Magnitude 4.9 earthquake detected off Vancouver Island coast

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USGS

A magnitude 4.9 earthquake was detected off the western coast of Vancouver Island early this afternoon.

According to the U.S. Geological Survey, the tremor occurred at 12:22 p.m. PST and its epicentre was 151 kilometres southwest of Port Hardy. It had a fairly shallow depth of just seven kilometres.

Given the location in the ocean and the relatively modest magnitude, no damage can be expected and a tsunami warning was not triggered.

Thousands of earthquakes hit B.C. every year, but only a small fraction of the events measure a magnitude of four or greater on the richter scale.


Analysis

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.

Earthquakes can also be a sign of possible volcanic activity. In October 2007, a cluster of small earthquakes near B.C.’s potentially active Nazco Cone, about 75 kilometres west of Quesnel, led the Geological Survey of Canada to believe that magma was moving underground within the area – a possible sign of a pending volcanic eruption.

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