基于附加层法的非规则剖面的瑞利波频散特性研究

Appendant layer method for dispersion characteristics of Rayleigh wave in irregular profiles

对于某些非规则水平层状地质剖面,采用传递矩阵法获得的瑞利波频散曲线可能会出现截止或截断现象,但采用附加层的方法可避免这些现象的发生。通过采用附加层法前后相速度与激发强度大小的对比,来论证附加层法的正确性。对3个典型的非规则剖面进行模拟计算,利用传递矩阵法算得添加附加层前后瑞利波频散曲线,以及某些特征点处位移分量随深度的变化情况。通过对计算结果的对比分析可知,附加层法不仅可计算出地质剖面的实数导波,还可算出其泄漏模式波;在固定的频率点上,附加层的埋深越大,则添加附加层后算得的激发强度大小与原模型的误差越小;当附加层的埋深固定时,添加附加层后计算出的位移曲线与原位移曲线之间的误差随着对比点频率的增大而减小。可见,今后根据实际工作的精度要求,可用附加层法计算某些非规则剖面的瑞利波频散曲线。

There are phenomena of cut-off or truncation for Rayleigh wave dispersion curves when transfer matrix approach is used to calculate dispersion curves of some irregular horizontal layered profiles. But these can be avoided if the appendant layer method is adopted. In order to study the validity of this new method, phase velocities and the excited intensities are compared before and after appendant layer method used. The author calculates dispersion curves and the change of displacement components with the depth of three irregular profiles by the appendant layer method. According to the calculating results and comparative analysis, the appendant layer method can calculate not only the guided waves, but also the leaky mode waves. At a fixed frequency point, the error of the excited intensity between modified and original models decreases with the appendant layer＇s burying depth increasing. And for an invariable burying depth of the appendant layer, the error is decreases with the frequency increasing. It is obvious that Rayleigh wave dispersion curves of some irregular profiles can be calculated by the appendant layer method on the basis of practical accuracy demand.