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Hawaii Institute of Geophysics Contribution 1104

After reevaluation of crustal seismic velocity structure based on refraction data, we are able to present a multichannel seismic reflection profile across the Peru-Chile Trench as a cross section with undistorted reflector depths. These data support previous suggestions that this portion of the western edge of the continent of South America is undergoing tectonic erosion by the subducting oceanic Nazca lithospheric plate. The reflection seismic data also reveal numerous unconformities in the bedded sediments of the upper continental slope. These unconformities have wide lateral extent and are taken to be evidence of periodic vertical tectonic motion, including intermittent episodes of uplift, during the long-term subsidence of the continental wall of the trench. The configuration of deeper crustal reflectors leads us to suggest that the top of the subducting oceanic plate is underthrusting itself, perhaps in response to the compression caused by restraightening of the subducting slab beneath the continental plate. The crustal thickening that would accompany this deformation of the subducted oceanic plate may contribute to the vertical tectonic events and tectonic erosion of the overriding continental plate.

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