摘要:
在海洋地震勘探中,地震反射特征对于AVO分析、海底参数反演以及构造分析等具有重要作用。地震波在海洋中传播,其产生的地震反射特征受到海水层和海底以下沉积物的综合影响,但目前业界主要针对海底以下沉积物对地震反射特征的影响开展研究,关于海水层对地震反射特征影响的研究较少。本文主要研究地震波在海水层中传播时地震波场的变化特征,首先从流体—固体分界面和自由界面的边界条件出发,推导出弹性界面入射和反射时的P-P振幅比,得到海水层效应的数学表达式。然后分析入射波频率、海水层深度、海底阻抗差和入射角等因素对海水层滤波效应的影响,分析结果表明:海水层对于地震P波具有周期性的选频滤波效应;选频滤波效应的周期与入射波频率和海水层深度成反比,与入射角成正比;入射角越大,地震P波衰减越严重;阻抗差对振幅的影响与入射波频率和海水层深度有关。最后利用数值模拟验证了海水层对地震反射特征的影响。
Abstract:
In marine seismic exploration,seismic reflection characteristics play an important role in AVO analysis,inversion for seabed parameters,and structural analysis.When seismic waves propagate in the ocean,their seismic reflection characteristics are affected by the seawater layer and the sediments beneath the seabed.However,previous studies mainly focus on the influence of the sediments beneath the seabed,while there is a lack of studies on the effects of the seawater layer on the seismic reflection characteristics.This study analyzed the changes in the seismic wave field during the seismic wave propagation in the seawater layer.Based on the boundary conditions of fluid-solid and free interfaces,this study derived the P-P amplitude ratio between the incident and reflected waves on an elastic interface and obtained the mathematical expression of the seawater layer effect accordingly.Then,this study analyzed the influencing factors,such as the frequency of incident waves,the depth of the seawater layer,the impedance contrast of the seabed,and the incident angle,on the filtering effect of the seawater layer.The analysis results are as follows:The seawater layer had a periodic frequency selective filtering effect on seismic P-waves;The period of the frequency selective filtering effect was inversely proportional to the frequency of incident waves and the depth of the seawater layer and was directly proportional to the incident angle;A higher incident angle corresponded to severer attenuation of seismic P-waves;The effects of impedance contrast on amplitude was related to the frequency of incident waves and the depth of the seawater layer.Finally,the study verified the effects of the seawater layer on seismic reflection characteristics through numerical simulations.
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