Effects of Love waves on microtremor H/V ratio amplitude

Titre du congrès :14th International Union of Geodesy and geophysics Ville du congrès :Perugia Date du congrès :02/07/2007

The H/V method has the potential to significantly contribute to site effects evaluation, in particular in urban areas. Within the SESAME European project (Site EffectS assessment using AMbient Excitations) we investigate the nature of ambient seismic noise in order to assess the reliability of this method. Through 1D seismic noise modeling, we simulate the ambient noise for a set of various horizontally stratified structures. We perform array analysis (f-k) for both vertical and horizontal synthetics and estimate the contribution of different seismic waves (body/surface waves, Rayleigh/Love waves) at the H/V peak frequency. We show that the very common assumption according which almost all the noise energy would be carried by fundamental mode Rayleigh waves is not justified. The proportion of different waves is dependent on site conditions, especially the impedance contrast. However, for the 1D horizontally layered media presented here and whatever the H/V peak origin (Rayleigh waves ellipticity, Love waves Airy phase, or the S-wave resonance), the H/V peak frequency always provides a good estimate of the fundamental resonance frequency; while the H/V peak amplitude is controlled by the relative proportion of Love waves in the horizontal ambient noise wavefield.