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  • 1
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    Seismic group velocities obtained at Campi Flegrei caldera by using ambient noise tomography with additional seismicity and geomorphology (2018)
    PANGAEA
    In:  Supplement to: De Siena, Luca; Sammarco, Carmelo; Cornwell, David G; La Rocca, Mario; Bianco, Francesca; Zaccarelli, Lucia; Nakahara, Hisashi (2018): Ambient seismic noise image of the structurally controlled heat and fluid feeder pathway at Campi Flegrei caldera. 45(13), 6428-6436, https://doi.org/10.1029/2018GL078817
    Details
    Publication Date: 2023-01-13
    Description: The files provide the measurement of seismic group-velocities obtained using ambient noise recorded at Campi Flegrei in 2011-13. Additional seismic locations and geomorphology are provided to reproduce the results of the study.
    Keywords: Campi_Flegrei_caldera; Phlegraean Fields, Italy
    Type: Dataset
    Format: application/zip, 24.6 MBytes
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    DATA PANGAEA
  • 2
    Electronic Resource
    Electronic Resource
    Shallow velocity model of the Northern Flank of Stromboli Volcano, deduced by high frequency surface wave dispersion (1999)
    Springer
    Journal of seismology 3 (1999), S. 83-94 
    Details
    ISSN: 1573-157X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The wavefield produced by the Stromboli volcano explosion quakes shows a significant amount of surface waves. Rayleigh waves recorded by a linear array have been investigated to infer the shear-wave velocity model of the Stromboli northern flank. The group velocity dispersion curve was obtained using the multiple filter technique, while the phase velocity dispersion curve was calculated both by phase-matched filtering and performing a p–ω stack on the observed waveforms. Through the inversion of these curves we were able to recover the shear-wave structure to a depth of about 190 m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009716203083
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    Paper (German National Licenses)
    Fulltext
  • 3
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    Array and spectral ratio techniques applied to seismic noise toinvestigate the Campi Flegrei (Italy) subsoil structure at differentscales (2020)
    EGU - Copernicus
    Details
    Publication Date: 2020-11-12
    Description: The purpose of this work is to study the subsoil structure of the Campi Flegrei area using both spectral ratios and array techniques applied to seismic noise. We have estimated the dispersion curves of Rayleigh waves by applying the Frequency–Wavenumber (f–k hereinafter) and Modified Spatial Autocorrelation (MSPAC) techniques to the seismic noise recorded by the underground short period seismic Array “ARF”, by the broadband stations of the UNREST experiment and by the broadband stations of the seismic monitoring network of INGV – Osservatorio Vesuviano. We have performed the inversion of a dispersion curve (obtained averaging the f–k and MSPAC dispersion curves of seismic noise and single phase velocity values of coherent transient signals) jointly with the H∕V spectral ratio of the broadband station CELG, to obtain a shear wave velocity model up to 2000 m depth. The best-fit model obtained is in a good agreement with the stratigraphic information available in the area coming from shallow boreholes and deep wells drilled for geothermal exploration. In active volcanic areas, such as Campi Flegrei, the definition of the velocity model is a crucial issue to characterize the physical parameters of the medium. Generally, a high quality characterization of the medium properties helps to separate the contributions of the volcanic source, path and site in the geophysical observables. Therefore, monitoring possible variations in time of such properties in general can help to recognize anomalies due to the volcano dynamics, i.e. fluid migration connected to the volcanic activity.
    Description: Published
    Description: 75–85
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Array tecniques and spectral ratios applied to seismic noise to investigate subsoil structures in Campi Flegrei (Italy) (2019)
    Details
    Publication Date: 2020-11-12
    Description: The purpose of this work is to study the subsoil structure (from shallow to deep layers) of the Campi Flegrei area using both spectral ratios and array techniques applied to seismic noise. The dataset consists of seismic noise recorded in the underground by the seismic Array “ARF” and the broadband stations of the mobile network. We estimated the dispersion curves of Rayleigh waves propagating through the array by applying the Frequency–Wavenumber (f-k) technique and the MSPAC method. The phase velocity dispersion curve of the fundamental mode of Rayleigh waves was obtained by plotting the inverse of slowness, as a function of frequency, and selecting the part of the curve bounded by the resolution limits defined through kmin and kmax. For the MSPAC method we divided the array in semi-circular sub arrays called Rings, which radius are defined by the sensor’s spacing, and we calculated the spatial autocorrelation coefficients for all the possible pairs of sensors. Further constrains on the dispersion curves are obtained from the estimate of the phase velocity of transient coherent signals recorded by the array. We used the DINVER computer code to perform a joint inversion of the autocorrelation coefficients, the dispersion curves, the single coherent noise values and the mean HVSR of the mobile network station to obtain a shallow shear wave velocity model for the first 200 m, which is in a good agreement with the stratigraphic information of the wells available in the area. The study of the velocity models is crucial to recognize anomalies due to the presence of fluids connected to the volcanic activity and a high quality characterization of the medium allows us to correctly identify, in the geophysical observables, the contribution of the volcanic source.
