Sunday, August 25, 2019
News, analysis and commentary by UBC Journalism students


Making earthquake predictions for B.C.

  Earthquakes are a nearly constant feature of British Columbia   Each point on the above map marks a significant…



 

Earthquakes are a nearly constant feature of British Columbia

 


Each point on the above map marks a significant earthquake magnitude felt in the province since the year 1700. The data are much more precise after 1985 and therefore the total number of quakes for the past 300 years is likely much greater. Each quake is clickable and will display the date and magnitude of that event.

 


 

British Columbia’s geological context

 

This map shows a geological summary of the patterns of earthquakes observed in the clickable map above. The Cascadia subduction zone represents one of the Earth’s tectonic plates being forced under the other: in this case, the Juan de Fuca plate under the Pacific Ocean is being pulled beneath the North American plate. The melting of this plate causes lava to push up through the crust, creating the Cascade volcanoes. Farther north, the Queen Charlotte fault marks where two plates slide past each other. This fault is also capable of large earthquakes. The Rocky Mountains to the east still experience some small activity.

 


 

Even in years with more quakes, pressure on the Cascadia fault grows


This graph shows the number of B.C. quakes per year since 1985. The number of quakes of each magnitude range is shown by the different coloured bars. The bars are stacked so the bar shows the total number of earthquakes for the year of any magnitude. The smaller the magnitude, the more likely a quake is to occur.

It may seem like common sense to assume many small earthquakes in a year will alleviate the stress and make a larger earthquake less likely, but UBC geologist Michael Bostock warns against this.

“Many small earthquakes don’t add up to one big earthquake,” he said. “It takes 30,000 magnitude 6 earthquake to equate to a magnitude nine. Smaller earthquakes, even a magnitude 6 which could cause considerable damage, is not going to do much to reduce the likelihood of a magnitude 9.”

Because of aftershocks following the magnitude 6.8 earthquake that struck Seattle in 2001, that year had an especially high number of earthquakes. There have been many earthquakes in the past five years and 2012 is shaping up to be another shaky year.

 


All data is from Natural Resources Canada Earthquake database. Data records all “significant” earthquakes from 1600 – 1985 then every earthquake above magnitude 2.5 thereafter.