采用非稳相偏振滤波的DAS-VSP数据P/S波分离方法及其应用

P/S wave separation of DAS-VSP data with non-stationary polarization filter

分布式光纤声学传感(DAS)因成本低、易布设以及高密度采样等优势正成为重要的地震观测技术,尤其是越来越多地与垂直地震剖面(VSP)结合,用于主动地震勘探或被动地震监测.DAS传感器通过感知弹性波场产生的轴向应变或应变速率来观测地震波场振动.然而,目前单分量DAS-VSP数据未完整地记录地下弹性波场的三维矢量振动信号,因此如何从中分离出P波或S波用于后续地震成像与参数反演是重要且很有挑战的课题.以弹性波传播理论为基础,本文根据P波和S波的频散关系估算接收点处各自的偏振方向,通过随频率和空间位置变化的偏振滤波实现DAS-VSP数据的P/S波分离.理论模型合成数据与东海实际DAS-VSP数据实验结果表明,该方法能有效地将P波和S波信号从单分量DAS-VSP数据中分离出来,可为后续纵横波速度反演、PP与PS波成像提供关键的数据预条件处理.

Distributed acoustic sensing(DAS)has become an important seismic observation technology due to its advantages of low cost,easy deployment and high-density spatial sampling.Particularly,it is increasingly combined with vertical seismic profiles(VSPs)for active seismic exploration or passive seismic monitoring.DAS sensors record seismic signals by detecting axial strain or strain rate generated by elastic wavefield.However,the current single component DAS-VSP data does not fully record the three-dimensional vector vibration signals of the underground elastic wavefield.Therefore,how to separate P or S waves from them for subsequent seismic imaging and parameter inversion is an important and challenging topic.Based on the theory of elastic wave propagation,this paper estimates the polarization directions at the receiver point using the dispersion relationship of P and S waves.The P/S wave separation of DAS-VSP data is achieved through polarization filtering that varies with frequency and spatial position.The results of synthetic data and real DAS-VSP data from the East China Sea indicate that this method can effectively separate P-wave and S-wave signals from single component DAS-VSP data,and provide essential data preconditioning for subsequent P-and S-wave velocity model building and PP/PS imaging.