Discontinuous nature of the lower part of the South American Wadati-Benioff zone in the Arica Elbow region

The Arica Elbow region represents that parr of Andean South America where t he azimuth of the strike of the Peru-Chile trench changes from 150 degrees to 190 degrees. The area under study is roughly bounded by latitudes 17 deg rees S and 23 degrees S. The shape of the Wadati-Benioff zone was studied i n terms of the distribution of ISC hypocentres dared between 1964 and 1993. A system of 22 vertical cross-sections, perpendicular to the trench axis, and a map of epicentres was used to derive the derailed shape of the Wadati -Benioff zone of the presently descending slab. The distribution of earthqu ake foci indicates a fingerlike shape of the lower part of the Wadati-Benio ff zone beneath the aseismic gap. The slab length shows small changes aroun d 350 km bl the northern sections pronounced length oscillations between 35 0 and 750 km in the neighbouring central sections and a constant value of 6 50 km in the southern sections. The dip and thickness of the Wadati-Benioff Zone are practically constant in all sections. Fault plane solutions separ ated spatially into three zones, were used to estimate the state of stress in the slab.