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The detailed analysis of volcanic seismicity can allow the identification of the processes occurring in a volcanic system and obtain information about its state and evolution. In the last decades, the seismicity of Mt. Vesuvius has consisted mainly of volcano-tectonic (VT) seismic events, with an average rate of some hundreds of earthquakes per year with magnitudes between −1.0 and 2.5, located up to 6-7 km below sea level (b.s.l.). Unusual low-frequency (LF) seismicity has also been observed, localized at a depth of 5-7 km. Previous seismic source analyses applied conventional methodologies based on first pulse characteristics, which are difficult due to high background noise, low magnitude and emergent first arrivals. To overcome these challenges, we analyze here the Mt. Vesuvius seismicity over the past 20 years by using a robust probabilistic seismic source inversion tool. This methodology provides the results in terms of moment tensor solutions estimated by using seismic waveforms and waveform attributes. In agreement with previous studies, two clusters of seismicity are clearly evidenced, both in terms of depth (0-4 km and 5-7 km b.sl. for VT and LF events, respectively) and frequency content (5-15 Hz and 2-6 Hz, respectively). Our preliminary results show that: a) the probabilistic approach for the whole waveform inversion provides acceptable results even for small magnitude earthquakes, and b) both seismicity clusters show strongly heterogeneous focal mechanisms, confirming past literature studies. We attribute the latter result to a highly heterogeneous stress field beneath Mt. Vesuvius., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Nelle aree vulcaniche, come l’Isola d’Ischia, l’ampia variabilità litologica e l’alto gradiente geotermico richiedono analisi sempre più accurate per la definizione di specifici modelli di velocità e di attenuazione delle onde sismiche. Nel distretto vulcanico campano, modelli di velocità e attenuazione sempre più accurati sono stati ottenuti per il Vesuvio e per l’area dei Campi Flegrei, meno o del tutto assenti per quel che riguarda l’attenuazione per l’isola d’Ischia. È ben noto come la dettagliata conoscenza del modello di velocità possa fornire risultati più affidabili in termini di localizzazione dei terremoti locali. A tal proposito, è bene ricordare che, dal 1999, almeno 78 terremoti sono stati registrati ad Ischia (elenco aggiornato al 21 febbraio 2018) e sono stati localizzati utilizzando il modello disponibile per i Campi Flegrei, scelto sulla base di similarità geologiche e vulcanologiche. Pertanto, l’obiettivo di questo lavoro è la definizione di un modello 1-D in velocità e attenuazione della crosta più superficiale (fino a 2 km di profondità) di Ischia utilizzando tecniche di array applicate al rumore sismico e rapporti spettrali valutati su segnali sismici registrati da sismometri a larga banda installati sull’isola ai fini della sorveglianza e del monitoraggio.

On August 21, 2017, at 18:57 UTC, an earthquake of MD 4.0 occurred in Casamicciola, district of Ischia island at about 2 km depth. In volcanic areas, such as the Ischia Island, the precise localization of the earthquakes requires specific velocity models, both for the wide lithological variability and for the high geothermal gradient. These models are available, for example, for the Vesuvius and for the Campi Flegrei areas, but not for the Island of Ischia because they need to use the local seismicity. Since 1999, at least 78 earthquakes have been recorded on Ischia (updated to 21 February 2018) and have been localized using the model used for the Campi Flegrei, on the basis of the similar geological and volcanological context of the two volcanoes. Therefore, the aim of this work is the definition of average 1-D shear-wave velocity model of the shallower crust of Ischia using ambient noise array techniques and spectral ratios evaluated on broad band seismic signals recorded by mobile and permanent networks deployed in the last year.

This contribution presents the general framework of the European project UPStrat-MAFA "Urban disaster Prevention Strategies using MAcroseismic Fields and FAult Sources" and its ongoing activities. A unique probabilistic procedure is being used for seismic hazard evaluation, using both macroseismic fields and characteristics of fault sources for the analysis of data from volcanic and tectonic areas: Mt. Etna, Mt. Vesuvius and Campi Flegrei (Italy), Azores Islands (Portugal), South Iceland (Iceland), Alicante-Murcia (Spain), and mainland and offshore Portugal. An improvement of urban scale vulnerability information on building and network systems (typologies, schools, strategic buildings, lifelines, and others) is proposed in the form of a global Disruption Index, with the objective to provide a systematic way of measuring earthquake impact in urbanized areas considered as complex networks. Disaster prevention strategies are considered based on an education information system, another effective component of the disaster risk reduction given by long-term activities., peer-reviewed

The calibration of the input parameters is the important task for stochastic finite-fault simulation in volcanic areas that we manage in the framework of the european project UPStrat-MaFa. The stochastic simulation method requires to know fault geometry, source, crust properties of the region and local site effect. We focused on the following pilot test areas: Mt Vesuvius, Campi Flegrei and Mt Etna , performing also two application for large magnitude event for Azores Islands and South Iceland. A general preliminary database of ground motion records has been collected in all test areas in order to set up the empirical laws of ground motion parameters. The results of the simulations are compared with observed waveforms and response spectra, to evaluate the suitability of the used parameters. The results show a good agreement between observed and simulated time histories and response spectra, encouraging further effort towards quantitative high resolution studies on input parameters. DE/NESDE 2012 24-28 setembro

