【摘要】 本文从衍射波的物理定义出发,简化了Trorey提出的断层上Kirchhoff-Helmholtz衍射方程的解法;计算了不同深度、不同测线方向下的断层衍射波理论地震图;计算了衍射波振幅谱与相位谱,给出了利用衍射波求断层位置的公式;得出了一些新的结论,通过人工地震测深与地震勘探的实例,对断层衍射波的特性有了更明确的认识。 本文的结果表明:断层衍射波发生在地球介质剧烈变化处;衍射点两侧的衍射波走时曲线呈双曲线状;波初动清晰且半周期小;其优势频率振幅谱与反射波的相同,在衍射波与反射波走时曲线相切处附近,记录图中出现衍射波最大振幅,且波反相;视断点与真实断点一般不重合。上述特点可能为判定衍射波并确定断层位置提供判据。更多还原

【Abstract】 According to the physical definition of diffracted wave, the solution of Kirchhoff-Helm-holtz diffraction equation at a fault give by Trorey is simplified and developed. Synthetic seismograms of diffracted wave at a fault of different depths and from different directions to the profile are computed, and compared with corresponding reflected wave. The amplitude spectrum and phase spectrum of diffracted wave on both sides of a fault are computed. Some usable formulas using diffracted wave along a profile for locating a fault are presented. Two practical examples are given for studying particular characteristics of diffracted wave at a fault.Results indicate that the diffracted wave at a fault originates from an abrupt change in the medium. On both sides of a diffraction point, the travl-time curve of diffracted wave is a hyperbola. The first arrival of the diffracted wave is distinct and with short half-period, and its amplitude spectrum at predominant frequency is similar to that of reflected wave. It is noted that at the tangent point of the travel-time curves of diffracted and reflected waves, the amplitude of the diffrated wave is maximum, but the phase is opposite to that of the reflected wave. The apparent diffracting point does not coincide with the real one. These charateristics might offer a criterion for identifying the diffracted waves and the position of a fault.更多还原