Abstract

There have been earthquakes of magnitude M ≥ 7 south of Newfoundland, in the St. Lawrence Valley below Quebec City, in the Queen Charlotte Islands, along the coast of Vancouver Island, and in the Canadian Arctic. Shocks of magnitude 5 ≤ M < 7 and minor seismic activity have occurred in all of these areas and also in the Ottawa Valley. None were accompanied by surface faulting and there seems to be no obvious connection with vertical crustal movements. East of 85 °W and west of 113° W, the seismic history has been used to define zones of seismic risk for the areal distribution of aseismic design recommended in the National Building Code.In 1968, three high-frequency, high gain seismographs were operated for six weeks in a large area north and east of Quebec City where precise levelling had disclosed differential vertical movement of about 1.25 ft (~0.38 m) per century. Few microearthquakes were observed. During three months of similar monitoring near Mount Edziza, B.C., only about 20 small earthquakes originated near the volcano, but approximately 8000 shocks with M ≤ 3 occurred west of the Stikine River near the Alaskan border. Only further research will establish whether microearthquake studies can give a useful measure of Canadian seismicity.

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