At least 200 tiny tremors were noted — not felt — between Victoria and Seattle on March 12.
According to John Cassidy, earthquake seismologist for Natural Resources Canada, the noted tremors are not earthquakes but shaking ground that can easily be recorded and monitored.
“[The wave recordings] look kind of like a windstorm coming in, things start to shake gradually, then they shake off a little more and then it rolls off slowly,” Cassidy explained.
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Typically, Vancouver Island moves towards the Lower Mainland at a rate of approximately one centimetre per year but every 15 months or so, a ‘slip’ is recorded. First discovered by two local scientists, Gary Rogers and Herb Dragert, a tremor and slip event is when the Island ‘slips’ back a few millimetres into the ocean.
“In this region where we see tremors, [the plates] are actually going back and forth like a tectonic dance that Vancouver Island does every 14 or 15 months,” Cassidy noted.
Episodic tremor and slip is a very small, slow slip that occurs more frequently than the massive, sudden shifts that characterize a bigger earthquake. By tracking the number of tremors over a period of days scientists are able to tell if an episodic tremor and slip is occurring. This helps them understand the subduction fault beneath the earth including where it’s locked in place and where it’s storing energy aiding in what to expect during future earthquakes.
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“We know from earthquakes around the world that awareness and preparedness make a huge difference in minimizing the impact of earthquakes,” Cassidy said. “Getting under a table, holding on, being away from windows that might break or chimneys that might collapse.”
Cassidy added there is no need for panic but said these tremors are good reminders about the rock that we live on.
“This is an earthquake zone and earthquakes occur here on a regular basis, but larger earthquakes have occurred here and will occur in the future,” Cassidy said.
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