Understanding the stress distribution around shallow magma chambers is vital for predicting eruption sites and magma propagation directions. To achieve accurate predictions, comprehensive insight into the stress field surrounding magma chambers and near the surface is essential. Existing stress models for magma chamber inflation often assume a homogenous elastic half-space or a heterogeneous crust with varying mechanical properties in horizontal layers. However, as many volcanoes have complex, non-horizontal, and heterogeneous layers, we enhance these assumptions by considering mechanically diverse layers with varying dips. We employed the Finite Element Method (FEM) to create numerical models simulating two chamber shapes: a circular form and a sill-like ellipse. The primary condition was a 10 MPa excess pressure within the magma chamber, generating the stress field. Layers dips by 20-degree increments, with differing elastic moduli, represented by stiffness ratios (EU/EL) ranging from 0.01 to 100. Our findings validate prior research on heterogeneous crustal modeling, showing that high stiffness ratios disrupt stress within layers and induce local stress rotations at mismatched interfaces. Layer inclination further influences stress fields, shifting the location of maximum stress concentration over varying distances. This study underscores the significance of accurately understanding mechanical properties, layer dip in volcanoes, and magma chamber geometry. Improving predictions of future eruption vents in active volcanoes, particularly in the Andes with its deformed, folded, and non-horizontal stratified crust, hinges on this knowledge. By expanding stress models to incorporate complex geological structures, we enhance our ability to forecast eruption sites and the paths of magma propagation accurately.

In an active volcanic arc, magmatically sourced fluids are channeled through the brittle crust by structural features. This interaction is observed in the Andean volcanic mountain belt, where volcanoes, geothermal springs and the locations of major mineral deposits coincide with NNE-striking, convergent margin-parallel faults and margin-oblique, NW/SE-striking Andean Transverse Faults (ATF). The Tinguiririca and Planchón-Peteroa volcanoes in the Andean Southern Volcanic Zone (SVZ) demonstrate this relationship, as both volcanic complexes and their spatially associated thermal springs show strike alignment to the outcropping NNE oriented El Fierro Thrust Fault System. This study aims to constrain the 3D architecture of this fault system and its interaction with volcanically sourced hydrothermal fluids from a combined magnetotelluric (MT) and seismicity survey. The 3D conductivity model and seismic hypocenter locations show correlations between strong conductivity contrasts and seismic clusters in the top 10km of the crust. This includes a distinct WNW-striking seismogenic feature which has characteristics of the ATF domains. As the surveyed region is characterized by high heat flow regimes, volcanic activity and hydrothermal systems related to the volcanic arc, the conductivity contrast suggests that magmatically derived fluids meet an impenetrable barrier, most likely the sealed core of the fault. The resulting increase in hydrostatic fluid pressure facilitates seismic activity on this WNW oriented structure. These results provides the first observation of the mechanism behind the reactivation and seismogenesis of ATF. The study also uncovers the role of the ATF the compartmentalization of magmatic-derived fluids that accumulate to form hydrothermal reservoirs in the SVZ.