Magnitude 7.5 quake, aftershocks shake B.C. and Alaska

Scott Sutherland
Séisme au large de l'Alaska : l'alerte au tsunami est levée
Un tremblement de terre de magnitude 7,5 s'est produit au large des côtes de l'Alaska, dans l'Océan pacifique, tôt samedi matin. Le Centre américain de géophysique (USGS) précise que l'épicentre est situé à 10 km de profondeur, à 102 km à l'ouest de la ville de Craig. Séisme Canada ajoute qu'il se situe également à 300 km à l'ouest-nord-ouest de Prince Rupert, en Colombie-Britannique et 600 km au sud de Whitehorse

A major earthquake struck off the coast of southern Alaska late last night (local time), roughly 300 kilometres north of where a similar quake shook the islands of Haida Gwaii, British Columbia, two months ago.

The quake registered 7.5 on the Richter scale, and set off tsunami warnings along the north and south coasts of Vancouver Island, including the City of Victoria. The warning was called off early this morning, as only minimal changes in sea level were detected.

[ Related: B.C. tsunami warning cancelled after Alaska quake ]

Since the initial quake, more than a dozen aftershocks have been recorded, ranging between magnitude 3.5 and 5.1, with more aftershocks likely before the Queen Charlotte fault system settles down once again.

To imagine what causes aftershocks, press your index finger down onto the surface of your desk, and then try to push your finger away from you. The exact moment that your finger overcomes the friction with the desk and slips forward is like the initial quake. All the movement your finger makes after that first moment is like the aftershocks.

[ Related: Aftershocks often more dangerous than initial, larger quake ]

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).

[ Related: Is it time to worry about quakes in B.C.? ]

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.

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