为了解决弹性波计算机断层(Computed Tomography,CT)工程速度反演在地下孤石探测时效果较差的问题,借鉴电磁波CT能量衰减方式进行弹性波CT衰减系数反演,以直达波第一个波峰幅值平方作为波形能量值,进行距离校正后,作归一化处理,拟合出单炮震源与检波器间扇形区域的介质整体衰减系数。根据拟合相对误差,计算出震源到各检波器间介质直线衰减系数,反演出衰减系数剖面,作为异常判别依据。经过武汉地铁机场线孤石弹性波CT勘察工程实际应用,结果表明:衰减系数反演对于小缺陷的灵敏性高于速度反演;衰减系数反演得到的衰减系数相对极差大于速度反演得到的速度相对极差,更利于异常划分。研究成果可供弹性波CT工程技术人员参考。

With reference to the energy attenuation of electromagnetic wave CT, we present a method for the attenuation inversion of elastic wave CT in an attempt to improve the unsatisfying efficiency of velocity inversion in detecting underground boulders. The square value of the first arrival peak of direct wave was regarded as the waveform energy value. First of all, the coefficient of holistic attenuation in the triangle medium between the single stimulation source and all geophones was calculated after distance correction and normalization processing. Subsequently the coefficient of linear attenuation in the medium from the source to each geophone was calculated according to the fitted relative error. The attenuation coefficient section was then obtained by inversion to be taken as the basis of abnormal discrimination. Practical application of this method to the exploration of boulders in the airport line of Wuhan Metro proves that inversion of attenuation coefficient is more sensitive to small defects than velocity inversion. The relative extreme difference of attenuation coefficient is larger than that of velocity, hence is more conducive to abnormal discrimination.