A string of nine earthquakes struck the coast of British Columbia over a three-day span, the most recent of which occurred on Christmas Day.
The seismic activity began on Monday, December 23, when six earthquakes were recorded within a 12-hour period. According to the US Geological Survey (USGS), the strongest of the first six earthquakes were two magnitude 6.0 quakes:
- 8:44 am: magnitude 5.2
- 11:13 am: magnitude 5.6
- 11:49 am: magnitude 6.0
- 12:56 pm: magnitude 6.0
- 3:38 pm: magnitude 4.8
- 9:32 pm: magnitude 4.3
Another strong magnitude 6.3 earthquake struck the coast of British Columbia on Christmas Eve at 7:36 pm PST.
On Christmas Day, two earthquakes also occurred: a magnitude 4.2 quake at approximately 8:25 am PST, and a magnitude 4.9 quake that happened at 12:38 pm PST.
Each earthquake occurred in the same general area, near the fault line that divides the Explorer Plate and the North American Plate. All quakes were relatively shallow, with the USGS reporting a depth of 10 km.
No tsunami warnings were issued for any of the events, and of the nine earthquakes, the quake that occurred on Christmas Eve was the strongest.
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Thousands of earthquakes occur in BC every year, but only a small fraction of these tremors have a notable magnitude of 3.0 and over.
An increase in an earthquake’s magnitude of 1.0 — such as the difference between a magnitude 4.0 earthquake and a magnitude 5.0 earthquake — is a 10-fold difference in the energy of an earthquake.
As a further example, a magnitude 8.0 earthquake is 1,000 times more powerful than a magnitude 5.0 earthquake. Shallow earthquakes with a magnitude of 5.0 can still cause significant damage when the epicentre is near urban areas, and the impact is amplified with a shallow depth.
In comparison, the devastating earthquake that hit Christchurch, New Zealand, in 2011 had a magnitude of 6.2, an epicentre located just 7 km from the city, and a depth of only 5 km. It resulted in 185 deaths, approximately 2,000 injuries, and over USD$10 billion in damage.
In 2001, the magnitude 6.8 earthquake in Washington State had an epicentre in Puget Sound in an area about 60 km southwest of Seattle. Even though the earthquake had an extreme depth of 57 km, it still caused 400 injuries and one death, created approximately USD$2 billion in property damage, and was strongly felt in Vancouver.
With files from Kenneth Chan.