Strollo, Roberta (2014) Vs crustal models in Campi Flegrei and Ischia island. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Lingua: English
Title: Vs crustal models in Campi Flegrei and Ischia island
Date: 28 March 2014
Number of Pages: 229
Institution: Università degli Studi di Napoli Federico II
Department: Scienze della Terra, dell'Ambiente e delle Risorse
Scuola di dottorato: Scienze della terra
Dottorato: Dinamica interna dei sistemi vulcanici e rischi idrogeologico-ambientali
Ciclo di dottorato: 26
Coordinatore del Corso di dottorato:
De Vivo,
Nunziata, ConcettinaUNSPECIFIED
Date: 28 March 2014
Number of Pages: 229
Uncontrolled Keywords: seismic noise cross-correlation; shear wave velocity models; Campi Flegrei-Ischia
Settori scientifico-disciplinari del MIUR: Area 04 - Scienze della terra > GEO/10 - Geofisica della terra solida
Date Deposited: 02 Apr 2014 12:01
Last Modified: 15 Jul 2015 01:01


1-D shear wave velocity (Vs) models have been defined in the uppermost 1-2 km of the crust in Campi Flegrei and Ischia volcanic areas (southern Italy) through the non-linear inversion of the group velocity dispersion curves of Rayleigh surface waves fundamental mode extracted from the seismic noise cross-correlation functions (NCF) between two receivers. The volcanic field of Campi Flegrei and the island of Ischia belong to the Phlegraean Volcanic District, a volcanic complex located in the southwestern part of the Campanian Plain. Campi Flegrei consists in a caldera originated by the Neapolitan Yellow Tuff eruption (15 ka B.P.), followed by numerous explosive and phreato-magmatic eruptions. Seismicity, bradyseism, fumaroles and hydrothermal activities are also present at Campi Flegrei. The main volcanic event occurred at Ischia is the Mt. Epomeo Green Tuff eruption (55 ka B.P.), which formed a caldera depression in the central part of the island. A 800-1,000 m uplift affected the Mt. Epomeo resurgent block (started about 33-28 ka B.P.). Recent volcanism concentrated in the last 10 ka in the eastern part of the island. Strong heat flow and hydrothermal manifestations are also present at Ischia. Seismic noise data have been recorded in February-April 2010 by 11 stations belonging to the INGV-OV seismic network at Campi Flegrei and by 2 stations of the Osservatorio Geofisico - sez. Sismologia ( of the Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse (University of Napoli Federico II), and during two field surveys executed in June 2011 and September-October 2012 at Ischia. Most of the NCF (Green functions) computed along 50 paths crossing Campi Flegrei are stable in terms of frequency content and waveforms. A total of 25 paths have resulted reliable to perform the Hedgehog non-linear inversion of the average group velocity dispersion curves and get Vs profiles vs. depth. Instead most of the NCF computed along 14 paths crossing Ischia are characterized by a low signal-to-noise ratio and a strong contribution at very low frequencies, so the computed average group velocity dispersion curves are affected by higher errors. The obtained distributions of Vs and Vp/Vs ratios in Campi Flegrei define a more complex setting in the Gulf of Pozzuoli, characterized by very low Vs and very high Vp/Vs ratios (2.8-3), and in the central area than in the northern sector characterized by a quite laterally homogeneous setting. The low velocities and the high Vp/Vs ratios correlate with the Bouguer gravity low and can be attributed to highly fractured rocks essentially saturated with liquid water. A funnel-shaped caldera model turns out in the Gulf of Pozzuoli where the 0.4-0.7 km/s layer, with density of 1.7 g/cm3, deepens to 1.3 km depth and the 1.0-1.3 km/s layer, with density of 2.1 g/cm3, deepens to the maximum investigated depth of 2 km. Vs reversals have been retrieved at about 0.5 km depth both in western (17% Vs reduction) and eastern (30%) sector of the gulf, which can be related to the anomalous high thermal state of the area, and in correspondence of the Solfatara crater (43%), where high temperature fumaroles are present. At Ischia a deepening trend of the seismo-layers has been recognized moving from the centre to the edges of the island. In the central area a body with Vs of 2.00-2.40 km/s has been identified at depth of 0.4-0.6 km b.s.l. and related to the lava basement, also recognized by the interpretation of gravity data. It deepens moving toward the edges of the island at depths greater than those (1.5 km) investigated in this study.


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