For the analysis of seismic wave amplification, modal methods are interesting tools to study the modal properties of geological structures. Modal approaches mainly lead to information on such parameters as fundamental frequencies and eigenmodes of alluvial basins. For a specific alluvial deposit in Nice (France), a simplified modal approach involving the Rayleigh method is considered. This approach assumes a set of admissible shape functions for the eigenmodes and allows a fast estimation of the fundamental frequency of the basin. The agreement with other numerical results (Boundary Element Method) and experimental ones is fully satisfactory. The simplified modal method then appears as an efficient mean for the global vibratory characterization of geological structures towards resonance. To cite this article: J.-F. Semblat et al., C. R. Geoscience 335 (2003).相似文献
We present a field procedure that has been extensively used in Italy to characterize local seismic response at accelerometric sites and to retrieve ground motion at reference soil conditions by deconvolution analysis. To allow a generalized application to large areas where borehole data are generally lacking or inadequate for the seismic characterization for soils down to the reference seismic bedrock, cost-effectiveness of the considered procedures is a main issue. Thus, major efforts have been devoted to optimize available information and exploit fast and cheap surface geophysical prospecting. In particular, geological/geomorphological survey and passive seismic prospecting (both in single- and multi-station configurations) were jointly considered to reconstruct seismo-stratigraphical site conditions. This information was then used to feed numerical modeling aiming at computing the local seismic response and performing a deconvolution analysis to reconstruct ground motion at reference soil conditions. Major attention was devoted to evaluate and manage uncertainty involved in the procedure and to quantify its effect on final outcomes. An application of this procedure to a set of sites included in the Italian Accelerometric Network is presented.
This paper introduces REXELite, an internet version of REXEL, a software for automatic selection of ground motion suites for
nonlinear dynamic analysis of structures. REXELite was developed with the aim of integrating an advanced earthquake records’
repository, such as the ITalian ACcelerometric Archive (ITACA), with a tool to define seismic input for engineering seismic
analysis according to international standards (with priority to Europe). In fact, REXELite allows to define target design
spectra according either to Eurocode 8 or to the Italian building code, and to search ITACA for suitable sets of seven records
(comprised of one or two horizontal ground motion components) matching such target spectra: on average, in a user-specified
period range, and with the desired tolerance. The records in the set also have, individually and according to some criteria,
the most similar spectral shape with respect to that of the code. Selection options include magnitude, source-to-site distance,
soil conditions and, if desired, linear scaling of records to reduce further record-to-record variability of the selected
suite. 相似文献
We present a set of ground motion prediction equations (GMPEs) derived for the geometrical mean of the horizontal components and the vertical, considering the latest release of the strong motion database for Italy. The regressions are performed over the magnitude range 4?C6.9 and considering distances up to 200?km. The equations are derived for peak ground acceleration (PGA), peak ground velocity (PGV) and 5%-damped spectral acceleration at periods between 0.04 and 2?s. The total standard deviation (sigma) varies between 0.34 and 0.38?log10 unit, confirming the large variability of ground shaking parameters when regional data sets containing small to moderate magnitude events (M?<?6) are used. The between-stations variability provides the largest values for periods shorter than 0.2?s while, for longer periods, the between-events and between-stations distributions of error provide similar contribution to the total variability. 相似文献
A new numerical method is presented for propagating elastic waves in heterogeneous earth media, based on spectral approximations of the wavefield combined with domain decomposition techniques. The flexibility of finite element techniques in dealing with irregular geologic structures is preserved, together with the high accuracy of spectral methods. High computational efficiency can be achieved especially in 3D calculations, where the commonly used finite-difference approaches are limited both in the frequency range and in handling strongly irregular geometries. The treatment of the seismic source, introduced via a moment tensor distribution, is thoroughly discussed together with the aspects associated with its numerical implementation. The numerical results of the present method are successfully compared with analytical and numerical solutions, both in 2D and 3D. 相似文献
