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自由状态下层状介质中平面瑞利波相速度与频率及层状介质特性参数有关,表面源激发的瑞利波以柱面波阵面传播,传播速度不仅与频率有关,而且还与传播距离有关,这样,自由状态下层状介质中平面瑞利波传播特性理论不能有效地用于激发瑞利波相速度分析。以薄层法得到的圆盘状表面垂直源激发瑞利波位移响应为基础,导出激发瑞利波相速度,比较激发模态与简正模态相速度差异,分析激发模态空间特性,揭示这种空间特性形成机制。结果表明:源对激发模态传播影响距离不超过一个波长,波场距源越近,激发模态竖直振动传播速度越低;在多模波场,激发模态间相长相干或相消相干导致表观相速度具有较明显的空间特性。该研究可为发展考虑瑞利波频率及空间特性反演数学模型及算法提供指导。
In the free state, the planar Rayleigh wave velocity in the layered media is related to the frequency and the characteristic parameters of the layered media. The Rayleigh wave excited by the surface source propagates through the cylindrical wave front. The propagation velocity is not only related to the frequency but also to the propagation distance In this way, the theory of plane Rayleigh wave propagation in layered media under the free state can not be effectively used to excite the Rayleigh wave phase velocity analysis. The phase velocity of excited Rayleigh waves is derived based on the vertical source-excited Rayleigh displacement response of the disc-shaped surface obtained by the thin-layer method. The phase velocity differences between the excitation mode and the normal mode are compared, and the spatial characteristics of the excitation mode are analyzed. Spatial characteristic formation mechanism. The results show that the distance between source and excitation mode propagation does not exceed one wavelength and the closer to the source the excitation mode is, the lower the vertical vibration propagation velocity is. In the multi-mode wave field, the coherence or cancellation Coherence leads to obvious spatial characteristics of apparent phase velocity. This study can provide guidance for the development of mathematical models and algorithms for considering the frequency and spatial characteristics of Rayleigh waves.