Active faults of the Andean Active Orogenic front (32° 30´S)

Abstract

The Andean active orogenic front, located in the Precordillera foothill at 32º 50'S, gathers the largest Quaternary deformation of Argentina. This region is related to intra-plate seismicity linked to the Pampean Flat Slab segment, the subduction of Juan Fernandez Ridge, a volcanism absence, and the particular morphostructural style of the morphotectonic unit of Precordillera (Southern Precordillera) that culminates at this latitude (32°S). Besides, a change in the style deformation of Quaternary structures is determined at this latitude, where folds limited by active faults and N-S reverse faults offsetting Late Pleistocene alluvial levels, predominate. In this study, the main Quaternary faults were studied. The maximum probable earthquake magnitude associated with these structures was established (~Ms=6.4) based on parameters measured along fault planes. The result was compared with values obtained indirectly by fault long. According to morphometric indices, the greatest current deformation area was located in the southern portion of the Andean piedmont. This zone shows as well the greater deformation detected by interferometry (DINSAR technique). Optically Stimulated Luminescence datings on sag ponds related to active faults allow to infer a regional slip rate during the Late Pleistocene.