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  • 1
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    H/V Spectral Ratios and Array Techniques Applied to Ambient Noise Recorded in the Colfiorito Basin, Central Italy (2006)
    Seismological Society of America
    Details
    Publication Date: 2006-04-01
    Description: The Colfiorito Basin is a small intramountain depression in the southern section of the Northern Apennine chain that is filled with Quaternary alluvial deposits. The presence of soft alluvial deposits has significantly influenced the level of local damage that was caused by two major earthquakes (M (sub L) 5.6 and 5.8) belonging to the swarm that started in September 1997. To verify the effects of the basin structure on the predominant frequency of seismic motion, ambient noise measurements were carried out in the Colfiorito Basin during two experiments in May and July of 2002. The horizontal-to-vertical spectral ratios (HVSRs) were calculated for data collected at four profiles in the basin. Array techniques were applied to determine the wave types that composed the noise, to estimate their apparent velocity and azimuth of propagation, and to calculate a velocity-dispersion curve from which a velocity-depth structure was derived. The data analysis shows a high amplification in the HVSR at low frequency. This feature is common to most of the sites, including the reference site, and it is interpreted as being due to weather disturbances. The peak frequencies of the spectral ratio calculated at the sites located in the center of the basin coincide with the theoretically estimated resonance frequencies. The array-averaged HVSR calculated for the array located in the middle of the plain has a pronounced peak at 0.9 Hz. This corresponds to the peak of the amplification function calculated on the basis of the velocity model deduced from the dispersion analysis. The HVSR method is instead unsuitable for the prediction of the resonance frequencies of sediments in the sites where strong lateral variations of basement topography are present. We measured apparent velocities in the range of 0.3-0.8 km/sec by applying f-k methods to array recordings. These values are compatible with the predominance of surface waves in the noise, as also confirmed by polarization analysis. Both Rayleigh and Love waves are present in the background seismic noise. The results obtained by applying the spatial autocorrelation method to the vertical component of the ground motion recorded at a 240-m-wide circular array deployed in the middle of the basin revealed the presence of Rayleigh waves, and f-k methods combined with polarization techniques revealed the presence of polarized Love waves. The wave-field analysis indicates two main propagation directions: the first is around N100 degrees E in the frequency band of 1.0-2.0 Hz; this radiation can be interpreted as being generated at the east-southeast step borders of the basin. The second main direction is around N300 degrees E in the frequency band of 2.0-3.0 Hz; its source may be a 180-m-deep depression located at the southwest corner of the basin.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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  • 2
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    Shallow Velocity Structure and Site Effects at Mt. Vesuvius, Italy, from HVSR and Array Measurements of Ambient Vibrations (2011)
    Seismological Society of America
    Details
    Publication Date: 2011-08-01
    Description: Ambient vibrations were recorded by two dense short-period seismic arrays located on Mount Vesuvius. The aim of this study is to derive the surface velocity structure through the application of array techniques and to interpret it in terms of resonance effects. Mount Vesuvius, which is located in proximity to the Apennines earthquake source-zone, is one of the most dangerous volcanoes of the world. We compared different array techniques to derive the dispersive properties of the surface waves composing the noise wave field. The frequency-wavenumber (f-k) spectral method applied to the data recorded by array A furnished the Rayleigh waves and Love waves dispersive functions and proved the time-space stationarity of the noise wave field. The existence of a stochastic wave field justifies the use of the spatial autocorrelation (SPAC) method and the time stationarity autocorrelation (TSAC) method, which appear to be most effective at the lowest frequencies. The TSAC method, which time averages, is confirmed as the most user-friendly, because it does not require circular geometries. The knowledge of the surface structure is an important goal in site-effects studies and is used to determine the frequency response of the near-surface geology. Velocity models have been derived from the dispersion curves, using both trial and standard inversion procedure. The results are compared with those obtained from array measurements in adjacent areas (Scarpa et al., 2003), revealing similar mechanical properties in the cover deposits and heterogeneities down to 40 m of depth. The shear-wave velocity profiles derived at the array-sites are used to model the 1D transfer functions for vertically incident shear waves. The fundamental resonance frequencies agree with the peak frequencies observed in the microtremor horizontal-to-vertical spectral ratios. The frequency band of amplification is also compatible with the results obtained from local earthquakes at sites located at the same elevation on Mount Vesuvius (Galluzzo et al., 2009).
