Abstract

In the summer of 1970, a microearthquake survey was conducted near La Malbaie, north-east of Quebec City. During 53 nights of recording, 28 events with graphic and average focal depth of 10 km were recorded. Their epicenters form a cluster which coincides with other epicenters of the last four centuries and with the large meteorite crater structure of Charlevoix County. This coincidence in space infers a possible causal relation, as the weakened crust under the crater could yield more easily to the postglacial strain field acting over a broader region. The analysis of the data suggests that accuracy in micromagnitude calculations is improved by the use of station corrections for the crustal effect. Distant local earthquakes may be used to calibrate each site. The observed seismicity in the La Malbaie area appears to be low and normal. Future surveys and permanent monitoring are needed to understand the tectonics of the St. Lawrence Valley.

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