Sediment signatures of the 25th December 2016 Chile earthquake to constrain detection thresholds of tidal marsh records

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On 25th December 2016 a magnitude 7.6 subduction zone earthquake struck south central Chile. The earthquake occurred within the rupture zone of the AD 1960 magnitude (M) 9.5 earthquake, the largest earthquake ever recorded during the instrumental era. The 25th December earthquake is the largest recorded within the 1960 rupture zone since the original event. While the sparse population spared the region from fatalities or substantial economic losses, this earthquake provides a critical opportunity to investigate variability in earthquake rupture zones and the contribution of earthquakes of this magnitude to releasing accumulated strain. Paleoseismological investigations Holocene sediments provide a means to assess the temporal and spatial variability of different earthquake rupture modes in many subduction zones, including Alaska, Cascadia, Chile, Japan, Indonesia and New Zealand. Crucially, we seek to assess the lower limit for detecting pre-20th century earthquakes using established paleoseismological methods and the potential for geological records to underestimate the frequency of major earthquakes.We seek urgency funding to make a rapid assessment of the coseismic surface deformation and sedimentation resulting from the 25th December earthquake. Two field campaigns, either side of the austral winter, will test the preservation potential of any recorded coseismic signal through the first few months of incorporation into the sediment profile, including survival through winter storms and any post-seismic vertical deformation caused by post-seismic creep on the plate interface. Sedimentary and microfossil analysis will reveal the sedimentary signature of the earthquake and constrain the lower limit of deformation detection. This proposal builds on our previous research and the recent shift in coastal paleoseismologgy from identifying the largest amounts of crustal deformation within the rupture segments of late Holocene earthquakes to seeking the spatial extent, therefore limits, of a rupture segment. This requires a methodology focussed on identifying the lower limit of vertical crustal deformation. We recently proposed a revised research framework to accomplish this, based on our own research and a comprehensive review of the paleoseismological literature, but noted the lack of sufficient detailed modern equivalents. The 2015 Chile earthquake provides a rare opportunity to collect time-critical samples from the contemporary environments in coastal areas affected by small coseismic vertical land motions, ground shaking and any associated tsunami.