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

152 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 PATA Days 2024 K E Y W O R D S San Ramón Fault, active tectonics, Santiago, fault trace, paleoseismological trenches. (1) Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile. (2) Subterránea Consultores (3) Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile. *Email :geaston@uchile.cl Gabriel Easton (1) Nicolás Campillay (1) Igor Aguirre (1, 2) Carolina Valderas (1) Angelo Villalobos (1) José González-Alfaro (1, 3) Sofía Rebolledo (1) SURFACE AND SUBSURFACE EXPLORATION OF THE SAN RAMÓN THRUST FAULT IN SANTIAGO AT THE WESTERN FOOT OF THE ANDES A B S T R A C T The San Ramón Fault is a thrust fault system located at the western edge of the Andes, along the piedmont of a more than 2000 m high mountain front that limits the central valley where Santiago, the capital city of Chile, is located. Paleoseismological and seismological results evidence that this is an active fault capable of producing large earthquakes with superficial rupture. Its potential activation constitutes a challenge for the city of Santiago as well as for the entire Metropolitan region. Here, from ongoing analysis of LiDAR data together with new outcrops from paleoseismological trenches and subsurface geophysical exploration, we provide new evidence focused on the location of the fault trace, improving knowledge about the fault geometry with implications for seismic hazard assessment. I N T R O D U C T I O N The San Ramón Fault (SRF) is an active west-vergent thrust fault system located at the foot of the western slope of the Andes, along the eastern border of Santiago, the capital city of Chile (Armijo et al., 2010; Fig. 1). The structural fault system is evidenced by conspicuous fault scarps of about 4-100 m height, which are systematically located along the fault trace affecting Quaternary piedmont units (Armijo et al., 2010; Rauld, 2011). Observations from paleoseismological trenches excavated across a prominent 5 m height escarpment revealed two last large episodes with superficial rupture, with the penultimate occurring near 17,000 years ago and the last close to 8,400 years, suggesting a slip rate in the order of ~0.5-0.6 mm/year (Vargas et al., 2014). The eastern border of Santiago has experienced an accelerated urban development in the last four decades considering the previous four centuries, with increasing urbanization directly