Evaluating the Correspondence of H/V Spectral ratio to Rayleigh Wave’s Ellipticity

Abstract

Surface wave identification is one of the conventional parts of site effect studies. Geophysical approaches reveal information about the medium that the waves propagate through. In case of site effect studies, researchers are interested in Rayleigh and Love waves. Ambient vibrations, called microtremors, imitate the surface wave’s behaviors which vibrate in low frequencies. Studying particle movements is an important part of surface studies that is describes an ellipse. The ratio of the horizontal to the vertical of the ellipse is called ellipticity. A simple method to evaluate the ellipticity of Raleigh waves uses the ratio of the horizontal to the vertical (H/V) of the Fourier transform of microtremors spectra. In spite of advantages of this method in the site effect studies due to its simplicity and low price, researchers have been investigating the disagreement of H/V spectral ratio shape and Rayleigh waves; the Rayleigh wave curve consist of a peak and a drop after the peak, however, in most of the H/V spectral ratio studies, the curve just illustrate the peak while the drop is omitted. The differences between the Rayleigh wave and H/V spectral ratio curve have been compared in this paper. To this end, microtremor data from seven stations from different sites were evaluated. The results confirm that the H/V spectral ratio curves imitate the same trend as Rayleigh waves, while the wave sources, the data processing approach, site effects, wave interferences and subsurface topography are identified as sources that cause mismatch between Rayleigh wave and H/V spectral ratio curves.