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Zacharopoulos, Stratos
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- PublicationRestrictedEmpirical evaluation of microtremor H/V spectral ratio(2008-02-08)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Haghshenas, E.; International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran ;Bard, P. -Y.; Laboratoire de Geophysique Interne et Tectonophysique, Université Joseph Fourier, Grenoble, France ;Theodulidis, N.; ITSAK Institute of Engineering Seismology and Earthquake Engineering, Tessaloniki, Greece ;Atakan, K.; University of Bergen ;Cara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cornou, C.; Laboratoire de Geophysique Interne et Tectonophysique, Université Joseph Fourier, Grenoble, France ;Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Di Giulio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Dimitriu, P.; ITSAK Institute of Engineering Seismology and Earthquake Engineering, Tessaloniki, Greece ;Fäh, D.; ETHZ ;De Franco, R.; CNR-IDPA ;Marcellini, A.; CNR-IDPA ;Pagani, M.; CNR-IDPA ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Savvaidis, A.; ITSAK Institute of Engineering Seismology and Earthquake Engineering, Tessaloniki, Greece ;Tento, A.; CNR-IDPA ;Vidal, S.; CETE-Nice ;Zacharopoulos, S.; ITSAK Institute of Engineering Seismology and Earthquake Engineering, Tessaloniki, Greece; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The objective of this work is to perform a purely empirical assessment of the actual capabilities of the horizontal-to-vertical (H/V) spectral ratio technique to provide reliable and relevant information concerning site conditions and/or site amplification. This objective has been tackled through the homogeneous (re)processing of a large volume of earthquakes and ambient noise data recorded by different research teams in more than 200 sites located mainly in Europe, but also in the Caribbean and in Tehran. The original recordings were first gathered in a specific database with information on both the sites and recorded events. Then, for all sites close to an instrumented reference, average site-to-reference spectral ratios (“spectral ratio method” (SSR)) were derived in a homogeneous way (window selection, smoothing, signal-to-noise ratio threshold, averaging), as well as H/V ratios (“HVSRE–RF”) on earthquake recordings. H/V ratios were also obtained from noise recordings at each site (either specific measurements, or extracted from pre- or post-event noise windows). The spectral curves resulting from these three techniques were estimated reliable for a subset of 104 sites, and were thus compared in terms of fundamental frequency, amplitude and amplification bandwidth, exhibiting agreements and disagreements, for which interpretations are looked for in relation with characteristics of site conditions. The first important result consists in the very good agreement between fundamental frequencies obtained with either technique, observed for 81% of the analyzed sites. A significant part of the disagreements correspond to thick, low frequency, continental sites where natural noise level is often very low and H/V noise ratios do not exhibit any clear peak. The second important result is the absence of correlation between H/V peak amplitude and the actual site amplification measured on site-to-reference spectral ratios. There are, however, two statistically significant results about the amplitude of the H/V curve: the peak amplitude may be considered as a lower bound estimate of the actual amplification indicated by SSR (it is smaller for 79% of the 104 investigated sites), and, from another point of view, the difference in amplitude exhibits a questioning correlation with the geometrical characteristics of the sediment/basement interface: large SSR/HV differences might thus help to detect the existence of significant 2D or 3D effects.273 31 - PublicationRestrictedInfluence of instruments on the H/V spectral ratios of ambient vibrations(2008)
; ; ; ; ; ; ; ; ; ;Guillier, B.; LGIT-IRD, Observatoire de Grenoble, BP 53-38041, Grenoble Cedex, France ;Atakan, K.; UiB, Bergen, Norway ;Chatelain, J.-L.; LGIT-IRD, Observatoire de Grenoble, BP 53-38041, Grenoble Cedex, France ;Havskov, J.; UiB, Bergen, Norway ;Ohrnberger, M.; IGUP, Potsdam, Germany ;Cara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Duval, A.