Queen Charlotte Islands Earthquake (2012)

john's picture

Yesterday a magnitude M7.7 earthquake occurred at 8:04 pm local time on the Queen Charlotte Islands fault system near Haida Gwaii, Canada.  This event occurred near the junction of a series of spreading centers (mid ocean ridge) with the Queen Charlotte Islands strike slip plate boundary.  Historically, most of the earthquakes in this region have a sense of motion that is parallel to the plate boundary.  These are called "right lateral strike slip" earthquakes.  Yesterday's event actually had normal faulting mechanism, characteristic of local crustal tension. 

For me, one of the interesting coincidences is that the event led to a relatively small tsunami in the state of Hawaii.  I had just left the ACES meeting in Maui at 5:00 pm HST and was enroute via air when the earthquake occurred.  Driving home from San Francisco to Davis, I had the somewhat odd experience of listening to news accounts piped over the radio from KHON in Hawaii to local radio stations in California from a place I had just left.  Apparently the hotel in Makena where the ACES meeting took place issued a series of tsunami warnings, and advised hotel guests to seek safety on upper floors or higher ground as a precaution.  The Pacific Tsunami warning center predicted a 1-2 meter tsunami, but the maximum height was only about half a meter. 

In the region west of Vancouver, recent research has revealed a sequence of small slip and earthquake burst that occur relatively regularly every 14 months or so.  Named "Episodic Tremor and Slip" (ETS) [1], these events play a poorly understood role in the generation process of great earthquakes in that region.  Recent research has also documented the occurrence of an ~M9 event on January 26, 1700 at about 9:00 pm [2].  Further work has documented that these great events occur about once every 500 years.  The event in 1700 led to a 3-4 meter tsunami in Japan.   A more recent previous earthquake in this region occured in 1949 with a magnitude of about M8.1

The interesting question is whether yesterday's earthquake is some kind of precursor to the next great Cascadia earthquake, or is perhaps related in some way.  For that reason, seismologists will be monitoring the ETS activity as well as other seismic activity in this region in the months to come.

[1] http://en.wikipedia.org/wiki/Episodic_tremor_and_slip

[2] http://en.wikipedia.org/wiki/1700_Cascadia_earthquake

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