H/V amplitude ratio measurement using multicomponent ambient noise cross-correlations and its relationship to Vp/Vs

Abstract:

Retrieval of sub-surface V_p-structure using Ambient Noise Cross-Correlation (ANCC) is more challenging than retrieving V_s-structure (by inversion of surface wave dispersion curves), and has been addressed by only a few researchers. We explore the potential of ANCC for V_p-imaging, using Rayleigh wave ellipticity, which has shown higher sensitivity to V_p and ρ in comparison to surface wave phase and group velocity dispersion. Our aim is to study the effect of V_p on H/V ratios measured from multicomponent ANCC waveforms, which are modelled rigorously using spatially uncorrelated but arbitrarily distributed noise sources. We utilize the analytical expression for the Rayleigh wave Green function in a 1-D (vertically stratified) medium. We simulate ANCC waveforms for a suite of subsurface models covering a range of V_p/ V_s values, and compute H/V ratios in each case. The dependence of these measurements on model V_p/V_s is contrasted with the that of the classic Rayleigh H/V, for a variety of source distributions ranging from uniform to strongly anisotropic. Finally, we add noise to our synthetic ANCC waveforms, to assess whether the sensitivity of the mesurements to V_p rises above typical noise levels in passive seismic data.