Seismic attenuation imaging of Campi Flegrei: Evidence of gas reservoirs, hydrothermal basins, and feeding systems

Abstract

[1] Passive high-resolution attenuation tomography is used here to image the geological structure in the first upper 4 km of the shallow crust beneath the Campi Flegrei caldera, southern Italy. The inverse Q was estimated for each source-receiver path using the coda-normalization method (S-waves) and the slope decay method (P-waves and S-waves). Inversion was performed using a multi-resolution method, which ensures a minimum cell-size resolution of 500 m. The study of the resolution matrix as well as the synthetic tests guarantee an optimal reproduction of the input anomalies in the center of the caldera, between 0 and 3.5 km in depth. High attenuation vertical structures are connected at the surface with the main volcanological features (e.g., the Solfatara and Mofete fumarole fields), and depict vertical Q contrast imaging important geological structures, such as the La Starza fault. These high attenuation volumes extend between the surface and a depth of about 3 km, where a hard rock layer is imaged by the sharp contrast of the quality factors. The retrieved image of the Campi Flegrei has been jointly interpreted taking into account evidence from seismological, geological, volcanological and geochemical investigations. This analysis has allowed an unprecedented view of the feeding systems in this area, and in particular it recognizes the vertically extending, high attenuation structures that correspond to gas or fluid reservoirs beneath Pozzuoli-Solfatara, Solfatara, Mofete-Mt. Nuovo and Agnano. This high-attenuation system is possibly connected with the magma sill revealed at about 7 km in depth by passive travel-time tomography.

Numerical models for ground deformation and gravity changes during volcanic unrest: simulating the hydrothermal system dynamics of a restless caldera

“…(Table 1). Atmospheric boundary conditions are fixed on the top (which is open to fluid and heat flow), lateral boundaries are assumed to be impervious and adiabatic, while a heat flux is assigned at the bottom impervious boundary at a rate of 0.195 W m −2 to ensure a temperature gradient comparable to that estimated for CF (∼ 130 • C km −1 , (Rosi and Sbrana, 1987;De Siena et al, 2010;Piochi et al, 2014)). …”

A 3D algorithm based on the combined inversion of Rayleigh and Love waves for imaging and monitoring of shallow structures

“…At a deeper level, the existence of a gas and/or fluid reservoir has been confirmed through recent seismic attenuation imaging (De Siena et al 2010) which could recognize a vertically extending and high-attenuating structure. Although diffuse soil degassing occurs throughout the entire area of the Solfatara crater (Chiodini et al 2011), fumarolic activity is mainly concentrated in its eastern part (so-called Bocca Grande, see Fig.…”

“…The comparison between the spatial variability of resistivity and gas flux emphasized a highly resistive body indicating that resistivity changes at this depth are related to high temperature gas saturation (Byrdina et al 2014). Further evidence of a gas fluid reservoir comes from recent seismic attenuation imaging, recognizing a vertically extending, high attenuation structure (De Siena et al 2010).…”

Great challenges in volcanology: how does the volcano factory work?

“…On the longer-term, shallow intrusions have been also suggested to induce resurgence at the surface (Kawakami et al, 2007), providing an additional cause of instability, independently of the deeper magma reservoir. Campi Flegrei caldera, Italy, one of the most dangerous volcanoes on Earth, provides an interesting example of restless volcano whose recent activity (last eruption in 1538 and successive unrest phases) results from the shallow emplacement of magma (De Siena et al, 2010;Chiodini et al, 2012). Shallow magma emplacement has also triggered large and recent eruptions.…”