Segmentation, kinematics and relative chronology of the late deformation of Salar del Carmen Fault, Atacama Fault System (23°40'S), northern Chile.

Abstract

The Salar del Carmen Fault is the most important strand of the Atacama Fault System exposed along the eastern border of the Sierra del Ancla. The younger slip event along this fault forms seven consecutive 8 km long north-south striking fault segments that cut Pliocene alluvial fans. The segments show a left stepping geometry, whose terminal parts are linked by transfer faults. The scarps were formed by east-down-dip-parallel slip along subvertical fault planes. The strain state is characterized by a N90E trending and 33° plunging extensional axis a N87W trending and 56° plunging shortening axis. Ruptures along the fault form 0.2-9 m high fault scarps. Older scarps are dominated by debris slope whereas younger scarps are free face dominated. Scarp ages, estimated by morphologic dating, indicate that the scarps are not older than the Late Pleistocene (< 400 Ka). Cracks with centimetric down-the-dip displacement were formed during the last subduction earthquake (Antofagasta, 30th de July 1995, Mw=8.1. This demonstrates that the Atacama Fault System experiences coseismic reactivation during large subduction earthquakes. Greater vertical slip documented along the Salar del Carmen Fault are interpreted to be triggered by subduction earthquakes with Mw >8.0.