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Despite their importance for eruption forecasting the causes of seismic rupture processes during caldera unrest are still poorly reconstructed from seismic images. Seismic source locations and waveform attenuation analyses of earthquakes in the Campi Flegrei area (Southern Italy) during the 1983–1984 unrest have revealed a 4–4.5 km deep NW-SE striking aseismic zone of high attenuation offshore Pozzuoli. The lateral features and the principal axis of the attenuation anomaly correspond to the main source of ground uplift during the unrest. Seismic swarms correlate in space and time with fluid injections from a deep hot source, inferred to represent geochemical and temperature variations at Solfatara. These swarms struck a high-attenuation 3–4 km deep reservoir of supercritical fluids under Pozzuoli and migrated towards a shallower aseismic deformation source under Solfatara. The reservoir became aseismic for two months just after the main seismic swarm (April 1, 1984) due to a SE-to-NW directed input from the high-attenuation domain, possibly a dyke emplacement. The unrest ended after fluids migrated from Pozzuoli to the location of the last caldera eruption (Mt. Nuovo, 1538 AD). The results show that the high attenuation domain controls the largest monitored seismic, deformation, and geochemical unrest at the caldera.

Summary Scattered waves observed at the seismographs of the National Italy's seismic network have been used to investigate the intrinsic dissipation and scattering properties of the lithosphere under the Southern Apennines, Italy. First, we investigate the coda‐Q properties, then we apply the MLTW analysis in the hypothesis of velocity and scattering coefficient constant with depth, and finally we interpret these results with the aid of numerical simulations in a medium with depth dependent velocity and scattering coefficient. Results obtained in the hypothesis of a uniform model show that a low scattering‐Q−1 and a relatively higher intrinsic‐Q−1 characterize the lithosphere of the Southern Apennines. Numerical simulations of the seismogram energy envelopes were performed hypothesizing a strongly scattering crust and trasparent upper mantle, both with reasonable intrinsic dissipation coefficients. In these symplifying assumptions the theoretical curves calculated for the homogeneous model fit to the synthetic envelopes with scattering attenuation coefficients always greater than the synthetic values. This results lead to the consideration that scattering‐Q−1 obtained using MLTW analysis under the assumption of uniform medium are overestimated. The values of the scattering‐Q−1 estimated for Apennines at low frequency (1–2 Hz) in the hypothesis of uniform medium are of the same order of those obtained in several areas around the world. The estimates obtained for frequencies ranging from 2 to 12 Hz are very low if compared with those obtained in the same hypothesis for other areas around the world. Coda Q−1 closely resembles intrinsic Q−1.

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Coda wave attenuation imaging is able to detect fluid/melt accumulation and ancient magmatic bodies in volcanoes. Here we use recently developed space‐weighting sensitivity functions to invert for the spatial distributions of multifrequency coda wave attenuation ( Qc−1), measured during the largest monitored unrest at Campi Flegrei caldera (1983–1984). High‐attenuation anomalies are spatially correlated with the regions of highest structural complexities and cross faulting. They characterize deep fluid circulation in and around the aseismic roots of the 1534 A.D. Mount Nuovo eruption and fluid accumulation in the areas of highest hydrothermal hazard. Just offshore Pozzuoli, and at the highest frequency (wavelengths of ∼150 m), the main cause of ground deformation and seismicity during the unrest is an aseismic low‐attenuation circular anomaly, similar in shape and nature to those produced by ancient magmatic reservoirs and active sills at other volcanoes.

We analysed short‐period seismograms from about 250 very local events recorded by a network of high dynamic range short‐period seismic stations deployed on Mt Vesuvius to estimate the site‐corrected short‐period seismic attenuation. We calculated QC− 1, the inverse of the quality factor for coda waves, for short lapse times (12 s), and QP− 1 and QS− 1, the inverse of the direct body wave quality factors for P and S waves follow‐ ing shallow ray paths. We used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands, obtaining a QC− 1 slowly varying with frequency, similar to values measured for other volcanoes at the same lapse time. Site‐corrected QP− 1 and QS− 1 were estimated using the frequency decay method for both P and S waves in two frequency bands, 1–6 Hz and 15–24 Hz. Results show that QP− 1 is 0.028 in both frequency bands, and QS− 1 is 0.015 and 0.017 at low and high frequencies respectively, almost independent of the frequency, and that the value of QP− 1 is about twice that of QS− 1, as measured worldwide. A check was made by measuring the broadening of the first P‐wave pulse with station–source distance, finding QP− 1=0.024. Using the independent estimates of QC− 1 and QS− 1, we separated the intrinsic from the scattering quality factor at Mt Vesuvius, obtaining a high scattering and a low intrinsi c Q− 1, as already observed for other volcanoes. This result confirms the hypothesis of the predominant role of the scattering phenomena with respect to the intrinsic dissipation in the seismogram formation for volcanic earthquakes.

Abstract. Campi Flegrei caldera (Southern Italy) is one of the most hazardous volcanic complexes in the world since it is located inside the densely inhabited urban district of Naples-Pozzuoli. In the past, the caldera has produced devastating to moderate eruptions and periodically undergoes from strong to minor uplift episodes, named “bradyseism”, almost always accompanied by seismic swarms. Starting from 2005 Campi Flegrei has undergone an unrest crisis, characterized by ground uplift, localized gas emissions and seismicity, often occurring in seismic swarms. As a consequence, the monitoring activities have been progressively increasing, producing a huge amount of data, difficult to manage and match. GIS (Geographical Information System) represents a potent tool to manage great quantity of data, coming from different disciplines. In this study, we show two GIS technology applications to the seismic catalogue of Campi Flegrei. In the first one, a high-quality dataset is extracted from the GeoDatabase addressed to seismological studies that require high precision earthquake locations. In the second application, GIS are used to extract, visualize and analyse the typical seismic swarms of Campi Flegrei. Moreover, density and seismic moment distribution maps were generated for these swarms. In the last application, the GIS allow to highlight a clear variation in the temporal trend of the seismic swarms at Campi Flegrei.

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