First-arrival wave travel time-based tomography inversion with surface wave information as constraints
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摘要: 射线层析反演过程中,有多种因素都会影响反演效果,如初始模型误差、低速夹层等。传统的初至波走时层析成像方法对模型进行约束或平滑处理,不仅会破坏模型参数与射线之间的相对关系,还会影响反演的稳定性。本文首先测试了不同初始模型下初至波走时层析反演的效果,提出一种面波信息约束的初至波走时层析反演方法。地震数据中面波具有能量强以及频散的特性,通过多道面波分析方法获取面波频散曲线,采用阻尼最小二乘法反演浅地表横波速度,以横波速度结构作为约束,建立纵波初始模型,在此基础上实现带有正则化的初至波走时层析反演。该方法充分利用了地震数据中的面波信息,弥补了层析反演的固有缺陷,提高了浅层结构反演的精度与稳定性,利用实际资料测试了该方法的有效性。Abstract: The performance of ray-based tomography inversion is affected by many factors,such as initial model error and low-velocity interlayer.The conventional tomography method based on first-arrival wave travel time,which constrains or smooths models,destroys the relative relationship between model parameters and rays and affects the inversion stability.By testing the performance of first-arrival wave travel time-based tomography inversion under different initial models,this study proposed a first-arrival wave travel time-based tomography inversion method with surface wave information as constraints.The process of this method is as follows:(1)Given that surface waves feature high energy and frequency dispersion in seismic data,the surface-wave frequency dispersion curves are obtained through the multi-channel analysis of surface waves;(2)Using the damped least squares method,the shallow-surface shear wave (S-wave) velocities are determined through inversion;(3)With the S-wave velocity structure as the constraint,the initial compressional wave (P-wave) model is established,and accordingly,the first-arrival wave travel time-based tomography inversion that considers regularization is achieved.This method improves the accuracy and stability of shallow structure inversion by fully utilizing the surface wave information in seismic data to counteract the inherent defects of tomography inversion.The effectiveness of this method has been verified using actual data.
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