oa Seismic wavefield distortion due to near surface anisotropic anomalies

It is important to take anisotropic properties into account for estimating accurate geological structure in seismic surveys. The recent development of unconventional hydrocarbon reservoirs has revealed that subsurface materials are much anisotropic than expected. Near surface materials could also be strongly anisotropic when complex nature of observed seismic waveforms and unconsolidated near surface sediments are considered. The effect of "strong" anisotropy on the behavior of seismic waves is still not well understood. In this study, we investigate the influence of strong anisotropy on received seismic waveforms using two three-dimensional numerical models to seeif near surface anisotropy is detactable or not. Our numerical models contain an isotropic and an anisotroic layer, respectively, in the subsurface. We took the difference of the received waveforms between the two models to see how the anisotgropic layer influeces the waveforms based on the orbital analysis of particle motion of the residual wavefield. Our results show that there are meaningful changes in the received waveforms mainly due to P-wave and converted-wave that are generated by the anisotropy layer. We concluded that analysis of waveforms is valid for estimating the anisotropic structure in the subsurface.