Stresses Induced by Magma Chamber Pressurization Altered by Mechanical Layering and Layer Dip

Understanding the stress distribution around shallow magma chambers is vital for forecasting eruption sites and magma propagation directions. To achieve accurate forecasts, comprehensive insight into the stress field surrounding magma chambers and near the surface is essential. Existing stress models for pressurized magma chambers 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 stratified layers with varying dips. We employed the Finite Element Method (FEM) to create numerical models simulating three chamber geometries: circular, sill-like and prolate. 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 of the successive layers (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 dip 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 forecasting 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 magma propagation paths. Understanding crustal stress distribution within active volcanoes is crucial to forecast how magma will propagate inside a volcano and where and when a volcanic eruption may occur. Currently, the models used to understand the stress field within volcanoes assume that the Earth's crust is made of the same materials or with horizontally layered different materials. Both cases are seldom correct. Volcanoes often have layers that are both mechanically diverse and dipping at different angles and directions. To improve forecast models, we considered a crust with layers of different mechanical properties and with variable dips. We used numerical models to simulate 3 pressurized magma chamber geometries. We changed the dip of the layers and investigated how the rocks respond to the applied pressure. We found that when the layers are inclined they respond differently to the applied pressure and the possible location of a new eruption is displaced by up to 2 km, compared to the expected location using common modeling protocols. This research improves volcano understanding, especially in regions like the Andes, where the crust is often made by geologically diverse dipping layers. By making our models more realistic we can better forecast where eruptions may occur. FEM models used to analyze the influence of layer dip on crustal stresses resulting from magma chamber pressurization Peak surface tensile stresses can shift by more than 2 km, deviating from homogeneous elastic half-space assumptions The effect is more pronounced with an idealized circular chamber when compared to a sill-like chamber