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  • 1
    Publication Date: 2020-12-15
    Description: We study the volcanic tremor time series recorded by a broadband three-component seismic network installed at Stromboli volcano during 1997. By using decomposition methods in both frequency and time domains, we prove that Strombolian tremor can be described as a linear combination of nonlinear signals in time domain. These ‘‘components’’ are similar to those obtained for explosion quakes, with the only difference being the amplitude enhancement. We characterize each of these nonlinear signals both in terms of their wavefield properties as well as dynamic systems. Moreover, we take into account the complex processes of magma flow and turbulent degassing, looking at time and amplitude modulation of tremor on a suitable scale. The distribution of tremor amplitudes is Gaussian while the intertimes between the maxima in a suitable scale are described by a Poisson clustered process. Starting from these analyses, a first approximate model for volcanic tremor field can be deduced. The recorded signals, i.e., the elastic vibrations at a point, can be described by a nonlinear equation which gives limit cycles (different observed ‘‘nonlinear modes’’). This equation is governed by a time-dependent threshold which represents the variability of bubble flux. We take into account some inelasticity in the medium perturbing the elastic potential with a Gaussian function on a suitable scale. It acts as a radiance function modulating the frequency of the limit cycle. This proposed model is able to reproduce waveform, Fourier spectrum, and phase space dimension of one of the extracted nonlinear wave packets.
    Description: Published
    Description: B02302
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Volcanic tremor ; Stromboli ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
    Publication Date: 2021-05-17
    Description: This paper presents the first results from the operation of a dense seismic array deployed in the underground Physics Laboratories at Gran Sasso (Central Italy). The array consists of 13 short-period, three-component seismometers with an aperture of about 550 m and average sensor spacing of 90 m. The reduced sensor spacing, joined to the spatially-white character of the background noise allows for quick and reliable detection of coherent wavefront arrivals even under very poor SNR conditions. We apply high-resolution frequency-slowness and polarization analyses to a set of 27 earthquakes recorded between November, 2002, and September, 2003, at epicentral distances spanning the 20-140 km interval. We locate these events using inversion of P- and S-wave backazimuths and S-P delay times, and compare the results with data from the Centralized National Seismic Network catalog. For the case of S-wave, the discrepancies among the two set of locations never exceed 10 km; the largest errors are instead observed for the case of P-waves. This observation may be due to the fact that the small array aperture does not allow for robust assessment of waves propagating at high apparent velocities. This information is discussed with special reference to the directions of future studies aimed at elucidating the location of seismogenetic structures in Central Italy from extended analysis of the micro-seismicity.
    Description: JCR Journal
    Description: open
    Keywords: seismic array ; microearthquakes ; Central Apennines ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 1997218 bytes
    Format: application/pdf
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  • 3
    Publication Date: 2021-05-17
    Description: This paper reviews the main observations on slow earthquakes and low frequency tremor made along the Apennines, the main seismic active zone of Italy. These observations have been made using a geodetic interferometer system operating since 1994 in the underground tunnel of Gran Sasso, central Italy, and an underground seismic array (UNDERSEIS) operating since 2002 in the same environment. The observations made in recent years indicate that both phenomena are quite rare and apparently uncorrelated. Slow earthquakes, mainly recorded in 1997 and occasionally later, have probably been caused by the activity of a shallow fault system located near the interferometers. Until now only one tremor episode characterized by low frequency content and duration of several hours has been detected in January 2004, without any correlations with the occurrence of slow or regular earthquakes. The signal to noise ratio of this event is very low, but the results of our detailed analysis show that its frequency contents and wave field characteristics are compatible with a low frequency non volcanic tremor.
    Description: 1.1. TTC - Monitoraggio sismico del territorio nazionale
    Description: 3.1. Fisica dei terremoti
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: open
    Keywords: Slow earthquakes ; Tremor ; Apennines ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
    Publication Date: 2017-04-04
    Description: Using data from two dense array of short period seismometers, we analyse the kinematic properties of volcanic tremor preceding and accompanying the 2004–2005 eruption of Etna Volcano, Italy. Results from slowness analyses indicate the action of at least two distinct sources. The first dominates the pre-eruptive period, and is likely associated with the main plumbing system feeding the Summit and southeast craters. Following the onset of the eruption, secondary directions of wave-arrival encompass the eruptive fissures, located on the lower eastern flank of the southeast crater. Nonetheless, significant energy radiation from this latter source was also occurring prior to the onset of the lava effusion, likely suggesting the presence of a resident magma batch, in agreement with independent petrologic and geochemical data.
    Description: Published
    Description: 699-705
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Mt. Etna ; Volcanic tremor ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
    Publication Date: 2012-02-03
    Description: Slow earthquakes and afterslips prove that the Earth does not have just two response time scales, i.e. that of tectonic loading and that of regular earthquakes. A swarm of slow earthquakes, with time constants of the order of hundreds of seconds, has been detected by a laser interferometer below the Gran Sasso massif (Italy). We analyse and model these observations to identify a very plausible source in a local fault, with no historic seismic behavior. While slow earthquakes occurring in subduction zones, and at the transition between locked and stably sliding segments of the San Andreas fault, are often associated with seismic events, in the case of the Apennines there is no correlation between local seismicity and slow earthquakes. Slow earthquakes, therefore, may also represent a specific failure behavior for a seismically locked fault, adding further complexity to the interpretation of geologic data for seismic hazard estimates.
