A. Troiano

Stratigraphy, structure, and volcano-tectonic evolution of Solfatara maar-diatreme (Campi Flegrei, Italy)

This study focuses on the Solfatara volcano within Campi Flegrei, a volcanic field located on the Tyrrhenian coast of southern Italy. Volcanism at the Campi Flegrei caldera has included phreatic to phreatomagmatic explosions and both magmatic (ranging from small scoria-producing events to those with Plinian columns) and effusive eruptions. These eruptions have formed tuff cones, tuff rings, minor scoria cones, and lava domes. A detailed stratigraphic, structural, and geophysical study of the area indicates that the Solfatara volcano is a maar-diatreme structure previously not recognized within the Campi Flegrei caldera. It is characterized by a crater cut into earlier volcanic deposits, a small rim of ejecta, and a deep structure (down to 2–3 km). This maar-diatreme has allowed the gases and fluids to flow up to the surface over a long time. A new geological map and cross sections show a complex architecture of different volcano-tectonic features including scoria cones, lavas, cryptodomes, feeder dikes, pipes, ring and regional faults, and explosive craters. Volcanological data were collected with the main aim of characterizing the eruptive activity in a limited sector of the caldera. Fault and fracture analyses, using the scan line methodology, highlight the role of the main structures that accompanied the volcanic evolution within this sector of the Campi Flegrei caldera. To better constrain the subsurface structure of the Solfatara crater, electrical resistivity tomography investigations were integrated with the volcano-tectonic information. All data suggest that the Solfatara area is dominated by a maar-diatreme evolution. Presently, the Solfatara area shows widespread hydrothermal and fumarolic activity that is localized along the major faults. The results allow us to define a particular type of volcanic activity in the recent past, in what is still considered today an area with a higher probability of opening new vents, particularly for possible phreatic activity.

Imaging 2D structures by the CSAMT method: application to the Pantano di S. Gregorio Magno faulted basin (Southern Italy)

A controlled source audiofrequency magnetotelluric (CSAMT) survey has been undertaken in the Pantano di San Gregorio Magno faulted basin, an earthquake prone area of Southern Apennines in Italy. A dataset from 11 soundings, distributed along a nearly N-S 780 m long profile, was acquired in the basins easternmost area, where the fewest data are available as to the faulting shallow features. A preliminary skew analysis allowed a prevailing 2D nature of the dataset to be ascertained. Then, using a single-site multi-frequency approach, Dantzigs simplex algorithm was introduced for the first time to estimate the CSAMT decomposition parameters. The simplex algorithm, freely available online, proved to be fast and efficient. By this approach, the TM and TE mode field diagrams were obtained and a N35°W ± 10° 2D strike mean direction was estimated along the profile, in substantial agreement with the fault traces within the basin. A 2D inversion of the apparent resistivity and phase curves at seven almost noise-free sites distributed along the central portion of the profile was finally elaborated, reinforced by a sensitivity analysis, which allowed the best resolved portion of the model to be imaged from the first few meters of depth down to a mean depth of 300 m b.g.l. From the inverted section, the following features have been outlined: (i) a cover layer with resistivity in the range 3–30 Ω m ascribed to the Quaternary lacustrine clayey deposits filling the basin, down to an average depth of about 35 m b.g.l., underlain by a structure with resistivity over 50 Ω m up to about 600 Ω m, ascribed to the Mesozoic carbonate bedrock; (ii) a system of two normal faults within the carbonate basement, extending down to the maximum best resolved depth of the order of 300 m b.g.l.; (iii) two wedge-shaped domains separating the opposite blocks of the faults with resistivity ranging between 30 Ω m and 50 Ω m and horizontal extent of the order of some tens of metres, likely filled with lacustrine sediments and embedded fine gravels.

Geothermal Investigations of Active Volcanoes: The Example of Ischia Island and Campi Flegrei Caldera (Southern Italy)

The active volcanic zone of Ischia Island and Campi Flegrei caldera (Campania) have been the site of many geothermal investigations, since the early 20th century. These areas are characterized by very high geothermal gradient and heat flow as consequence of upward migration of magmatic sources coupled with vigorous hydrothermal circulation. After the increment of installed geothermal power in Larderello (Tuscany), the extensive geothermal exploration of Campania was not followed by exploitation projects. In recent time, the attention on the possibility to exploit electric energy has been drawn by the new Italian regulation for exploitation leases. The larger geothermal potential of Campi Flegrei caldera and Ischia Island, located west to the Bay of Naples, makes these areas as possible sites of new geothermal plants installation. We present here the results of recent geothermal researches of Campi Flegrei caldera and Ischia Island, which integrate and improve the information obtained during the exploration performed by SAFEN and AGIP-ENEL companies from the earlier 1940 to 1985. These data are useful to characterize the geothermal reservoirs of this active volcanoes and also to increase the knowledge of volcanic processes and related risk.

Numerical Simulation Applied to the Solfatara-Pisciarelli Shallow Hydrothermal System

The Solfatara-Pisciarelli area represents the most active zone within the Campi Flegrei caldera (CFc) in terms of hydrothermal manifestations and local seismicity. Periodic injections of hot CO2-rich fluids at the base of a relatively shallow hydrothermal system has already been correlated to ground uplift in a wide range of numerical modelling of the CFc unrests, that highlight a strong correlation between chemical composition of the Solfatara and Pisciarelli fumaroles, seismicity and ground movements. In particular, a new simulation has been realised via the coupling of TOUGH2©and Comsol Multiphysics©. Recent uplift episodes in the in the centre of Pozzuoli Bay have been reconstructed imposing fluid flows in the system as experimentally recorded. Numerical studies, geochemical data and Magnetotelluric (MT) survey have been integrated, to guess the main features of the shallower part of the hydrothermal system of the Solfatara-Pisciarelli area.

Modelling Coulomb Stress Changes due to Fluid Injection and Withdrawal - A Step to Understand Induced Seismicity

Fluid injection and withdrawal in deep wells is a basic procedure in a series of mining and deep resources exploitation, i.e. oil and gas extraction, geothermal exploitation and EGS permeability enhancement. All these activities have the potential to indu