Seismotectonics of the Andean Southern Volcanic Zone: insights from crustal seismicity

The interaction of faults and fluids in the crust plays a fundamental role on fluid migration as well as on the location, frequency and style of earthquakes. Therefore, understanding these interactions at all scales is key for assessing a diverse range of topics from geohazards, the location and exploitation of mineral and energy resources and for understanding tectonic processes. The area covering the upper Tinguiririca and Teno river valleys, in the Southern Volcanic Zone of the Chilean Andes provides an excellent natural laboratory for studying this. It has undergone recent volcanic and seismic activity, with clear spatial correlations between outcropping faults and arc-sourced fluids outflow (e.g., volcanic features, hot springs and hydrothermally altered areas). To study this, seismicity data was collected locally by 12 seismometers deployed between 2017 and 2018 together with a coeval magnetotelluric survey in the study area. In this thesis I present a seismicity data analysis complemented by the study of the resistivity architecture of the area studied that reveal the relationship of faults and hydrothermal fluids stored in the upper crust. Through location and relative relocation of earthquakes, I show that both the regional El Fierro Fault System and other previously unknown Andean Transverse Faults act as barriers to lateral fluid flow and thus control the distribution of fluid accumulations. Temporal variations of the seismicity rate, the seismic b-value and rupture style of seismicity clustered around the Teno river valley, denote fluctuations of the local differential stress that can be related to pore fluid pressure changes within nearby hydrothermal fluids reservoirs. The interaction of fluids on nearby faults is further evidenced by apparent stress field rotations coetaneous with the changes in rate, b-value and rupture style constrained from the seismicity dataset. These results suggest I have captured part of a long-lasting seismic swarm linked to changes in natural hydrothermal reservoirs. The fault-fluid interactive configuration found in the Tinguiririca - Teno area represents an optimum scenario for the development of ore porphyry deposits, being of high interest to understand the geomechanical and hydrogeological processes that favour the generation of such mineral deposits