1,721,046 research outputs found
Comparison of site classification from VS30, VS10, and HVSR in Italy
No full textThe aim of this work is to verify if (1) the average of shear-wave velocity from the surface to 30 m depth (VS30) is a good proxy of site amplification in a country
with complex geology like Italy, (2) the grouping of VS30 in different soil classes and relevant spectra in the Italian seismic codes is adequate, and (3) shallow shear-wave profiles (VS10) could be a more economical tool for site classification. To answer the first two questions, we examined 40 estimates of VS30 derived from microzonation projects we performed in Italy (27 obtained with downhole measurements, plus 13 velocity profiles obtained with surface techniques). In all the sites, we installed seismic
instrumentation to record earthquakes and to estimate site response using horizontal to vertical spectral ratios (HVSR). The comparison between HVSR and VS30 showed in about one-third of the sites that VS30 is not a good proxy of observed amplification effects if the site does not have a monotonically increasing velocity profile. The reason
VS30 does not provide satisfactory estimates in Italy is linked to peculiar geological settings that are widespread in the country. We then compared the observed amplifications from earthquake HVSR data with the ones provided by the Italian seismic code, noting a substantial underestimation by the code, a somewhat unsettling situation because HVSR is usually considered to be a lower bound for amplification estimated with other techniques. Finally, we studied 45 VS downhole profiles to 30 m depth performed also at sites where earthquake recordings are not available. On this data set, we noticed that VS10 could predict site classification with the same performances of VS30. We consider alternative soil classification schemes that include soil frequency besides the velocity profile. In this two-parameter approach, VS10 could be substituted for VS30
The HVSR technique from microtremor to strong motion: empirical and statistical considerations
No full textNon-parametric analysis of a single seismometric record to obtain building dynamic parameters
No full textThe stability of Horizontal-to-Vertical Spectral Ratio by triggered noise and earthquake recordings
No full text
Dall'esperimento di Bagnoli alla città virtuale: influenza delle vibrazioni indotte da edifici sull'accelerazione in campo libero.
No full textAmbient noise measurements to support emergency seismic microzonation: the Abruzzo earthquake experience
No full textAfter the 2009 Abruzzo earthquake (Italy), a surface geophysical survey was undertaken to support emergency microzonation studies. The technique most used was the Horizontal-to-Vertical Spectral Ratio (HVSR) applied to ambient seismic noise. More that 200 single-station measurements were performed by a group that comprised also of volunteer professionals over a two-week time span. The availability of such a large database, which is homogenous both from the instrumentation and the processing point of view, allowed us to compare the results with other expeditious techniques for microzonation. The main findings of our study reveal that: 1) the HVSR results obtained from seismic noise measurements are well correlated with the ones obtained by strong motion recordings; 2) available geological maps, even in a digital form, are unable to correlate with the observed presence/absence of amplification revealed by seismic measurements; 3) the simple lithological classification of outcrops, however detailed, cannot be used as a standalone tool to identify the presence/absence of seismic amplification phenomena. Surface geological data are not sufficient. Borehole and geophysical data are also needed to identify the seismic bedrock and provide estimates of the VS average value in the sedimentary cover
Comparison between VS30 and other estimates of site amplification in Italy
No full textDuring 5 microzonation projects in Italy, we had access to 46 estimates of Vs30 (30 obtained with down-hole or
cross-hole measurements, plus 10 velocity profiles obtained with surface techniques, 6 sites were considered A
without drilling, being rock sites). In all the sites we performed HVNR measurements to verify the presence of a
resonant frequency and in 34 sites we installed seismic instrumentation to record earthquakes and estimate site
amplification using HVSR. It is important to note that we did not pre-selected the sites, but just followed the
requests of two Regional governments (Marche and Basilicata) to study a set of localities that were chosen for
reasons other than geo-morphological ones (previous earthquakes, pilot studies, design of new infrastructures).
The comparison between site seismic amplification and Vs30 showed that this last parameter is not a good proxy
of observed site effects. The reason why in Italy Vs30 does not provide satisfactory estimates is linked to
peculiar geological settings that are widespread in our country. The main problems encountered are
underestimations by Vs30 at sites with velocity inversions and overestimations on deep basins. Vs30 seems to
work fine only if a site has a strictly monotonic velocity profile increasing with depth and a strong impedance
contrast in the first dozen meters. Further data will be available thanks to an ongoing national project funded by
the Civil Defence Department that is focusing on Vs30 estimates in the presence of velocity inversions, fractured
rock masses, landslides and karst areas.PublishedGenevaope
An attenuation study in Southern Italy using local and regional earthquakes recorded by seismic network of Basilicata
No full textComparison between VS30 and other estimates of site amplification in Italy
No full textDuring 5 microzonation projects in Italy, we had access to 46 estimates of Vs30 (30 obtained with down-hole or
cross-hole measurements, plus 10 velocity profiles obtained with surface techniques, 6 sites were considered A
without drilling, being rock sites). In all the sites we performed HVNR measurements to verify the presence of a
resonant frequency and in 34 sites we installed seismic instrumentation to record earthquakes and estimate site
amplification using HVSR. It is important to note that we did not pre-selected the sites, but just followed the
requests of two Regional governments (Marche and Basilicata) to study a set of localities that were chosen for
reasons other than geo-morphological ones (previous earthquakes, pilot studies, design of new infrastructures).
The comparison between site seismic amplification and Vs30 showed that this last parameter is not a good proxy
of observed site effects. The reason why in Italy Vs30 does not provide satisfactory estimates is linked to
peculiar geological settings that are widespread in our country. The main problems encountered are
underestimations by Vs30 at sites with velocity inversions and overestimations on deep basins. Vs30 seems to
work fine only if a site has a strictly monotonic velocity profile increasing with depth and a strong impedance
contrast in the first dozen meters. Further data will be available thanks to an ongoing national project funded by
the Civil Defence Department that is focusing on Vs30 estimates in the presence of velocity inversions, fractured
rock masses, landslides and karst areas.PublishedGenevaope
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