Investigation of very shallow structures with the inversion techniques of multichannel surface wave data

In this thesis study, the applicability of the multichannel active surface wave analysis (MASW) to the near surface structures was investigated. Dispersive properties of the Rayleigh type surface waves were exploited to obtain S-wave velocity profiles. The process of obtaining the S-wave velocity profiles with the MASW was achieved in three stages as collection of data of multichannel surface waves, determination of dispersion curve and inversion.Firstly, the accurateness of MASW results depends on the appropriate selections of parameters including seismic source used in the data collection, near offset spread, geophone separation and geophone frequency. Parameter selection for this purpose was investigated with the experimental measurements in the antique town of Magnesia. The experimental results indicated that offset distance which was three times as the geophone offset was appropriate for shallow underground structures, and the results with different near offset distances indicated that use of 14 Hz geophone was more successful than 4.5 Hz geophone when seismic source and geophone separation were considered. Secondly, MASW calculation method was used to obtain the dispersion curves from the surface wave data recorded in the time-distance domain.Thirdly, the local (Levenberg-Marquardt) and global (Genetic Algorithm) optimization methods were used to obtain S-wave velocity profiles. Also, a Hybrid optimization method has been developed in this study to eliminate the problems which have been encountered in the solutions of the local and global algorithms. The results show that the Hybrid inversion method is more successful in calculations than the classical local and global optimization approaches.