Stress changes caused by exsolution of magmatic fluids within an axisymmetric inclusion

Abstract

Summary In volcanic regions ascending magma is subject to depressurization and is generally accompanied by exsolution of volatiles. We blackassume a process in which these volatiles propagate upward across newly fractured and permeable rock layers, bringing a sharp increase of pore pressure and temperature within a thin disk-shaped region (inclusion). Thermo-poro-elastic (TPE) inclusion models provide a mechanism to explain seismicity and deformation induced by p and T changes in absence of new magma emplacement in volcanic contexts. They are also suitable to represent the mechanical effects due to fluid extraction and re-injection in geothermal fields. In the present work analytic solutions are provided for the displacement, strain and stress fields assuming a thermo-poro-elastic unbounded medium. Significant deviatoric stress is generated by positive increments of pore pressure and temperature: the stress field is fully deviatoric outside the TPE inclusion, but a strong isotropic stress component is present within, leading to highly heterogeneous faulting mechanisms: if the disk plane is horizontal, thrust faulting mechanisms are favoured within the TPE disk over optimally oriented faults and normal mechanisms above. The model is easily generalized to a vertically thick disk with variable temperature and pore-pressure changes: then, an extensional environment can be obtained even within the TPE inclusion assuming upward decreasing of pore pressure and temperature changes. The supplied analytical solution may be used to model near-field TPE inclusion effects and to validate more complex numerical modelling.

Evidence of poro-elastic inflation at the onset of the 2021 Vulcano Island (Italy) unrest

“…1−] ΔV (Belardinelli et al, 2019;Belardinelli et al, 2022). Closed analytical solutions to Eqs 1-3 can be derived only under simplified assumptions for material properties, pore-pressure and temperature change distributions, and domain and source geometries.…”

“…Examinations of both gravity (Na et al, 2015) and, more recently, thermo-poro-elastic deformation (Mantiloni et al, 2020) have shown that the solutions are accurate under the assumption that the height h of the cylinder is much smaller than its radius R (h/R ≪ 1). The analytical solutions for thin diskshaped sources (Mantiloni et al, 2020) can be easily generalized to model thick cylindrical sources by stacking two or more disks (Nespoli et al, 2021;Belardinelli et al, 2022).…”

“…4). Thermal effects can be much greater than those due to pressure (e.g., Nespoli et al, 2021;Belardinelli et al, 2022) but are usually much slower than the pore-pressure buildup (Coco et al, 2016;. However, thermal effects may be faster when advection processes develop.…”

The Porothermoelastic Stress Evolution of Inhomogeneous Solid due to Near-Surface Reservoir

“…The stress evolution with considering 4D analysis of strain-dependent elasticity and application in subsalt carbonates was investigated in comparison with FEM results. The special geometry of a thin diskshaped resource subject to depressurization was explored via the thermoporoelastic inclusion model [15]. In addition, the related topics on the stress response to pore pressure fluctuations around resources [16,17] and the nonprobabilistic model to solve the effect of crack size uncertainty [18] were analytically evaluated.…”