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Haida Gwaii, Alaska quakes many be linked

Preliminary research indicates two powerful earthquakes may be linked, offering seismologists a rare research opportunity.
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Evidence is mounting that the two powerful earthquakes last October and January may be linked

~Quinn Bender

Preliminary research indicates the two powerful earthquakes that shook the north several months ago may be linked, offering seismologists a rare research opportunity into the predictability of earthquake and tsunami behaviour.

Scientists in Washington State are preparing an article on the topic for peer review, while Natural Resources Canada seismologist Dr. John Cassidy has undertaken his own field studies that are pointing toward the same conclusion.

“This is something that’s not really understood,” says Cassidy. “There’s a potential triggering by smaller earthquakes from a larger, distant earthquake, as waves from somewhere around the world pass through a certain region. That was discovered just over a decade ago. Our research will provide better assessments of hazards and how earthquake hazard varies with time. So when a large earthquake happens you may be able to highlight areas that are more susceptible to future earthquakes.”

Since the two powerful temblors that struck just 70 days and 300 kilometres apart—a 7.7-magnitude earthquake near Haida Gwaii last October and a 7.5-magnitude earthquake Jan. 5 off the coast of Alaska—Cassidy installed instruments on Haida Gwaii to measure surface movements from the smaller aftershocks to get an accurate picture of the seismic fault and how it slipped. Instruments were also added to the sea floor to help determine whether the quakes have added pressure to the fault.

It’s hoped the research will show what controls an earthquake, and what dictates where it stops slipping along the fault. Cassidy’s ultimate goal is to improve earthquake and tsunami response for Haida Gwaii but also Vancouver Island. The Haida Gwaii quake is seen as a miniature version of the mega-thrust earthquakes in these highly-populated areas.

Haida Gwaii is still experiencing small aftershocks on a magnitude of one and two, which Cassidy says is normal after a strong earthquake as the 7.7 tremblor last October. The west coast of Moresby Island is also still active, moving very slowly toward the ocean. At the time of the earthquake sections of the coast moved by as much as one metre.

In the coming months Cassidy will monitor the after-slip to determine precisely when it changes direction, to better understand the timing of when things return to a normal pattern of movement.

It could be months, or even years, before the research is concluded and peer reviewed.