各向异性场地动力特性的地微动研究
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摘要
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 frequency 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 hypocenter.By calculation of the Nakamura's H/V spectral ratios and the wavelet spectrum in N-S and E-W directions,the result shows the anisotropic characteristic of spectrum character of ground microtremor on this site.By analysis 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.
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 frequency 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 hypocenter.By calculation of the Nakamura's H/V spectral ratios and the wavelet spectrum in N-S and E-W directions,the result shows the anisotropic characteristic of spectrum character of ground microtremor on this site.By analysis 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.
引文
[1]谢忠球.各向异性介质中的场地微动理论及其应用研究[D].长沙:中南大学,2002
[2]李英民,杨洁,赖明.双向水平地震动峰值特性的相关性研究[J],重庆建筑大学学报,1999,21,(2):5-18.
[3]陈国兴,孙士军.多维地震动输入下结构的地震反应分析[J].南京建筑工程学院学报,1999,(1)19-24
[4]Vincenzo Fioravante.Anisotropy of small strain stiffness of Ticino and Kenyasands from seismic wave propagation measured in triaxial testing[J].Soils and Foundations,2000,40(4):129-142.
[5]Cheng-Hsing chen,Hwang-Chieh chiu.Anisotropic seismic ground responses identified From the Hualian Vertical array[J].Soil Dynamics andEarthquake Engineering,1998,17:371-395.
[6]Mario De Stefano,Giuseppe Faella.An evaluation of the inelastic response of systems under biaxial seismic excitations[J].Engineering structures,1996,18(9):724-731.
[7]Wright J.The effects of transverse isotropy on reflection amplitude versus offset[J].Geophysics,1987,52(4):564-567.
[8]Konno K,Ohmachi.Ground-motion characteristics estimated from spectral ratio between horizonal and vertical components of microtremor[J].Bull.Seismol.Soc.Am1998,88(1):228-241.
[9]Yang J,Saturation effects on horizontal and vertical motion in a layered soil-bedrock system due to inclined SV waves[J],Soil Dynamics andEarthquake Engineering,(2001,21):527-536.
[10]Masanobu Oda,et al.Microstructural interpretation on Reliquefaction of Saturated Granular Soila Under Cyclic Loading[J].Journal of Geotechni-cal and Geoenvironmental Engineering May,2001:416-423.
[11]Nakamura Y.Real Time Information Systems for Seismic Hazards Mitigation UrEDAS,HERAS and PIC[J].Quarterly Report of RTRI 1996,37(3):112-127.
[12]ThomsenL Weak elasticanisotropy[J],Geophysics,1986,51(10),1954-196.
[13]Takashi T.Seismic response behaviour of soft deposits[C]//.Proc of9WCEE.Tokyo:Published by9WCEE Organizing Committee,Japan Asso-ciation for Earthquake Disaster Prevention,1988:423-428.
[14]Bates C R,Phillips D R.Multi-component seismic surveying for near surface investigations:examples from central Wyoming and Southern England[J].Journal of Applied Geophysics,(2000,44):257-273.
[15]Rebecca L,Saltzer,James B Gaherty,Thomas HJordan.How are vertical shear wave splitting measurements affected by variations in the orienta-tion of azimuthal anisotropy with depth?[J],2000RAS,GJI 141:374-390.
[16]张之颖,张景绘.卓越周期对反应谱最大值的影响[J].环境与强度,1999(2):1-6.
[17]周锡元,王广军,苏经宇.场地分类和设计反应谱的特征周期-《建筑抗震设计规范》修订简介(八)[J].工程抗震,1999,4:3-8.
[2]李英民,杨洁,赖明.双向水平地震动峰值特性的相关性研究[J],重庆建筑大学学报,1999,21,(2):5-18.
[3]陈国兴,孙士军.多维地震动输入下结构的地震反应分析[J].南京建筑工程学院学报,1999,(1)19-24
[4]Vincenzo Fioravante.Anisotropy of small strain stiffness of Ticino and Kenyasands from seismic wave propagation measured in triaxial testing[J].Soils and Foundations,2000,40(4):129-142.
[5]Cheng-Hsing chen,Hwang-Chieh chiu.Anisotropic seismic ground responses identified From the Hualian Vertical array[J].Soil Dynamics andEarthquake Engineering,1998,17:371-395.
[6]Mario De Stefano,Giuseppe Faella.An evaluation of the inelastic response of systems under biaxial seismic excitations[J].Engineering structures,1996,18(9):724-731.
[7]Wright J.The effects of transverse isotropy on reflection amplitude versus offset[J].Geophysics,1987,52(4):564-567.
[8]Konno K,Ohmachi.Ground-motion characteristics estimated from spectral ratio between horizonal and vertical components of microtremor[J].Bull.Seismol.Soc.Am1998,88(1):228-241.
[9]Yang J,Saturation effects on horizontal and vertical motion in a layered soil-bedrock system due to inclined SV waves[J],Soil Dynamics andEarthquake Engineering,(2001,21):527-536.
[10]Masanobu Oda,et al.Microstructural interpretation on Reliquefaction of Saturated Granular Soila Under Cyclic Loading[J].Journal of Geotechni-cal and Geoenvironmental Engineering May,2001:416-423.
[11]Nakamura Y.Real Time Information Systems for Seismic Hazards Mitigation UrEDAS,HERAS and PIC[J].Quarterly Report of RTRI 1996,37(3):112-127.
[12]ThomsenL Weak elasticanisotropy[J],Geophysics,1986,51(10),1954-196.
[13]Takashi T.Seismic response behaviour of soft deposits[C]//.Proc of9WCEE.Tokyo:Published by9WCEE Organizing Committee,Japan Asso-ciation for Earthquake Disaster Prevention,1988:423-428.
[14]Bates C R,Phillips D R.Multi-component seismic surveying for near surface investigations:examples from central Wyoming and Southern England[J].Journal of Applied Geophysics,(2000,44):257-273.
[15]Rebecca L,Saltzer,James B Gaherty,Thomas HJordan.How are vertical shear wave splitting measurements affected by variations in the orienta-tion of azimuthal anisotropy with depth?[J],2000RAS,GJI 141:374-390.
[16]张之颖,张景绘.卓越周期对反应谱最大值的影响[J].环境与强度,1999(2):1-6.
[17]周锡元,王广军,苏经宇.场地分类和设计反应谱的特征周期-《建筑抗震设计规范》修订简介(八)[J].工程抗震,1999,4:3-8.
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