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

Tenerife, Spain 31May-4June 2010

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.