GEOMORPHIC STUDIES OF LONG-LIVED FAULT SYSTEMS (ARICA BEND, PERU AND CHILE): ACTIVE FAULTING AND FOREARC DEFORMATION OF THE CENTRAL ANDES

Forearc deformation in the Arica Bend do not seem to account for much of the relative Nazca–South American plate motion recorded by the permanent GPS network. However, the central Andes forearc is composed of discontinuous sets of trench-parallel and/or trench-perpendicular fault systems extending in the coastal area or along the western cordillera. And few studies has been done to examine how active are the superficial tectonic structures of the overriding plate. We thus examine the surface expression of active faulting in the Andean forearc, based on satellite imagery interpretation, geomorphologic studies with field work in numerous key areas of the Arica bend. The arid climate in this desertic environment with an almost complete lack of vegetation and human occupation implies the preservation in the morphology of subtle indications of surface deformation due to active faulting. Most of the fault systems show indications of recent activity and movements at scales ranging from drainage re-organisation to ground deformations likely to result from movements during a single earthquake. We also studied the actual morphologic signature of the main fault systems crossed with geological features on different segments to identify long-lived tectonic structures in northern Chile or southern Peru. The geomorphology of faults in the forearc of the Bolivian Orocline suggests that although little shortening is accommodated across this region, they might still be active, and hence capable of producing destructive earthquakes.