1,721,219 research outputs found
Between-event and between-station variability observed in the Fourier and response spectra domains: Comparison with seismological models
No full textA study of rupture characteristics of the 40 s subevent of the 1980 Irpinia earthquake
No full textThe Irpinia project, as carried out by ISMES under a commission from ENEL, had as objectives the developement of a general methodology to simulate broad-band seismic ground motion at near-source and regional distances, and the application of this methodology to the 1980 Irpinia earthquake. Within this general framework, one goal was the comparison of four previously published models for this earthquake in order to arrive at a plausible description of the source process. The comparative study was cast as an inverse problem: that of inferring the spatial extent and temporal behaviour of the rupture process, from geodetic measurements of surface deformation and near-source recordings of ground velocity. This study was complicated by the fact th the Irpinia earthquake was a complex event, involving at least three distinct rupture episodes in a time span of 40 s. However, this same complexity offers the opportunity of illustrating the use of inversion methodologies to 1) infer the spatial slip distribution on a multiple fault system; 2) address the problem of determining the accuracy of the inferred slip models, and 3) use information describing the static characteristics of an earthquakes as an aid in understanding the kinematics of the rupture. This last point is illustrated for the 40 s subevent through the results of a forward modeling study of high-frequency acceleration waveforms using a rupture model based on the inversion results.JCR Journalope
Depth-Dependent Shear-Wave Attenuation in Central Apennines, Italy
No full textWe used 1029 earthquakes, with magnitudes ranging from M 3.0 to M 6.5, located in central Apennines, Italy, and recorded by 414 local stations to study the variation of the quality factor QS of shear waves with depth. We first determined average nonparametric attenuation functions in the frequency band from 0.5 to 20 Hz and hypocenter distances less than 155 km to correct the observed acceleration spectra for attenuation effects. Then, we separated source and site effects from the corrected spectral records to determine the changes of QS with depth. We used a 1D local shear-wave velocity model to calculate the travel times of the source-station paths, and we inverted the observed spectra to determine QS in three different depth intervals (0–4 km, 4–10 km and 10–15 km) and five frequencies (0.5, 1, 4, 10 and 20 Hz). We found that QS increases with frequency at all depths considered and tends to have lower values at shallow depths. The average value of QS is consistent with previous studies made in central Italy and can be approximated by QS = 43f0.94. To describe the frequency dependence of QS with depth (H), we determine the following relations: QS = 5.5f1.39, 0.5 ≤ f ≤ 10 Hz and QS = 151.5, f > 10 Hz for 0–4 km, QS = 52f0.87 for 4 < H < 10 km and QS = 51f0.92 for 10 ≤ H ≤ 15 km. We conclude that the Q-depth-dependent model can be useful to improve estimates of source parameters and ground motion prediction in the central Apennines region of Italy
Foreword to the Special Issue on the ITACA Strong Motion Database
No full textThe Special Issue of the Bulletin of Earthquake Engineering devoted to the new Italian strong motion database ITACA (ITalian ACelerometric Archive) is introduced in this foreword. An overview of the papers published in this issue is presented, providing an idea of the number of problems encountered in the compilation of a database as rich of information as ITACA, of the solutions adopted and of the possible research and practical applications. Most of the contents, though specifically addressed to ITACA and to its accelerograms, can be usefully thought of as an exemplification of approaches and methods that can be used for, and extended to, similar databases in other countries
REXELite, Internet-based record selection on ITACA. Convenzione-Quadro tra Dipartimento della Protezione Civile e Istituto Nazionale di Geofisica e Vulcanologia Triennio 2007-09
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Italian strong motion records in ITACA: overview and record processing
No full textThe published version 1.0 of the new Italian strong-motion database ITACA (Italian ACcelerometric Archive,http://itaca.mi.ingv.it) 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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Space-time evolution of the rupture process from the inversion of strong-motion waveform
No full textJCR Journalope
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