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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  • 3
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    Effects of Surface Geology on Seismic Ground Motion Deduced from Ambient-Noise Measurements in the Town of Avellino, Irpinia Region (Italy) (2011)
    Springer
    Details
    Publication Date: 2011-08-03
    Print ISSN: 0033-4553
    Electronic ISSN: 1420-9136
    Topics: Geosciences , Physics
    Published by Springer
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  • 4
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    Predominant frequency variations in the ambient noise recorded in the Colfiorito basin (Umbria, Italy) (2007)
    Details
    Publication Date: 2017-04-04
    Description: The Colfiorito basin is located at the boundary between Umbria and Marche districts in Central Italy. The area was struck by several strong earthquakes in the past, and during the September 1997 to April 1998 seismic sequence, the macroseismic intensity was as large as IX (MCS scale) in the region. Ambient noise measurements are carried out over fifty points in the basin; H/V spectral ratios as well as spectral ratios using a reference rock site are calculated. Polarization analyses are also performed in narrow frequency bands where spectral amplitude peaks are observed to dominate, to discriminate preferential directions of propagation in the noise wave field which could be related to source or path effects, other than site effects. In the spectral ratios, the frequencies of the most pronounced peaks generally agree with the resonance frequencies computed for the measurement sites on the basis of 1-D velocity models, at least where no strong lateral variations of the sediment thickness are present.
    Description: Unpublished
    Description: Nice, France
    Description: open
    Keywords: microtremors ; H/V spectral ratios ; polarization ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Poster session
    Format: 900748 bytes
    Format: application/pdf
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  • 5
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    H/V spectral ratios and array techniques applied to ambient noise recorded in Colfiorito basin, Central Italy. (2007)
    Seismological Society of America
    Details
    Publication Date: 2017-04-04
    Description: The Colfiorito Basin is a small intramountain depression in the southern section of the Northern Apennine chain that is filled with Quaternary alluvial deposits. The presence of soft alluvial deposits has significantly influenced the level of local damage that was caused by two major earthquakes (ML 5.6 and 5.8) belonging to the swarm that started in September 1997. To verify the effects of the basin structure on the predominant frequency of seismic motion, ambient noise measurements were carried out in the Colfiorito Basin during two experiments in May and July of 2002. The horizontal-to-vertical spectral ratios (HVSRs) were calculated for data collected at four profiles in the basin. Array techniques were applied to determine the wave types that composed the noise, to estimate their apparent velocity and azimuth of propagation, and to calculate a velocity-dispersion curve from which a velocity-depth structure was derived. The data analysis shows a high amplification in the HVSR at low frequency. This feature is common to most of the sites, including the reference site, and it is interpreted as being due to weather disturbances. The peak frequencies of the spectral ratio calculated at the sites located in the center of the basin coincide with the theoretically estimated resonance frequencies. The arrayaveraged HVSR calculated for the array located in the middle of the plain has a pronounced peak at 0.9 Hz. This corresponds to the peak of the amplification function calculated on the basis of the velocity model deduced from the dispersion analysis. The HVSR method is instead unsuitable for the prediction of the resonance frequencies of sediments in the sites where strong lateral variations of basement topography are present. We measured apparent velocities in the range of 0.3–0.8 km/sec by applying f-k methods to array recordings. These values are compatible with the predominance of surface waves in the noise, as also confirmed by polarization analysis. Both Rayleigh and Love waves are present in the background seismic noise. The results obtained by applying the spatial autocorrelation method to the vertical component of the ground motion recorded at a 240-m-wide circular array deployed in the middle of the basin revealed the presence of Rayleigh waves, and f-k methods combined with polarization techniques revealed the presence of polarized Love waves. The wave-field analysis indicates two main propagation directions: the first is around N100 E in the frequency band of 1.0–2.0 Hz; this radiation can be interpreted as being generated at the east-southeast step borders of the basin. The second main direction is around N300 E in the frequency band of 2.0–3.0 Hz; its source may be a 180-m-deep depression located at the southwest corner of the basin.
    Description: Published
    Description: 490–505
    Description: reserved
    Keywords: NONE ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 556544 bytes
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  • 6
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    A seismic array on Mt. Vesuvius (2007)
    Details
    Publication Date: 2017-04-04
    Description: In November 1997 a seismic antenna (array) of short period seismometers was installed on the south-western flank of Mt. Vesuvius; aim of the experiment was to test the use of non-conventional devices for the seismic monitoring of this volcano. In 7 months local seismicity, regional earthquakes and samples of seismic noise were recorded by the array and organised in a data base. Local earthquakes and seismic noise have been analysed with array techniques to investigate the spectral, kinematic and polarization properties of the wavefield. Preliminary results show that the backazimuth of local earthquakes is oriented in the direction of the crater area. For some events, the source location has been constrained using a simplified back propagation in a 2-D velocity structure. The noise wavefield is characterized by the predominance of a sustained low frequency component (〈 1Hz) whose source is located S-SE of the array. This low frequency signal has been interpreted as associated to the sea-loading in the gulf of Naples.
