Guidelines for implementation of the H/V spectral ratio technique on ambient vibrations measurements, processing and interpretation. SESAME European research project WP12 - Deliverable D23.12. European Commission - Research General Directorate. Project No. EVG1-CT-2000-00026 SESAME.

The horizontal-to-vertical (H/V) method has the potential to significantly contribute to site effects evaluation, in particular in urban areas. Within the European project, site effects assessment using ambient excitations (SESAME), we investigated the nature of ambient seismic noise in order to assess the reliability of this method. Through 1D seismic noise modeling, we simulated ambient noise for a set of various horizontally stratified structures by computing efficiently the displacement and stress of dynamic Green's functions for a viscoelastic-layered half-space. We performed array analysis using the conventional semblance-based frequence-wavenumber method and the three-component modified spatial autocorrelation method on both vertical and horizontal components and estimated 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 that almost all the ambient noise energy would be carried by fundamental-mode Rayleigh waves is not justified. The relative proportion of different wave types depends on site conditions, and especially on the impedance contrast. For the 1D horizontally layered structures presented here, the H/V peak frequency always provides a good estimate of the fundamental resonance frequency whatever the H/V peak origin (Rayleigh wave ellipticity, Airy phase of Love waves, S-wave resonance). We also infer that the relative proportion of Love waves in ambient noise controls the amplitude of the H/V peak.