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MASW結合非線性波形反算法同時反算地層剪力波速與壓力波速之研究

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

作者:李瑞騰
畢業學校:國立聯合大學
出版單位:國立聯合大學
核准日期:2010-09-10
類型:Electronic Thesis or Dissertation
權限:Copyright information available at source archive--National United University....

中文摘要

本研究提出以非線性波形反算法(Nonlinear Waveform Inversion Theory)結合多頻道表面波分析法(Multi-channel Analysis of Surface Wave 簡稱MASW)同時推算地層剪力波速與壓力波速剖面,此法先利用MASW轉換折射震測資料以求得雷利波頻散曲線,再利用非線性波形反算法同時推算地層剪力波速與壓力波速剖面,以改進MASW無法同時推算地層剪力波速度與壓力波速度之缺點。由本研究得知影響地層的雷利波頻散曲線有四個主要的獨立參數(包含剪力波速cs,壓力波速cp,地層厚度h,地層密度ρ),其中以剪力波速影響最大,其次為地層厚度與壓力波速度,而密度影響甚小,因此在反算地層參數中,地層剪力波速度的反算結果也最為精確,而密度則較難獲得準確的數值,因此在實際推算地層的波速參數時可將密度視為定值處理。本法可應用於同時推得地層所有的參數,亦可自訂逆推順序推算各參數。本文在非線性波形反算法中進行的最佳化運算採用準牛頓法,此法具有快速收斂性的優點。本研究假定五種三層層狀地層模型(包含低波速層模型),並以傳遞矩陣求得理論頻散曲線,進行地層參數的逆推驗證,得到地層剪力波速與壓力波速剖面的逆推結果相當正確,最後本研究以三筆實際震測資料進行反算研究,並與MASW套裝軟體ReMi的分析結果進行比較。

英文摘要

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 ), 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.

 

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