Mechanical stability of Mt. Vesuvius volcano: effects of asymmetries on the stress field

The effect of nonaxisymmetric elasticheterogeneities on the mechanical stability of a nearly axisymmetric volcanic structure, with particular reference to Mt. Vesuvius (Italy) is investigated. This is done solving numerical models using a finite element code in the framework of linear elasticity. The models include gravity,anisotropic depth-dependent regional stress, the edifice, the possible presence of a pressurized feeding system and of heterogeneities in the elastic behavior of country rocks. The criteria to assess instability are the development of tensile stresses and, in compression, the Navier–Coulomb criterion. The presence of asymmetric heterogeneous structures with lateral elastic contrast has been considered by solving three-dimensional (3D) models. To have computationally tractable models, axis-symmetric models were solved first, considering lateral symmetric heterogeneities of different shapes and sizes around the symmetry axis. This allowed us to assess the minimum size of smaller models (submodels) to be developed in 3D. The submodels were then solved including asymmetrical heterogeneities. In all the analyzed cases, the main characteristics of the instabilities/stabilities found with the 3D asymmetric models are very similar to those found by the analogous symmetric models. Moreover, the presence of sharp lateral elastic contrast at shallow depth appear to produce a greater instability on the flanks of the volcanic edifice.