The Effects of Seismic Activity on the Soils of the Charlevoix Area—Quebec, Canada

Abstract

The Charlevoix area is a well-known active seismic area. Seismic records, comprising felt reports and instrumental data, extend back only to 1534 A.D. but the marine deposits laid down since the end of the last glacial episode (10 000 years before now) “witnessed” the seismic activity that affected them. Intraformational deformation, usually attributed in Quebec to glacial processes, may also result from seismic activity. A study by Chagnon and Locat (1984) has shown that some types of deformation (sand dykes filled from the bottom and sand volcanoes) can be associated with seismic activity. Such structures have been observed in the Charlevoix area; a conical mound 2 m high and 10 m in diameter was excavated in the fall of 1985 in order to observe its internal structure. The abrupt, almost chaotic, changes in grain size from fine to coarse sand, combined with the numerous faults strongly suggest that the mound is a sand volcano and that it does not results from glacial processes. An inventory, based on airphoto interpretation, shows the presence of numerous such mounds as well as circular structures of even larger dimensions, but similar aspect. The observation of these structures represents a new approach to the study of seismicity in the Charlevoix area, an approach which has implications for practical as well as hazard mitigation purposes.