Holocene Event Record of Aysen Fjord (Chilean Patagonia): An Interplay of Volcanic Eruptions and Crustal and Megathrust Earthquakes

Abstract

In the first months of 2007, the Aysen region in southern Chile was affected by a crustal seismic swarm. Its largest earthquake (M-w 6.2) occurred in April and had its epicenter in Aysen Fjord. Seismic intensities became so high that hundreds of onshore mass movements were triggered, several of which entered into the fjord, resulting in mass transport deposits (MTDs) preserved at the fjord bottom. Here we present a Holocene record of paleo-earthquakes in the previously unstudied Patagonian fjordland based on MTD stratigraphy. High-resolution seismic data retrieved using two different seismic systems (sparker and TOPAS) reveal multiple older MTDs on different stratigraphic levels. Correlation of the seismic stratigraphy with sedimentological data obtained from a long Calypso core (MD07-3117) allows conclusion on the seismic origin of these deposits. Additionally, radiocarbon dating permits constructing an age model, validated by tephrochronology, providing an age for the different MTD levels. We thus present a highly detailed paleoseismological history of the Aysen region, including at least six major Holocene earthquakes, one of which is likely related to a known megathrust earthquake. Other earthquakes are related to activity of the Liquine-Ofqui Fault Zone (LOFZ), forming the main source of seismic hazard in the area. We can infer a general average recurrence time for LOFZ earthquakes of -2,100years in the vicinity of Aysen Fjord with clustered events during the early and late Holocene. Finally, we argue that cascading events (causal link between volcanic and seismic events) may be a frequent phenomenon along the LOFZ.