Abstract
AbstractThe Campi Flegrei caldera (Italy) has been undergoing unrest over the past five decades including episodes of rapid ground deformation, seismicity, and variations in gas emissions. Hydrothermal fluids and gases are released most vigorously in the central sector of the caldera at the fumarolic fields of Solfatara volcano and Pisciarelli. We conducted a high‐precision gravity survey coupled with inverse modeling to image the shallow (<2‐km depth) structure of the hydrothermal feeder system. Results indicate the presence of three low density bodies beneath Pozzuoli, Astroni volcano and the Solfatara/Pisciarelli fumarolic fields. The first two are inferred to be sealed hydrothermal systems trapped beneath impermeable cap rock, while the latter depicts a plume‐like geothermal feeder system reaching the surface via a combination of Solfatara's maar‐diatreme structure and the intersection of NW‐SE and NE‐SW trending regional faults. The density contrasts of the reservoirs from background values are best explained by a multiphase mixture of caldera fill containing a secondary and interconnected void volume fraction of between 0.2 and 0.3 that hosts a vapor volume fraction ψv of between 0.38 and 1 and a liquid volume fraction ψl fraction of between 0 and 0.62. This work highlights the control of volcano‐tectonic structures on fluid movement in the shallow crust of hydrothermally active volcanic systems undergoing sustained or periodic unrest.
Highlights
Volcanic unrest is often characterised by anomalous seismicity, gas emissions and surface deformation, and is usually attributed to sub-surface magma movement (Sparks, 2003)
The di↵erent spacing permitted us to investigate the expression of the hydrothermal plume at Solfatara volcano at a similar scale to several local geophysical studies while exploring the spatial distribution of the hydrothermal system across the central sector of the Campi Flegrei caldera (CFc) (Fig. 2)
The amplitudes of all anomalies are orders of magnitude above the uncertainties associated with individual measurements or the terrain correction and are robust indicators of sub-surface density variations
Summary
Volcanic unrest is often characterised by anomalous seismicity, gas emissions and surface deformation, and is usually attributed to sub-surface magma movement (Sparks, 2003). Volcanic calderas have complex sub-surface structures resulting not at least from the vertical collapse of a pre-existing volcanic edifice and often host both extensive hydrothermal and magmatic reservoirs (Gottsmann & Battaglia, 2008). We present results from a new gravimetric survey of the central sector of the CFc includ ing a high-resolution gravity survey of Solfatara volcano coupled with data inversion to 57 image the density structure of the upper-most part of the hydrothermal system. This document provides supporting information on the gravity data reduction and inverse modelling as part of the gravity study of the central sector of the Campi Flegrei caldera (Italy). Drilling encountered a zone of thermo-metamorphic rocks below the fill at depths between 2.5 km and 3.1 km, several small igneous intrusions, high ther mal gradients of 100-170 K km 1 and locally raised isotherms in the central-eastern part 79 (Piochi et al, 2014) of the caldera
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