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Authors: Amoruso, A.* 
Crescentini, L.* 
Berrino, G.* 
Title: Simultaneous inversion of deformation and gravity changes in a horizontally layered half-space: Evidences for magma intrusion during the 1982–1984 unrest at Campi Flegrei caldera (Italy)
Issue Date: 2008
Series/Report no.: 1-2/272(2008)
DOI: 10.1016/j.epsl.2008.04.040
Keywords: volcanic hazard
caldera unrest
Subject Classification04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations 
04. Solid Earth::04.03. Geodesy::04.03.05. Gravity variations 
04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring 
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring 
Abstract: A very large uplift (about 1.8 m) occurred in the period 1982–1984 at Campi Flegrei caldera, Italy, without culminating in an eruption. A still-standing controversy accompanies the interpretation of deformation and gravity changes recorded during the unrest, which were interpreted to result from the sub-surface magmatic reservoir by some authors and from the hydrothermal system or hybrid sources by others. Here for the first time we take into account crustal layering while inverting leveling, EDM, and gravity data using uniformlypressurized sources, namely small vertical spheroids and finite horizontal penny-shaped sources. The weight of EDM data in the misfit function is chosen from a trade-off curve in order to balance the compromise between fitting the leveling and the EDM data well. Models using a homogeneous medium cannot give a good simultaneous fit to leveling and EDM deformation data of the 1982–1984 unrest, whereas incorporating a layered structure (determined from seismically derived estimates of the P wave speed for the crust, and not adjusted to improve the fit in any of the inversions) allows a significantly better fit. Also, layering affects the sub-surface mass redistribution effects on gravity changes, and we show that the retrieved intrusion density is in full agreement with densities for highly evolved magmas expected at the Campi Flegrei caldera for depths of 3 to 4 km, ruling out hydrothermal fluids as the primary cause of the 1982–1984 unrest. The source of the 1982–1984 CF unrest was probably a shallow (about 3-km deep) penny-shaped magma intrusion fed by a deeper magma chamber; source overpressure was few MPa.
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