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

48 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 Crustal fault, Tomography, Mejillones Fault, Mejillones Peninsula, Northern Chile. (1) Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile. (2) Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile (3) Departamento de Obras Civiles, Facultad de Ciencias de la Ingeniería, Universidad Católica del Maule, Talca, Chile (4) Department of Civil and Environmental Engineering, Imperial College London, South Kensington, London, UK (5) Departamento de Ingeniería Civil, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile (6) Millennium Institute on Volcanic Risk Research - Ckelar Volcanoes, Antofagasta, Chile. (7) Departamento de Ciencias Geológicas, Universidad Católica del Norte, Chile. (8) Centro de Investigación para la Gestión Integrada del Riesgo de Desastres (CIGIDEN), Santiago, Chile *Email: Kellen.azua@gmail.com Kellen Azúa (1, 2) Francisco Pastén-Araya (3) José González-Alfaro (2) José Salomón (4) Sergio Ruiz (1) César Pastén (5) Pablo Salazar (6, 7, 8) LITHOLOGICAL CONTROL OF THE ACTIVE MEJILLONES FAULT FROM TRIASSIC TO QUATERNARY, NORTHERN CHILE A B S T R A C T Understanding the lithological control of crustal faults near cities is important for assessing the seismic hazard. We studied the Mejillones Fault (MF), located in northern Chile. We built an S-wave tomography model using seismic ambient noise. We found lower velocities in the western part of the MF, with a shear wave velocity (Vs) of about 2.4 km/s, associated with fractured metamorphic rocks (Triassic) and marine sediments (Neogene- Quaternary). Higher velocities (Vs > 3.0 km/s) in the eastern part of the fault are related to igneous rocks fromtheUpper Jurassic. The potential depth of the MF could be greater than 4 km and delimits the boundary between 2 different geological zones. Intermediate Vs (~2.8 km/s), observed up to 4 km depth, can be associated with andesitic rocks deposited in an intra-arc basin (Upper Triassic) and accommodated by the MF over the last ~200 Myr, evidencing the activity of this fault from Triassic to Quaternary.