Effects of seawater layer on seismic reflection characteristics

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.