    Description: Published
    Description: Naples
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Keywords: Campi Flegrei ; velocity structure
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 5
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    Statistical moments of power spectrum: a fast tool for the classification of seismic events recorded on volcanoes (2021)
    EGU - Copernicus
    Details
    Publication Date: 2021-01-22
    Description: Spectral analysis has been applied to almost thou-sand seismic events recorded at Vesuvius volcano (Naples,southern Italy) in 2018 with the aim to test a new tool fora fast event classification. We computed two spectral pa-rameters, central frequency and shape factor, from the spec-tral moments of order 0, 1, and 2, for each event at sevenseismic stations taking the mean among the three compo-nents of ground motion. The analyzed events consist ofvolcano-tectonic earthquakes, low frequency events and un-classified events (landslides, rockfall, thunders, quarry blasts,etc.). Most of them are of low magnitude, and/or low maxi-mum signal amplitude, therefore the signal to noise ratio isvery different between the low noise summit stations andthe higher noise stations installed at low elevation aroundthe volcano. The results of our analysis show that volcano-tectonic earthquakes and low frequency events are easily dis-tinguishable through the spectral moments values, particu-larly at seismic stations closer to the epicenter. On the con-trary, unclassified events show the spectral parameters valuesdistributed in a broad range which overlap both the volcano-tectonic earthquakes and the low frequency events. Since thecomputation of spectral parameters is extremely easy and fastfor a detected event, it may become an effective tool for eventclassification in observatory practice.
    Description: Published
    Description: 67–74
    Description: 1SR TERREMOTI - Sorveglianza Sismica e Allerta Tsunami
    Description: N/A or not JCR
    Keywords: Vesuvius ; Spectral Analisys ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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    PAPER (OA)
  • 6
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    Analysis of background seismicity recorded at Mefite d’Ansato CO2 emission field in the framework of FURTHER project: first results. (2021)
    Details
    Publication Date: 2021-03-09
    Description: FURTHER – “The role of FlUids in the pReparaTory pHase of EaRthquakes in Southern Apennines” is an INGV Departement Strategic Project devoted to define the role of fluids in earthquake genesis. One of the target areas of the multidisciplinary study is Mefite d’Ansanto, which is the largest area of non-volcanic low temperature CO2 emission field on the Earth. In particular, Work Package 1.4 is dedicated to the application of analysis methodologies in time and frequency domains, aimed to intercept eventual variations in fluid behavior before or in correspondence of local and regional earthquakes, using recordings from the INGV National Seismic Network (IV) and local networks. Here we present the first results of the ongoing investigation of the seismic noise wavefield in the Mefite area.
    Description: Published
    Description: Gather Online
    Description: 1T. Struttura della Terra
    Description: 3T. Sorgente sismica
    Keywords: Furher Project ; Seismic noise ; Mefite d'Ansanto
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 7
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    Non-stability of the noise HVSR at sites near or on topographic heights (2021)
    Oxford University Press
    Details
    Publication Date: 2021-01-18
    Description: The horizontal to vertical spectral ratio (HVSR) of seismic noise is often used to investigate site effects, and it is usually assumed to be a stable feature of the site considered. Here we show that such an assumption is not always justified, and may lead to incorrect conclusions. The HVSR analysis was performed on ambient seismic noise recordings lasting from weeks to months at many sites in Calabria, Italy. Results show a variety of site effects, from the resonance of a shallow sedimentary layer to the polarized amplification of horizontal ground motion associated with topographic effects. We describe the results of seven sites whose HVSR is characterized by dual content: one that is persistent, and another appearing only occasionally. Two sites very near the coast of the Tyrrhenian sea and five sites in the Calabrian Arc mountains show the most remarkable results. The shape of the HVSR changes significantly at these sites when the amplitude of background noise increases in a broad frequency band during periods of bad weather. The occasional contribution to the HVSR consists of one or more peaks, depending on the site, that appear only when the amplitude of ambient noise is higher than usual. The seven sites where we observe the HVSR variability are all located in complex geological environments, on mountains, ridges or foothills. A variation of the HVSR correlated with the day–night cycle is also observed at some of these sites.
