【摘要】 目前,场地影响评价方法可以分为理论法和经验法。地脉动水平分量与竖向分量谱比法属经验法。这种方法将地脉动水平分量与竖向分量谱比的最大值对应的频率和幅值分别看作是观测场地的卓越频率和放大因子。虽然该法在国内外很多工程实例中得到了理想的结果。但由于这种方法建立过程中应用了许多假设,所以很多地震工程学家对这种方法持怀疑态度。本文讨论了基岩地脉动水平分量与竖向分量谱比为 1 这一假定的合理性。并采用泊松弹性半空间模型,应用概率分析方法考虑地脉动的随机性,推导了地下体波斜入射弹性半空间自由表面形成地脉动的水平分量与竖向分量谱比表达式。通过计算论证体波斜入射泊松弹性半空间形成的地脉动水平分量与竖向分量谱比特性。结果表明:当地脉动主要成分为体波时,基岩表面地脉动水平分量与竖向分量谱比接近于 1;当地脉动主要成分为面波时,基岩表面地脉动水平分量与竖向分量谱比介于 0.54～0.79 之间。对泊松基岩,该比值是 0.68。更多还原

【Abstract】 Present approaches for site effect evaluation are either theoretical or empirical. The ratio of microtremor horizontal to vertical spectra of one station (H/V method or H/V) is empirical. The highest amplitude of H/V is considered to be site amplification and the lowest frequency corresponding to the largest H/V amplitude is considered to be the site predominant frequency. In practical, the H/V method of microtremor measurement provides accurate site amplification and site predominant frequency. However, many engineering scientists considered that the H/V method lacks sufficient theoretical background, because numerous assumptions were introduced in formulating the method. Some assumptions are discussed in this paper. The microtremor spectral ratio method is assumed that the spectra ratio of the horizontal component to the vertical component of microtremors on the rock surface is equal to unit. Is this correct? There is no satisfying theoretical explanation. Microtremors are been divided into body microtremors and surface microtremor. In order to reflect the random of microtremors, body microtremor is considered by superposing inclined P-SV waves under different incident angles. Surface microtremor is assumed to be Rayleigh wave on elastic half space. Expressions of the spectra ratio of the horizontal component to the vertical component of body microtremors on the elastic half rock surface are deduced in this paper. The characteristics of the spectral ratio of the horizontal to vertical spectra on the Poisson rock surface are discussed. It is shown that the H/V is close to unit for body microtremors and approximately 0.68 for surface wave microtremors on the Poisson rock surface.更多还原