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In Canada: strong acceleration ....

In Canada: Strong acceleration . . .

An earthquake in a remote area of Canada was responsiblefor the highest acceleration--a measurement of one aspect of the power of an earthquake--yet observed. The magnitude 6.8 earthquake occurred along the east side of the Canadian Rockies in December 1985.

Acceleration is a way to quantify the force and strength withwhich an object moves, in comparison to the force and strength that gravity has upon it. Gravity's acceleration is equivalent to 1 g. Most earthquakes have vertical accelerations in the 0 to 1 g range; the Canadian earthquake had a vertical acceleration of more than 2 g, making it capable of tossing objects not bolted to the ground into the air.

The accelerometer that recorded the event was put in place(and bolted to the ground) after a strong quake in September 1985. It was not designed to measure more than 1 g, notes Peter W. Basham of the Geological Survey of Canada in Ottawa, who headed the staff that installed the instruments. "So we're a little uncertain of the exact measurement.' Nevertheless, he and others say, it was the highest yet recorded.

Basham has no explanation for why the earthquake causedsuch an unusually high acceleration, but notes that because of similarities between the quake area and parts of the eastern United States, such accelerations could conceivably occur there as well. Like the quake area, the East has highly "competent,' solid rocks that could transmit the force in a similar manner. The East also has thrust faults where one part of the earth's crust shoves up over another, which is the type of faulting that caused the Canadian quake. And the same rock type that underlies the Canadian earthquake is under most of the eastern United States.
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Title Annotation:earthquake in western Canada causes highest acceleration yet observed
Author:Silberner, Joanne
Publication:Science News
Date:Apr 11, 1987
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