Reconstructing paleoseismic deformation, 1: modern analogues from the 1960 and 2010 Chilean great earthquakes

Abstract

The 1960, and 2010 Chilean great earthquakes provide modern analogues for the sedimentary signatures of the largest megathrust events and their accompanying tsunamis. This paper presents lithological and diatom assemblage data from five sites and provides key insights for the development of longer earthquake chronologies, essential for assessing the seismic hazards associated with a subduction zone. We find that the 1960 and 2010 tsunami deposits are fragmentary, variable and have no unique, diagnostic diatom assemblage. Where rapid postseismic sedimentation occurs, our diatom-based transfer function model gives estimates of coseismic deformation that agree with independent estimates of land-level change. Sedimentary hiatuses at two sites following the 2010 earthquake suggest that the magnitude of coseismic deformation may be underestimated in fossil records. Where sediment accumulation allows, criteria for distinguishing between seismic and non-seismic stratigraphies based on evidence for the largest plate boundary earthquakes are corroborated by the lesser magnitude earthquake of 2010. The key to reconstructing earthquake characteristics, such as rupture magnitude and differences between plate-boundary and upper plate sources, depends on applying explicit stratigraphic assessment criteria at multiple sites in order to identify the spatial pattern of deformation associated with each earthquake.