Análisis neotectónico y paleosísmico de la falla Loma Negra Oriental, frente orogénico de la Precordillera Central, Argentina.

The reverse fault known as Loma Negra Oriental is located on the orogenic front of the Central Precordillera, characterized by N-S trending thrusts with eastern vergence. This fault limits the eastern flank of the Loma Negra brachianticline, a fault propagation fold that deforms Neogene rocks and Quaternary deposits outcropping on the eastern piedmont of the Sierra de Talacasto. The faults related to this fold trend N-S and affect progressively younger deposits to the east, showing the advance of the Andean deformation in that direction. In the northern section of the Loma Negra Oriental Fault, a natural exposure shows deposits associated with single-event displacements, allowing us to determine its kinematics. The Loma Negra Oriental thrust shows a NNW trend (130°) and dips with low angle (22° SW) affecting recent alluvial deposits of early Holocene age (8,700 ± 1,370 years BP). To characterize the morphology of the scarps associated with this fault, we constructed detailed topographic profiles transverse to the analysed structure. Two scarps of 0.9 m and 3.1 m high were recognized, suggesting several seismic events. The fault seems to continue to the north and south as a blind (buried) structure that limits the entire eastern flank of the brachianticline, with a length of at least 16.5 km. Based on the scarps measurement, the surface and subsurface rupture extension, and the paleoseismic analysis of a natural exposure, with a total vertical slip of 0.9 ± 0.1 m (~ 0.4 m for the last event and ~ 0.5 m for the penultimate) and a dip-slip per event of 1.16 ± 0.15 m, we suggest the occurrence of two seismic events during the Late Pleistocene-Holocene. In this way, we consider this structure as a potential seismogenic source which could generate a maximum probable earthquake of magnitude Mw 6.5 or larger, with an estimated recurrence period of ~9,000 years, posing a threat to infrastructure and populated areas of the province of San Juan (>800,000 inhabitants). [ABSTRACT FROM AUTHOR]