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GIPSA-Lab, CNRS, Grenoble, France
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- PublicationRestrictedGround structure imaging by inversions of Rayleigh wave ellipticity: sensitivity analysis and application to European strong-motion sites(2013-01)
; ; ; ; ; ; ; ; ; ; ; ; ;Hobiger, M.; Institut des Sciences de la Terre (ISTerre), IRD, IFSTTAR, CNRS, Université de Grenoble I, France ;Cornou, C.; Institut des Sciences de la Terre (ISTerre), IRD, IFSTTAR, CNRS, Université de Grenoble I, France ;Wathelet, M.; Institut des Sciences de la Terre (ISTerre), IRD, IFSTTAR, CNRS, Université de Grenoble I, France ;Di Giulio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Knapmeyer-Endrun, B.; Institut für Geowissenschaften, Universität Potsdam, Germany ;Renalier, F.; Institut des Sciences de la Terre (ISTerre), IRD, IFSTTAR, CNRS, Université de Grenoble I, France ;Bard, P. Y.; Institut des Sciences de la Terre (ISTerre), IRD, IFSTTAR, CNRS, Université de Grenoble I, France ;Savvaidis, A.; Institute of Engineering Seismology and Earthquake Engineering (ITSAK - EPPO), Thessaloniki, Greece ;Hailemikael, S.; Dipartimento della Protezione Civile, Rome, Italy ;Bihan, N.; GIPSA-Lab, CNRS, Grenoble, France ;Ohrnberger, M.; Institut für Geowissenschaften, Universität Potsdam, Germany ;Theodoulidis, N.; Institute of Engineering Seismology and Earthquake Engineering (ITSAK - EPPO), Thessaloniki, Greece; ; ; ; ; ; ; ; ;; ; The knowledge of the local soil structure is important for the assessment of seismic hazards. A widespread, but time-consuming technique to retrieve the parameters of the local underground is the drilling of boreholes. Another way to obtain the shear wave velocity profile at a given location is the inversion of surface wave dispersion curves. To ensure a good resolution for both superficial and deeper layers, the used dispersion curves need to cover a wide frequency range. This wide frequency range can be obtained using several arrays of seismic sensors or a single array comprising a large number of sensors. Consequently, these measurements are time-consuming. A simpler alternative is provided by the use of the ellipticity of Rayleigh waves. The frequency dependence of the ellipticity is tightly linked to the shear wave velocity profile. Furthermore, it can be measured using a single seismic sensor. As soil structures obtained by scaling of a given model exhibit the same ellipticity curve, any inversion of the ellipticity curve alone will be ambiguous. Therefore, additional measurements which fix the absolute value of the shear wave velocity profile at some points have to be included in the inversion process. Small-scale spatial autocorrelation measurements or MASW measurements can provide the needed data. Using a theoretical soil structure, we show which parts of the ellipticity curve have to be included in the inversion process to get a reliable result and which parts can be omitted. Furthermore, the use of autocorrelation or high-frequency dispersion curves will be highlighted. The resulting guidelines for inversions including ellipticity data are then applied to real data measurements collected at 14 different sites during the European NERIES project. It is found that the results are in good agreement with dispersion curve measurements. Furthermore, the method can help in identifying the mode of Rayleigh waves in dispersion curve measurements.302 63 - PublicationRestrictedJoint inversion of Rayleigh wave ellipticity and spatial autocorrelation measurements(2010-09-06)
; ; ; ; ; ; ; ;Hobiger, M.; LGIT, University J. Fourier, Grenoble, France ;Le Bihan, N.; GIPSA-Lab, CNRS, Grenoble, France ;Endrun, B.; University of Potsdam, Germany ;Renalier, F.; LGIT, University J. Fourier, Grenoble, France ;Di Giulio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Savvaidis, A.; ITSAK, Thessaloniki, Greece ;Bard, P.; LGIT, University J. Fourier, Grenoble, France; ; ; ; ; ; The local soil structure (i.e. shear and pressure wave velocities) can be obtained by inversion of dispersion curves ranging over a sufficiently large frequency band. However, measurements of such dispersion curves using ambient seismic vibrations require a large number of seismometers and a long measuring time. As a simple alternative, we propose to invert Rayleigh wave ellipticity obtained by ambient seismic noise measurements at a single site using a method based on the random decrement technique (Hobiger et al., 2009). Indeed, the freSeismological Research Letters Volume 81, Number 2 March/April 2010 305 quency-dependency of Rayleigh wave ellipticity is tightly related to the shear wave profile of the soil. However, as different soil structures can result in the same ellipticity curve (e.g. homothetic structures in velocity and thickness), the inversion of ellipticity curves alone is ambiguous. Therefore, additional measurements fixing the shearwave velocity in the superficial layers have to be included into the inversion process. We suggest using a small number of seismic stations to measure spatial autocorrelation curves. In this way, three seismic sensors and one hour of measurements can be sufficient to invert the local soil structure. We will present the method to extract the Rayleigh wave ellipticity curve, show which parts of the ellipticity curve have to be included in the inversion process and demonstrate the benefit of the additional spatial autocorrelation curve measurements. Then, we will present an example application to real noise data collected within the framework of the European NERIES project at well-known European accelerometric sites and the results will be compared to th197 55