1,721,140 research outputs found
Soil amplification in probabilistic ground motion hazard analysis
No full textThe article presents a comparison of different probabilistic methods for ground motion hazard assessments that include site effects. The approaches examined here were selected and refined during the different phases of the S2-Project, which this journal volume is addressed to. Different procedures characterized by different levels of sophistication, from the simpler one based on the use of standard ground motion predictive equations for specific ground types to the more complex one based on the convolution of a site-specific amplification function (and its variability) with the hazard curve for reference rock, are compared and contrasted with the aim of pointing out strengths and weaknesses of each of them. In addition, a fully non-ergodic approach that separates the epistemic contribution (i.e., the epistemic uncertainty affecting the soil properties) from the total variability in site amplification is presented. To fulfill the scope of the work, the study focuses on three test sites in Italy characterized by different geological conditions and seismicity levels: Mirandola and Soncino in the Po Plain (northern Italy) and Peglio in central Italy
Utilizzo di misure di rumore ambientale per la definizione degli effetti di sito: limiti di applicabilità della metodologia Nakamura.
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Disaggregation of Probabilistic Ground-Motion Hazard in Italy
No full textProbabilistic seismic hazard analysis is a process that integrates over
aleatory uncertainties (e.g., future earthquake locations and magnitudes) to calculate
the mean annual rate of exceedance (MRE) of given ground-motion parameter values
at a site. These rates reflect the contributions of all the sources whose seismic activity is
deemed to affect the hazard at that site. Seismic hazard disaggregation provides insights
into the earthquake scenarios driving the hazard at a given ground-motion level. This
work presents the disaggregation at each grid point of the Italian rock ground-motion
hazard maps developed by Gruppo di Lavoro MPS (2004), Meletti and Montaldo
(2007), and Montaldo and Meletti (2007). Disaggregation is used here to compute
the contributions to the MRE of peak ground horizontal acceleration (PGA) and
5%-damped 0.2, 1.0, and 2.0 sec spectral acceleration values corresponding to different
mean return periods (MRPs of 475 and 2475 yr) from different scenarios. These sce-
narios are characterized by bins of magnitude, M, source-to-site distance, R, and
number, ε, of standard deviations that the ground-motion parameter is away from its
median value for that M R pair as estimated by a prediction equation. Maps showing
the geographical distribution of the mean and modal values of M, R, and ε are presented
for the first time for all of Italy. Complete joint M–R–ε distributions are also presented
for selected cities. Except for sites where the earthquake activity is characterized by
sporadic low-magnitude events, the hazard is generally dominated by local seismicity.
Moreover, as expected, the MRE of long-period spectral accelerations is generally con-
trolled by large magnitude earthquakes at long distances while smaller events at shorter
distances dominate the PGA and short-period spectral acceleration hazard. Finally, for a
given site, as the MRP increases the dominant earthquakes tend to become larger and to
occur closer to the site investigated
Seismicity and crustal structure beneath the western Ligurian Sea derived from local earthquake tomography
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