    Description: Published
    Description: 2219
    Description: open
    Keywords: Earthquake dynamics and mechanics ; Seismic hazard assessment and prediction ; Seismicity and seismotectonics ; 04. Solid Earth::04.01. Earth Interior::04.01.05. Rheology ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article , article
    Format: 398488 bytes
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  • 6
    Publication Date: 2017-04-04
    Description: The properties of the tremor wave field at Stromboli are analyzed using data from small-aperture arrays of short-period seismometers deployed on the north flank of the volcano. The seismometers are configured in two semi-circular arrays with radii of 60 and 150 m and a linear array with length of 600 m. The data are analyzed using a spatiotemporal correlation technique specifically designed for the study of the stationary stochastic wave field of Rayleigh and Love waves generated by volcanic activity and by scattering sources distributed within the island. The correlation coefficients derived as a function of frequency for the three components of motion clearly define the dispersion characteristics for both Rayleigh and Love waves. Love and Rayleigh waves contribute 70% and 30%, respectively, of the surface-wave power. The phase velocities of Rayleigh waves range from 1000 m/sec at 2 Hz to 350 m/sec at 9 Hz, and those for Love waves range from 800 to 400 m/sec over the same frequency band. These velocities are similar to those measured near Puu Oo on the east rift of Kilauea Volcano, Hawaii, although the dispersion characteristics of Rayleigh waves at Stromboli show a stronger dependence on frequency. Such low velocities are consistent with values expected for densely cracked solidified basalt. The dispersion curves are inverted for a velocity model beneath the arrays, assuming those dispersions represent the fundamental modes of Rayleigh and Love waves.
    Description: Published
    Description: 653-666
    Description: reserved
    Keywords: volcanic tremor ; array ; velocity structure ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 2836423 bytes
    Format: application/pdf
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  • 7
    Publication Date: 2019-11-04
    Description: Jeffreys-Bullen (absolute) and relative P-wave travel-time residuals were analyzed over Italy and its surrounding using P arrival times from the ISC bulletins supplemented by the data from local observatories. We analyzed the travel-time station corrections by two independent methods to obtain information on lateral variations of the velocity structure over the area and a view of possible upper mantle anisotropy. In the first method, the station corrections are computed as a constant and two cosine terms with appropriate phase shifts. Besides a static term, the second method allows us to study the relative residuals in dependence both on azimuths and incidence angles and thus to investigate their spatial variations and to map lateral variations of anisotropic structure of the subcrustal lithosphere. The high and low-velocity directions inferred from the spatial distribution of the relative residuals as well as the high- and low-velocity upper mantle heterogeneities reflect the geodynamic development of the region, governed by the collision between the African and Eurasian plates
    Description: JCR Journal
    Description: open
    Keywords: teleseismic P residual ; lateral variations of mean residual ; azimuth and spatial variations of the residuals ; 3D anisotropic structure ; subcrustal lithosphere ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 5922536 bytes
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  • 8
    Publication Date: 2019-11-04
    Description: This paper describes two geophysical instruments, installed in the underground physics laboratories of Gran Sasso (LNGS-INFN), located in the seismic zone of the Central Apennines, Italy. These instruments monitor strain and seismic radiation with very high sensitivity: one is a 90 m-long laser interferometer, sensitivity 3 x 10-12, frequency response 10-7-10-2 Hz, and has been operating since 1994. The other is a small-aperture seismic array composed of 21 three-component short period (Mark L4C-3D) and 3 broadband (Guralp CMG-3ESP) seismometers. This dense array will be in operation at the beginning of 1998.
    Description: JCR Journal
    Description: open
    Keywords: strain ; seismic array ; seismometry ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 3637283 bytes
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  • 9
    Publication Date: 2019-11-04
    Description: Earthquake locations and fault-plane solutions are investigated in Sicily and the surrounding areas, by using local network data for the period 1988-1995, and a recently proposed 3D model of the local crustal structure. The results were used for local-to-regional scale stress inversion and strain tensor computations, after integration by a set of selected focal mechanisms taken from the literature. The area under study appears to be affected by heterogeneity of seismic deformation and the stress field. The contraction-to-extension transition from west to east on a regional scale can find a reasonable explanation in the framework of current geodynamic models, such as those assuming the activity of two main tectonic sources in the South Italy region, e.g., the Africa-Europe north-south slow convergence and the faster eastward roll-back of a westward-dipping Ionian subducting slab (Cinque al., 1993). The analysis of low-magnitude (2.5-4.0) earthquakes permitted us to perform an investigation of local-scale strain heterogeneities in this region and to evidence notable changes in the deformation style when processes at different scales are considered.
    Description: JCR Journal
    Description: open
    Keywords: stress ; strain ; lithosphere ; Sicily ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 05. General::05.02. Data dissemination::05.02.02. Seismological data
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 3980697 bytes
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  • 10
    Publication Date: 2022-05-04
    Description: We present the first results of long- term monitoring of temperature profiles at the Campi Flegrei caldera. The measurements were carried out along a 76 meters-deep borehole already equipped with a borehole strain-meter. We installed a cable containing a loop of optical fiber in order to use a fiber-optics distributed sensor based on stimulated Brillouin scattering. The obtained data are consistent with results of both deep and surface geothermal explorations and indicate that geothermal gradient can be efficiently measured and monitored by the proposed technique.
    Description: I.N.G.V.
    Description: Published
    Description: Malta
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: open
    Keywords: MONITORING ; TEMPERATURE ; 04. Solid Earth::04.04. Geology::04.04.11. Instruments and techniques ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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