Abstract

Silt layers in organic-rich lake sediments are interpreted to represent the historic earthquakes of 1638, 1663, 1791, 1870, and 1925 of the Charlevoix region of eastern Canada. This interpretation is based on the relative spacing of the layers and the accelerator-mass spectrometer 14C dating of a twig in one of the cores. The silt layers were presumably caused by landslides on tributary streams and by resuspension of the sediment. The cores contain up to 22 layers, 1 to 45 mm thick, over a depth equivalent to about 2300 yr. If there is a correlation between thickness and magnitude, there would have been four events of Richter magnitude 7.5 or greater in A.D. 1663, 1320, 60, and 320 B.C. The 18 other layers could correspond to earthquakes of magnitude 6 to 7. The recurrence interval from 300 B.C. to A.D. 800 is 120 yr, followed until A.D. 1500 by a quiet period, when there was a single large event. The recurrence interval from A.D. 1500 to the present is 75 yr.

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