Influence of topography on ground deformation at Mt. Vesuvius (Italy) by finite element modelling

Abstract

Ground deformations are observed in connection with volcanic activity, and therefore geodetic monitoring can provide significant indication of changes of equilibrium conditions. The aim of this paper is to study the deformation of Mount Vesuvius (Italy) caused by overpressure sources at various depths, using a commercial (Ansys) 3D finite element code, in the framework of linear elastic isotropic material behaviour. Both homogenous and heterogeneous media with carbonate basement were analyzed to understand the influence of topography on the ground deformations. The topography of the Somma-Vesuvius was taken into account, using a digital terrain model, and the carbonate basement was schematically modelled by assuming two horizontal layers with different Young moduli. The presence of a strong deviation from axially symmetric pattern of the displacement field, and of small subsidence areas, was found. These characteristics are completely unknown from the simple Mogi model and by simplified topography model, as verified by ad hoc simulations. These preliminary results, showing areas of the volcanic edifice experiencing high deformation, can improve the determination of the sources of deformations, i.e. the most relevant problem in the volcano monitoring. Moreover, the knowledge of the deformation pattern, including the topography effects, can provide significant indications to optimize the A c c e p t e d m a n u s c r i p t location of sensors and the characteristics needed to design an efficient and reliable geodetic monitoring network able to detect shallow intrusion events.

Tilt prior to explosions and the effect of topography on ultra‐long‐period seismic records at Fuego volcano, Guatemala

“…Volcanic deformation is often modeled using analytical solutions to either an isotropic volumetric point source [ Mogi , 1958] or an Okada dislocation surface (dike or sill) [ Okada , 1985] due to the simplicity of these models and the ease of implementation. However, these models do not incorporate topography which has been shown to have a strong effect on the deformation field, particularly for slopes above 20° [ Cayol and Cornet , 1998; Meo et al , 2008], and neither of these models are able to replicate the tilt signals we recorded. Based on these results, we choose to include the 3D topography in forward models of the tilt signal through the finite‐difference method of Ohminato and Chouet [1997].…”

Precursory tilt changes associated with a phreatic eruption of the Hakone volcano and the corresponding source model

“…Many studies have demonstrated that surface deformation resulting from underground pressure sources can be affected by topography (e.g., Cayol and Cornet 1998;Lungarini et al 2005;Meo et al 2008;Seismology and Volcanology Research Department, MRI 2008). Such topographic effects are more prominent when the observation sites are located on steep slopes (i.e., the average slope of the flanks of the volcano exceed 20°); the topographic effect cannot be ignored when the slope exceeds 30°.…”

Modeling of the three‐dimensional subsidence diffusion–convection problem above a trapdoor

“…Þ, the dimensionless domain parameter b = 2 H/B 1 cot(b), and a critical parameter for the magnitude of the central subsidence expressed by the geometrical ratio b c = B 2 /B 1 = cos h 2 (u)/(cos h 2 (u) À 1). Equation (19) converges to the axisymmetric model [3,20] when b c ! 1 (i.e.…”

“…arching effects , shallow and deep subsidence mechanisms ), and 3D numerical analyses (e.g. ) using elastic, elastoplastic, viscoelastic, viscoplastic, distinct element, poromechanical models. Because finite element methods or other computational methods are simulating, in most of the cases, a more realistic setup of the actual conditions, they are providing more accurate results.…”