The earthquake occurred near the boundary of the Nazca and South American plates. In this region, the Nazca plate is moving easterly with respect to the South American plate with a velocity of about 60 mm/year and subducting beneath it. The location and focal mechanism of the earthquake are consistent with the shock's occurring on the thrust interface between the plates. The Mw = 7.2 earthquake of November 11, 1991 had a very similar location and focal-mechanism; the 1991 shock killed two people.