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面波多道分析方法(MASW)是获取垂向剪切波速度剖面的一种有效方法。频散曲线反演是MASW中关键的一步。由于瑞雷波频散曲线反演具有非线性、多参数和多极值的特征,这对于常规的局部线性化反演方法是极大的挑战。为此,本文采取确定性的全局优化算法,广义模式识别算法(GPS)对瑞雷波频散曲线进行反演。其原理可以简述为:算法首先通过模式以确定性的方式对目标函数进行采样来搜索一个点序列;然后使序列中每一个点到下一个点的目标函数值逐渐减少,从而使点序列逐渐逼近全局最优解,最后的解便为待求的最优模型参数。为验证GPS的有效性,首先利用设计的3种典型的6层地质模型通过快速矢量传递算法正演模拟产生基模式频散曲线(频率范围为5~101 Hz,频率间隔为2 Hz,频点数为49),并对理论频散曲线进行反演。反演结果表明,模型的真实值已经被高度精确地重建。说明GPS可以用于实际勘探中的基模式频散曲线反演。为进一步验证GPS的有效性,在吉林大学校园采集瑞雷波实测数据,并提取基模式频散曲线,应用GPS进行反演。反演重建的横波速度剖面与先验的地质信息吻合得很好。理论模型和真实数据的反演结果表明,GPS可以应用在瑞雷波频散曲线非线性反演中。
Multi-channel surface analysis method (MASW) is an effective method to obtain the vertical shear wave velocity profile. Dispersion curve inversion is a key step in MASW. Due to the non-linear, multi-parameter and multi-extremum characteristics of Rayleigh wave dispersion curve inversion, this is a great challenge for the conventional local linearization inversion method. To this end, this paper takes a deterministic global optimization algorithm, generalized pattern recognition algorithm (GPS) to inverse Rayleigh wave dispersion curve. The principle can be briefly described as follows: Firstly, the algorithm searches for a sequence of points by sampling the objective function in a deterministic way through the pattern; and then gradually decreases the value of the objective function from every point to the next in the sequence, Approximating the global optimal solution, the final solution is the optimal model parameter to be solved. In order to verify the validity of GPS, first, three kinds of typical 6-layer geological models are designed to generate base-mode dispersion curves by forward modeling of fast vector transfer algorithm (the frequency range is 5 ~ 101 Hz, the frequency interval is 2 Hz, the number of frequency points 49), and the theoretical dispersion curve inversion. Inversion results show that the true value of the model has been reconstructed with high accuracy. This shows that GPS can be used for inversion of base-mode dispersion curves in actual exploration. In order to further verify the validity of GPS, the measured data of Rayleigh wave were collected on the campus of Jilin University, and the dispersion curve of base mode was extracted, and GPS was used for inversion. The inversion of the reconstructed shear-wave velocity profile is in good agreement with the prior geological information. The inversion results of theoretical model and real data show that GPS can be used in nonlinear inversion of Rayleigh dispersion curve.