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Sensitivity of tidal marshes as recorders of major megathrust earthquakes: constraints from the 25 December 2016 Mw 7.6 Chiloé earthquake, Chile

Brader, Martin and Garrett, Ed and Melnick, Daniel and Shennan, Ian (2021) 'Sensitivity of tidal marshes as recorders of major megathrust earthquakes: constraints from the 25 December 2016 Mw 7.6 Chiloé earthquake, Chile.', Journal of Quaternary Science, 36 (6). pp. 991-1002.


We present evidence of land-level change resulting from the 2016 Mw 7.6 Chiloé earthquake from tidal wetlands along the southern coastline of Isla de Chiloé, Chile, to test criteria for the detection of low-level, <0.1 m, coseismic land-level change. In order to record coseismic land-level change in tidal wetland sediments, both the creation and preservation thresholds must be exceeded. High-resolution diatom analyses of sediment blocks at two tidal marshes reveal that the 2016 earthquake exceeded the creation threshold and a statistically significant change in diatom assemblage is recorded. In contrast, the preservation threshold was not exceeded and the record of coseismic land-level motion is not preserved at any location visited. After nine months, interseismic and coseismic changes are statistically indistinguishable. The most sensitive part of the tidal wetland is not consistent between research locations, possibly as a result of changes in sedimentation after the earthquake. We compare records of change from great earthquakes in Alaska with the record from the Chiloé earthquake to explore the detection limit. We propose that coastal palaeoseismological records are highly likely to underestimate the frequency of major (Mw 7–8) earthquakes, with important implications for recurrence intervals and assessment of future seismic hazards.

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Publisher statement:© 2021 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Date accepted:11 April 2021
Date deposited:17 June 2021
Date of first online publication:19 May 2021
Date first made open access:17 June 2021

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