located closer to Vancouver and Victoria, they could have registered as up to Violent or Intense on the Mercalli Intensity Scale (which is a measure of the effects of an earthquake, rather than energy released).

In a report from CBC News from just after the October 27th earthquake, Vancouver mayor Gregor Robertson said "We are very much worried about a big earthquake here. We're due for one in Vancouver, and we're doing everything we can do as a city to prepare for that over these last couple of years."

Just last year, in an interview with CTV News, he commented about how many buildings in the city were at risk, however, he now emphasized that the city has been preparing for such an event over the past four years. Still, a report on Wednesday stated that the Pattullo Bridge, that links Surrey and New Westminster, is 25 years past its expected lifetime, and whereas it is safe under normal conditions (due to inspections), it does not meet current seismic standards. Plans are to replace the bridge by 2018.

It's possible that may be pushing their luck, though. As was reported by The Vancouver Sun back in August, Oregon State University geologist Jay Patton said: "By the year 2060, if we have not had an earthquake, we will have exceeded 85 per cent of all the known intervals of earthquake recurrence in 10,000 years."

With no way of accurately predicting the next earthquake, though, the key is to be prepared. The B.C. provincial government has a website that details how to prepare for an earthquake beforehand, and what to do during and after a quake to stay safe. Also, just last month, the city of Vancouver held an earthquake drill, apparently the second of its kind.

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