Canadian quake hits East.

Canadian quake hits East

When a magnitude 6.0 earthquake struck northeastern Canada last week, geoscientists collected important details about the underground fault producing the tremors, thanks to instruments set up in the area only hours before the main shock hit on Nov. 25.

Two days earlier, a magnitude 4.7 quake shook this region 150 kilometers north of Quebec, leading investigators from the Geological Survey of Canada (GSC) in Ottawa, Ontario to deploy instruments to monitor aftershocks there. Scientists rarely have such a chance to monitor eastern North American quakes so closely.

The instruments revealed the main quake resulted from a rupture along a fault 19.5 km below ground, and it occurred within several kilometers of the Nov. 23 foreshock. Such a strong earthquake surprise geologists who were not expecting anything larger than a magnitude 5 in this region, says Goetz Buchbinder of the GSC. A hundred kilometers to the south lies the Charlevoix seismic zone that has broken several times in the last few hundred years with earthquakes in the range of magnitude 7.

Last week's quake sent seismic waves rippling through the Earth's crust that set dinner tables swaying in Connecticut and caused noticeable shaking as far south as Washington, D.C. The older, less fractured crust in the eastern part of North America transmits seismic waves farther than does rock west of the Rockies.