Stress can undergo rapid temporal changes in volcanic environments, and this is particularly true during eruptions. We use two independent methods, coda wave interferometry (CWI) and shear wave splitting (SWS) analysis to track stress related wave propagation effects during the waning phase of the 2002 NE fissure eruption at Mt Etna. CWI is used to estimate temporal changes in seismic wave velocity, while SWS is employed to monitor changes in elastic anisotropy. We analyse seismic doublets, detecting temporal changes both in wave velocities and anisotropy, consistent with observed eruptive activity. In particular, syn-eruptive wave propagation changes indicate a depressurization of the system, heralding the termination of the eruption, which occurs three days later.

The Campi Flegrei caldera is one of the highest risk volcanic fields worldwide, because of its eruptive history and the large population hosted within the caldera. It experiences bradiseismic crises: sudden uplift with low energetic seismic swarm occurrences. No seismicity is recorded out of these deformation rate changes. Therefore, a continuous seismic monitoring of the caldera is possible only by means of the ambient seismic noise. We apply a noise-based seismic monitoring technique to the cross correlations of 5 year recordings at the mobile seismic network. The resulting relative velocity variations are compared to the temporal behavior of the geophysical and geochemical observations routinely sampled at Campi Flegrei. We discriminate between two kinds of crustal stress field variations acting at different timescales. They are related to a possible magmatic intrusion and to the gradual heating of the hydrothermal system, respectively. This study sets up the basis for future volcano monitoring strategies.

Earthquakes at Campi Flegrei have been low magnitude and sparse since 1985, denying onshore monitoring observations of their usual source for structural constraint: seismic tomography. Here we used continuous seismic records from 2011–2013 to reconstruct period-dependent Rayleigh wave group velocity maps of the volcano. The Neapolitan Yellow Tuff rim faults bound high-velocity intracrater products of historical eruptions, which act as a barrier for deep fluid migration. The anomaly with lowest group velocity is aseismic and corresponds to the portion of a fluid storage zone that was fractured during the 1984 volcanic unrest under Pozzuoli town. Earthquake locations show that fluids migrate from this area toward the Solfatara and Pisciarelli fumaroles along shallower low-velocity fractures. The aseismic anomaly is likely fed by a deep-seated offshore magmatic source. Its spatial relation with regional dynamics and observations from historical unrests mark the area as the most likely feeder pathway for fluid and magmatic inputs from depth.

The aim of this paper is to study the temporal variations in the seismic wavefield associated with the stress changes in the dynamic features of the Mt Etna volcanic activity. We used shear wave splitting analysis on a huge data set of local earthquakes, in order to identify changes of the local stress field at Mt Etna during the time interval from 2006 to 2011. This analysis allows us to obtain two parameters: the polarization direction of the fast shear wave (φ) and the time delay of the slow shear wave (Td, time delay between the split shear waves). Orientation of φ generally provides information about the anisotropic symmetry and stress direction whereas Td provide information about the average crack density along the ray path. Based on our findings it is possible to divide Etna Volcano in three different sectors, each one distinguished by typical fast wave polarization direction. We find that the western part of the volcano is controlled by the regional tectonic stress field having a NS and EW directions. Instead, the eastern part of the volcano is mainly controlled by the local volcanic stress, particularly an EW local stress field in the NE sector (Pernicana), and a quasi NS local stress field in the SE sector (Mascalucia, Timpe), where previous studies evidenced: (i) some low- Qp anomaly regions between 0 and about 6 km depth, probably associated with high pore pressure and the intense faulting and (ii) by magnetotelluric surveys, several high conductivity zones, up to 8 km depth, related to a diffuse presence of hydrothermal activity and fluid circulation. Temporal variations in time delay, mostly before the 2008–2009 lateral eruption, can be interpreted as stress accumulation increase with a consequent release of stress due to coalescing of microcracks in the conduit for the eruption of magma.

Open-conduit basaltic volcanoes are susceptible to sudden transitions from mild activity to violent explosive eruptions with little to no warning. Such was the case at Stromboli in the summer of 2019, when two paroxysmal explosions occurred within approx- imately two months (July 3 and August 28). We apply coda wave interferometry to identify possible transitions in behavior in the build-up to these events, computing seismic velocity changes using five broadband seismic stations on the volcano between 2013–2022. This timeframe encompasses a range of volcanic activity including effusive activity, major explosions and parox- ysms. Cross-correlation functions are computed both between pairs of stations and single-station cross-components in multiple frequency bands that allow the sampling of different depths (between approximately 100–1000 m) within the plumbing system. Shallow velocity changes (1–2 Hz and 2–4 Hz) reveal mid-to-long term precursors prior to the paroxysms in 2019. For example, we observe that 2–4 Hz velocities recorded at the station closest to the active crater show an increase of 0.2–0.3 % relative to velocities recorded at other stations. This increase is largely accumulated from mid-2017, coinciding with previously observed heightened activity at the volcano, peaking approximately one month prior to the first paroxysm. A long-term decrease is also observed in deeper velocity changes (0.5–1.0 Hz) during the same time interval. It is hypothesized that these changes represent greater magma overpressure from increased volatile input from depth. The different response in the shallow subsurface may reflect a local response due to the same source within the vicinity close of the crater terrace. These findings illustrate how coda wave interferometry can provide meaningful insights into the evolving dynamics of open-conduit basaltic volcanoes.

The Campi Flegrei caldera has been experiencing volcanic unrest since 2005, rising concern in the population and in local and national authorities. On May 20, 2024, the largest local earthquake ever instrumentally recorded up to that time produced substantial damage, forcing the evacuation of tens of buildings west of the epicenter. At Campi Flegrei, M > 4 earthquakes are rare and their analysis is crucial to understand the unrest dynamics and the relation between rupture and ground shaking pattern, which is essential to mitigate the damage of future earthquakes. We analyse seismic waveforms at local to regional distances to reconstruct the source geometry and kinematics. We estimate millimetric to submillimetric coseismic surface subsidence– below the sensitivity of any standard geodetic technique– which, compared to the general uplift, highlights the crucial role of deep pressurized fluids in earthquakes’ generation. Our results also indicate that rupture directivity and local amplification determined the damage distribution.