Earthquake-triggered deposits in the subduction trench of the north Ecuador/south Colombia margin and their implication for paleoseismology

Along the ETS, core-to-core correlation based on 210Pb excess revealed that 20th Century sedimentation occurred mainly in the proximal levee. There, a temporal relationship was established between the 1906, 1942, and 1979 earthquakes, and three coarse-grained beds showing features of earthquake-induced turbidites, suggesting the Esmeraldas Canyon was the main source for sediments to be remobilized during these earthquakes. The fining and thinning observed between the 1906, 1942 and 1979 turbidites correlate with the increasing distance of the rupture zone of each earthquake with the Esmeraldas Canyon. Earthquakes with magnitudes lower than 7 also affected the margin during the 20th Century but were not recorded in the trench sedimentation, suggesting that the turbidite levee acts as a natural filter so that potentially the highest the levee the strongest the earthquake magnitude recorded. At least ten earthquakes with the highest magnitudes were recorded on the turbidite levee within the last 800 years with a recurrence time ranging from about 268 years to 42-82 years, or less for the 20th Century earthquakes. The comparison of the main features of the 1906 turbidite with older earthquake-triggered turbidites identified in a core collected in the trench suggests that one or two earthquakes similar to the 1906 event might have occurred ~ 600 years ago.