1,720,977 research outputs found
Liquefaction damage potential for seismic hazard evaluation in urbanized areas
No full textThe liquefaction susceptibility of granular soils under seismic actions is commonly estimated by means of the liquefaction safety factor and recently by the potential index also. Since its original formulation the potential index has been developed and modified according to both deterministic and probabilistic approaches in order to draw liquefaction microzonation maps. In this study a new approach to potential index definition is proposed in order to relate the liquefaction potential prediction to the loss of bearing capacity for shallow foundation. Such new method has been used to estimate the so called liquefaction damage potential PDL at Barletta site, located in Puglia Region, where strong seismic events may occur. © 2011 Elsevier Ltd
Tomographic Study of the Adriatic Plate
No full textTwo well-known methodologies have been used, for the first time, to derive a detailed and reliable lithospheric model of the Adriatic Plate, consistent with the thus far available data: non linear inversion of phase and group velocity dispersion curve obtained from surface-wave tomography, and body-waves tomography. To carry out the body-waves tomography, about 16500 P phases and 2000 S phases from 1219 seismic events, 73 seismic stations located at the border of the investigated region and a vertically heterogeneous starting model derived from the nonlinear inversion of average dispersion measurements, are used. The 3-D velocity model of the upper lithosphere, obtained from the combined analysis, shows a rather clear structural anomaly on the northeastern side, where the crust is thicker, and an uprising of the top of the lid in the northern part of the plate with a very thin, if any, transition zone from crust to mantle
Polarisation and spectral properties of the seismic site response of landslide-prone hillslopes: a case study from Italy
No full textRevisione della sismicità murgiana
No full textL’integrazione di documentazioni sulla sismicità storica e di osservazioni strumentali
recenti, supportate anche da alcuni indicatori geologici, suggeriscono che nella parte centrale della
Puglia, generalmente considerata asismica, esiste un’attività sismica di bassa energia legata a
strutture tettoniche locali. È stata condotta una revisione delle caratteristiche della sismicità murgiana,
considerando la sua distribuzione spaziale, temporale ed energetica e i meccanismi focali. Per
determinare i tassi di sismicità, si sono integrati i dati storici disponibili, con un catalogo di eventi
strumentali di bassa energia (M < 3.5) registrati tra il 1985 e il 2001. I risultati ottenuti mostrano che
l’area Murgiana è caratterizzata da una sismicità sporadica, probabilmente associata ad un regime
generale tensionale e stimolata dall’interazione con l’attività sismogenetica dell’Appennino e della
Puglia settentrionale. Anche se poco energetica, la sismicità locale contribuisce ad aumentare la
probabilità di eventi con potenzialità di danno, associata all’attività di strutture sismogenetiche vicine,
così da giustificare l’adozione di almeno un minimo livello di cautela in relazione alla definizione locale
di misure di protezione sismica
Tomographic image of the Adriatic area from the combined analysis of seismic and gravimetric data
No full textUse of Refraction Microtremor (ReMi) technique for the determination of 1-D shear wave velocity in a landslide area
No full textIn the context of an ongoing study on seismic response of landslide-prone hill-slopes in Central Italy (area of Caramanico Terme), we tested the applicability of the Refraction Microtremor (ReMi) analysis technique (Louie, 2001) to obtain geometrical and physical parameters needed for numerical modelling. In particular, we used this technique to determine one-dimensional shear-wave velocity profiles (Vs) at sites located on and close to a recent landslide that mobilized 30-40 m thick Quaternary colluvium overlying Pliocene mudstones. The use of this technique in unstable slope areas presents difficulties related to rough topography and lateral lithological heterogeneities, which prevent the extension of geophone array up to the minimum lengths (100 - 200 m) commonly adopted in standard applications. Moreover, sites distant from anthropic sources of microtremors can have unfavourable noise conditions in comparison with other well established cases of application. To check the stability of the ReMi data in these operative conditions and the confidence level of the results, three ReMi campaigns were conducted at different times using different acquisition parameters (seismograph channel number, geophone frequency and spacing). We also tested simultaneous noise recording along orthogonal arrays to investigate a possible presence of directional variations of soil properties. The Rayleigh wave velocity dispersion data derived from picking carried out on p (slowness)-f (frequency) matrix showed the presence in noise recordings of different Rayleigh wave vibration modes (fundamental and first two higher modes), which prevail at different frequency intervals. This indicates that it is essential to correctly identify the different vibration modes to avoid erroneous data interpretation (e.g. fictitious identification of velocity decrease with depth). An analysis of the influence of changing environmental conditions and of different acquisition parameters was conducted through the comparison of data obtained from different campaigns with equal acquisition parameters and from simultaneous acquisition with different parameters. We show that different data acquisition can give quite stable results if spatial aliasing does not contaminate the signal in the p-f matrix near the picking area. Regarding the presence of directional variations, the differences found between velocities measured in two orthogonal directions were not very large (up to 10-20 %). These differences were more probably due to an anisotropic distribution of the noise sources rather than to lateral variations in material properties. The Rayleigh wave velocity dispersion curves, obtained from microseismic noise recording, were then inverted with the software Dinver (Wathelet, 2005) to derive shear-wave vertical distribution. This resulted in a large number of models compatible with data uncertainties estimated from measurement repetitions. The major variability characterizing the models at depth implies that this part of profiles is poorly constrained. However, if different vibration modes are recognised, the number of solutions can be considerably reduced by simultaneously inverting the relative dispersion curves and also by introducing into the models additional constraints (e.g. subsurface information from boreholes and seismic refraction data). References Louie J.N.; 2001: Shear wave velocity to 100 meters depth from refraction microtremor arrays. Bull. Seism. Soc. Am., 91, (2), 347-364. Wathelet M.; 2005: Array recordings of ambient vibrations: surface-wave inversion. PhD thesis, Université de Liège, Belgium
Combined analysis of seismic and gravimetric data in the Adriatic plate
No full textThe presence of a structural heterogeneity between the northern part of the Adriatic plate (Central Mediterranean) and its southernmost sector was hypothesised by different authors and also confirmed recently by 3D velocity models obtained through surface wave tomography and local earthquake tomography. However, the seismological data leave some uncertainty about the location of the lateral limits of this heterogeneity and about its "structural" meaning. The analysis of the Bouguer anomalies observed on a profile running from NW to SE along the Italian side of the plate has allowed to obtain a laterally improved and better constrained integrated model of the area. In particular, the gravimetric data have been interpreted through a 2(1/2)D density modelling developed adopting the seismic tomography model as starting point: the obtained results support the hypothesis of a 10 km thinning of the crust from NW to SE, compensated by the presence of a thick transition zone under the crust in the southern part of the Adriatic plate. The location of the boundary of this lateral heterogeneity was better defined, being marked by an increase of the Bouguer anomalies. The estimated density contrasts of the transition zone with respect to the contiguous layers of lower crust and mantle (about +0.5 and -0.1 g/cm3, respectively) and the comparison with the corresponding velocity contrasts, suggest that the material constituting this transition zone might have a composition more similar to that of the mantle. © 2004 Elsevier B.V. All rights reserved
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