Comparison of earthquake-triggered turbidites from the Saguenay (Eastern Canada) and Reloncavi (Chilean margin) Fjords: implications for paleoseismicity and sedimentology

G. St-Onge (1) , Emmanuel Chapron (2) , S. Mulsow (3) , M. Salas (1, 3) , M. Viel (3) , Maxime Debret (4) , Anthony Foucher (5) , T. Mulder (6) , T. Winiarski (7) , Marc Desmet (5) , P.J.J. Costa (8) , Bassam Ghaleb (9) , A. Jaouen (10) , Jacques Locat (11)

1 ISMER - Institut des Sciences de la MER de Rimouski
2 ISTO - Institut des Sciences de la Terre d'Orléans
3 Instituto de Geociencias [Valdivia]
4 M2C - Morphodynamique Continentale et Côtière
5 Transferts continentaux : forçages anthropiques, climatiques et géodynamiques
6 EPOC - Environnements et Paléoenvironnements OCéaniques
7 Équipe 5 - Impacts des Polluants sur les Écosystèmes
8 Centro de Geologia [Lisboa]
9 GEOTOP - Centre de recherche sur la dynamique du système Terre
10 IPEV - L'Institut polaire français Paul-Emile Victor
11 LERN - Laboratoire d'études sur les risques naturels

High-resolution seismic profiles along with physical and sedimentological properties of sediment cores from the Saguenay (Eastern Canada) and Reloncavi (Chile) Fjords allowed the identification of several decimeter to meter-thick turbidites. In both fjords, the turbidites were associated with large magnitude historic and pre-historic earthquakes including the 1663 AD (M > 7) earthquake in the Saguenay Fjord, and 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 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. In the Saguenay Fjord, the earthquake-triggered turbidites are sometimes underlying a hyperpycnite associated with the rapid breaching and draining of a natural dam formed by earthquake-triggered landslides. Similar hyperpycnal floods were also recorded in historical and continental geological archives for the 1960 and 1575 AD Chilean subduction earthquakes, highlighting the risk of such flood events several weeks or months after main earthquake. In both fjords, as well as in other recently recognized earthquake-triggered turbidites, the decimeter-to meter-thick normally-graded turbidites are characterized by a homogeneous, but slightly fining upward tail. Finally, this paper also emphasizes the sensitivity of fjords to record historic and pre-historic seismicity.

Mots clés: active and passive margins; tsunami; hyperpycnites; paleoseismology; submarine landslides; rapidly deposited layers (RDL)

Domaines: Interfaces continentales, environnement; Milieux et Changements globaux

G. St-Onge, Emmanuel Chapron, S. Mulsow, M. Salas, M. Viel, et al.. Comparison of earthquake-triggered turbidites from the Saguenay (Eastern Canada) and Reloncavi (Chilean margin) Fjords: implications for paleoseismicity and sedimentology. Sedimentary Geology, 2012, 243-244, pp.89-107. ⟨10.1016/j.sedgeo.2011.11.003⟩. ⟨insu-00648918⟩