 In the Andean volcanic arc, margin-parallel and blind oblique fault systems control volcanic, hydrothermal and ore-porphyry processes  Subsurface conductivity structure and seismicity show a WNW-trending active fault in the Andean Southern Volcanic Zone  Results show magmatic/hydrothermal fluids are compartmentalised by local faults, and elevated fluid pressures promote fault reactivation

Understanding the relationship between crustal faults and volcanic activity in transpressional environments is a main goal in geosciences and could help to understand geothermal resources and evaluate geological hazards. In the Andean Southern Volcanic Zone (SVZ), Chile, recorded seismicity is scarce, and few studies have evaluated the relationship between volcanic activity and crustal faults from seismic observations. Thus, in this study, we deployed a seismic network for almost 1 year to understand the brittle deformation of the upper crust within the Puyuhuapi area, located at~44°S in the SVZ. We analyzed the location and kinematics of seismicity together with previously published field structural geological data. Considering these results, we developed an integrative tectonic model for the area and discussed which faults facilitate magma transport through the crust. Our results indicate the existence of two NNE-oriented seismogenic dextral to dextral-reverse regional faults that generate a duplex in a continental-scale fault setting. Inside the duplex, we observed normal to strike-slip normal focal mechanisms which recurrently have NE trending nodal planes. At a regional scale, a strike-slip tectonic environment has a N60°E/18°shortening direction and a N151°E/03°extension direction. We conclude that stratovolcanoes are located inside the duplex in a local transtensional environment where NE oriented normal faulting may occur. These faults facilitate magma transport since they represent the preferential orientation for dilatational fractures. Conversely, in local transpressional environments such as the Puyuhuapi fault (NNE oriented dextral to dextral-reverse kinematics), only minor eruptive centers of small volume are emplaced, suggesting a less productive magma transportation process.

The San Ramón Fault (SRF) runs for 30 km along the western flank of the Andes in front of the city of Santiago, Chile (33.5°S). Geological studies have highlighted the SRF role in the Neogene uplift of the Andes at this latitude, but the fault geometry at depth is not well constrained. Here we infer the structure of the sedimentary cover and bedrock up to a depth of 500 m along the SRF by integrating gravimetric, electrical resistivity, seismic, and magnetic methods. In a section crossing the central segment of the SRF, lateral variations in P wave velocity models indicate that the sedimentary cover is more deformed close to SRF scarps, while coincident low‐density and low‐resistivity zones suggest that the presence of two depocenters in the sedimentary cover below the SRF scarps. Gravimetric profiles distributed along the entire trace of the SRF show the same configuration of two depocenters, but the geometry of these depocenters is complex and varies along strike. Our findings suggest that the bedrock and sediments deformation along the SRF exhibit a complex geometry, which can be explained by the interplay of reverse and strike‐slip movements during the late Cenozoic. Based on our results, the distribution of crustal seismicity and shortening rates interpreted across the Andes, we estimated that SRF deformation represents 5–20% of the whole Andean shortening for the last 4 Ma. Using empirical length scales for crustal seismicity, this deformation pattern is consistent with a maximum earthquake magnitude in the range of 6.0–6.5 Mw.

No abstract