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  • 1
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    Realistic modelling of observed seismic motion in compIex sedimentary basins (2006)
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    Publication Date: 2019-11-04
    Description: Three applications of a numerical technique are illustrated to model realistically the seismic ground motion for complex two-dimensional structures. First we consider a sedimentary basin in the Friuli region, and we model strong motion records from an aftershock of the 1976 earthquake. Then we simulate the ground motion caused in Rome by the 1915, Fucino (Italy) earthquake, and we compare our modelling with the damage distribution observed in the town. Finally we deal with the interpretation of ground motion recorded in Mexico City, as a consequence of earthquakes in the Mexican subduction zone. The synthetic signals explain the major characteristics (relative amplitudes, spectral amplification, frequency content) of the considered seismograms, and the space distribution of the available macroseismic data. For the sedimentary basin in the Friuli area, parametric studies demonstrate the relevant sensitivity of the computed ground motion to small changes in the subsurface topography of the sedimentary basin, and in the velocity and quality factor of the sediments. The relative Arias Intensity, determined from our numerical simulation in Rome, is in very good agreoment with the distribution of damage observed during the Fucino earthquake. For epicentral distances in the range 50 km-100 km, the source location and not only the local soil conditions control the local effects. For Mexico City, the observed ground motion can be explained as resonance effects and as excitation of local surface waves, and the theoretical and the observed maximum spectral amplifications are very similar. In general, our numerical simulations estimate the maximum and average spectral amplification for specific sites, i.e. they are a very powerful tool for accurate micro-zonation
    Description: JCR Journal
    Description: open
    Keywords: wave-propagation modelling ; seismic strong ground motion ; sedimentary basin ; seismic micro-zonation ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Application of numerical simulations for a tentative seismic microzonation of the city of Rome (2006)
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    Publication Date: 2019-11-04
    Description: A hybrid technique, based on mode summation and finite differences, was used to silnulate the ground motion induced in the city of Rome by possible earthquakes occurring in the main seisrnogenetic areas surrounding the city: the Central Apennines and the Alban Hills. The results of the numerical simulations are used for a seismic inicrozonation in the city of Rome, which can be used for the retrofitting of buildings of special social and cultural value. On the basis of our analysis Rome can be divided into six main zones: (1) the edges and (2) the central part of the alluvial basin of the River Tiber; (3) the edges and (4) the central part of the Paleotiber basin; the areas outside the large basins of the Tiber and Paleotiber, where we distinguish between (5) areas without, and (6) areas with a layer of volcanic rocks close to the surface. The strongest amplification effects have to be expected at the edges of the Tiber basin, with maximum spectral amplification of the order of 5 to 6, and strong arnplifications occur inside the entire alluvial basin of the Tiber. The presence of a near-surface layer of rigid material is not sufficient to classify a location as a 〈〈hard-rock site〉〉 when the rigid material covers a sedimentary complex. The reason is that the underlying sedimentary complex causes amplifications at the surface due to resonance effects. This phenomenon can be observed in the Paleotiber basin, where spectral amplifications in the frequency range 0.4-1.0 Hz reach values of the order of 3 to 4.
    Description: JCR Journal
    Description: open
    Keywords: Rome ; wave-propagation modelling ; seismic strong ground motion ; seismic microzonation ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Mitigation of seismic hazard of a megacity: the case of Naples (2006)
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    Publication Date: 2019-11-04
    Description: The seismic ground motion of a test area in the eastern district of Naples was computed with a hybrid technique based on the rnode surnrnation and the finite difference methods. This technique allowed the realistic modelling of source and propagation effects, including local soil conditions. In the modelling, as seismic source we considered the 1980 Irpinia earthquake, a good example of strong shaking for the area of Naples, located about 90 km from the source. Along a profile through Naples, trencling N86°W, the subsoil is mainly formed by alluvial (ash, stratified sand and peat) and pyroclastic materials overlying a pyroclastic rock (yellow Neapolitan tuff) representing the Neapolitan bedrock. The detailed information available on the subsoil mechanical properties and its geometry warrants the application of the sophisticated hybrid technique. For SH waves, a comparison was made between a realistic 2-D seismic response and a standard I-D response, based on the vertical propagation of waves in a plane layered structure. As expected the sedimentary cover caused an increase in the signal's amplitudes and duration. If a thin uniform peat layer is present, the amplification effects are reduced, and the peak ground accelerations are similar to those observed for the bedrock model. This can be explained by the backscattering of wave energy at such a laqer. The discrepancies evidenced between the l -D and the 2-D seismic response suggest that serious caution must be taken in the formulation of seismic regulations. This is particularly true in the presence of the thin peat laqer where the misinatch between the l -D and the 2-D amplification functions is particularly evident in correspondence of the dominant peak and of the second significant peak.
    Description: JCR Journal
    Description: open
    Keywords: Seismic hazard ; microzoning ; numerical modelling ; Naples ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    H/V ratio: a tool for site effects evaluation. Results from 1-D noise simulations (2006)
    In:  Geophysical Journal International
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    Publication Date: 2020-02-12
    Type: info:eu-repo/semantics/article
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