MASW with Nonlinear Waveform Inverse Theory to Simultaneously Invert Shear Wave and Primary Wave Velocities of Soil Layers

• Main Authors: Yui-teng Lee, 李瑞騰
• Other Authors: 鄭玉旭
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/30073269758745622038

碩士 === 國立聯合大學 === 土木與防災工程學系碩士班 === 98 === This study proposes a nonlinear waveform inversion method combined with multi-channel analysis of surface wave (referred to as MASW) to simultaneously invert shear-wave velocity and pressure-wave velocity of strata profile. This method is first using MASW to convert seismic refraction data to obtain Rayleigh wave dispersion curve, then the nonlinear waveform inversion method is used to simultaneously calculate the shear wave velocity and pressure wave velocity of profiles, thus to improve the shortcomings of MASW which unable to calculate the shear wave velocity and the pressure wave velocity simultaneously. The results revealed that the influence of strata’s Rayleigh wave dispersion curve has four main independent parameters (including shear wave velocity cs, pressure wave velocity cp, thickness h, density ρ), shear wave velocity of which the greatest impact, followed by the stratum thickness and pressure wave velocity, while the density influence is very small. Therefore in the inverse results of formation parameters, the shear wave velocity is also the most accurate, while the density is more difficult to obtain accurate values, so in the practical inversion of velocity parameters can treat the density as a fixed value. This method can be applied to invert all parameters of strata at the same time as well as can also customize the sequence to invert group parameters step by step. In this study, the optimization algorithm in the nonlinear waveform inversion process is employed the quasi-Newton method which has the advantage of rapid convergence. This research supposes five kinds of three layered models (including low-velocity layered model) and obtains the theoretical dispersion curve by the propagator matrix method for the verification of formation parameters inversion. The shear wave velocity and pressure wave velocity profiles of the inversion results are quite correct. Finally, this method is applied to inverse studies of three items of actual seismic data and the results are compared with those from the software package ReMi of MASW.