Potential seismogenic structures in populated areas of NW Argentina: the Medeiros anticline and the growing capital of Salta province

GARCÍA, VÍCTOR; HONGN, FERNANDO; MONTERO, CAROLINA; ARNOUS, AHMAD; ELÍAS, LEONARDO; CRIADO SUTTI, EMILIO; ZECKRA, MARTIN; FIGUEROA, SARA; ARANDA, GERMÁN; ESCALANTE, LEONARDO; PEYERL, WILLIAM; SALAMUNI, EDUARDO; ORTÍZ, GUSTAVO; MONTEROS, EUGENIA; PUPIM, FABIANO; KRUGER, FRANK; BOOKHAGEN, BODO; STRECKER, MANFRED

Roma

Congreso; XXI INQUA Congress; 2023

Historical and instrumental seismicity records from the Central Andes of north-western Argentina spanning the last 350 years has been the primary data source to characterize this region’s exposure to seismic hazard as “moderate” to “high” (0.18-0.25 PGA). The lack of detailed studies regarding widespread evidence of Quaternary seismogenic deformation has prevented a more accurate seismic hazard assessment (SHA) in the vicinity of the metropolitan regions of San Salvador de Jujuy, Salta, and San Miguel de Tucumán, which together total almost 2 million inhabitants and host important infrastructure.In order to improve the neotectonic characterization of potential seismogenic sources in this region we have employed a multidisciplinary and multimethodological research approach that includes remote sensing analysis, detailed structural and geomorphic mapping and topographic surveying, interpretation of seismic reflection lines and near-surface geophysical surveys, structural modeling, the deployment of temporary local seismic networks, as well as geochronology. The geochronological methods include terrestrial cosmogenic nuclide (TCN) dating and U-Pb dating of volcanic ashes to establish the age of abandoned fluvial terraces (104to 105yrs), and optically stimulated luminescence and AMS14C dating to constrain the depositional ages of sedimentary sequences on centennial to multi-millennial timescales.In this context, the Medeiros anticline has been already characterized as an N-S oriented, 16 km-long, fault-propagation fold deforming the entire sedimentary cover through a blind 30°W dipping ramp and a sub-horizontal detachment located in the contact with the metamorphic basement. Syntectonic unconformities in the synorogenic deposits allowed to establish the onset ofthe fold growth by upper Pliocene times. The Medeiros anticline is the southern termination of the La Caldera-Vaqueros ranges, representing as a whole a more than 60 km-long structural block.Recently obtained TCN ages from two (T3 and T5) of the six (T1-T6 from oldest to youngest) folded fluvial strata terraces of the Vaqueros River, which cross the Medeiros anticline in an E-W direction, allow us to calculate average slip rates of 2.8 mm/a for the last ca. 45 ky implying a much higher potential seismic risk for the capital of Salta province that has rapidly expanded over the Medeiros anticline in the previous decades.