    Description: Published
    Description: 2162–2171
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Volcanic tremor at Mt Vesuvius associated with low frequency shear failures (2018)
    Details
    Publication Date: 2021-03-18
    Description: Mt Vesuvius has been dormant since the eruption occurred in 1944, after which the conduit closed and the volcano entered a quiescent state. Only a minor seismic activity, characterized by low magnitude volcano-tectonic (VT) earthquakes, testifies that the magmatic system is still active. In this paper we report the fist quantitative analysis of volcanic tremor discovered at Vesuvius through the analysis of array data. A seismic array installed in 2012 improved the monitoring performance of the local network, permitting the identification of low amplitude coherent signals. Many of such coherent signals recorded during the last few years have been classified as volcanic tremor. We selected 22 tremor events based on their amplitude and on the number of available stations, and performed detailed analysis aimed at location and characterization of the source. They are characterized by low frequency, duration of a few minutes, and the strongest episodes are recorded at distance up to 90 km from the volcano. In many cases we could identify P–S wave pairs in the seismograms that allowed a precise location of the source depth, which is in the range between 5 km and 6.5 km below the crater. Waveform features, spectral analysis, and comparison with VT earthquakes located at the same depth indicate that the source mechanism of the Vesuvius non-eruptive tremor is a sequence of low frequency shear failures.
    Description: Published
    Description: 32-38
    Description: 2T. Sorgente Sismica
    Description: JCR Journal
    Keywords: 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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    PAPER (OA)
  • 9
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    The Borehole Experiment: Investigation of Cortical Structures Through 3D Array Techniques (2019)
    Miscellania INGV
    Details
    Publication Date: 2020-09-15
    Description: Over the last few years it is growing the need to monitor the volcanic activity with modern technology in order to mitigate volcanic hazard through the detection of any possible precursor phenomena. The use of high performance seismic stations, such as borehole instruments, may increase the signal to noise ratio (SNR), improving the capability to detect very small signals. Over the past 40 years much attention has been given to the use of seismic arrays to measure the slowness vector of coherent signals. The main advantage of seismic arrays consists in their ability to detect weak or emergent signals, and to allow for an effective noise reduction through multichannel waveform stacking. A reliable prediction of the ray-path back-propagated from the recording site to the source is strongly limited by the poor knowledge of the local shallow velocity structure. Usually in volcanic environments the propagation of seismic signals through the shallow layers is strongly affected by lateral heterogeneity, attenuation, scattering, and interaction with the free surface. Driven by these motivations, on May 2014, in collaboration with the colleagues of Osservatorio Vesuviano (INGV), we deployed a 3D seismic array in the area where the borehole seismic station called Pozzo Pitarrone is installed at a depth of about 130 meters. This will improve our knowledge about: • the structure of the top layer and its relationship with geology; • analysis of the signal to noise ratio (SNR) of volcanic signals as a function of frequency; • study of seismic ray-path deformation caused by the interaction of the seismic waves with the free surface; • evaluation of the attenuation of the seismic signals correlated with the volcanic activity. The results of these analyses will improve the general knowledge of wave propagation in the shallow layers and will give a new contribution to the seismic monitoring of Etna volcano.
    Description: Published
    Description: Nicolosi (Catania), Italy
    Description: 1T. Struttura della Terra
    Keywords: 3D-Array Techniques ; Mt. Etna
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Extended abstract
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  • 10
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    Site Effects in the Pollino Region from the HVSR and Polarization of Seismic Noise and Earthquakes (2018)
    Details
    Publication Date: 2021-06-15
    Description: Site effects have been studied at 15 sites in the area of Mt. Pollino (Italy) through the analysis of seismic noise and earthquakes by horizontal-to-vertical spectral ratios (HVSRs) and polarization methods. The HVSR method has been applied to seismic noise and to 83 local and regional earthquakes with the goal to investigate site effects in the 0.5–20 Hz frequency band. At least 20 hrs of seismic noise were selected at each site by taking into account day and night hours, and week days during several months to include any possible environmental condition. Results show stable HVSR curves characterized by small standard deviation, without high peaks at most stations. The same method was also applied to S waves and early coda waves of earthquakes, showing, for most of the sites, results very similar to the HVSR curve obtained from the seismic noise. At some sites, the HVSR is very flat, with amplitude levels between 0.7 and 2 in the entire considered frequency band. Some other sites show well-defined peaks of amplitude up to 4.5. The relationship of site effects seen in the HVSR curves with the local structure has been further investigated through polarization analysis of seismic noise. Results indicate that topography gives the main contribution to site effects in four cases, whereas the effects possibly associated with fault zones near some stations are less obvious.
    Description: Published
    Description: 309-321
    Description: 4T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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