Immersive Virtual Reality and numerical modelling application to study a dyke-induced asymmetric graben: the 1971 Mt. Etna (Italy) case

Abstract

In the present study we integrated data collected using field and Immersive Virtual Reality surveys with numerical models, in order to characterise a unique dyke-induced graben system, exposed both in section and plan view, characterised by an unexpected asymmetric fault geometry. Such volcanotectonic feature was formed during the 1971 eruption and is located near the northern wall of the Valle del Bove, Mt. Etna, southern Italy.We firstly created a new structural map obtained from the analysis of historical aerial stereophotos encompassing a time interval from before to after the 1971 eruption; afterwards, we collected quantitative data on high-resolution drone-derived 3D models and field surveys carried out in the summer of 2022. Data collection on the vertical cliff was entirely carried out thanks to Immersive Virtual Reality techniques.In plan view, the graben is 2-km-long and its width ranges 27-143 m from the bottom to the upper part of the section view, with about 82 m of difference in elevation from top to bottom. Graben faults clearly show an asymmetric setting in terms of attitude, with one fault dipping 70° to the south, and the other one dipping 50° to the north. Vertical offset values are greater at higher elevations. We also ran a set of numerical models, aimed at investigating the distribution and orientation of stresses around the inferred dyke tip and within the host rock. Comparison between field data and numerical models suggests the key role played by the inclined topography, as shown in section view, in determining the orientation of dyke-induced σ1 and σ3 in the host rock. This, in turn, controls the geometry of the graben faults, resulting in the observed asymmetric setting. Additionally, dyke-induced stress concentrations and vertical offset values support the hypothesis of a downward propagation of the graben faults, from the surface down to the dyke tip.