The Italian Strong Motion Database, ITACA, was developed within projects S6 and S4, funded in the framework of the agreements
between the Italian Department of Civil Protection (Dipartimento della Protezione Civile, DPC) and the Istituto Nazionale
di Geofisica e Vulcanologia (INGV), starting from 2005. The alpha version of the database was released in 2007 and subsequently
upgraded to version 1.0 after: (i) including the most recent strong motion data (from 2005 to 2007) recorded in Italy, in
addition to the 2008 Parma earthquake, M 5.4, and the M ≥ 4.0, 2009 Abruzzo seismic events; (ii) processing the raw strong
motion data using an updated procedure; (iii) increasing the number of stations with a measured shear wave velocity profile;
(iv) improving the utilities to retrieve time series and ground motion parameters; (v) implementing a tool for selecting time
series in agreement with design-response spectra; (vi) compiling detailed station reports containing miscellaneous information
such as photo, maps and site parameters; (vii) developing procedures for the automatic generation of station reports and for
the updating of the header files. After such improvements, ITACA 1.0 was published at the web site , in 2010. It presently contains 3,955 three-component waveforms, comprising the most complete catalogue of the Italian accelerometric
records in the period 1972–2007 (3,562 records) and the strongest events in the period 2008–2009. Records were mainly acquired
by DPC through its Accelerometric National Network (RAN) and, in few cases, by local networks and temporary stations or networks.
This paper introduces the published version of the Italian Strong Motion database (ITACA version 1.0) together with main improvements
and new functionalities. 相似文献
In the present work the seismic site response of Narni ridge (Central Italy) is evaluated by comparing experimental results
and numerical simulations. The inhabited village of Narni is located in central Apennines at the top of a steep massive limestone
ridge. From March to September 2009 the site was instrumented with 10 weak-motion stations, 3 of which located at the base
of the ridge and 7 at the top. The velocimetric network recorded 642 events of ML up to 5.3 and hypocentral distance up to about 100 km. The great amount of data are related to the April 2009 L’Aquila sequence.
The site response was analyzed using both reference (standard spectral ratio, SSR) and non reference spectral techniques (horizontal
to vertical spectral ratio, HVSR). Moreover directional analyses were performed in order to evaluate the influence of the
ridge orientation with respect to the selected source-site paths. In general the experimental results show amplification factors
for frequencies between 4 and 5 Hz for almost all stations installed along the crest. The SSR technique provides amplification
factors up to 4.5 in a direction perpendicular to the main elongation of the ridge. The results obtained from the data analyses
were used as a target for bidimensional and tridimensional numerical simulations, performed using a hybrid finite-boundary
element method and a boundary element method for 2D and 3D modelling, respectively. In general, the results obtained through
numerical simulation fit well the experimental data in terms of range of amplified frequencies, but they underestimate by
a factor of about 2 the observed amplifications. 相似文献
The published version 1.0 of the new Italian strong-motion database ITACA (Italian ACcelerometric Archive, ) includes to date (December 2010) about 4,000 three-component waveforms up to M 6.9, from more than 1,800 earthquakes up
to 6.9, recorded by about 400 stations in the period 1972–2009. The uncorrected and corrected strong motion data are archived
and can be retrieved with their metadata, concerning events, stations and waveforms. The aim of this paper is to present the
procedures for processing the records included in ITACA, accounting for the heterogeneity of this data set, both in terms
of quality and amplitude of records as well as illustrating the main features of the ITACA strong-motion dataset. Later, we
focus on the “exceptional” ground-motion records, that we, conventionally, denote as those having peak acceleration and peak
velocity larger than 300 cm/s2 and 15 cm/s, respectively. These records are less than 2% of the whole ITACA dataset but they are the most relevant for the
seismic hazard and engineering implications. Such large peak values, recorded at distances up to 30 km, are related not only
to the strongest Italian earthquakes, but also to events with magnitude down to 4. Furthermore, we investigate the dependence
of the largest peak values on horizontal and vertical directions and on source-to-site distance. 相似文献