THE SESAME PROJECT : AN OVERVIEW AND MAIN RESULTS

Recent years have seen many studies using ambient vibration measurements for a priori estimations of site effects: assessing the actual reliability of such results is a major challenge for engineering seismologists in order to both foster their use and prevent their misuse, for an improved, cost-effective and reliable risk mitigation. Such an assessment has been one of the major objectives of the SESAME European project. Two techniques the very simple H/V technique ('Nakamura'), and the more advanced array technique have been thoroughly considered under different viewpoints, in order to a) better understand their physical basis, b) assess their actual meaning in view of site effect estimation, and c) propose user guidelines and processing software to ensure a correct use. After a brief presentation of the overall architecture of the 3year project (2001-2004), the main accomplishments and findings are outlined. Comparing the results of noise numerical simulation with actual observations allowed to draw some conclusions on the composition of the actual noise wavefield, and on the ability of H/V and array techniques to deal with 2D or 3D structures. Comprehensive tests and checks allow to better assess the reliability and meaning of H/V measurements, especially as a standard processing software is now proposed together with user guidelines. A lot of theoretical and software development could also be achieved in relation with the array techniques, leading to a set of practical recommendations and analysis tools. The project certainly does not pretend to answer all the issues regarding noise measurements, but it is hoped that the scientific outcomes and the resulting practical recommendations and guidelines, freely distributed through the SESAME web site http://SESAME-FP5.obs.ujf-grenoble.fr, will be helpful for site effect assessment and improved seismic risk mitigation, especially in developing countries and moderate seismicity areas..