Abstract
An elastic 3-D axi-symmetric model based on Finite Element Method (FEM) is proposed to compute ground deformation and gravity changes caused by overpressure sources in volcanic areas. The numerical computations are focused on the modeling of a complex description of Mt Etna in order to evaluate the effect of topography, medium heterogeneities and source geometries. Both ground deformation and gravity changes are investigated by solving a coupled numerical problem considering a simplified ground surface profile and a multi-layered crustal structure inferred from seismic tomography. The role of the source geometry is also explored taking into account spherical and ellipsoidal volumetric sources. The comparison between numerical results and those predicted by analytical solutions disclosed significant discrepancies. These differences constrain the applicability of simple spherical source and homogeneous half-space hypotheses, which are usually implicitly assumed when analytical solutions are applied.
Highlights
Microgravity and geodetic observations have proven to be useful methods for monitoring volcanic activity and for the quantitative evaluation of the geophysical processes preceding and accompanying volcanic unrest (Carbone et al, 2003; Gottsmann et al, 2006)
Numerical models over the past decade have emphasized that topography engenders perturbations on the surface deformation (Williams and Wadge, 1998, 2000; Cayol and Cornet, 1998; Lungarini et al, 2005), few studies have been carried out to assess how topography together with source geometry can influence gravity anomalies. To fill these gaps we propose a numerical procedure based on Finite Element Method (FEM) to evaluate both elevation and gravity changes expected in volcanic region
The finite element model is applied to evaluate deformation and gravity changes produced by pressurized volcanic sources
Summary
Attempts at modeling gravity changes expected to accompany crustal deformation often involve a great deal of effort due to the complexity of the problem. Initial attempts to estimate the effect of heterogeneity were made solving a coupled self-gravitational model of magma intrusion in an elastic-gravitational layered medium (Rundle, 1980; Fernandez et al 1999) These semi-analytical solutions assessed the effects of both elastic and density stratifications on gravity changes (Tiampo et al, 2004). Numerical models over the past decade have emphasized that topography engenders perturbations on the surface deformation (Williams and Wadge, 1998, 2000; Cayol and Cornet, 1998; Lungarini et al, 2005), few studies have been carried out to assess how topography together with source geometry can influence gravity anomalies To fill these gaps we propose a numerical procedure based on Finite Element Method (FEM) to evaluate both elevation and gravity changes expected in volcanic region. A comprehensive model is realized to understand how this more complex framework could affect the deformation and gravity field caused by likely overpressure source
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