'Where earthquakes happened before, they’ll happen again,'

Baffin earthquakes puzzle the experts


Some of the biggest earthquakes recorded in Canada have occurred in the eastern Arctic, at places far from the fault lines deep within the Earth where quakes usually begin.

That puzzles seismologists – the scientists who study earthquakes. They suspect earthquakes felt in Nunavut and Nunavik are produced by weaknesses in the Earth's crust. The region may be far from existing tectonic fault-lines, but old faults may rupture.

The Arctic may also be susceptible to earthquakes because the tundra is slowly rising in many places, by a centimetre or so each year, as the Earth rebounds from the pressure of glaciers that once weighed it down hundreds of years ago.

In any case, forces beneath the Arctic produce some big shakes.

On Nov. 20, 1933, an earthquake that registered 7.3 on the Richter scale shook Baffin Bay, not far from Pond Inlet. It was the equivalent to a 50-megaton atomic bomb exploding 10 km beneath the Earth.

The quake was felt in Upernavik, Greenland. But Dr. Allison Bent, a seismologist with Natural Resources Canada, had never heard any reports of Nunavut's Big One being felt on Baffin Island until she gave a public talk in Iqaluit on Monday, Oct. 15 about Arctic earthquakes.

Ed Picco, who worked as a teacher in Clyde River, told Bent he spent time flipping through old Hudson Bay Co. logbooks to find evidence that people had felt the earthquake of 1933, and another that shook Baffin Bay with a magnitude of 6.1. on Sept. 4, 1963

"Buildings were shaken. People came off the land. People were scared," he said.

The Eastern Arctic probably experiences 200 earthquakes a year with a magnitude of at least 2, Bent said. Most are shivers, barely felt, if at all.

The 1933 quake is the biggest on record, but another is worth remembering. It happened on Christmas Day, 1989, when an earthquake shook the Ungava Peninsula of Nunavik with a magnitude of 6.1. The tundra tore open and lakes shifted and drained.

Yet Nunavut residents probably don't need to resort to sleeping in lifejackets, as some in Qikiqtarjuaq did following a false report in August 2006 that a monstrous wave triggered by an earthquake, or tsunami, was headed their way.

Nunavut's Big One of 1933 was produced by a side-slipping action of the Earth's crust, rather than the more typical motion of one tectonic plate being pushed beneath another. These side-slip earthquakes usually don't produce tidal waves.

"That's probably a reassuring bit of information," said Bent.

Usually, but not never. An earthquake off the Grand Banks of Newfoundland that occurred on Nov. 27, 1929, with a magnitude of 7.2, was caused by a side-slip. A 27-metre wave followed, probably because of an underground mudslide triggered by the quake. Twenty nine people died as houses and fishing boats were swept out to sea.

As there's large quantities of sediment in Arctic waters as well, it's not impossible that a similar wave may happen here. But it would require a monster quake in the right spot.

"It's minimal. But it's not zero," Bent said.

As to the odds of another Big One occurring in Nunavut, there's no sure way to know. But Bent cautions: "Where earthquakes happened before, they'll happen again," she said.

"We don't know if it'll be 100 years, or 1,000 years. Probably not 100 years. Yes, it could happen, but not in your lifetime."

If an earthquake does happen, earthquake experts suggest, if you are indoors, take cover beneath a desk, bed, table or door-frame. Face away from windows.

If outdoors, stay away from anything that could collapse, such as houses or rocky outcrops.

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