P波入射下断层参数对地表地震动的影响
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摘要
基于应用透射人工边界条件的显式有限元法计算断层破碎带宽度及力学参数变化、地震动入射角变化时二维断层场地模型P波入射下地表地震动场的分布。结果表明:(1)低速度破碎带的存在导致整个场地都有P波转换为SV波的分量,且在断层破碎带的区域出现断层陷波;(2)低速度破碎带的存在使输入场地恒定的能量向破碎带集聚放大,随着破碎带宽度增大或其介质波速降低集聚放大效应增大;(3)场地放大效应是频率相关的,宽度较宽或介质波速较低的断层破碎带对输入地震动中较低的频率成份放大显著;(4)竖向断层破碎带能阻隔斜入射地震P波,随着入射角增加隔震效应更显著。
In this study,a numerical solution for a 2-D fault site model under incident P waves using the explicit finite element method combined with transmission of artificial boundary condition was derived.The distribution rules of peak ground acceleration(PGA)and the spectrum characteristics influenced by fault characteristics such as width and shear wave velocity of the fault and the incidence angle of the seismic waves were discussed.Numerical simulations shown that transform SV waves developed in the low velocity fault zone(LVFZ)when it struck by external incident P waves,and many trapped waves obviously developed in it.This result implied that the external incident seismic radiation congregated in the LVFZ,and the agglomeration effect increased with the increased width and decreased shear wave velocity of the LVFZ.Vertical LVFZs blocked the spread of oblique incident P waves,and the isolation effect decreased with the increased incidence angle of P waves.The seismic response of a variety of LVFZ models withdifferent width and shear wave velocity struck by external vertically incident P waves was determined,and the results implied that the ground motion amplification characteristics in the near fault zone site are frequency dependent.The higher frequency components of ground seismic waves are obviously amplified by LVFZs with narrower widths and higher shear wave velocities,while the lower frequency components of ground seismic waves are obviously amplified by LVFZs with wider widths and lower shear wave velocities.In other words,the site amplification coefficient is frequency dependent,such that the widening the width or decreasing the shear wave velocity of fault fracture zone,the predominant frequency of a larger site amplification coefficient is becoming lower.
In this study,a numerical solution for a 2-D fault site model under incident P waves using the explicit finite element method combined with transmission of artificial boundary condition was derived.The distribution rules of peak ground acceleration(PGA)and the spectrum characteristics influenced by fault characteristics such as width and shear wave velocity of the fault and the incidence angle of the seismic waves were discussed.Numerical simulations shown that transform SV waves developed in the low velocity fault zone(LVFZ)when it struck by external incident P waves,and many trapped waves obviously developed in it.This result implied that the external incident seismic radiation congregated in the LVFZ,and the agglomeration effect increased with the increased width and decreased shear wave velocity of the LVFZ.Vertical LVFZs blocked the spread of oblique incident P waves,and the isolation effect decreased with the increased incidence angle of P waves.The seismic response of a variety of LVFZ models withdifferent width and shear wave velocity struck by external vertically incident P waves was determined,and the results implied that the ground motion amplification characteristics in the near fault zone site are frequency dependent.The higher frequency components of ground seismic waves are obviously amplified by LVFZs with narrower widths and higher shear wave velocities,while the lower frequency components of ground seismic waves are obviously amplified by LVFZs with wider widths and lower shear wave velocities.In other words,the site amplification coefficient is frequency dependent,such that the widening the width or decreasing the shear wave velocity of fault fracture zone,the predominant frequency of a larger site amplification coefficient is becoming lower.
