Mapping the continuity of the Nazca plate through its aseismic part in the arica elbow (Central Andes)

Along the Peru-Chile trench, the subduction of the Nazca Plate under South America is well underlined by the Wadati Benioff zone. In the Central Andes, the seismicity defines a moderately deepening slab down to about 325 km. The occurrence of a scarce seismicity in the 550–650 km depth range, after a complete seismic quiescence, raises the question of the continuity of the slab. To answer this question we performed a 3-D teleseismic tomography of the mantle at 20°S. On the tomographic image, a higher velocity zone is associated with the subducted plate where it is defined by the Wadati Benioff zone. At greater depth, this higher velocity body can be followed through the model down to the lower mantle. Our results provide clear evidence of the continuity of the slab throughout its seismically quiescent part. Moreover, they allow the imaging of the bending of the Nazca Plate in the Arica Elbow, where the general strike of the Andean chain changes and no deep seismicity has never been recorded. Finally, our results confirm the increase of the dip of the slab between 350 and 550 km in depth.