Multi-wave AVO seismic responses of coal bearing strata

The traditional AVA analysis of coal seam is based on the seismic isotropic theory,while the coal seam usu- ally shows the characteristics of small thickness,cross layer distribution,low velocity and low density,which makes the coal bearing strata appears anisotropic. Therefore,the seismic responses of coal bearing strata are difficult to be de- scribed by the seismic isotropic theory. In order to obtain the multi-wave seismic responses more accurately,the coal bearing strata are equivalent to transversely isotropic media with vertical symmetry axis based on the seismic anisotropy and long-wavelength theory. The models are established according to the ratio of the total thickness of coal seam to the coal bearing strata and to the wavelength. By using the reflection coefficient equations of Ruger,the multi-wave seismic responses of different models with varying incident angle are analyzed in terms of AVA curves and AVO gathers. The results show that:both the interlayer structure and the ratio of the thickness of coal seam to the wavelength will affect the multi-wave seismic responses of coal bearing strata. Neglecting the anisotropy of coal bearing strata will cause a large error in the study of actual seismic responses,and using PP wave and PS wave simultaneously can better describe the anisotropy of coal bearing strata.