用上海强震土层垂直观测系统研究软土层对地震动的放大作用
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摘要
利用上海曹杨公园土层垂直数字强震观测系统提供的井下基岩和地面自由场三分向数字地震波资料,使用经验转换函数方法,研究了该处软土层对地震动的放大作用。该场地软土层厚达310m。利用2002~2005年记录到的5次地震的数字波形进行的研究结果表明,经验转换函数方法描述场地效应是可靠的。东西、南北、上下三个分量的共振频率分别为5.4Hz、7.5Hz和10.9Hz,对应不同的共振振型;相应的放大倍数依次为20.2±7.1,27.8±2.9和20.7±9.6。并从理论上初步探讨了软土层对地震动放大作用的机理。软土层对地震动的放大作用取决于软土层的厚度,软土层及其下卧基岩的密度、波速,以及地震波的入射角。理论研究表明上海曹杨公园软土层的基础自振频率为0.28Hz。由于整个上海市坐落在软土层上,几百公里外发生强震,都可能在上海市造成灾害,必须引起重视。上海市的防震减灾规划除了需要考虑未来本区内发生破坏性地震的危险之外,还必须考虑到行政边界以外几百公里以内发生强烈地震带来的灾害。高层楼房和大跨度桥梁的设计必须考虑远距离地震传来的长周期地震动的影响。
Ground motion amplification induced by sediment layer is studied via empirical transfer function with the 3 compounent digital seismic data from both the free surface and borehole at Caoyang Park,Shanghai.The sediment layer at Caoyang Park is 310m in height.The results from 5 earthquakes erupted between 2002 to 2005 show that empirical transfer function can characterize site response well.Along EW,NS and UD directions,the resonant frequencies of the sediment layer are 5.4Hz,7.5Hz and 10.9Hz respectively,corresponding different resonant modes,and the corresponding amplification factor are 20.2±7.1,27.8±2.9 and 20.7±9.6 respectively.The mechanism on ground motion amplification induced by sediment layer is explored by theory primitively.The amount of ground motion amplificaiton induced by sediment layer is pending on the height of the sediment,the densities,velocities of both the sediment and underlying rock and the incident angle of the seismic ray.From theory,the fundamental resonant frequency of the sediment layer at Caoyang Park is 0.28Hz.Because whole Shanghai City is sitting on the thick sediment layer,strong earthquakes from hundrends of kilometres away may cause damage for Shanghai.Attention must be paid on this.The earthquake mitigation and preparation measure in Shanghai must take the potential distant strong earthquakes into account as well as local earthquakes.The effect of long-period seismic ground motion from distant strong motion earthquakes must be taken into account when high buildings and extensive bridges have been designed.
Ground motion amplification induced by sediment layer is studied via empirical transfer function with the 3 compounent digital seismic data from both the free surface and borehole at Caoyang Park,Shanghai.The sediment layer at Caoyang Park is 310m in height.The results from 5 earthquakes erupted between 2002 to 2005 show that empirical transfer function can characterize site response well.Along EW,NS and UD directions,the resonant frequencies of the sediment layer are 5.4Hz,7.5Hz and 10.9Hz respectively,corresponding different resonant modes,and the corresponding amplification factor are 20.2±7.1,27.8±2.9 and 20.7±9.6 respectively.The mechanism on ground motion amplification induced by sediment layer is explored by theory primitively.The amount of ground motion amplificaiton induced by sediment layer is pending on the height of the sediment,the densities,velocities of both the sediment and underlying rock and the incident angle of the seismic ray.From theory,the fundamental resonant frequency of the sediment layer at Caoyang Park is 0.28Hz.Because whole Shanghai City is sitting on the thick sediment layer,strong earthquakes from hundrends of kilometres away may cause damage for Shanghai.Attention must be paid on this.The earthquake mitigation and preparation measure in Shanghai must take the potential distant strong earthquakes into account as well as local earthquakes.The effect of long-period seismic ground motion from distant strong motion earthquakes must be taken into account when high buildings and extensive bridges have been designed.
引文
郭增建,陈鑫连,1991,城市地震对策,502,北京:地震出版社,502。
上海市地震局,2005,上海市地震监测志,318,上海:同济大学出版社。
谢礼立,1999,唐山响堂三维场地影响观测台阵,《地震工程与工程振动》,19(2):1~8。
Borcherdt,R.D.,1970,Effects of local geology on ground motion near San Francisco Bay.Bull SeismSoc Amer,60,29~61.
Coutel,F.and Mora,P.1998,Simulation-based comparison of four site-response estimation techniques,Bull.Seismol.Soc.Am.,88:30~42.
Lay,T.and Wallace,T.1995,Modern Global Sesimology,Academic Press,San Diego,USA,521.
Lermo,J.1993.Site Effect Evaluation Using Spectral Ratios with only One Station.BSSA,V83(5):1574~1594.
Ma,S.2004.Calibration of Wellington3DShaking Hazard Model.MSc thesis,School of Earth Sciences,Victoria University of Wellington,NewZealand,163.
Ma,S,Savage M,Yu J.2007.Modelling seismic ground motion in Hutt Valley,NewZealand by discrete wavenumber method.Bulletin ofthe NewZealand Societyfor Earthquake Engineering,NewZealand,accepted.
Taber,J.1992.Frequency dependent amplificaiton of weak ground motions in Porirua and Lower Hutt,NewZealand.Bull.NZ Natl.Soc.Earthquake Engineering,25:303~331.
上海市地震局,2005,上海市地震监测志,318,上海:同济大学出版社。
谢礼立,1999,唐山响堂三维场地影响观测台阵,《地震工程与工程振动》,19(2):1~8。
Borcherdt,R.D.,1970,Effects of local geology on ground motion near San Francisco Bay.Bull SeismSoc Amer,60,29~61.
Coutel,F.and Mora,P.1998,Simulation-based comparison of four site-response estimation techniques,Bull.Seismol.Soc.Am.,88:30~42.
Lay,T.and Wallace,T.1995,Modern Global Sesimology,Academic Press,San Diego,USA,521.
Lermo,J.1993.Site Effect Evaluation Using Spectral Ratios with only One Station.BSSA,V83(5):1574~1594.
Ma,S.2004.Calibration of Wellington3DShaking Hazard Model.MSc thesis,School of Earth Sciences,Victoria University of Wellington,NewZealand,163.
Ma,S,Savage M,Yu J.2007.Modelling seismic ground motion in Hutt Valley,NewZealand by discrete wavenumber method.Bulletin ofthe NewZealand Societyfor Earthquake Engineering,NewZealand,accepted.
Taber,J.1992.Frequency dependent amplificaiton of weak ground motions in Porirua and Lower Hutt,NewZealand.Bull.NZ Natl.Soc.Earthquake Engineering,25:303~331.
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