GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.1 57 event in island geological history is the caldera forming eruption of the Green Tuff of the Mt. Epomeo occurred 55 ka, that caused the collapse of Island central sector, followed by the resurgence of the Mt. Epomeo block starting from 30 ka (Orsi et al. , 1991). After this eruption, volcanic activity continued in three main periods. The last one from 10 ka, with eruptions mainly located in the eastern part of the island, closed with the last effusive Arso eruption in 1302 (Vezzoli, 1988; Orsi et al., 1991; de Vita et al. , 2006; de Vita et al., 2010). The Island is characterized by slope instability, mainly linked to the Mt. Epomeo resurgence (Del Prete and Mele, 1999; Esposito et al. , 2006; Della Seta et al. , 2012) and historical and recent seismic activity (Alessio et al. , 1996; Rovida et al. , 2015). The main faults system bording the resurgent Mt. Epomeo consists of NW-SE to N-S striking faults in the western sector and of NE-SW to E-W faults in its northern sector (Fig.1). In the eastern sector of the island, N-S and NE- SW striking fractures and faults control the location of the vents (Carta Geologica dell’Isola d’Ischia della Regione Campania in scala 1:10.000, Foglio 464, 2011). The slope instability is mainly concentrated in the northern and western sectors of the Island and in the southern flank of Mt. Epomeo (Del Prete and Mele, 1999). The strongest historical earthquakes (VIII<I<X MCS) occurred in the eighteenth and nineteenth centuries with epicenters in the northern sector of the island (Alessio et al. , 1996; Cubellis and Luongo, 1998; Luongo et al. , 2006; Rovida et al. , 2015); the best-known destructive events of 1881 (I=VIII MCS) and 1883 (I=X MCS), caused more than 2,000 victims Fig. 1 - Location of the observed surface coseismic effects collected in the field: sliding in green circle, fractures in light blue with the strike and dip in black line. The base map is the Geological map of Ischia Island from Carta geologica dell’Isola d’Ischia della Regione Campania, sheet 464, scale 1:10,000; line red are the faults from De Vita et al. (2006), and line light blue are from Nappi et al. (2010). The red star shows the epicentral location of the August 21, 2017 mainshock; the rose diagram shows the trends of the coseismic surface fractures.