The US Geological Survey says it detected a magnitude 4.9 earthquake off the west coast of Vancouver Island earlier this morning.
At 4:28 am, the seismic event had an epicentre 158 km southwest of Port Hardy, on the Explorer Plate, and shallow depth of 10 km. No damage can be expected given the location and modest magnitude of the tremor.
This is the fourth earthquake with a magnitude of 4.0 and over within the past week, including earthquakes that hit one hour apart Wednesday night in Seattle and off the BC coast.
Thousands of earthquakes hit BC every year, but only a small fraction have a magnitude of 4.0 or greater. This morning’s earthquake was the 10th earthquake this year to date with a magnitude of 4.0.
While it is generally believed that smaller earthquakes may delay the “Big One” by relieving pressure along the fault lines, seismologists say this is incorrect. Smaller seismic events do relieve some pressure, however, it requires many small earthquakes to release the same energy given off by one significant earthquake. For instance, an earthquake releases 10 times more energy for every one point increase on the richter magnitude scale.
In fact, smaller earthquakes could precipitate larger earthquakes, such as the magnitude 7.3 seismic event that hit the coast of Japan on March 9, 2011. Two days later on March 11, the powerful magnitude 9.0 earthquake occurred and caused a devastating tsunami that reached far inland. In the weeks and months after the main event, Japan detected more than 900 aftershocks.
Additionally, every 14 months, the subduction zone under the Pacific Northwest enters a heightened phase that adds stress to where the Juan de Fuca and North American plates are locked together.