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

30 PATA Days 2024 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E ASSESSING LATE QUATERNARY SHORTENING RELATED TO FOOTWALL SPLAYS AT THE SOUTHERN SECTION OF LAS PEÑAS THRUST SYSTEM , SOUTHERN PRECORDILLERA, ARGENTINA K E Y W O R D S Southern Precordillera Argentina, Trishear modelling, shortening estimations, Las Peñas Thrust System, foot-wall splays Victoria Alvarellos (1) Carlos Costa (2) Lucía Sagripanti (1, 3) Andrés Richard (2, 4) Lucía Jagoe (1) Soledad Morales Volosín (3,5) Andrés Folguera (1, 3) (1) Instituto de Estudios Andinos “Don Pablo Groeber” (IDEAN), CONICET-Universidad de Buenos Aires, Argentina. (2) Departamento de Geología, Universidad Nacional de San Luis, San Luis, Argentina. (3) Departamento de Geología, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina. (4) Consejo Nacional de Investigaciones Científicas y Técnicas, San Luis, Argentina. (5) Instituto de Geociencias Básicas y Aplicadas de Buenos Aires (IGeBA), CONICET – Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina *Email: vicoalvarellos@gmail.com A B S T R A C T At the southern Pampean flat-slab of the Central Andes, the active deformation zone is located at the easternmost thrusts of the Southern Precordillera along the Las Higueras-Las Peñas range (32° 10’-32° 45’ S). This range is bounded by the Las Peñas Thrust System (LPTS), which juxtaposes Cenozoic sedimentary rocks over a suite of Quaternary alluvial deposits showcasing variable shortening rates. This study is focused on the southern part of this range -La Escondida Creek-, where the Quaternary thrust front migration affects Neogene and Pleistocene strata. We estimated shortening values by retrodeforming trishear models constructed from alluvial surfaces, which served as geometric markers of deformation for propagating structures in the piedmont. Dip-slip rates were estimated ranging from 0.90mm/yr and 1.79mm/yr for the last ∼12 and 3 ka, respectively. I N T R O D U C T I O N The Pampean Flat Slab (27°-33°S) of the Central Andes concentrates most of the Quaternary deformation with thrusts located at the easternmost edge of Precordillera, where intense shallow crustal seismicity at its southern end defines an area of very high seismic hazard (Bastías, 1993; INPRES, 1993). The Southern Precordillera, located south of 32° 10' S, is characterised by NNW-striking east-verging thrusts related to the Neogene inversion of Triassic normal faults (Ramos and Kay, 1991; Cortés et al., 2006; Giambiagi et al., 2011; Fig.1). Within this domain, the Las Higueras-Las Peñas range (32°10'-32° 45'S), concentrates the most recent deformation and provides one of