黄土地区场地条件对地震动放大效应影响研究
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摘要
汶川Ms8.0特大地震在甘肃黄土灾区局部场地的震害和地震动具有明显的放大效应。通过在该区布设的地形调查流动强震动观测台阵,获取了同一山体不同高程的余震加速度记录,结果呈现出山顶记录到的峰值加速度大于山腰,而山腰记录也略大于山脚的规律。为了进一步分析黄土地区地震峰值加速度的放大机理,运用地脉动观测手段调查了其局部场地条件,得到了山体不同高程的卓越频率。并以典型黄土塬为背景,运用二维等价线性时程响应动分析法对不同覆盖层厚度和不同坡度的黄土塬进行了地震荷载作用下的动力响应分析,分析了不同条件下的山顶和山腰的地震峰值加速度放大特征。结果表明,地震峰值加速度放大效应和黄土覆盖层厚度及黄土边坡坡度有直接的关系。数值计算结果与实际震害观测吻合较好,证实了黄土覆盖层厚度和坡度是峰值加速度放大的重要因素。
Loess is widely distributed in China and in the loess plateau of Gausu province,The seismic amplification effects were discovered during the Wenchuan Ms8.0 earthquake.Based on the acceleration records of aftershocks,it is discovered that the Peak ground acceleration(PGA) is larger at the mountaintop and mountainside than the value at the foot of mountain.In order to analyze the mechanism of the seismic amplification effects in loess area,a microtremor survey was carried out to detect the ground condition and the predominant frequency of the different sites at the same mountain was obtained as well.Moreover,the typical loess plateau mesa is studied applying the dynamic finite element analysis method of two dimensions linearly equivalent for dynamic response numerical calculation,with different loess thickness and different slope grades.The magnifications of PGA at the mountaintop and mountainside are analyzed under different conditions.It is found that the magnification is related to the loess thickness and slope grades,which is in accordance with the earthquake damage observation.The result shows that the loess thickness and slope are important factors influencing earthquake damages.
Loess is widely distributed in China and in the loess plateau of Gausu province,The seismic amplification effects were discovered during the Wenchuan Ms8.0 earthquake.Based on the acceleration records of aftershocks,it is discovered that the Peak ground acceleration(PGA) is larger at the mountaintop and mountainside than the value at the foot of mountain.In order to analyze the mechanism of the seismic amplification effects in loess area,a microtremor survey was carried out to detect the ground condition and the predominant frequency of the different sites at the same mountain was obtained as well.Moreover,the typical loess plateau mesa is studied applying the dynamic finite element analysis method of two dimensions linearly equivalent for dynamic response numerical calculation,with different loess thickness and different slope grades.The magnifications of PGA at the mountaintop and mountainside are analyzed under different conditions.It is found that the magnification is related to the loess thickness and slope grades,which is in accordance with the earthquake damage observation.The result shows that the loess thickness and slope are important factors influencing earthquake damages.
引文
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[12]甘肃省地震局.天水市地震危险性分析及地震小区划[Z].2011.(Gansu Seismology Bureau.Analysis onseismic danger in Tianshui City and seismic zoning[Z].2011.(in Chinese))
[2]张振中.黄土地震灾害预测[M].北京:地震出版社,1999.(Zhang Zhenzhong.Forecast of seismic disastersin loess area[M].Beijing:Earthquake Press,1999.(in Chinese)
[3]王兰民,吴志坚.汶川地震局部场地条件对地震动放大效应影响的研究[J],土木建筑与环境工程,2010,32(增2):175-178.(Wang Lanmin,Wu Zhi-jian.Influence of site condition on seismic amplificationeffects during the Wenchuan Earthquake[J].Journal ofCivil,Architectural&Environmental Engineering,2010,32(Supp.2):175-178.(in Chinese))
[4]石玉成,王兰民,张颖.黄土场地覆盖层厚度和地形条件对地震动放大效应的影响[J],西北地震学报,1999,21(2):203-208.(Shi Yucheng,Wang Lan-min,Zhang Ying.Effects of overburden thickness andtopography of loessial sites on earthquake ground motion[J].Northwestern Seismological Journal,1999,21(2):203-208.(in Chinese))
[5]袁丽侠.场地土对地震波的放大效应[J].世界地震工程,2003,19(1):113-120.(Yuan Lixia.Analysison amplification effect of seismic wave caused by sitesoil[J].World Earthquake Engineering,2003,19(1):113-120.(in Chinese))
[6]姚凯,卢大伟,刘旭宙,等.利用汶川余震流动观测资料探讨地形对峰值加速度的影响[J].西北地震学报,2009,31(1):46-50.(Yao Kai,Lu Dawei,LiuXuzhou,et.al.Using observational data from the after-shocks of Wenchuan great earthquake to study the influ-ence of geography on peak ground acceleration[J].Northwestern Seismological Journal,2009,31(1):46-50.(in Chinese))
[7]Che Ailan,Iwatate Takahiro,Ge Xiurun.Study on theapplicability of frequency spectrum of micro-tremor anddynamic characteristics of surface ground in Asia area[J],Journal of Zhejiang University(Science),2006,7(11):1 856-1 863.
[8]Sun Chongshao et.a1.The Characteristics of groundMotion during Strong Earthquake in Lanzhou,Proceed-ings of the 7th International Congress of IAEG,1994
[9]姚文波,刘文兆,侯甬坚,等,汶川大地震陇东黄土高原崩塌滑坡的调查分析[J],生态学报,2008,28(12):5 917-5 926.(Yao Wenbo,Liu Wenzhao,HouYongjian,et al.Investigation and analysis of collapsesand landslides on the Loess Plateau of East Gansu Prov-ince after the 5.12 Wenchuan Earthquake[J].ActaEcologica Sinica,2008,28(12):5 917-5 926..(inChinese))
[10]石玉成,卢育霞.汶川8.0级地震甘肃灾区震害特点及恢复重建对策[J].西北地震学报,2009,1(1):1-7.(Shi Yucheng,Lu Yuxia.The damage features ofWenchuan 8.0 earthquake in Gansu disaster area andcountermeasures of reconstruction[J].NorthwesternSeismological Journal,2009,31(1):1-7.(in Chi-nese))
[11]车爱兰,岩楯敞广,葛修润.关于地铁地震响应的模型振动实验及数值分析[J].岩土力学,2006,27(8):1 293-1 298.(Che Ailan,Iwatate Takahiro,GeXiurun.Dynamic behaviors of subway structure subjec-ted to strong earthquake motions using shaking tabletests and dynamic analyses[J].Rock and Soil Mechan-ics,2006,27(8):1 293-1 298.(in Chinese))
[12]甘肃省地震局.天水市地震危险性分析及地震小区划[Z].2011.(Gansu Seismology Bureau.Analysis onseismic danger in Tianshui City and seismic zoning[Z].2011.(in Chinese))
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