均匀半无限体中表面源激发的浅部波场由瑞利波主导且能量主要分布于一个波长深度,当瑞利波遇浅部洞穴时,瑞利波不能保持原有传播特性,波会在洞穴边界发生散射.为了分析这一现象,本文采用轴对称模型,数值模拟均匀半空间中洞穴散射波场响应.由偏移距-波长域表面波能量(振幅)谱变化,研究洞穴埋深及几何参数对散射波影响.对表面波场谱扰动特征分析,建立洞穴上方能量分界面对应特征波长与埋深的关系.结果表明:洞穴埋深是影响表面波场谱扰动一个重要参数,埋深约是特征波长1.5倍,波在洞穴边界面绕射会导致洞穴周围表面波场形成能量分界面,由表面波谱这些扰动特征可预测洞穴方位及埋深.%The shallow wave fields induced by the surface sources in homogenous half spaces are dominated by Rayleigh waves,whose energy is distributed within the depth of one wavelength. When the forward Rayleigh waves encounter the shallow cavities,the behavior of Rayleigh waves changes and the waves are scattered at the boundaries of the cavities. To analyze this phenomenon,the axisymmetrical models were used to numerically simulate the responses of the waves scattered at the cavities present in the half space. Effects of the depth and geometrical size of the cavity on the wave scattering were investigated from the disturbances of the surface wave spectrum in the domain of the offset and the wavelength. With the analysis of disturbances characteristics of the surface wave field spectrum,the relationship between the cavity depth and the characteristic wavelength corresponding to the energy interface above the cavities was established. The results showed that the depth of cavity was a major parameter influencing the disturbances of the surface wave field spectrum. When the depth of cavityis was about 1.5 times the characteristic wavelength,the energy interfaces could be formed in the surface wave fields around the cavities due to the wave scattering at the boundaries. Thus it is feasible to predict the depth and location of the cavity by the disturbances characteristics of the surface wave field spectrum.
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