Seismo‐turbidites in Aysén Fjord (Southern Chile) Reveal a Complex Pattern of Rupture Modes Along the 1960 Megathrust Earthquake Segment

Type Article
Date 2020-09
Language English
Author(s) Wils Katleen1, Daele Maarten Van1, Kissel Catherine2, Moernaut Jasper3, Schmidt Sabine4, Siani Giuseppe5, Lastras Galderic6
Affiliation(s) 1 : Renard Centre of Marine Geology (RCMG), Department of Geology Ghent University Ghent ,Belgium
2 : Laboratoire des Sciences du Climat et de l’Environnement/IPSL, CEA/CNRS/UVSQUniversité Paris‐Saclay Gif‐sur‐Yvette ,France
3 : Institute of Geology, University of Innsbruck Innsbruck ,Austria
4 : EPOC, UMR CNRS 5805Université de Bordeaux Pessac, France
5 : GEOPSUMR 8148 Université de Paris Orsay, France
6 : GRC Geociències Marines, Universitat de Barcelona Barcelona, Spain
Source Journal Of Geophysical Research-solid Earth (2169-9313) (American Geophysical Union (AGU)), 2020-09 , Vol. 125 , N. 9 , P. e2020JB019405 (23p.)
DOI 10.1029/2020JB019405
WOS© Times Cited 1
Keyword(s) megathrust earthquakes, turbidite paleoseismology, Valdivia segment, south-central Chile, variable rupture mode
Abstract

Grain‐size analysis and end‐member modelling of a long sediment core from Aysén Fjord (southern Chile) allows to identify over 25 seismo‐turbidites in the last 9000 years. Considering the shaking intensities required to trigger these turbidites (V½‐VI½), the majority can be related to megathrust earthquakes. Multiple studies in south‐central Chile have aimed at finding traces of giant, tsunamigenic megathrust earthquakes leading to the current 5500‐year‐long paleoseismological record of the Valdivia Segment. However, none of these cover the southern third of the segment. Aysén Fjord allows to fill this data gap and presents the first, crucial paleoseismic data to demonstrate that the 1960 event was not unique for the Valdivia Segment, yielding a recurrence rate of 321 ± 116 years in the last two millennia. Moreover, the oldest identified events in Aysén Fjord date back to 9000 cal years BP, and thus also extend the regional paleoseismological record in time. We infer a large temporal variability in rupture modes, with successions of full‐segment ruptures alternating with partial and cascading ruptures. The latter seem to significantly postpone the occurrence of another full rupture when consecutively occurring in different parts of the segment. Additionally, one outstanding period of seismic quiescence – during which no megathrust earthquake evidence has been found at any paleoseismic site – occurred after a full rupture in AD ~745 that presents an unusual uplift/subsidence pattern. Such variability makes it highly speculative to anticipate the rupture mode of the next megathrust earthquake along the Valdivia Segment.

Key Points

Oldest evidence for megathrust earthquakes in southern Chile

Confirmation of variable rupture model and first evidence for 1960‐like full‐segment ruptures along the Valdivia Segment

Different rupture types influence full‐segment rupture recurrence rates

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Supporting Information S1 2 62 KB Open access
Table S1 2 367 KB Open access
Table S2 7 73 KB Open access
Table S3 3 78 KB Open access
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How to cite 

Wils Katleen, Daele Maarten Van, Kissel Catherine, Moernaut Jasper, Schmidt Sabine, Siani Giuseppe, Lastras Galderic (2020). Seismo‐turbidites in Aysén Fjord (Southern Chile) Reveal a Complex Pattern of Rupture Modes Along the 1960 Megathrust Earthquake Segment. Journal Of Geophysical Research-solid Earth, 125(9), e2020JB019405 (23p.). Publisher's official version : https://doi.org/10.1029/2020JB019405 , Open Access version : https://archimer.ifremer.fr/doc/00646/75832/