Vancouver Island hit by more than 4200 quakes! End is near!

Seismologists have been recording thousands of “episodic tremor
and slip events” occurring at a rapid rate since March 20 moving
in a southeasterly direction down the Island.
More than 4,200 tiny tremors have been recorded so far between
25 and 40 kilometres below the surface, said John Cassidy, an
earthquake seismologist with Natural Resources Canada and
a professor at the University of Victoria. “They’re not earthquakes.
On the instruments they look like series of a trains rolling by,”
Cassidy said.
He said these bursts of small tremors and slips occur about every
15 months along faults that form the boundaries of tectonic plates
 - in our case, the Cascadia subduction zone from Brooks Peninsula
on the Island to Northern California, where the Juan de Fuca plate
system curves west beneath the North American plate.
The repeated episodes of slow fault slips - measuring about the
size of five stacked dimes  -  usually occur over a period of several
weeks, accompanied by tremors that appear on seismic records as
prolonged, intermittent ground vibrations, Cassidy said.
The ETS activity has been going on for centuries, but has only
recently been recorded using sophisticated GPS technology at more
than 40 sites up and down the Island. They differ from earthquakes,
which generate large, sharp shock waves that subside very quickly,
but ETS can help in improving estimates on where and when the
next earthquake might occur, Cassidy said.
By mapping out the areas on the subduction fault where stress is
not accumulating over the long term, tremor events define the
landward limit of the zone that could rupture during the next great
earthquake.
That provides a more accurate estimate of how close the rupture
could be to major West Coast cities such as Victoria, Vancouver
and Seattle, and what shaking could occur, he said.
He said although it’s been 322 years since the last big one - which
is safely within the 500- to 600- year average estimate - exact
predictions on mega-thrust quakes (over magnitude 8) are impossible.
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