【摘要】 针对复杂近地表地震波旅行时层析成像的数据特征,设计和推导了基于广义逆的近似算法,避开了大型矩阵的求解问题,提出了复杂近地表速度广义近似反演方法。这种广义近似反演方法是一种考虑了复杂地表区地震记录旅行时拾取误差的层析成像方法,能够获得较稳定的近地表速度模型。根据旅行时误差与速度模型误差的关系,给出了误差传递方程,可应用于反演精度的控制。将广义近似层析反演方法应用于南方海相碳酸盐岩复杂地表区实际地震资料,用炮检距小于2 500m的旅行时数据反演出了射线分布与近地表速度模型。针对无约束广义近似层析反演结果存在的射线分布不均衡问题,提出了4种约束方法,获得了较好的射线覆盖,反演出的速度分布清晰地展示出近地表地层结构。用3 200m/s作为门槛值划分出低、降速带后,将约束广义近似层析反演的速度模型用于地震资料静校正,消除了复杂近地表对反射波旅行时的影响,得到了理想的反射波同相轴形态。更多还原

【Abstract】 Aiming at the data characteristics of the seismic wave traveltime tomography imaging for complex nearsurface structures,the approximate algorithm based on generalized inverse was designed and deduced.Meanwhile,ageneralized approximate inversion method was put forward to avoid the problem of solving a large matrix.The generalized approximate inversion is a kind of tomography method which considers the picking error of traveltime on seismic records for complex near-surface structures and can obtain relatively stable near-surface velocity model.In terms of the relationship between the error of traveltime and velocity model,the error propagation equation is given,which is expected to control the inversion accuracy.The generalized approximate tomography inversion method is applied to the seismic data from the southern marine carbonate area with complex surface conditions;the traveltime data(offset smaller than 2500m)is used to invert the distribution of seismic ray and near-surface velocity model.For uneven distribution of seismic ray in unconstrained inversion,four constraint methods are proposed to get a better ray coverage.The inverted velocity model shows clear near-surface structure.By setting 3 200m/s as threshold for classifying low-velocity layer and normal-velocity layer,statics are calculated and applied on seismic records.This eliminates the impact of complex near-surface conditions on reflection traveltime and restores hyperbolic characteristic of reflection events.更多还原