Struttura e Dinamica del Distretto Vulcanico dei Colli Albani da misure gravimetriche:implicazioni geodinamiche e vulcanologiche

Abstract

In 2005-2006 in the framework of an INGV-DPC projects, in co-operation with the University of Rome “La Sapienza”, a gravity research started in the Colli Albani Volcanic District aimed: i) to realize a new gravity network to detect gravity changes due to mass redistribution in the underground inferred by the local volcanic activity; ii) to upgrade the already available Bouguer gravity map by means of new stations and to carry out new analyses and interpretations to outline a more detailed structural setting of the area. The gravity network has been designed so as to incorporate an old net of 7 stations, settled in 1981 by the same University group and periodically reoccupied until 2004. The new network is presently formed by 30 stations covering the whole volcanic area and all close to levelling benchmarks to remove the effect of the vertical ground movements. Taking into account the logistic situation of the area, three absolute gravity stations have been settled. Two of them have been located out of the volcanic area to be adopted as references (Sant'Angelo Romano and Palestrina). The third ones has been realized inside the most active part of the volcanic district to calibrate in future (Castel Gandolfo), through its repetition, the gravity changes detected by relative measurements. In the absolute sites the measurements of the vertical gravity gradient have been carried out because g is not directly measured on the ground. Each absolute station is completed with an external satellite ones, then included in the relative network, where the absolute value of g has been also transported through relative measurements. Moreover, 13 selected stations are also sites of vertical gravity gradient measurements. Those measurements helpful to reduce the effect of height changes on gravity variations and their space distribution is useful to reduce the prospecting gravity data. Four surveys of both relative and gradiometric measurements has been carried out (March and June 2006 - January and June 2007). In order to outline a more structural setting of the investigated area, a new set of about 900 new prospecting gravity stations have been settled inside an old survey made by 1500 stations measured partly by the Servizio Geologico d’Italia (SGI) in 1969 and partly by the University of Rome in 1995. Up today, the new stations have been partly measured and all the available data have been reprocessed and uniformed. The results from both the dynamics and the static gravimetry will be presented and discussed. 3-D density model of the Colli Albani Volcanic District was obtained. Based on its volcano-tectonic evolution, we interpret volcanic structures that have never been imaged before.