Proposed focal process of the Chilean earthquake of 1960 (Kanamori & Cipar. 1074) - a) An initial aseismic slip occurred along the lithosphere-asthenosphere boundary at depth; b) small foreshock triggered by the stress concentration caused by the aseismic slip; c) Subsequent resulting rupture at the upper lithosphere-lithosphere boundary resulting in the destructive May 22, 1960 earthquake. The insert shows the vertical cross-section of seismicity in this area given by Stauder (1973).