含流体孔隙介质中面波的传播特性及应用  

Characteristics and application of surface wave propagation in fluid-filled porous media

作　　者：张煜[1,2,3,4] 徐义贤[4,5] 夏江海[4] 张双喜[1,2,3] 平萍[6,4] 

机构地区：[1]武汉大学测绘学院,武汉430079 [2]武汉大学地球空间环境与大地测量教育部重点实验室,武汉430079 [3]武汉大学地球空间信息科学协同创新中心,武汉430079 [4]中国地质大学(武汉)多尺度地球成像湖北省重点实验室,武汉430074 [5]中国地质大学(武汉)地质过程与矿产资源国家重点实验室,武汉430074 [6]中国科学院测量与地球物理研究所大地测量与地球动力学国家重点实验室,武汉430074

出　　处：《地球物理学报》2015年第8期2759-2778,共20页Chinese Journal of Geophysics

基　　金：国家重点基础研究计划(2013CB733303);国家自然科学基金(41304077;40974079);中国博士后科学基金(2014T70740;2013M531744);教育部地球空间环境与大地测量重点实验室(12-02-03);湖北省多尺度地下成像重点实验室(SMIL-2014-01)联合资助

摘　　要：基于单相介质中地震波理论的高频面波法已广泛应用于求取浅地表S波的速度.然而水文地质条件表明,普遍的浅地表地球介质富含孔隙.孔隙中充填的流体会显著地影响面波在浅地表的传播,进而造成频散和衰减的变化.本文研究了地震勘探频段内针对含流体孔隙介质边界条件的面波的传播特性.孔隙流体在自由表面存在完全疏通、完全闭合以及部分疏通的情况.孔隙单一流体饱和时,任何流体边界条件下存在R1模式波,与弹性介质中的Rayleigh波类似,相速度稍小于S波并在地震记录中显示强振幅.由于介质的内在衰减,R1在均匀半空间中也存在频散,相速度和衰减在不同流体边界下存在差异.Biot固流耦合系数(孔隙流体黏滞度与骨架渗透率之比)控制频散的特征频率,高耦合系数会在地震勘探频带内明显消除这种差异.介质的迂曲度等其他物性参数对不同流体边界下的R1波的影响也有不同的敏感度.完全闭合和部分疏通流体边界下存在R2模式波,相速度略低于慢P波.在多数条件下,如慢P波在时频响应中难以观察到.但是在耦合系数较低时会显现,一定条件下甚至会以非物理波形式接收R1波的辐射,显示强振幅.浅表风化层低速带存在,震源激发时的运动会显著影响面波的传播.对于接收点径向运动会造成面波的Doppler频移,横向运动会造成面波的时频畸变.孔隙存在多相流体时,中观尺度下不均匀斑块饱和能很好地解释体波在地震频带内的衰减.快P波受到斑块饱和显著影响,R1波与快P波有更明显关联,与完全饱和模型中不同,也更易于等效模型建立.频散特征频率受孔隙空间不同流体成分比例变化的控制,为面波方法探测浅地表流体分布与迁移提供可能性.通常情况孔隙介质频散特征频率较高,标准线性黏弹性固体可以在相对低频的地震勘探频带内等效表征孔隙介质中R1波的传播特�High frequency surface wave method based on seismic wave propagation in single-phase media has been widely applied for acquiring near surface shear wave velocity in several fields.However,the near surface earth media,consolidated and unconsolidated,for the general hydrogeological conditions,bear plenty of pores.Fluid in pores affects the surface wave propagation in the media remarkably,which is represented in dispersion in velocity and attenuation.The pore fluid behaviors through the free surface make the boundary more complex as fully drained,fully sealed and partially drained conditions.These effects are taken into account in surface wave secular equation derivation and closed-form dynamic response investigation.Complex searching algorithm and fast coverage quadrature are applied in the dispersion and response calculation.Typical near surface earth media are selected.For weakly consolidated media in which the surface wave propagates in an extremely low velocity,the effects of the motion of source are obtained.The partial saturation of mesoscopic loss significant in seismic frequency band is introduced beyond the Biot model.The effective viscoelastic model that has been used for body waves in porous media is extended to solve the boundary value problem of surface wave propagation by coupling body wave representations on the free surface.For one fluid saturated,R1 mode wave can propagate under each boundary condition,which is similar with classic Rayleigh wave in elastic media.Its phase velocity is a little less than the S wave and amplitude is strong in seismograms.Due to the intrinsic attenuation,R1 wave is dispersive in the homogeneous half space.The velocities and attenuation coefficients are different under different fluid boundary conditions.Biot solid-fluid coupling coefficient controls the critical frequency of dispersion as for the body waves.High solid-fluid coupling can eliminate the differences.Tortuosity affects R1 waves for different fluid boundaries with different sensitivities.R2 mode appears and

关 键 词：流体 孔隙介质 面波 频散 衰减 

分 类 号：P631[天文地球—地质矿产勘探]