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Abstract:
Mejillones peninsula located in the north of Chile is considered a potential seismic barrier. Two major earthquakes have occurred south and north of it: The M8.1 1995 Antofagasta and the M7.8 2007 Tocopilla earthquakes. Slip and aftershock distribution show the central axis of this peninsula as the limit. We use travel time data of earthquakes recovered by three networks, overlapping in space but not in time, including offshore stations (CINCA network 1995; TaskForce 2007, and MEJIPE 2013-2015). A three-dimensional local tomographic inversion was performed using ~4000 events. The resolution of tomographic images was analysed by the model resolution matrix and numerical tests. Vp velocity and Vp/Vs ratio images are capable of resolving main tectonic units up to 80 km depth. Our work shows the presence of two basal possible underplating structures: The first is located below the peninsula with similar dimensions of it (~60 km) found at depths > 35 km and a second structure of smaller dimensions is located to the north where the Tocopilla earthquake nucleated. This evidence justifies the possible segmentation in the rupture zones of both earthquakes in the north of Chile.
