On the relationship of peaks and troughs of the ellipticity (H/V) of Rayleigh waves and the transmission response of single layer over half-space models

Abstract

SUMMARY One of the key challenges in the context of local site effect studies is the determination of frequencies where the shakeability of the ground is enhanced. In this context, the H/V technique has become increasingly popular and peak frequencies of H/V spectral ratio are sometimes interpreted as resonance frequencies of the transmission response. In the present study, assuming that Rayleigh surface wave is dominant in H/V spectral ratio, we analyse theoretically under which conditions this may be justified and when not. We focus on ‘layer over half‐space’ models which, although seemingly simple, capture many aspects of local site effects in real sedimentary structures. Our starting point is the ellipticity of Rayleigh waves. We use the exact formula of the H/V‐ratio presented by Malischewsky & Scherbaum (2004) to investigate the main characteristics of peak and trough frequencies. We present a simple formula illustrating if and where H/V‐ratio curves have sharp peaks in dependence of model parameters. In addition, we have constructed a map, which demonstrates the relation between the H/V‐peak frequency and the peak frequency of the transmission response in the domain of the layer's Poisson ratio and the impedance contrast. Finally, we have derived maps showing the relationship between the H/V‐peak and trough frequency and key parameters of the model such as impedance contrast. These maps are seen as diagnostic tools, which can help to guide the interpretation of H/V spectral ratio diagrams in the context of site effect studies.

Antarctic ice sheet thickness estimation using the horizontal-to-vertical spectral ratio method with single-station seismic ambient noise

“…Konno and Ohmachi (1998) found such feature in the H / V spectrum in the case of a soft sediment layer atop a hard bedrock. As pointed out by Tuan et al (2011), the appearance of a trough probably suggests that the overlying layer has higher Poisson's ratio (or impedance contrast) than that of the underlying layer. Despite this, the H / V peak frequency is commonly accepted as a proxy for the resonance frequency of a particular layer.…”

Application of Surface-Wave Methods for Seismic Site Characterization

“…As an example, the NHV values around the maximum have been discarded by Parolai et al (2006) and instead taken into account by D'Amico et al (2008). Recent theoretical studies Albarello and Lunedei 2010;Tuan et al 2011) indicated that the NHV curve around the fundamental resonance frequency f 0 (i.e., around the NHV maximum) can be significantly affected by the damping profile in the subsoil and by the distribution of sources around the receiver. In particular, they showed that sources located within a few hundred meters of the receiver can generate seismic phases that strongly affect the shape of the NHV curve around and below f 0 .…”

“…An analogous approach was also proposed by considering earthquake records (Lermo and Chavez-Garcia 1993), but, being not directly related to surface waves analysis (at least in its original form) it will not be discussed here. Theoretical considerations (e.g., Tuan et al 2011) and numerical modelling (e.g., Lunedei and Albarello 2010) suggest that the pattern of the H/V ratios vs. frequency (NHV curve) presents a complex relationship with subsoil major features. On the other hand, most researchers, on the basis of comparison of noise H/V spectral ratios and earthquake site response, agree that, at least with respect to simple stratigraphic configurations, the maximum of the NHV curve provides a fair estimate of the fundamental resonance frequency of a site.…”

New developments in ambient noise analysis to characterise the seismic response of landslide-prone slopes

“…Indeed, considering that on soft soil body wave contribution to noise vertical ground motion is dominated by P waves, a strong contrast of V p values between shallow layer and substratum would imply a decrease of H /V ratios as effect of vertical motion amplification; on the other hand, low V p values at surface generally implies a low Poisson's ratio as well, which can cause a considerable decrease of Rayleigh wave ellipticity (Tuan et al, 2011).…”