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Bianco, Francesca
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Bianco, Francesca
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francesca.bianco@ingv.it
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staff
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7007158530
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A-7811-2011
135 results
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- PublicationRestrictedSeismic source dynamics at Vesuvius volcano, Italy(2004)
; ; ; ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Saccorotti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; On October 9, 1999 an earthquake of ML =3.6 occurred about 3 km beneath the central cone of Mt. Vesuvius, near Naples, Italy. The event had the highest magnitude recorded for at least 25 years, and possibly since the last eruption of this volcano (1944), and was not accompanied by other geophysical or geochemical changes. The present paper essentially deals with the seismological data collected at Mt. Vesuvius for 29 years before the October 9 earthquake till the end of 2001, and describes the time pattern distribution of seismic slip release and the b-parameter of the Gutenberg^Richter distribution. The self-similarity of the source process is investigated through the scaling law of the seismic spectrum. Results indicate a two-fold pattern of stress release, with high values (up to 100 bar) for earthquakes occurring close to the top of the carbonate basement that underlies the volcano at 2^3 km of depth, and low values (down to 0.1 bar) for the shallow events occurring within the volcanic edifice. The scaling law of the seismic spectrum is non-self-similar, indicating that the source dimensions do not scale with the seismic moment. For this reason the low-magnitude events substantially contribute to the overall cumulative seismic slip release. The bparameter of the Gutenberg^Richter distribution shows a variation around 1980, and a substantial constancy in the other time periods. The presence of extended aquifers, with their tops at about 1 km beneath the crater, favors the hypothesis of the triggering of the shallowest events by water-level changes. This hypothesis is in agreement with the low values of the stress drop measured for the shallowest seismic events. The existence of a carbonate basement with its top at about 2.5 km beneath the crater and the higher stress drops for the deeper events make reasonable the hypothesis that the pre-fractured carbonate basement may be the site of tectonic stress release.189 97 - PublicationOpen AccessDepth and Spatial Variation of the Shear Wave Attenuation Parameters in the Shallow Crust and Lower Crust/Upper Mantle of Mt. Etna (Italy)(2024)
; ; ; ; ; ; ; Seismic wave attenuation is a key feature of seismic wave propagation that provides constraints on the composition and physical state of the medium within the Earth. We separated intrinsic and scattering attenuation coefficients for the shallow crust and lower crust/upper mantle in the Mt. Etna area. For this purpose, the Multiple Lapse Time Window Analysis (MLTWA) was applied to two groups of earthquakes, well separated in depth. We also studied the spatial variation of the attenuation parameters by dividing the study area into four sectors around Etna. The results show an effective homogeneity of the propagation characteristics inside Etna and, in particular, some lateral variations and minor variations with depth. We observe that structural discontinuities and lithology control scattering losses at all frequencies, with higher scattering in the shallow crust. The intrinsic absorption shows no sensitivity to the presence of these main geological structures and is quite uniform for different depths. Furthermore, compared to the northern sector of the volcano, the southern one shows stronger scattering attenuation at low frequencies. This pattern correlates well with the high seismic activity along most of Etna’s active tectonic structures and ascending magmatic fluids that characterize this sector of the volcano. Although we only discuss the differences in the ‘‘average’’ scattering and inelastic properties of the investigated volumes, the results of this study are very informative about the characteristics of each region. Moreover, they suggest that a future study is necessary, providing a more detailed picture of the spatial distribution of seismic attenuation in the study area, through a 3D inversion of the attenuation parameters estimated along the single source-receiver paths.106 11 - PublicationOpen AccessObservation of coda signals from regional and local earthquakes recorded from a downhole-uphole couple of broad-band sensors at Mt Etna(2007-07)
; ; ; ; ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Patané, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Ferrari, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; ; ; Seismic coda of regional and local earthquakes recorded at a couple of broad band seismometers located at the bottom of a 125 m deep borehole and up-hole at surface show interesting spectral features. We observe strong similarity between the waveforms recorded from up- and down-hole sensors at low frequency (0.1 -3 Hz) and measurable differences in the higher frequency limit. We interpret this observation assuming that at high frequency the up-hole coda is produced by body-tosurface wave scattering in the near surface. We compare the experimental results with numerical simulations done using the Monte Carlo scheme of Yoshimoto et al. (2000) carried out in the assumption of velocity and scattering coefficient which smoothly vary with depth, with the addition of a body-to-surface wave conversion for the energy particles which reach the surface. The comparison of the experimental coda envelopes with those obtained through numerical simulation allow for a quantification of the turbidity parameter at surface.144 189 - PublicationRestrictedTwo-layer earth model corrections to theMLTWA estimates of intrinsic- and scattering-attenuation obtained in a uniform half-space(2010-08)
; ; ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Following the numerical scheme of Yoshimoto we synthesized seismogram envelopes in the multiple scattering framework.We supposed the earth model constituted by a inhomogeneous crust overlying a transparent mantle. In this model velocity is assumed depth-dependent through a continuous function of the depth, v = v(h); Moho discontinuity is approximated by a sharp increase of the velocity around the crust–mantle boundary; inhomogeneity in the crust is parametrized through a depth-dependent scattering coefficient (the inverse of mean free path) g = g0 f (h), with f (h) function of depth, and g0 the scattering coefficient at zero depth; intrinsic attenuation is parametrized in terms of the intrinsic attenuation coefficient, ηi , that is assumed independent of depth. Generating a suite of energy envelopes as a function of lapse time and distance, for reasonable values of B0 , the seismic albedo and Le−1, the extinction length inverse (which are functions of g0 and ηi ), we span a wide range including most of the measurements done through the world. Then, we apply the ordinary MLTWA technique to these synthetic envelopes. In this application, we assume a constant g and a constant velocity, v = which equals the average of v(h) calculated in the depth range characteristic of the volume encompassed by the scattered waves. In this way, we obtain the estimates of B0, and Le−1, for a constant half-space. The relationship between the estimates of B0 and Le−1, obtained assuming half-space, and the correspondent values used in the simulation, results to be well approximated by a second-order polynomial. Then, evaluating the best fit polynomial coefficients, we obtain a correspondence map between attenuation parameters retrieved for a uniform model with those characteristic of a more realistic structure. This map is useful to reinterpret all the couples B0 and Le−1 already calculated through the world in geological structures similar to the one adopted in our simulation. Results show that scattering and intrinsic-attenuation coefficients estimated using MLTWA in the assumption of a uniform half-space are always overestimated128 35 - ProductOpen Access30 years of coda observations: Qc, Qi and Qs(2007)
; ; ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; A summary of the main results obtained worldwide, in memory of Keiiti Aki.180 132 - PublicationOpen AccessIl Monitoraggio dei Vulcani Campani - Primo semestre 2021L'Istituto Nazionale di Geofisica e Vulcanologia (INGV) è componente del Servizio Nazionale di Protezione Civile, ex articolo 6 della legge 24 febbraio 1992 n. 225 ed è Centro di Competenza per i fenomeni sismici, vulcanici e i maremoti per il Dipartimento della Protezione Civile Nazionale (DPC). L’Osservatorio Vesuviano, Sezione di Napoli dell’INGV, ha nei suoi compiti il monitoraggio e la sorveglianza H24/7 delle aree vulcaniche attive campane (Vesuvio, Campi Flegrei e Ischia). Tali attività sono disciplinate dall’Accordo-Quadro (AQ) sottoscritto tra il DPC e l’INGV per il decennio 2012-2021 e sono dettagliate negli Allegati A e B del suddetto AQ. Il presente Rapporto sul Monitoraggio dei Vulcani Campani rappresenta l’attività svolta dall’Osservatorio Vesuviano e dalle altre Sezioni INGV impegnate nel monitoraggio dell’area vulcanica campana nel primo semestre 2021.
