Subduction of the Nazca Plate beneath Peru as determined from seismic observations

Abstract

A detailed reinvestigation of seismicity in the southern half of Peru using data from a local seismic network and a focal mechanism study using P wave first motions reveal that for the first 100 km of descent the slab (as defined by this seismicity) enters at a normal dip angle near 30° and that below this depth it is bent to a nearly horizontal angle. This horizontal slab extends eastward for about 300 km and then dips steeply below the thick continental lithosphere. ScSp observations are found to be consistent with the profile of the subducting plate as determined from the local seismicity. Beneath the region from southern Peru to northern Chile, the Nazca plate descends with an almost constant dip angle (∼30°) down to at least 300‐km depth. Between the 30° dipping plate in southern Peru and the horizontal profile beneath central Peru, there is a contortion over a 100‐km‐wide continuous lateral section of the subducting plate. We infer that, at least in the upper 150 km depth range, the descending Nazca plate is contorted rather than torn.