Postglacial faulting in eastern Canada: nature, origin and seismic hazard implications

Abstract

At more than 70 locations in southeastern Canada and the adjacent United States tiny bedrock faults displace glacial striations that are about 10,000 years old. These reverse faults, mostly of small displacement, occur in a broad arc from western Ontario to Newfoundland. The faults lie near the margin of the Laurentian ice sheet, strike generally tangential to it, and imply compression nearly normal to the ENE-directed contemporary regional stress. These observations and some age relationships suggest that the faults formed very soon after deglaciation, perhaps in the first few thousand years after ice melting in each place, and probably represent the release of stresses caused by flexural deformation of the upper crust. Although the individual offsets are small, the faults are believed to be pervasive, and individual outcrops reflect amounts of stress-relief consistent with stresses implied by the postglacial tilt of nearby lake shorelines.