151 231 - PublicationRestrictedMultiple resolution seismic attenuation imaging at Mt. Vesuvius(2009)
; ; ; ; ;De Siena, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Tramelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; ; A three-dimensional S wave attenuation tomography of Mt. Vesuvius has been obtained with multiple measurements of coda-normalized S-wave spectra of local small magnitude earthquakes.We used 6609 waveforms, relative to 826 volcano-tectonic earthquakes, located close to the crater axis in a depth range between 1 and 4 km (below the sea level), recorded at seven 3-component digital seismic stations. We adopted a two-point ray-tracing; rays were traced in an high resolution 3-D velocity model. The spatial resolution achieved in the attenuation tomography is comparable with that of the velocity tomography (we resolve 300m side cubic cells). We statistically tested that the results are almost independent from the radiation pattern. We also applied an improvement of the ordinary spectral-slope method to both P- and S-waves, assuming that the differences between the theoretical and the experimental high frequency spectral-slope are only due to the attenuation effects. Consequently we could check the codanormalization method also comparing the S attenuation image with the P attenuation image. The images were obtained inverting the spectral data with a multiple resolution approach. Results have shown the general coincidence of low attenuation with high velocity zones. The joint interpretation of velocity and attenuation images allows us to interpret the low attenuation zone intruding toward the surface until a depth of 500m below the sea level as related to the residual part of solidified magma from the last eruption. In the depth range between −700 and −2300 images are consistent with the presence of multiple acquifer layers. No evidence of magma patches greater than the minimum cell dimension (300m) has been found. A shallow P wave attenuation anomaly (beneath the southern flank of the volcano) is consitent with the presence of gas saturated rocks. The zone characterized by the maximum seismic energy release cohincides with a high attenuation and low velocity volume, interpreted as a cracked medium.226 15 - PublicationOpen AccessANNALS OF GEOPHYSICS: AD MAJORA(2014)
; ; ; ; ; ; ; ; ; ;Florindo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Muscari, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Caprara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Chiodetti, A. G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Gresta, S.; Univ Catania; ; ; ; ; ; ; ; Annals of Geophysics (ISSN: 1593-5213; from 2010, 2037-416X) is a bimonthly international journal, which publishes scientific papers in the field of geophysics sensu lato. It derives from Annali di Geofisica (ISSN: 0365-2556), which commenced publication in January 1948 as a quarterly periodical devoted to general geophysics, seismology, Earth magnetism, and atmospheric studies....1541 255 - PublicationRestrictedEffects of Surface Geology on Seismic Ground Motion Deduced from Ambient-Noise Measurements, in the Town of Avellino, Irpinia Region (Italy)(2012)
; ; ; ; ; ;Maresca, R.; Università del Sannio ;Nardone, L.; Università del Sannio ;Pasquale, G.; Università del Sannio ;Pinto, F.; Università del Sannio ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; ; ; The effects of surface geology on ground motion provide an important tool in seismic hazard studies. It is well known that the presence of soft sediments can cause amplification of the ground motion at the surface, particularly when there is a sharp impedance contrast at shallow depth. The town of Avellino is located in an area characterised by high seismicity in Italy, about 30 km from the epicentre of the 23 November 1980, Irpinia earthquake (M = 6.9). No earthquake recordings are available in the area. The local geology is characterised by strong heterogeneity, with impedance contrasts at depth. We present the results from seismic noise measurements carried out in the urban area of Avellino to evaluate the effects of local geology on the seismic ground motion. We computed the horizontal-to-vertical (H/V) noise spectral ratios at 16 selected sites in this urban area for which drilling data are available within the first 40 m of depth. A Rayleigh wave inversion technique using the peak frequencies of the noise H/V spectral ratios is then presented for estimating Vs models, assuming that the thicknesses of the shallow soil layers are known. The results show a good correspondence between experimental and theoretical peak frequencies, which are interpreted in terms of sediment resonance. For one site, which is characterised by a broad peak in the horizontal-to-vertical spectral-ratio curve, simple one-dimensional modelling is not representative of the resonance effects. Consistent variations in peak amplitudes are seen among the sites. A site classification based on shear-wave velocity characteristics, in terms of Vs30, cannot explain these data. The differences observed are better correlated to the impedance contrast between the sediments and basement. A more detailed investigation of the physical parameters of the subsoil structure, together with earthquake data, are desirable for future research, to confirm these data in terms of site response.455 26 - PublicationOpen AccessRete Sismica Mt.Etna: relazione sull'intervento di installazione della Rete Permanente(1992-04)
; ; ; ;Castellano, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Capello, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; Not present112 75