基岩表面地脉动谱比研究
|
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。
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.
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.
引文
[1]傅淑芳,刘宝诚.地震学教程[M].地震出版社,北京:1991.
[2]郑仙种,崔力科.波动理论在地震勘探中的应用[M].北京:石油工业出版社,1987.
[3]FieldE,JacobK.A comparison and test of various site-response estimation techniques, including three that are not reference-site dependent[J].BulltinSeismologySociety ofAmerica,1995,85:1127-1143.
[4]LermoJ,Chavez-GarciaJ.Are microtremors useful in site response evaluation[J].BulltinSeismologySociety ofAmerica,1994,84:1350-1364.
[5]Nakamura.Clear identification of fundamental idea ofNakamura technique and its applications[A].12thWorldConferenceEarthquakeEngineering[C],NewZealand:[s.n.],2000,#656.
[6]郭明珠,宋泽清.论地脉动场地特性分析中的“Nakamura法”[J].世界地震工程,2000(2):88-92.
[7]郭明珠.地脉动波场分析及其在场地动力特性测试中的应用[博士学位论文D].北京:中国地震局工程力学所,2000.
[8]谢和平,周宏伟,王金安等.FLAC 在煤矿开采沉陷预测的应用及对比分析[J].岩石力学与工程学报,1999,18(4):397-401.
[2]郑仙种,崔力科.波动理论在地震勘探中的应用[M].北京:石油工业出版社,1987.
[3]FieldE,JacobK.A comparison and test of various site-response estimation techniques, including three that are not reference-site dependent[J].BulltinSeismologySociety ofAmerica,1995,85:1127-1143.
[4]LermoJ,Chavez-GarciaJ.Are microtremors useful in site response evaluation[J].BulltinSeismologySociety ofAmerica,1994,84:1350-1364.
[5]Nakamura.Clear identification of fundamental idea ofNakamura technique and its applications[A].12thWorldConferenceEarthquakeEngineering[C],NewZealand:[s.n.],2000,#656.
[6]郭明珠,宋泽清.论地脉动场地特性分析中的“Nakamura法”[J].世界地震工程,2000(2):88-92.
[7]郭明珠.地脉动波场分析及其在场地动力特性测试中的应用[博士学位论文D].北京:中国地震局工程力学所,2000.
[8]谢和平,周宏伟,王金安等.FLAC 在煤矿开采沉陷预测的应用及对比分析[J].岩石力学与工程学报,1999,18(4):397-401.
版权所有：© 2023 中国地质图书馆 中国地质调查局地学文献中心