-M.; CETE, Nice, France ;Zacharopoulos, S.; ITSAK, Thessaloniki, Greece ;Teves-Costa, P.; ICTE-UL, Lisbon, Portugal; ; ; ; ; ; ; ; For an optimal analysis of the H/V curve, it appears necessary to check the instrument signal to noise ratio in the studied frequency band, to ensure that the signal from the ground noise is well above the internal noise. We assess the reliability and accuracy of various digitizers, sensors and/or digitizer-sensor couples. Although this study is of general interest for any kind of seismological study, we emphasize the influence of equipment on H/V analysis results. To display the impact of the instrumental part on the H/V behavior, some series of tests have been carried out following a step-by-step procedure: first, the digitizers have been tested in the lab (sensitivity, internal noise...), then the three components sensors, still in the lab, and finally the usual user digitizers-sensors couple in lab and outdoors. In general, the digitizer characteristics, verified during this test, correspond well to the manufacturer specifications, however, depending on the digitizer, the quality of the digitized waveform can be very good to very poor, with variation from a channel to another channel (gain, time difference etc.). It appears very clearly that digitizers need a warming up time before the recording to avoid problems in the low-frequency range. Regarding the sensors, we recommend strongly to avoid the use of “classical” accelerometers (i.e., usual force balance technology). The majority of tested seismometers (broadband and short period, even 4.5 Hz) can be used without problems from 0.4 to 25 Hz. In all cases, the instrumentation should be checked first to verify that it works well for the defined study aim, but also to define its limit of use (frequency, sensitivity...).177 21 - PublicationOpen AccessSesame Project - Deliverable D04-04 - Report of the WP04 H/V Technique : Empirical Evaluation - Homogeneous Data Set of Noise and Earthquake Recordings at Many Sites(2003-07)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Atakan, Kuvvet; University of Bergen, Norway ;Azzara, Riccardo Mario; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bard, Pierre-Yves; LGIT, Grenoble, France ;Cara, Fabrizio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cultrera, Giovanna; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Dimitriu, Petros; ITSAK, Thessaloniki, Greece ;Duval, Anne-Marie; CETE, Nice, France ;Faeh, Donat; ETHZ, Zurich, Swiss ;Di Giulio, Giuseppe; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Hagshenas, Ebrahim; LGIT, Grenoble, France ;Havskov, Jens; University of Bergen, Norway ;Koller, Martin; Resonance, Geneva, Swiss ;Pagani, Marco; CNR-IDPA, Milan, Italy ;Panou, Areti; ITSAK, Thessaloniki, Greece ;Papaioannou, Christos; ITSAK, Thessaloniki, Greece ;Rovelli, Antonio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Savvaidis, Alexandros; ITSAK, Thessaloniki, Greece ;Spohler, Eva; ETHZ, Zurich, Swiss ;Tento, Alberto; CNR-IDPA, Milan, Italy ;Daminelli, Rossella; CNR-IDPA, Milan, Italy ;Marcellini, Alberto; CNR-IDPA, Milan, Italy ;Theodoulidis, Nikos; ITSAK, Thessaloniki, Greece ;Zacharopoulos, Stratos; ITSAK, Thessaloniki, Greece; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; In this Report the homogeneous data set of earthquake and noise recordings at many sites that is generated under the framework of the SESAME Project (Site Effects Assessment Using Ambient Excitations, EC- RGD, Project No. EVG1-CT-2000-00026 SESAME), Task A (H/V technique), Work Package 04 (WP04– H/V Technique: Empirical Evaluation), is presented. Three main topics are included in the Report: (a) The Standard Information Sheet (SIS) structure, (b) The SESAME Ascii Format (SAF) files, and (c) The SESAME SIS-database. The SIS compiled in this sub-task and SAF format adopted for all data, constitute a homogeneous data set to be processed for further scientific results in the framework of the WP04. In addition, the SIS-database is going to facilitate data selection and management.284 447 - PublicationOpen AccessSesame Project - Deliverable D01-02 - WP02: Controlled Instrumental Specifications - Final report of the Instrument Workshop 22-26 October 2001, University of Bergen, Norway(2002-04)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Acerra, Catello; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Alguacil, Gerardo; University of Granada, Spain ;Atakan, Kuvvet; University of Bergen, Norway ;Azzara, Riccardo Mario; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bard, Pierre-Yves; LGIT, Grenoble, France ;Blarel, Fabien; LGIT, Grenoble, France ;Borges, Antonio; ICTE-UL, Lisbon, Portugal ;Cara, Fabrizio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Teves-Costa, Paula; ICTE-UL, Lisbon, Portugal ;Duval, Anne-Marie; CETE, Nice, France ;Guillier, Bertrand; LGIT, Grenoble, France ;Grandison, Margaret; University of Bergen, Norway ;Havskov, Jens; University of Bergen, Norway ;Ohrnberger, Matthias; IGUP, Potsam, Germany ;Rao, Sandro; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Theodoulidis, Nikos; ITSAK, Thessaloniki, Grrece ;Tvedt, Eirik; University of Bergen, Norway ;Utheim, Terje; University of Bergen, Norway ;Vidal, Sylvain; CETE, Nice, France ;Vollmer, Daniel; IGUP, Potsam, Germany ;Zacharopoulos, Stratos; ITSAK, Thessaloniki, Grrece; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; In the following we report the preliminary results from a workshop arranged at the Institute of Solid Earth Physics, University of Bergen, in the period 22-26 October 2001 in Bergen, Norway. The workshop was arranged under the framework of the SESAME Project (Site Effects Assessment Using Ambient Excitations, EC-RGD, Project No. EVG1-CT-2000-00026 SESAME), Task A (H/V technique), Work Package 02 (WP02 – Experimental conditions).222 576