各向异性场地动力特性的地微动研究

Research on dynamic properties of inhomogeneous anisotropic site by ground microtremor

采用非均匀横观各向同性层状介质模型模拟半空间之上的层状场地,对垂直入射的剪切波引起的地面响应进行了模拟。考虑震源特性的影响,分析了不同深度位置两种不同卓越频率的入射子波的响应,结果表明,非均匀横观各向同性层状场地的地震动响应具有明显的各向异性特征,并且随着震源特性的不同而变化。以某场地实测资料为例,计算了场地E-W向和N-S向的Nakamura谱比及小波谱,表明该场地的地微动频谱特性具有各向异性特征。场地微动水平方向的振动位移图分析进一步表明,场地振动具有优势方位,场地动力特性具有各向异性。在数值模拟和试验观测的基础上,提出了场地微动各向异性及各向异性主轴的概念,分析了场地微动各向异性主轴及各向异性机制。

A model of inhomogeneous transversely-isotropic layered medium is used to simulate the layered site situated on a half space, the response induced by shear wave with vertical incidence was simulated. To consider the effect of hypocenter characteristic, the response of two kinds of incident wavelet with different predominant frequen- cy at different depths was analyzed. The modeling result shows the characteristic of anisotropy of seismic response in inhomogeneous transversely-isotropic elastic layered site and also the difference of characteristics to different hypo- center. By calculation of the Nakamura＇ s H/V spectral ratios and the wavelet spectrum in N - S and E-W direc- tions, the result shows the anisotropic characteristic of spectrum character of ground microtremor on this site. By a- nalysis of vibration displacement graph on horizontal direction of ground microtremor, the result demonstrates the dominant direction of vibration and anisotropy of dynamic behaviour. In this paper, the conception of the anisotropy of ground microtremor and the anisotropy principal-axis were put forward according to numerical simulation and test observation. Based on the theory of elastic wave in anisotropy medium, the characteristics of the ground microtremor, the principal axis and the mechanism of the ground microtremor also were studied in this paper.