N. Bouden-Romdhane - Assoc.Professor, Department of Civil Eng., Ecole Nationale d’Ingénieurs de Tunis, Tunis, Tunisia
P. Mechler - Professor, Director of Applied Geophysics Department, Université Pierre et Marie Curie, Paris, France

Uninterrupted weak motion measurements (SSR method) for the assessment of the seismic site effect encounter major practical difficulties, mainly the difficulty of carrying acquisition in noisy urban area. When the weak seismicity is worsened by high levels of background noise, the seismic site response can be masked on large frequency windows, often the most useful in earthquake engineering.We propose here a new method to overcome this problem, by using an optimum Wiener filtering. The application of the Wiener filter allowed us to increase the frequency range over which the spectral ratio is used.