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

26 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 K E Y W O R D S San Ramón Fault trace, La Reina, Santiago, rock aquifer, ERT (1) Subterránea Consultores. iaguirre@subterranea.cl (2) Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile. geaston@uchile.cl *Email: igor.aguirre.araneda@gmail.com Igor Aguirre (1,2) Gabriel Easton (2) HYDROGEOLOGICAL CONCEPTUALIZATION OF ROCK AQUIFERS BASED ON GEOPHYSICAL AND DRILLING DATA AS INSIGHT FOR SUBSURFACE EXPLORATION OF THE SAN RAMÓN THRUST FAULT IN SANTIAGO, CHILE A B S T R A C T The San Ramón Fault is a thrust fault system located at the western foot of the Andes, along the piedmont of the mountain front that limits the central valley where Santiago, capital city of Chile, is located. According topaleoseismological and seismological evidence, the fault is capable to produce large earthquakes with superficial rupture, constituting a challenge for the city of Santiago as well as for the entire Metropolitan region. Here, from ongoing subsurface geophysical exploration, drilling data and LiDAR data from La Reina district, in the eastern border of the city, we provide new evidence focused on the location of the fault trace, improving knowledge about the fault geometry and its control on the rock aquifer development and main recharge process. 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 western foot of the Andes, along the eastern border of Santiago, capital city of Chile (Armijo et al., 2010; Fig. 1). This structural fault system is evidenced by fault scarps of about 4- 100 m height, which are systematically located along the fault trace affecting Quaternary piedmont units, and overthrusting rocks over unconsolidated alluvial sediments (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, which occurred near 17,000 years ago and close to 8,400 years (Vargas et al., 2014).