ARTICLE - CLIMATE CHANGE AND EARTHQUAKES

CLIMATE CHANGE AND QUAKES: A LINK?
(Montreal Gazette) - By Wiliam Marsden

Earth's 'elastic' crust at issue; Melting glaciers may be lightening load, allowing tectonic plates to shift

MONTREAL - Severe earthquakes in Haiti, Chile and most recently Japan have raised the question of whether the world's tectonic plates are becoming more active and if so what is the cause.

Some scientists theorize that the sudden melting of glaciers due to man-made climate change is lightening the load on the Earth, allowing its mantle to rebound upward, causing the plates to become unstuck.

These scientists point to the historical increase in volcanic and earthquake activity that occurred about 12,000 years ago, when the glaciers that covered most of Canada in an ice sheet several kilometres thick suddenly melted.

The result was that most of Canada's crust has lifted and is still rising.

Scientists have discovered that the accelerated melting of the Greenland ice sheet over the last 10 years is already lifting the southeastern part of that island several millimetres every year.

The surface of the Earth is elastic. A heavy load like a glacier will cause it to sink, pushing aside the liquid rock underneath.

The Greenland glacier is about three kilometres at its thickest and it is believed that its weight has depressed sections of the land under the glacier about one kilometre. In fact, the weight of the glacier is so great that significant portions of Greenland have been pushed well below sea level.

"There is certainly some literature that talks about the increased occurrence of volcanic eruptions and the removing of load from the crust by deglaciation," said Martin Sharp, a glaciologist at the University of Alberta. "It changes the stress load in the crust and maybe it opens up routes for lava to come to the surface."

Sharp added that "it is conceivable that there would be some increase in earthquake activity during periods of rapid changes on the Earth's crust."

Other scientists, however, believe that the kind of tectonic movements similar to the one that last week caused the Japanese quake are too deep in the Earth to be affected by the pressure releases caused by glacier melt.

These scientists theorize, however, that glacier melts could cause shallower quakes.

Andrew Hynes, a tectonics expert at McGill University, said the issue is not so much the load shift on the Earth's crust, but rather the increased fluid pressure in the fault that lubricates the rock, allowing the plate to slide.

"All earthquakes except those produced by volcanic activity are essentially the unsticking of faults," he said.

In other words, if you pump fluid into a fault, it will reduce the friction and the rock can slide.

Could the stress transfers and the added melt from glaciers inject more fluid into the rocks creating earthquakes?

Hynes said this is a serious issue with large hydro reservoirs, where increased amounts of water into otherwise stable faults can cause them to move.

"It would only apply to earthquakes that are at shallow depths," he said. "But I wouldn't push it any further than that."

He added, however, that the decompression from melting glaciers could cause an increase in volcanism by releasing the liquid rock and its explosive potential.

Yet, at the same time, the number and severity of earthquakes appears to have increased over the last 30 years in parallel to accelerating glacial melt.

Some experts claim the increase can be explained by increased number of seismograph stations to more than 8,000, from 350 in 1931, allowing scientists to pinpoint earthquakes that would otherwise have been missed.

But this does not explain the recent increase in major earthquakes, which are defined as above 6 on the Richter magnitude scale. (Japan's earthquake was a 9.) Scientists have been tracking these powerful quakes for well over a century and it's unlikely that they have missed any during at least the last 60 years.

According to data from the United States Geological Survey, there were 1,085 major earthquakes in the 1980s. This increased in the 1990s to 1,492 and to 1,611 from 2000 to 2009. Last year - and up to and including the Japanese quake - there were 247 major earthquakes, which puts us on a path to yet another increase.

There has also been a noticeable increase in the sort of extreme quakes that hit Japan. In the 1980s, there were four mega-quakes, six in the 1990s and 13 in the last decade. So far this decade, we have had two.

This increase, however, could be temporary. Hynes said there is some evidence that one earthquake can snowball into another until the earth's crust has adjusted to the new pressure transfers.

The coast of British Columbia sits on the Pacific fault line that curves around the southern coast of Alaska, travelling southwest to Japan.

Hynes said the upper plate of Vancouver Island is flexing like a bow. It's stuck and bending upward. Ultimately it will release itself and produce a major quake, he predicted. Japan's big earthquake could change the tectonic stresses in the Pacific and possibly affect Vancouver.

"I'm afraid to say that Canada is by no means as careful about its building codes as Japan," Hynes said.

Montreal sits on a fault line that travels along the St. Lawrence River Valley. Hynes said the fault is smack in the middle of a tectonic place, making it harder to understand the stresses.