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The Mw = 7.8 November 2007 Tocopilla earthquake ruptured a subduction interface between the cities of Tocopilla and Antofagasta in North Chile. So far, 445 aftershocks have been relocated by a local seismic network. The aftershock zone depicts the plate interface dipping 20° east, with a width of about 40 km wide and broadening towards the south. Some shallow events located offshore of the Mejillones peninsula appear to have occurred above the slab interface, possibly suggestive of shallow crustal faulting.
The coseismic deformation field observed by satellite interferometry data is used to constrain the distribution of slip associated with the earthquake.
We construct two hypothetical models: the first one considers a single thrust fault, and the second one considers the interaction of a thrust and a shallow crustal fault offshore of the Mejillones peninsula. Both inversion models are based on the aftershock distribution, and suggest that an area of ∼ 160 km by 50 km along the Nazca–South America convergent margin, between latitudes 22°S and 23.5°S, ruptured during the mainshock. Towards the south, the region of slip broadens, and reaches a peak slip of 2.5 m to the northeast of the Mejillones peninsula. The depth of faulting is estimated to be between 30 and 50 km. While the first model assigns the whole seismic energy release to the slip on the main subduction interface, the second model assumes that parts of this energy were released by the reactivation of a shallow crustal fault offshore of the Mejillones peninsula, as suggested by aftershock data. We have shown that the latter model is supported by Coulomb stress transfer model simulations, but its kinematics cannot be constrained well with the InSAR data alone.