SUMMARY Following the Mw 3.9 earthquake that occurred in the Ischia island (Naples, southern Italy) on 21 August 2017, the local monitoring seismic network was significantly improved in terms of both number of stations and instrumentation performance. Due to the huge amount of collected seismic ambient noise data, in this paper we present a first 3-D shear wave velocity model of the island retrieved from the inversion of horizontal-to-vertical spectral ratio curves by fixing the shear wave velocities (Vs) and modifying the thicknesses to get the corresponding 1-D Vs models. We are confident about the robustness of the attained models since the inversion process provided a good convergence towards the best-fitting solutions. Then, a first 3-D velocity model was obtained by contouring all the 1-D models obtained for the selected seismic stations to highlight possible lateral variations of the layer thicknesses and to reconstruct the morphology of the deeper interface characterized by a high-impedance contrast. A good correspondence between the 3-D Vs model and the geological features of the island was observed, especially in the northern sector where most of the stations are installed. In particular, the top of the high-impedance contrast interface appears deeper in the northern coastal areas and shallower in the central sector. This result agrees with the structural settings of the island likely due to the resurgence of Mount Epomeo.

Mt. Vesuvius is a high-hazard active volcano surrounded by a densely populated area. Since human activities generate high levels of seismic noise, recognizing low-amplitude seismic events in the signals recorded by the local seismic monitoring network operating at Vesuvius is very difficult. Here, we describe an automatic procedure applied to continuous data with the aim of finding low-amplitude–low-frequency events hidden in the recorded signals. The methodology is based on the computation of two spectral parameters, central frequency Ω and shape factor ẟ, at selected sites, and the coherence of the seismic signal among different sites. The proposed procedure is applied to 28 months of recordings from 2019 to 2021, tuning the search parameters in order to find low-frequency signals similar to those occasionally observed in the past at the same volcano. The results allowed us to identify 80 seismic events that have the spectral features of low-frequency earthquakes or tremor. Among these, 12 events characterized by sufficiently high signal-to-noise ratio have been classified as deep low-frequency earthquakes, most of which are not reported in the catalog. The remaining events (more than 60) are characterized by similar spectral features but with an extremely low amplitude that prevents any reliable location of the source and definitive classification. The results of this work demonstrate that the low-frequency endogenous activity at Mt. Vesuvius volcano is more frequent that previously thought.

Spectral analysis has been applied to almost thousand seismic events recorded at Vesuvius volcano (Naples, southern Italy) in 2018 with the aim to test a new tool for a fast event classification. We computed two spectral parameters, central frequency and shape factor, from the spectral moments of order 0, 1, and 2, for each event at seven seismic stations taking the mean among the three components of ground motion. The analyzed events consist of volcano-tectonic earthquakes, low frequency events and unclassified events (landslides, rockfall, thunders, quarry blasts, etc.). Most of them are of low magnitude, and/or low maximum signal amplitude, therefore the signal to noise ratio is very different between the low noise summit stations and the higher noise stations installed at low elevation around the volcano. The results of our analysis show that volcano-tectonic earthquakes and low frequency events are easily distinguishable through the spectral moments values, particularly at seismic stations closer to the epicenter. On the contrary, unclassified events show the spectral parameters values distributed in a broad range which overlap both the volcano-tectonic earthquakes and the low frequency events. Since the computation of spectral parameters is extremely easy and fast for a detected event, it may become an effective tool for event classification in observatory practice.

In volcanic areas, accurate localization of earthquakes requires detailed velocity and, possibly, attenuation models, taking into account wide lithological variability and high geothermal gradients. Ischia island (Campania region, Italy) is a seismically-active volcano recently affected by a Mw 3.9 event (Casamicciola, August 21, 2017, 1 km depth). Due to the lack of a specific velocity model, the earthquakes occurred on the island were localized using the one developed for the nearby Campi Flegrei caldera. The aim of this work is the definition of a mean representative 1D shear-wave velocity (Vs) and attenuation (Q) model of the shallower crust (up to 2 km depth) of Ischia. Seismic noise array and spectral ratios techniques were applied to broad band seismic signals recorded by temporary and permanent networks updated after the August 2017 earthquake. The values of both shear-wave velocity (Vs) and quality factor (Q) are realistic, with Q values comparable with those obtained for Campi Flegrei and Stromboli volcanic areas. By taking into account stratigraphic information from deep wells and ultrasonic measurements of velocity on granite and trachytic lava samples, a geological interpretation of the resulting velocity model is provided. Such a model can have significant implications for understanding the dynamics of a volcano, mainly those leading to seismic activity.