Title: Piedmont deposits as seismic energy dissipators, sierras pampeanas of Argentina

Abstract

This study shows the neotectonic deformation in the southern piedmont of the Cumbres Calchaquíes (Fig.1). Seismic energy dissipated from 630 BP to now through less cohesive materials filling the valley, generated discrete fault scarps, and folding into layered conglomerates. In the study region many earthquakes of ≥ 3 and ≥ 4 magnitude coincide with regional faults evidencing its neotectonic activity. The research was carried out based on the collection of bibliographic antecedents, interpretation of satellite images and field data surveys. The Amaicha valley is bounded to the north by the Tafí del Valle normal fault, vergent to the NE and, to the south, by the Los Cardones fault, vergent to SW. In the foothills of this valley, the strata of the Andalhuala Formation override the conglomerates of the Yasyamayo Formation and the fault is affecting Quaternary gravels. The Cumbres Calchaquíes ride over the Sierra de Aconquija through the Los Cardones and Carapunco faults, verging west. In the Tafí valley, faults and folds are affecting the conglomerate sequences of the Pleistocene Lomitas Pegadas Formation. The Carapunco fault has 176 m of fault offset. It generated an imbricate system of contractional fractures, curved in plan, in the piedmont deposits. The foothills deposits, as they have less cohesion and frictional resistance than the fillings of the pre-existing faults, absorb and attenuate most of the seismic energy released and propagated during the reactivation of the faults. On the other hand, the strike of the pre-existing faults and the arrangement of the stratification planes of the sedimentary sequence with respect to the Andean compression can be favorable to the reactivation of these planes. In the Los Sosa River, the reverse reactivation of the Chasquivil fault, verging west, produced the dip to the SE of Quaternary conglomeratic deposits (110°/12°) and Paleogene red sediments (160°/40°).