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

Martin Brader, Ed Garrett, Daniel Melnick, Ian Shennan

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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.
Original languageEnglish
Pages (from-to)991-1002
JournalJournal of Quaternary Science
Issue number6
Early online date19 May 2021
Publication statusPublished - Aug 2021

Bibliographical note

© 2021 The Authors.


  • diatoms
  • Holocene
  • micropalaeontology
  • sea-level changes
  • South America

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