I Congreso de Postgrado fcfm: ingeniería, ciencias e innovación

48 Santiago, 10 al 12 de agosto, 2022 LITHOLOGICAL CONTROL OF ACTIVE NORMAL FAULT FROM TRIASSIC TO QUATERNARY, NORTHERN CHILE Kellen Azúa¹ , ²*, Francisco Pastén-Araya¹ , ³, José González-Alfaro², José Salomón⁴, Sergio Ruiz¹, César Pastén⁴, Pablo Salazar⁵ ¹Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile. ²Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile. ³Departamento de Obras Civiles, Facultad de Ciencias de la Ingeniería, Universidad Católica del Maule, Talca, Chile. ⁴Departamento de Ingeniería Civil, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile. ⁵National Research Center for Integrated Natural Disaster Management, Universidad Católica del Norte, Antofagasta, Chile. *Email: kellen.azua@uchile.cl ABSTRACT Understanding the lithological control of crustal faults near cities and localities and their potential depth is important for geophysics to assess the seismic hazard and characterize complex fault systems. We studied the Mejillones Fault (MF), which is close to one of the most important ports in northern Chile in Mejillones city. The MF is an active geological fault of 40 km in length that is part of an extensive complex system of normal faults called the Atacama Fault System. We built up an S-wave tomography model using ambient seismic data recorded by a dense network of stations registered continuously from 2013 until 2015. The tomographic maps present significant features that correlate with surface geology. We found lower velocities in the western part of the MF than in the eastern zone, with a shear wave velocity of around 2.0 km/s. We can associate this 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 the presence of igneous rocks from the Upper Jurassic. The difference in velocity of these two anomalies remains with increasing depth. The potential depth of the MF could be greater than 5 km and delimits the boundary between 2 different geological zones. Middle Vs (~2.8 km/s) at -23.25° are associated with andesitic rocks, that would have been deposited in an Upper Triassic intra-arc basin and accommodated by the MF over the last ~150 Myr. C I E NC I A S D E L A T I E R R A 03