Research on Inversion of Surface Wave Base Mode Dispersion Curve Based on Generalized Pattern Search

Multichannel Analysis of Surface Waves (MASV0 is an efficient method to obtain the vertical shear-wave profile. Inversion of dispersion curve is a key step of Multichannel Analysis of Surface Waves(MASW).Inversion of Rayleigh-wave dispersion curves is challenging for most local-search methods due to its high nonlinearity, its multiparameters and its multimodality. In this paper, we impIement a deterministic global optimization algorithm named generalized pattern search (GPS). The algorithm is adopted to inverse Rayleigh-wave dispersion curve. The basic principle can be summarized as follows: the objective function is sampled by the algorithm through a pattern in a deterministic way in order to search a point sequence;then the objective function value of each point in the sequence to the next point should be reduced, so that the point sequence gradually approximates the global optimal solution, and the final solution is the optimal model parameter. First of all, the base mode dispersion curve (frequency range is 5-101 Hz, frequency interval is 2 Hz, the number of frequency point is 49) of three typical six-layer geological model is forwarded by the fast vector-transfer algorithm. And the theoretical dispersion curve is inversed. The inversion results show that the true value of the model has been reconstructed with high precision. It is shown that the GPS algorithm can be used for the inversion of the basic mode dispersion curves in actuat exploration. In this paper, we gather the real data of Rayleigh-wave in Jilin University campus and base mode dispersion curve is extracted. The inversion is proceeded in order to verify the effectiveness of GPS algorithms, furtherly. The reconstructed S-wave velocity profile through inversion is in good agreement with prior geological information. The inversion results of theoretical model and real data show that GPS algorithm can be applied to nonlinear inversion of Rayleigh-wave dispersion curves.