Sensitivity of tidal marshes as recorders of major megathrust earthquakes: constraints from the 25 December 2016 M_w7.6 Chiloé earthquake, Chile

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