    Description: Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano
    Description: Published
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: open
    Keywords: seismic array ; Mt. Vesuvius ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: report
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  • 7
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    Confronto di differenti tecniche per la valutazione dell'amplificazione di sito nella città di Benevento (2007)
    Università degli Studi del Sannio, Benevento
    Details
    Publication Date: 2017-04-04
    Description: In the text
    Description: Regione Campania Provincia di Benevento Comune di Benevento C.C.I.A.A. Benevento ESRI Italia Delisa S.p.a., Trento Infotel S.r.l., Taranto
    Description: Published
    Description: Benevento, Italy
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: open
    Keywords: noise spectra ; site response ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 8
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    Site effects Estimation and Source_Scaling Dynamics for Local Earthquakes at Mt. Vesuvius, Italy (2007)
    Details
    Publication Date: 2017-04-04
    Description: Local microearthquakes were used to estimate site effects and source dynamic-scaling characteristics at Mt. Vesuvius, Italy. The selected data set is composed of low magnitude events (1.1 £ Md £ 3.6) recorded in 1996 and 1999 by nine digital shortperiod (1-Hz) seismic stations. Site response was evaluated by analysing data with three different approaches: 1) spectral ratios method of S-waves with respect to the average amplitude spectrum; 2) generalized inversion for site and source from the S-waves; and 3) generalized inversion from the coda waves. The results obtained with all three methods showed amplification of a factor of 1.5-2.5 in the 8-14 Hz frequency band for BKE and SGV sites and an amplification of 3 in a narrow band around 8 Hz for the CDT site. Method 2 allowed simultaneous determination of the source spectral shape for each earthquake. By assuming an w2 source model, we estimated the seismic moment Mo and corner frequency fc. The results show that most of the selected earthquakes are characterized by stress drops of 10 bars. The present results are encouraging for further investigation into the techniques for site-effect evaluation and for improving our knowledge of the scaling law of the source spectrum at Mt. Vesuvius.
    Description: Unpublished
    Description: Grenoble, France
    Description: open
    Keywords: NONE ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
    Format: 2195870 bytes
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  • 9
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    Local Site Effects in the Town of Benevento (Italy) from Noise Measurements (2007)
    Birkhauser Verlag
    Details
    Publication Date: 2017-04-04
    Description: The study of ground motion amplification produced by surface geology is extremely interesting in the Benevento area, Southern Italy, as it is characterized by high seismic hazard. The present moderate-to-low seismicity makes the noise method appropriate to estimate the seismic site response in the area. The three components of seismic noise have been recorded in five sites in the Benevento metropolitan area characterized by different surface geology, in order to estimate the seismic site response. In evaluating site amplification effects we used the direct interpretation of amplitude spectra and standard spectral ratio techniques, evaluating sediment-to-bedrock, sediment-to-average and H/V spectral ratios. The temporal evolution of the noise spectra is analysed within one day, in order to assess the stationarity of the noise signal. The noise wavefield properties have been studied through polarization analyses in selected bands of frequency, where spectral peaks are observed to dominate, to better understand the real nature of those peaks. Results give evidence of low amplification levels, missing any correlation between spectral amplitudes and sediment thickness over the basement. We interpret this result as due to the poor impedance contrast between sediments and basement, which is characterized by low values of shear waves velocity. Moreover, sharp amplitude peaks are observed in the raw spectra of the sediment-sites, in the 2–4 Hz frequency band; a numerical simulation interprets this effect as possibly associated with a wide-scale structure, invoking the presence of a sharper impedance contrast at greater depth. At high frequencies the action of ambient noise sources, mainly active on horizontal components of motion, is retained dominant to generate the prominent peaks observed in the H/V spectral ratios; in some cases the presence of a nearsurface low-velocity layer can contribute to amplify the seismic motion generated at these frequencies.
    Description: Published
    Description: 1745-1764
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: reserved
    Keywords: Site response ; noise ; Benevento ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
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    Earthquake focal mechanisms and stress inversion in the Irpinia Region (southern Italy) (2010)
    SPRINGER
    Details
    Publication Date: 2017-04-04
    Description: The goal of this study was to estimate the stress field acting in the Irpinia Region, an area of southern Italy that has been struck in the past by destructive earthquakes and that is now characterized by low to moderate seismicity. The dataset are records of 2,352 aftershocks following the last strong event: the 23 November 1980 earthquake (M 6.9). The earthquakes were recorded at seven seismic stations, on average, and have been located using a three-dimensional (3D) P-wave velocity model and a probabilistic, non-linear, global search technique. The use of a 3D velocity model yielded amore stable estimation of take-off angles, a crucial parameter for focal mechanism computation. The earthquake focal mechanisms were computed from the P-wave first-motion polarity data using the FPFIT algorithm. Fault plane solutions show mostly normal component faulting (pure normal fault and normal fault with a strikeslip component). Only some fault plane solutions show strike-slip and reverse faulting. The stress field is estimated using the method proposed by Michael (J Geophys Res 92:357–368, 1987a) by inverting selected focal mechanisms, and the results show that the Irpinia Region is subjected to a NE–SW extension with horizontal σ3 (plunge 0◦, trend 230◦) and subvertical σ1 (plunge 80◦, trend 320◦), in agreement with the results derived from other stress indicators.
    Description: Published
    Description: 107-124
    Description: 3.1. Fisica dei terremoti
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: Irpinia Region ; Seismicity ; Focal mechanisms ; Stress inversion ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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