地脉动产生机理和传播特性的研究

Study on formation mechanism and propagating characteristics of ground micro-tremor

以福建省沿海地区场地地脉动和地基固有特性为研究对象,采用室内与现场原位测试相结合、快速傅立叶变换方法进行数据采集和处理,并采用数理统计方法对它们的相关性进行分析,间接地定量研究地脉动的产生机理和传播特性,通过震害反分析得到进一步验证.研究结果揭示了地脉动是一种以剪切波为主的体波,为地脉动体波成因理论提供了有力的支持;剪切波在覆盖层中的等效剪切波速是影响地脉动卓越周期的主要因素,覆盖层厚度、软土层厚度及刚度是影响地脉动卓越周期的重要因素;剪切波在覆盖层中的传播时间与地脉动卓越周期密切相关,能够较好地反映地脉动卓越周期的变化.

The ground micro-tremor signals observed in coastal area of Fujian Province were analyzed and processed by fast Fourier transform (FFT) method. The indicatrixes of physical and mechanical properties of ground soil were also tested by combining indoor test with in-situ one. The formation mechanism and propagating characteristics of ground micro-tremor were studied, which was confirmed by earthquake damages. The conclusions obtained are as follows: First, the equivalent shear wave in overburden layer is one main factor affecting the predominant period of ground micro-tremor. Second, the thickness of overburden layer, soft soil and its stiffness are three other important factors affecting the predominant period of ground micro-tremor. Third, the relationship between the predominant period of ground micro-tremor and the shear wave propagation time in the overburden layer is closely related. Fourth, the propagating time of shear wave in overburden layer can better reflect the change of predominant period of ground micro-tremor, and vice versa. Fifth, the results indirectly reveal quantitatively that ground micro-tremor is one of body waves that is mainly a shear wave, which backs the theory on body-wave cause of ground micro-tremor formation.