1. School of Geosciences,China University of Petroleum(East China),Qingdao,Shandong 266555,China;
2. Research Institute of Petroleum Exploration and Development,Tarim Oilfield Company Ltd.,Pet-rochina,Korla,Xinjiang 841000,China
Abstract：We discuss in the paper frequency changecaused by stratum absorption and thin-layer filter,and find that both of them can cause the center Ere-quency shifted to the lower direction. Using pre-stack seismic data, a new conception called FVOrelative gradient is proposed based on a time-fre-quency S transform analysis method.And then,approximate relationship between the center Ere-quency and offset in the absorbing media is de-rived.With different distribution model analysis，we have found that the center frequency of the ab-sorption model moves toward lower frequency withoffset increase.Finally，four models are built toestimate the FVO relative gradient，which is esti-mated from synthesis CMP gathers numericallysimulated by nonzero-offset one-way wave equa-tion. The numerical result indicates that FVO rela-tive gradient can distinguish thick absorption medi-um with thin inter-bedded medium.
