Evènements sociaux > Conférence Plénière 1

Earthquake-triggered turbidites from eastern Canada and the southern Chilean margin

Guillaume St-Onge

Institut des sciences de la mer de Rimouski (ISMER)

Université du Québec à Rimouski & GEOTOP

The Charlevoix-Kamouraska/Lower St. Lawrence Estuary seismic zone (CK/LSLE) is the most active intraplate seismic zone in Canada, where at least five earthquakes of magnitude of 6 or stronger occurred during the last 350 years. In addition, due to very high sedimentation rates, the deposition of marine clays by the Laflamme and Goldthwait postglacial seas in the Saguenay Fjord and St. Lawrence Estuary, respectively, and the influence of postglacial rebound, the thick Quaternary sedimentary sequence is prone to remobilisation following strong earthquakes. Here, using geophysical, sedimentological and geochronological data collected from several expeditions on board different research vessels, including a recent cruise conducted in 2020 on board the R/V Coriolis II, we will overview some of the Holocene and historical submarine mass wasting events recorded in the Saguenay Fjord and St. Lawrence Estuary. The sediment cores recovered from the submarine landslides reveal the presence of several rapidly deposited layers such as turbidites. The dating of these turbidites led to the identification of several periods of synchronous deposition corresponding to the strongest historical earthquakes. The dating, concordance with historical earthquakes and synchronicity of the turbidites over a distance reaching more 220 km strongly argue for their triggering by strong earthquakes.

Similarly, several turbidites from the southern Chilean marginwere identified, dated and associated with large magnitude historic and pre-historic earthquakes including the 1960 (M 9.5), 1837 (M~8) and 1575 AD major Chilean subduction earthquakes in the Reloncavi Fjord. In addition, a sand layer with sea urchin fragments and the exoscopic characteristics typical of a tsunami deposit was observed immediately above the turbidite associated with the 1575 AD earthquake in the Reloncavi Fjord and supports both the chronology and the large magnitude of that historic earthquake. Radiocarbon results indicate that at least 19 earthquake-triggered turbidites were recorded in the Reloncavi Fjord during the last 7500 cal BP.

Prof. Guillaume St-Onge

Institut des sciences de la mer de Rimouski (ISMER), Université du Québec à Rimouski & GEOTOP

Prof. St-Onge holds the Tier I Canada Research Chair in Marine Geology and have led numerous expeditions at sea and on land in both Hemispheres. He is currently working on natural hazards, sedimentology, climate change, Quaternary stratigraphy and paleomagnetism in eastern Canada, the Arctic, the Gulf of Alaska, Patagonia, Tibet, New Zealand and the Lesser Antilles. He has established and was the founding director of the Réseau Québec maritime (RQM) and the Institut France-Québec maritime (IFQM) from 2016 to 2019 before taking the direction of the Institut des sciences de la mer de Rimouski (ISMER) at the Université du Québec à Rimouski (UQAR) where he also presides the board of directors of Reformar, the organization that manages the research vessels Coriolis II, Lampsilis and Louis-Edmond-Hamelin for the Canadian scientific community. He is also involved in several national and international programs such as ArcticNet, the International Ocean Discovery Program (IODP) and the International Continental Scientific Drilling Program (ICDP). He has received several awards and distinctions for the quality of his research and training.