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  • 1
    Electronic Resource
    Electronic Resource
    Travel-time residuals and velocity structure beneath Italy
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 51 (1988), S. 214-221 
    Details
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(88)90047-7
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Site response obtained from array techniques applied to the seismic noise: Two examples in Italy (1999)
    Springer
    Journal of seismology 3 (1999), S. 31-43 
    Details
    ISSN: 1573-157X
    Keywords: site response ; seismic noise ; seismic array
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The vertical component of the seismic noise has been recorded in two different sites near the towns of Mercato S. Severino and Benevento in Southern Italy by a small aperture array, in order to investigate the characteristics of the noise propagation and to study the site response. Three different array techniques have been applied in the two investigated sites: Beam Forming, High Resolution and Spatial Correlation methods. We used two simple array geometry for localising possible noise sources and estimating local shallow structure using ambient noise. The cross shaped array results effective for determining the phase velocity of waves in the case when the noise is from a single localised source; the circular array, on the other hand, is successfully used when the noise sources are distributed. The main results are: the analysis of a coherent component of the noise recorded in the two sites, interpreted as Rayleigh waves, results in reasonable velocity models; the noise recorded in the M.S.S. Plain is a space stationary signal, while the noise at the Benevento site is possibly produced by a stable noise source located close to the array. Due to this evidence, the correlation method does not yield satisfactory results when applied to the Benevento site. The 2–6 Hz spectral peaks of the noise recorded in the M.S.S. Plain can be interpreted as due to a site effect, considering the satisfactory agreement of the noise spectrum at those frequencies with the theoretical transfer function computed on the basis of the velocity model deduced from the Rayleigh waves dispersion analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009739303582
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  • 3
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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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  • 4
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    Site Response in the Irno Valley, Southern Italy, From Noise Measurements (1994)
    Seismological Society of America
    Details
    Publication Date: 1994-07-01
    Description: Seismic noise measurements have been carried out in the Irno Valley (Southern Italy) at seven sites characterized by different surface geology. The geology is known under the investigated sites and a one-dimensional flat-layered earth model was used to predict the ground motion spectrum for each site. A classical Haskel-Thomson approach was used to calculate theoretical transfer functions using three input motions given at the base of the layers: delta function, earthquake and noise signal recorded on the carbonate rock. Modeling shows good the agreement with experimental data, which show relevant peaks in the 2–5 Hz frequency band. This agreement justifies the hypothesis that the experimental peaks are generated by the resonance response of the uppermost layers.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America
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  • 5
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    Site response obtained from array techniques applied to the seismic noise: Two examples in Italy (1999)
    Springer
    Details
    Publication Date: 1999-01-01
    Description: The vertical component of the seismic noise has been recorded in two different sites near the towns of Mercato S. Severine and Benevento in Southern Italy by a small aperture array, in order to investigate the characteristics of the noise propagation and to study the site response. Three different array techniques have been applied in the two investigated sites: Beam Forming, High Resolution and Spatial Correlation methods. We used two simple array geometry for localising possible noise sources and estimating local shallow structure using ambient noise. The cross shaped array results effective for determining the phase velocity of waves in the case when the noise is from a single localised source; the circular array, on the other hand, is successfully used when the noise sources are distributed. The main results are: the analysis of a coherent component of the noise recorded in the two sites, interpreted as Rayleigh waves, results in reasonable velocity models; the noise recorded in the M.S.S. Plain is a space stationary signal, while the noise at the Benevento site is possibly produced by a stable noise source located close to the array. Due to this evidence, the correlation method does not yield satisfactory results when applied to the Benevento site. The 2-6 Hz spectral peaks of the noise recorded in the M.S.S. Plain can be interpreted as due to a site effect, considering the satisfactory agreement of the noise spectrum at those frequencies with the theoretical transfer function computed on the basis of the velocity model deduced from the Rayleigh waves dispersion analysis.
    Print ISSN: 1383-4649
    Electronic ISSN: 1573-157X
    Topics: Geosciences , Physics
    Published by Springer
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  • 6
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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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  • 7
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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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  • 8
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    Design of a flight qualified long-life cryocooler (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A second generation Stirling cycle cryogenic refrigerator with a linear drive, magnetic bearings, and clearance seals; designed to produce 5 watts of cooling at 65 Kelvin and to meet Space Shuttle mission requirements is described. The first generation refrigerator met all performance specifications, and operated with no failure for over 12,030 hours. Meeting launch requirements necessitated improvements in the electromagnetic bearings, the radial position sensors, and in the structural design of the moving elements. Organic contamination was eliminated by the use of all metal and ceramic construction. Reductions in system input power are attained by an integral magnetic spring/motor for the displacer and by more efficient linear motors and drive electronics.
    Keywords: ENGINEERING (GENERAL)
    Type: NBS Proc. of the 3rd Cryocooler Conf.; p 99-118
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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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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  • 10
    facet.materialart.
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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
    Format: application/pdf
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