GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.3 193 Gonzalez P.J., and Palano M.; 2014: Mt. Etna 2001 eruption: New insights into the magmatic feeding system and the mechanical response of the western flank from a detailed geodetic dataset . J. Volcanol. Geotherm. Res., 274, 108- 121, DOI:10.1016/j.jvolgeores.2014.02.001. Pallister J. and McNutt S.R.; 2015: Synthesis of volcano monitoring . In: Sigurdsson H, Houghton B, McNutt S, Rymer H, Stix J (eds) Encyclopedia of Volcanoes (2 nd Ed), Elsevier, Amsterdam, pp 1151-1171. Viccaro M., Zuccarello F., Cannata A., Palano M. and Gresta S.; 2016: How a complex basaltic volcanic system works: Constraints from integrating seismic, geodetic, and petrological data at Mount Etna volcano during the July–August 2014 eruption . J. Geophys. Res. 121, 5659–5678 DOI:10.1002/2016JB013164. Magnetotelluric survey of Ischia active volcanic island (Southern Italy): inference for volcano-tectonics and dynamic S. Carlino, M.G. Di Giuseppe, A. Troiano Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Napoli, Italy Introduction. Ischia is an active volcanic island, emerging from the western edge of the Bay of Naples (Rittman, 1930; Vezzoli, 1988). The presence of a stable population of about 65,000 units, and more than 1,500,000 visitors during the spring-summer season, makes the volcanic risk of this area very high. The volcano dynamic of the island is thus necessarily to be evaluated, firstly by improving the knowledge of shallow and deep geology of the island. The main structural features of Ischia are the result of the large ignimbrite eruption of Mount Epomeo Green Tuff (MEGT), occurred 55ka ago, and a subsequent resurgence process, accompanied by small to moderate eruptions along the boundary of the resurgent structure (Vezzoli, 1988; Tibaldi and Vezzoli, 2004). The last eruption in the island took place in 1302, while the resurgence was likely active since about 5ka (Vezzoli et al. , 2009). The resurgence process possibly started subsequent to the MEGT eruption (Sbrana et al. , 2009) or alternatively in a later stage, 33ka (Vezzoli, 1988), and has been associated to a sill intrusion which developed in form of laccolith, whose top is assumed located at about 2km of depth (Rittman, 1930; Sbrana et al. , 2009; Carlino et al. , 2006; Carlino, 2012 and references therein). The resurgence and the correlated exhumation of the geothermal system produced a diffuse large heat flow and very high geothermal gradients (>180°Ckm -1 ) in the shallow crust (Sbrana et al. , 2009; Carlino, 2012; Carlino et al. , 2014). The volcanic activity was localized around the resurgent area represented by the Mount Epomeo block, which has undergone to progressive faulting during the resurgence, since at least 33 ka (Carlino, 2012), with an average uplift of about 800 m and a variable rate around few centimeters per year. The volcano-tectonic models proposed for the island of Ischia are aimed to understand the relationship between the magma dynamic at depth, the tectonic structures evolution and the volcanic activity localized in the resurgent area (Civetta et al. , 1991; Orsi et al. , 1991, Acocella et al. , 1997; Piochi et al. , 1999; Carlino et al. , 2006; Carlino, 2009; de Vita et al. , 2010). Rittman (1930) firstly suggested the hypothesis of a shallow magma intrusion beneath the island, whose increment in pressure and volume produced the uplift of the central part of the island, the progressive faulting of the crust and the volcanic activity (Carlino, 2012 and references therein). The existence of a possible magmatic body has been successively inferred from gravity surveys (Nunziata and Rapolla, 1987). More recently, the model of laccolith intrusion has been resumed by interpreting stratigraphy, deep temperature, self-potential and gravity data (Sbrana et al. , 2009; Paoletti et al. , 2009; Di Napoli et al. , 2011). The top of this magma body is slightly decentered in the southwestern part of Ischia Island, where a robust geothermal circulation occurs. Paoletti et al. (2009), using an integrated analysis of magnetic, gravimetric and self- potential data, highlight the presence of a possible magmatic intrusion, with temperature below the Curie point, density of about 2.4 g/cm 3 and the top at about 2 km of depth.