Deglacial and postglacial paleoseismological archives in mass movement deposits of lakes of south-central Quebec

Investigation of seismic activity in eastern Canada is important for natural hazard management as two major active seismic zones with many historical records are located in the region: the Western Quebec seismic zone (WQSZ) and the Charlevoix-Kamouraska seismic zone (CKSZ), with the latter being the most active in northeastern America. This paper describes and analyses a dataset of high-resolution swath bathymetric imagery, sub-bottom profiles, and sediments cores collected in three lakes (Maskinonge, Aux-Sables, and St-Joseph) located between two active seismic zones. The geomorphology observed on high-resolution swath bathymetric imagery, the acoustic sub-bottom profiles, and the sediment analysis indicate that the lakes were disturbed by three phases of seismically induced mass movements since deglaciation: (i) during the deglacial Champlain Sea transgression and the rapid initial glacio-isostatic rebound between similar to 13 and 10.5 ka cal BP; (ii) around 1180 AD; and (iii) the well-documented CKSZ 1663 AD M >7 historical earthquake. The second phase of earthquake events (1180 AD) corresponds chronologically to a previously documented large landslide in western Quebec, dated at similar to 1020 years BP. This earthquake is responsible for remobilizing the largest volume of sediments in the entire stratigraphic sequence of Lake Maskinonge, the westernmost lake. This earthquake was not recorded in Lake Aux-Sables and St-Joseph, which are located eastward from Maskinonge, but the largest mass movement deposits are associated with the well-known 1663 AD event of eastern Quebec. Therefore, both earthquake events are interpreted to have different epicenters and the lakes of southeastern Quebec recorded earthquakes from both seismic zones.