Abstract

A combination of geological and historical records from south-central Chile provides a means to address general questions about the stability of megathrust rupture patches and the range of variation expected among earthquakes and tsunamis along a particular stretch of a subduction zone. The Tirua River estuary (38.3 degrees S) records four large tsunamis and coseismic land-level changes over the past 450 years within the overlapping rupture zones of the great subduction-zone earthquakes of A.D. 1960 (M-w 9.5) and 2010 (M-w 8.8). Sand layers 2 km up the Tirua River represent the 2010 and 1960 tsunamis and two historical tsunamis, most likely in A. D. 1751 and 1575. Differing land-level changes during these earthquakes likely denote differences in the spatial distribution of slip on the megathrust in both the strike and dip directions within the overlapping rupture zone, with the uplift at Tirua in 1751 and 2010 probably caused by slip extending farther landward and to greater depth than in 1575 and 1960, which showed subsidence or little change.