Stefano Carlino

Design and test of a laser-based optical-fiber Bragg-grating accelerometer for seismic applications

We report on a proof-of-principle work aimed at the development of fast-response fiber-optic accelerometers for seismic monitoring. The system is based on a semiconductor diode-laser source that interrogates a newly devised two-dimensional inertial sensor suitable for measurement of horizontal ground accelerations. Plane acceleration components of the sensors mass are detected by two fiber Bragg gratings anchored to its structure. Calibration and comparison with a commercial accelerometer are presented. A great potential, in terms of frequency response and sensitivity, is demonstrated in view of possible field applications in active seismic areas.

Progressive approach to eruption at Campi Flegrei caldera in southern Italy

Unrest at large calderas rarely ends in eruption, encouraging vulnerable communities to perceive emergency warnings of volcanic activity as false alarms. A classic example is the Campi Flegrei caldera in southern Italy, where three episodes of major uplift since 1950 have raised its central district by about 3 m without an eruption. Individual episodes have conventionally been treated as independent events, so that only data from an ongoing episode are considered pertinent to evaluating eruptive potential. An implicit assumption is that the crust relaxes accumulated stress after each episode. Here we apply a new model of elastic-brittle failure to test the alternative view that successive episodes promote a long-term accumulation of stress in the crust. The results provide the first quantitative evidence that Campi Flegrei is evolving towards conditions more favourable to eruption and identify field tests for predictions on how the caldera will behave during future unrest.

The Campi Flegrei Deep Drilling Project (CFDDP): New insight on caldera structure, evolution and hazard implications for the Naples area (Southern Italy)

The 501 m deep hole of the Campi Flegrei Deep Drilling Project, located west of the Naples metropolitan area and inside the Campi Flegrei caldera, gives new insight to reconstruct the volcano-tectonic evolution of this highly populated volcano. It is one of the highest risk volcanic areas in the world, but its tectonic structure, eruptive history, and size of the largest eruptions are intensely debated in the literature. New stratigraphic and 40Ar/39Ar geochronological dating allow us to determine, for the first time, the age of intracaldera deposits belonging to the two highest magnitude caldera-forming eruptions (i.e., Campanian Ignimbrite, CI, 39 ka, and Neapolitan Yellow Tuff, NYT, 14.9 ka) and to estimate the amount of collapse. Tuffs from 439 m of depth yield the first 40Ar/39Ar age of ca. 39 ka within the caldera, consistent with the CI. Volcanic rocks from the NYT were, moreover, detected between 250 and 160 m. Our findings highlight: (i) a reduction of the area affected by caldera collapse, which appears to not include the city of Naples; (ii) a small volume of the infilling caldera deposits, particularly for the CI, and (iii) the need for reassessment of the collapse amounts and mechanisms related to larger eruptions. Our results also imply a revaluation of volcanic risk for the eastern caldera area, including the city of Naples. The results of this study point out that large calderas are characterized by complex collapse mechanisms and dynamics, whose understanding needs more robust constraints, which can be obtained from scientific drilling.

Application of Laser Scanning for Monitoring Coastal Cliff Instability in the Pozzuoli Bay, Coroglio Site, Posillipo Hill, Naples

This study presents a Terrestrial Laser Scanning (TLS) application to monitor the slope stability along tuffaceous cliffed coast of Pozzuoli Bay, at Coroglio test site, Naples, Italy. We tested TLS technique based on Time of Flight method in order to obtain a 3D model of the coastal cliff, along with a classification of the rock discontinuities on the basis of their spatial orientation. A high-resolution digital model of the study outcrop has been produced, with a cell dimension of 5 cm. The analysis of spatial orientation of planar-like surfaces derived from the digital 3D model shows an excellent correlation with the sets of fractures and faults actually measured in the outcrop by classic geo-structural analysis. The results obtained from the Coroglio test suggest that the use of TLS application is an effective method for the monitoring of instability and evolution of coastal cliffs in volcanic settings.

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.

Distributed-Temperature-Sensing Using Optical Methods: A First Application in the Offshore Area of Campi Flegrei Caldera (Southern Italy) for Volcano Monitoring

A temperature profile 2400 m along the off-shore active caldera of Campi Flegrei (Gulf of Pozzuoli) was obtained by the installation of a permanent fiber-optic monitoring system within the framework of the Innovative Monitoring for Coastal and Marine Environment (MON.I.C.A) project. The system consists of a submerged, reinforced, multi-fiber cable containing six single-mode telecom grade optical fibers that, exploiting the stimulated Brillouin scattering, provide distributed temperature sensing (DTS) with 1 m of spatial resolution. The obtained data show that the offshore caldera, at least along the monitored profile, has many points of heat discharge associated with fluid emission. A loose association between the temperature profile and the main structural features of the offshore caldera was also evidenced by comparing DTS data with a high-resolution reflection seismic survey. This represents an important advancement in the monitoring of this high-risk volcanic area, since temperature variations are among the precursors of magma migration towards the surface and are also crucial data in the study of caldera dynamics. The adopted system can also be applied to many other calderas which are often partially or largely submerged and hence difficult to monitor.

Caldera subsidence in extensional tectonics

We consider here the effect of extensional tectonics on the dynamics of large calderas. Active calderas are generally characterised by different periods of uplift and subsidence, in some cases spaced out by eruptions. Understanding of mechanisms which produces caldera uplift/subsidence is one of the main topics of volcanological research but is still a matter of debate. Using a simple conceptual model, we show analytically that the tectonic extension and its rate can produce the condition for the subsidence, in early stage, which in turn can also yield the magma migration (uplift) and, eventually, eruption. This work provides a possible hypothesis for caldera dynamic, which initiates due to chamber depressurisation and evolves towards potential conditions for magma re-mobilization as a consequence of tectonic loading. The conceptual model is also applied to the Campi Flegrei caldera (Italy), showing that the observed subsidence may be a result of extensional processes.

Multiscale integrated approach to understand the structure and evolution of the Neapolitan Yellow Tuff (NYT) caldera off the Campi Flegrei, eastern Tyrrhenian margin

Abstract from 88th Congress of the Italian Geological Society, 2016-09-07 - 2016-09-09, NaplesAbstract from 88th Congress of the Italian Geological Society, 2016-09-07, 2016-09-09, Naplesbook Edited by D. Calcaterra, S. Mazzoli, F.M. Petti, B. Carmina & A. Zuccari doi: 10.3301/ROL.2016.79