Colli Albani Volcanic District Structure Revealed By Three Dimensional Gravity Field Modeling (Rome, Italy).

Abstract

Understanding the factors controlling the most recent hydromagmatic activity at the Colli Albani Volcanic District is crucial for the assessment of volcanic hazard in the densely populated area of Rome. At present, the area is characterised by almost continuous low-level seismic activity and by the presence of an intense deep CO2 degassing process.In order to assess the inner structure of the volcanic district, we carried out a detailed gravity survey, more than 900 new prospecting gravity stations. 3D gravity modelling reveals the previously unknown geometry of the dense substratum of the Vulcano Laziale (VL) and evidences the presence of a collapsed structure beneath the caldera filled up with low density material. A complex system of faults surrounds the volcanic area. Many tectonic lineaments with prevalent Apennine and anti-Apennine directions can be singled out; some of these are quite coincident with the volcanic fault lines. This zone could have guided both the development of the volcano activity and the emplacement of the VL caldera and hydromagmatic maars. The VL caldera collapse area enclosed by these two structures is elliptical and about 20×30 km in size. Our observations suggest an asymmetric subsidence along the fault zone resulted in trapdoor subsidence in the western part. Other new information regards the Colli Albani structure. It consists of a circular volume of rocks around the Campi di Annibale volcanic vent and that extends down to the carbonate basement. It results to be denser with respect to the surrounding sedimentary cover of the Vivaro Plain and to the material located just along the central axis of the volcanic structure.