瑞利波勘探中“之”形频散曲线的形成机理及反演研究

MECHANISM OF ZIGZAG DISPERSION CURVES IN RAYLEIGH EXPLORATION AND ITS INVERSION STUDY

对瑞利波勘探中“之”字形频散曲线形成的物理机理进行了理论分析，研究了诸波模的传播特性及相互关系．指出在地表下存在具有水平界面的软弱夹层和地层裂缝时，瑞利波频散曲线中的“之”字形结构是低速夹层或地层裂缝中出现多模现象的结果．利用阻尼最小二乘法和遗传算法对瑞利波频散曲线反演介质参数进行了研究和分析，发现最小二乘法不适合瑞利波“之”字形反演问题研究，而用遗传算法得到了较好的结果．

The mechanism of zigzag dispersion curves in the Rayleigh wave exploration is theoretically analyzed. The propagation characteristics and interrelation of the guided waves are studied thoroughly. It is presented that the zigzag stature of Rayleigh wave dispersion curves is the result of many modes generated by the low-velocity layers or fractures in multilayered. The inverse problems are also investigated on the formation structure with the dispersion curves of the Rayleigh wave by the damping method of least squares and the genetic algorithm. It is found that the damping method of least squares is not suitable to the inversion of zigzag dispersion problem of Rayleigh wave, while the genetic algorithm is a good method for this problem.