abstract

Previous seismicity studies of the Charlevoix zone of the mid-St. Lawrence Valley have defined the extent of the active zone. Continued monitoring of this zone has yielded more hypocenters that, together with the previous data, give a more detailed picture of the hypocentral distribution of the microactivity. A more definite correlation can now be made with the known structure in this region and the faults of the St. Lawrence VAlley in general.

The cumulative data permit a definition of lateral boundaries of the seismic activity, range of focal depths, and anomalous nonseismic zones. It is also possible to make a correlation with the normal faults that were probably associated with the paleorifting of the St. Lawrence Valley but are now under compression. In this seismically active region, part of these preexisting partially sealed faults were most likely weakened again at the time of formation of the Charlevoix impact structure.

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