Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

the best opportunities for outcrop-scale neotectonic analysis throughout the entire Andes (Costa et al., 2000, 2014, 2019; Fig. 1). This mountain range comprises the Las Peñas Thrust System (LPTS) to the east, which overrides Neogene sediments of the folded bedrock over Quaternary conglomerates and has variable shortening rates along its trace (Harrington, 1971; Costa et al., 2000, 2014, 2019; Ahumada et al., 2006; Ahumada and Costa, 2009; Schmidt et al., 2011b; Fig. 1). This structure, over 30 km long and NW-SE trend, has a geomorphic signature visible and prominent in certain areas at the front but the most recent activity propagates to the east and vanishes beneath the piedmont alluvium along its entire trace (Schmidt et al., 2011b; Vazquez et al., 2016; Costa et al., 2019). Throughout the LPTS, shortening rates have been estimated in the central-southern sector of the Las Higueras-Las Peñas mountain range. At La Escondida and Baños Colorados creeks, shortening rates were calculated obtaining values of 2 ± 0.4 mm/a for the last ~12 ka and 1.2 ± 0.2 mm/yr during the last 13-16 ka, respectively. At the Las Peñas creek, the shortening rate resulted in 0.27 ± 0.11 mm/a for the last 200Ka (Costa et al., 2019). Therefore, there is a difference, in order of magnitude, between the shortening rates of the Las Peñas creek and the La Escondida and Baños Colorados creeks, located about 5 km to the south. In this work, we have analyzed the LPTS at the La Escondida Creek area (Fig. 1). Shortening rate estimations using two alluvial surfaces resulted in values ranging from 0.66 to 0.94 mm/yr for the last 12.6 ka and 0.63 to 2.53 mm/yr for the last 3.3 ka. These data assess the shortening rates of the area and enable the understanding of how the active thrust front is progressing. M E T H O D S We choseQuaternary alluvial surfaces as deformationmarkers and the shortening values were estimated by line length retrodeformation of the trishear models which reconstructed the enveloping of those deformationmarkers with known ages (Fig. 2; Schmidt et al., 2011a). We used FaultFold 7 software (https://www.rickallmendinger. net/faultfold) and a high resolution DEM (0.2 m) for modelling purposes. Due to the uncertainties of this method (Cardozo & Aanonsen, 2009; Hardy & Allmendinger, 2011), we considered a range of maximum and minimum of possible shortening scenarios using different combinations of the parameters, without counting the erosion effect. To effectuate the fault propagation foldmodelswe considered the fault dip, X and Y positions, total slip, propagation-to- Fig. 1: Satellite image downloaded from Bing Maps services displaying the central and southern parts of Las Higueras-Las Peñas range (Mendoza province, Argentina). Solid black lines display the main structures of the area and dashed lines indicate blind thrusts. PFS (Pampean flat slab); LHTS (Las Higueras Thrust System); LPTS (Las Peñas Thrust System); Montecitos anticline (MA); Salagasta Thrust (ST); Jocolí Ridges (JR); Barda Negra anticline (BN). Numbers identify the places where Quaternary shortening rates have been estimated in previous works. Red square indicates the location of the study area.