Experimental Relationship Between Ambient Vibration H/V Peak Amplitude and Shear‐wave Velocity Contrast

Originally proposed by Nogoshi and Igarashi (1970, 1971), the ambient vibration H/V spectral ratio (HVSR) method consists of estimating the ratio between the Fourier amplitude spectra of the horizontal (H) to vertical (V) components of ambient noise vibrations recorded at a single station. This method, widespread by Nakamura (1989, 2000), is now widely used for evaluation of site effects and in seismic micro‐zoning studies (e.g., Gueguen et al. , 2000; Alfaro et al. , 2001; Duval et al. , 2001; Guillier et al. , 2004; Panou et al. , 2005; Chatelain et al. , 2008a; Bensalem et al. , 2010; Hellel et al. , 2010). These studies are based on the HVSR peak‐frequency value and distribution, which reflect both the value and spatial variation of the soft sediment topmost‐layer resonance frequency. The frequency of the HVSR peak is related to the topmost‐layer thickness, while its amplitude is proportional to the shear‐wave velocity contrast between the surficial layer and the underlying seismic bedrock. The shape of the HVSR curve is controlled by the S ‐wave transfer function between the underlying rock and the surface sediments. Theoretical investigations of 1D structure from synthetic noise have shown that the HVSR peak is pronounced around the S ‐wave fundamental frequency when the surficial layer has a sharp shear‐wave velocity contrast with the seismic bedrock (Field and Jacob, 1993; Lachet and Bard, 1994; Lermo and Chavez‐Garcia, 1994; Wakamatsu and Yasui, 1996; Tokeshi and Sugimura, 1998). To our knowledge, no experimental study has yet been completed on this subject. A second peak may appear on HVSR curves, indicating the …