Magma, faults, and gravitational loading at Mount Etna: The 2002–2003 eruptive period

Abstract

Mount Etna is characterized by a complex structural setting that influences its evolution. In order to understand how the interaction between dike-forming intrusions and faulting influences the kinematics of the volcanic edifice, we developed a numerical model. It takes account of the topography, the medium heterogeneities, the gravitational loading, and the most active crustal discontinuities. A parameterization of the apparent coefficient of friction, as a function of the depth, has been considered in the range from 0.01 to 0.5. The density values used, Young’s modulus, and Poisson’s ratio range from about 1700 to 3200 kg/m3, 8.5 to 140 GPa, and 0.15 to 0.35, respectively. The model was applied to the 2002–2003 Etna eruption. The resulting deformation pattern was in agreement with the data provided by the continuous GPS stations and the seismological knowledge, obtaining displacements up to 1 m. Some discrepancies between the recorded ground deformation field and the modeled displacements allowed us to make some hypotheses on the volcano-tectonic (e.g., for the Pernicana fault) or regional-tectonic origin (Acireale – S. Alfio fault system) of the crustal discontinuities. Moreover, our results suggested that the Pernicana fault is characterized by a very low apparent coefficient of friction, less than 0.1. Furthermore, we evaluated the contribution of the gravitational loading and found that it implies a variation of about 10% of the overall deformation pattern. Our results clearly showed that the weight of the volcanic edifice acts in opposition to the magmatic intrusions. Conversely, we found that the presence of medium heterogeneities may favor the eastern flank movements toward the SE and the spreading of the summit area, playing a fundamental role in ascending magma. Finally, we investigated the shallow sliding model and found that dike-forming intrusions produce negligible displacements, less than 1 mm, along the subhorizontal detachment surface. Therefore, the gravitational loading during dike-forming intrusions is not able to trigger sliding processes along this plane.