Tectonic Movement in the Chile Trench

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Abstract
An acoustic reflection profile across the Chile Trench off Valparaiso shows the trench floor to have a substantial sediment accumulation that is far from flat-lying. The morphology is transitional between the flat-lying sediment fill to the south (labeled a type I trench) and the bare V-notch character farther north (labeled type II). A sharp seaward slope break, downbowed reflectors, and a landward downthrown normal fault suggest that the oceanic lithosphere is failing in shear. This mode of failutre is more consistent with the observed features of trenches and Benioff zones than is the concept of bending and underthrusting.