引文
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[13]刘必灯,周正华,刘培玄,等.SV波入射下V型河谷地形对地震动的影响分析[J].地震工程与工程振动,2011,31(2),17-24.LIU Bi-deng,ZHOU Zheng-hua,LIU Pei-xian,et al.Influence of V-shaped Canyon Site on Ground Motion for Incident SV Waves[J].Journal of Earthquake Engineering and Engineering Vibration,2011,31(2):17-24.(in Chinese)
[14]刘必灯,王伟,李小军,等.汶川地震中鲜水河断裂带的隔震效应[J].震灾防御技术,2014,9(4),855-861.LIU Bi-deng,WANG Wei,LI Xiao-jun,et al.Isolation Effect of Xianshuihe Fault Zone in Wenchuan Earthquake[J].Technology for Earthquake Disaster Prevention,2014,9(4):855-861.(in Chinese)
[15]夏峰,宋成科,孟庆筱,等.天津地区覆盖层土动力学参数统计分析[J].地震工程学报,2015,37(1):49-54.XIA Feng,SONG Cheng-ke,MENG Qing-xiao,et al.Analysis of Soil Dynamic Parameters of Overburden in the Tianjin Area[J].China Earthquake Engineering Journal.2015,37(1):49-54.(in Chinese)
[16]廖振鹏.工程波动理论导论[M].第二版.北京:科学出版社,2002.LIAO Zhen-peng.Introduction to Wave Motion Theories for Engineering[M].Second Edtion.Beijing:Science Press,2002.(in Chinese)
[2]刘必灯.断陷盆地及断层破碎带场地地震动效应[D].哈尔滨:中国地震局工程力学研究所,2011.LIU Bi-deng.Site Effect of Strong Ground Motion for Dislocation Basin and Fault Fracture Zone[D].Harbin:Institute of Engineering Mechanics,China Earthquake Administration,2011.(in Chinese)
[3]刘必灯,王伟,于淼.西昌断陷盆地场地地震动差异分析[J].地震工程学报,2014,36(3):489-494.LIU Bi-deng,WANAG Wei,YU Miao.The Study About Difference of the Ground Motion for Dislocation Basin in Xichang[J].China Earthquake Engineering Journal,2014,36(3):489-494.(in Chinese)
[4]Li Y G,Leary P C.Fault Zone Trapped Seismic Waves[J].Bulletin of the Seismological Society of America,1990,80:1245-1271.
[5]Li Y G,Leary P C,Aki K,et al.Seismic Trapped Modes in the Oroville and San Andreas Fault Zones[J].Science,1990,249:763-766.
[6]Feng R,McEvilly T V.Interpretation of Seismic Reflection Profiling for the Structure of the SAF Zone[J].Bulletin of the Seismological Society of America,1983,73:1701-1720.
[7]Michelini A,McEvilly T V.Seismological Studies at Parkfield:I.Simultaneous Inversion for Velocity Structure and Hypocenters Using Cubic B-splines Parameterization[J].Bulletin of the Seismological Society of America,1991,81:524-552.
[8]Yu T,Cui J W,Li X J,et al.Analysis of Ground Motion Attenuation Characterization for Moderate Earthquakes in the Sichuan-Yunnan Region[J].Earthquake Research in China,2015,29(2):237-246.
[9]刘祖荫,皇甫岗,金志林.一九七〇年通海地震[M].北京:地震出版社,1999.LIU Zu-yin,HUANGFU Gang,JIN Zhi-lin.1970 Tonghai Earthquake[M].Beijing:Seismological Press,1990.(in Chinese)
[10]刘恢先.唐山大地震震害[M].北京:地震出版社,1985.LIU Hui-xian.Earthquake Damage of Tangshan Great Earthquake[M].Beijing:Seismological Press,1985.(in Chinese)
[11]Sieh K,Jones L,Hauksson E,et al.Near-field Investigations of the Landers Earthquake Sequence,April to July 1992[J].Science,1993,260:171-176.
[12]Thurber C H,Roecker S,Ellsworth W,et al.Two-dimensional Seismic Image of the San Andreas Fault in the Northern Gabilan Range,Central California:Evidence for Fluids in the Fault Zone[J].Geophysical Research Letters,1997,24:1591-1594.
[13]刘必灯,周正华,刘培玄,等.SV波入射下V型河谷地形对地震动的影响分析[J].地震工程与工程振动,2011,31(2),17-24.LIU Bi-deng,ZHOU Zheng-hua,LIU Pei-xian,et al.Influence of V-shaped Canyon Site on Ground Motion for Incident SV Waves[J].Journal of Earthquake Engineering and Engineering Vibration,2011,31(2):17-24.(in Chinese)
[14]刘必灯,王伟,李小军,等.汶川地震中鲜水河断裂带的隔震效应[J].震灾防御技术,2014,9(4),855-861.LIU Bi-deng,WANG Wei,LI Xiao-jun,et al.Isolation Effect of Xianshuihe Fault Zone in Wenchuan Earthquake[J].Technology for Earthquake Disaster Prevention,2014,9(4):855-861.(in Chinese)
[15]夏峰,宋成科,孟庆筱,等.天津地区覆盖层土动力学参数统计分析[J].地震工程学报,2015,37(1):49-54.XIA Feng,SONG Cheng-ke,MENG Qing-xiao,et al.Analysis of Soil Dynamic Parameters of Overburden in the Tianjin Area[J].China Earthquake Engineering Journal.2015,37(1):49-54.(in Chinese)
[16]廖振鹏.工程波动理论导论[M].第二版.北京:科学出版社,2002.LIAO Zhen-peng.Introduction to Wave Motion Theories for Engineering[M].Second Edtion.Beijing:Science Press,2002.(in Chinese)