Inversion généralisée de données accélérométriques KIK-net, comparaison à d'autres approches d'évaluation de l'effet de site et implications sur la détermination de Ko

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Optimization of a simulation code coupling extended source (k−2^{−2}) and empirical green’s functions: Application to the case of the middle durance fault

International audienceWe developed a ground-motion simulation code base on extended rupture modeling combined with the use of empirical Green’s functions (EGFs), adapted for low-to-moderate seismicity regions (with a limited set of EGFs), and extended its range of applicability to the lowest source-to-site distances. This code is based on a kinematic source description of an extended fault and is designed to allow complex fault geometries and togenerate a ground motion variability in agreement with that of the recorded databases. The code is developed to work with a sparse set of EGFs. Each available EGF is therefore used in several positions on the rupture area. To be used in positions different of their original position, we applied to the EGFs some adjustments. In addition to the classical adjustments (i.e. time delay correction, geometrical spreading correction and anelastic attenuation correction), we propose here a radiation pattern adjustment. The effectiveness of it is tested in a numerical application. We showed noticeable improvements at the lowest distances, and some limitations when approaching the nodal planes of the subevents the recording of which were used as EGFs. We took advantage of the development of this code, its ability to work with a sparse set of EGFs, its ability to take into account complex fault geometries and its ability to master the general variability, to perform a groundmotion simulation scenario on the Middle Durance Fault (MDF).We perform simulations for a hard rock site (V$_{S30}$ = 1800 m/s) and a sediment site (V$_{S30}$ = 440 m/s) of the CEA Nuclear Research Site of Cadarache (France), and compared the computed ground motion with several ground motion prediction equations (GMPEs). The GMPEs slightly underestimate the sediment site but strongly overestimate the ground motion amplitude on the hard rock site, even when using a specific correction factor which adapts GMPEs predictions from rock site to hard rock site. This general ascertainment confirms the need to continue efforts towards the establishment of consistent GMPEs applicable to hard-rock conditions

TOWARDS THE DEFINITION OF REFERENCE MOTIONS (1000 ≤ VS ≤ 3000 M/S): ANALYSIS OF THE KIK-NET DATA AND CORRECTION OF THE LOCAL SITE EFFECTS

International audienceA key scientific component in Seismic Hazards Analysis (SHA) is the assessment of a local hazard for hard rock sites (1000 < V S30 < 3000 m/s), either for applications to installations built on this site category, or as a reference motion for site effect computation. Within the context of SHA, empirical ground motion prediction equations (GMPEs) are the traditional basis for estimating shaking intensities and V S30 , the time-averaged shear-wave velocity in the upper 30 meters from the surface, is the basis to account for site conditions. The current GMPEs, however, are not well constrained for V S30 larger than 1000 m/s (only a few records on high V S30 sites are included in the main accelerometric databases). The presently used approach is based on host-to-target adjustment techniques based on V S30 and κ 0 values. This study is investigating alternative methods to estimate reference motions on site effect free, very hard rocks (1000 < V S30 < 3000 m/s). We explore methodologies to obtain a prediction for reference motions (1000 < V S30 < 3000 m/s) by using the " rock " Japanese KiK-net sites with 500 < V S30 < 1350 m/s. Each site presents the advantages of having sensor pairs (one at the surface, and one installed in a borehole at depth between 100 and 200 m for most sites and up to 2000 m) and geotechnical characterization (P-and S-wave velocity profiles) for surface and down-hole sensors. Firstly, the " rock " transfer functions are estimated in two ways: empirically (spectral ratios between surface and depth records) and theoretically (linear SH1D simulation). These two approaches are compared to validate the input parameters and also to select the stations for which the 1D approximation is verified. Then, two new accelerometric datasets characterizing hard rock sites (1000 < V S30 < 3000 m/s) in free surface condition are developed: 1. Down-hole recordings are modified from within motion to outcropping motion with the depth correction factor developed by Cadet et al. (2012), 2. Surface recordings are deconvolved from site-specific effects with a (surface / outcrop rock) amplification factor derived with the site velocity profile and 1D simulation. GMPEs with simple functional forms are then developed for each dataset, with a site term based on V S30 (assumed to be equal to V S at downhole sensor depth) and the results are compared, for a specific scenario, to the result obtained with the traditional host-to-target adjustment approach: our hard-rock GMPEs lead to significantly lower estimates at short periods

Numerical and Empirical Simulation of Linear Elastic Seismic Response of a Building: The Case of Nice Prefecture

International audienceThe structural motion of a tall reinforced concrete (RC) building on alluvial soil in Nice (France) is continuously recorded using accelerometers. The structural behavior of the building is studied using operational modal analysis (OMA) to identify its dynamic properties, a finite element (FE) model to reproduce the building response, and empirical Green's functions (EGFs) to generate the structural response to ground motions stronger than those registered in the analyzed seismic area. These different approaches are applied for the analysis of seismic response of the instrumented building and results are consistent. The FE model is calibrated by comparing natural frequencies and mode shapes with those obtained using OMA. Numerically-simulated time histories are qualitatively and quantitatively compared with recordings showing good agreement. Based on regional earthquakes, linear seismic response of the building is simulated for a stronger scenario earthquake using EGF. This approach allows for structural deformation analysis of existing buildings without the need of structural plans and mechanical parameter calibration in the case where the seismic response is within linear elastic regime

Characterization of site conditions (soil class, VS30, velocity profiles) for 33 stations from the French permanent accelerometric network (RAP) using surface-wave methods

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