TOWARDS THE DEFINITION OF REFERENCE MOTIONS 1000 ≤ VS ≤ 3000 M-S: ANALYSIS OF THE KIK-NET DATA AND CORRECTION OF THE LOCAL SITE EFFECTSReport as inadecuate




TOWARDS THE DEFINITION OF REFERENCE MOTIONS 1000 ≤ VS ≤ 3000 M-S: ANALYSIS OF THE KIK-NET DATA AND CORRECTION OF THE LOCAL SITE EFFECTS - Download this document for free, or read online. Document in PDF available to download.

1 LDG - Laboratoire de Détection et de Géophysique CEA 2 ISTerre - Institut des Sciences de la Terre 3 Centre de recherche du Commissariat à l-Energie Atomique - CEA Cadarache Saint Paul-lez-Durance, France 4 University of Greenwich

Abstract : A 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.





Author: Aurore Laurendeau - Pierre-Yves Bard - Fabrice Hollender - Olga-Joan Ktenidou - Laetitia Foundotos - Bruno Hernandez - Vincent Pe

Source: https://hal.archives-ouvertes.fr/



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