Estimation of azimuthal angle of S-wave anisotropy using virtual cross-dipole data generated by the Virtual Source Method

Abstract

A novel scheme we proposed for analyzing S-wave azimuthal anisotropic angle in the subsurface below the seafloor has been applied to a tilted transversally isotropic medium of horizontal axis of symmetry (HTI). The proposed method utilizes the virtual source method to acquired data set with single ocean bottom seismometer and an air-gun array. To evaluate the effectiveness of our scheme, we conducted the numerical experiments for 3D model with a tilted anisotropic target. We applied this method to the synthetic data to make the virtual cross-dipole data at each shot location. Finally we applied the Alford rotation to estimate an azimuthal angle of the anisotropy of the target layer. Our numerical results show the limitations of the Alford rotation. Especially, the Alford rotation assumes that a dipole signal in one direction has an amplitude equivalent to the other dipole to the other normal direction in the cross dipole measurements. Since our approach could not assume the equality of the amplitudes for each of the cross dipole signals, we conclude that a strategy using full waveforms needs to be taken into consideration for estimating azimuthal angle of tilted targets.