SV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,计算了断层破碎带宽度及其物理力学参数变化、入射地震动角度变化时二维断层场地模型地表地震动场的分布。结果表明:低速度断层破碎带的存在导致整个场地都有SV波转换为P波的分量,且在破碎带区域出现断层陷波;低速度断层破碎带的存在使输入场地恒定的能量向破碎带中集聚放大,且随着破碎带宽度增大或破碎带介质波速降低,集聚放大效应增大;场地放大效应是频率相关的,具有不同卓越频率的断层场地会有选择性地放大和场地卓越频率相近的地震动,破碎带宽度增大或介质波速降低时,断层场地的卓越频率降低,显著放大效应选择的地震动卓越频率也相应越低,即宽度较宽或介质波速较低的低速度断层破碎带场地的卓越频率较低,对输入场地的较低频率成分的地震动放大显著;竖向低速度断层破碎带能阻隔斜入射地震波,且随着入射角增加,这种隔震效应更显著。
A numerical solution to 2-D fault site model for incident SV waves was derived by using the explicit finite element combining transmitting boundary,and the distribution rules of site ground motion influenced by different fault characteristics,such as width and shear wave velocity of fault fracture zone,incidence angle of the seismic radiation,are discussed.The numerical simulation shows that transform waves can develop inside low-velocity-fault-zone(LVFZ)when struck by external incident seismic radiation,and trapped waves can develop obviously inside the LVFZ.This result implies that the invariance of energy,struck by external incident seismic radiation,is congregated at the LVFZ,and the convergence effect increases with the increasing of the width and the decreasing of the shear wave velocity of the LVFZ.The vertical LVFZ can obstruct the spread of oblique incidence seismic wave,and the isolation effect decreases with the increasing incidence angle.The study about the seismic response of a variety of LVFZ models with different width and velocity struck by external vertically incident seismic radiation implies that,the amplification characteristics of ground motion in near fault zone site are frequency dependent.The lower frequency components of seismic radiation are amplified obviously by the LVFZ sites with lower dominant frequency(these have wider width or lower shear wave velocity),rather than vice versa.
A numerical solution to 2-D fault site model for incident SV waves was derived by using the explicit finite element combining transmitting boundary,and the distribution rules of site ground motion influenced by different fault characteristics,such as width and shear wave velocity of fault fracture zone,incidence angle of the seismic radiation,are discussed.The numerical simulation shows that transform waves can develop inside low-velocity-fault-zone(LVFZ)when struck by external incident seismic radiation,and trapped waves can develop obviously inside the LVFZ.This result implies that the invariance of energy,struck by external incident seismic radiation,is congregated at the LVFZ,and the convergence effect increases with the increasing of the width and the decreasing of the shear wave velocity of the LVFZ.The vertical LVFZ can obstruct the spread of oblique incidence seismic wave,and the isolation effect decreases with the increasing incidence angle.The study about the seismic response of a variety of LVFZ models with different width and velocity struck by external vertically incident seismic radiation implies that,the amplification characteristics of ground motion in near fault zone site are frequency dependent.The lower frequency components of seismic radiation are amplified obviously by the LVFZ sites with lower dominant frequency(these have wider width or lower shear wave velocity),rather than vice versa.
引文
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[10]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 F,Song Ch K,Meng Q X,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)
[11]Michelini A,McEvilly T V.Seismological studies at Parkfield I.Simultaneous inversion for velocity structure and hypocentersusing cubic B-splines parameterization[J].Bulletin of the Seismological Society of America,1991,81:524-552.
[12]Mooney W D,Ginzburg A.Seismic measurements of theinternal properties of fault zones[J].Pure&Applied Geophysics,1986,124:141-157.
[13]Scholz C H.The mechanics of earthquakes and faulting[M].Cambridge:Cambridge University Press,1990.
[14]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.
[15]Leary P C,Li Y G,Aki K.Observation and modeling of fault zone fracture seismic anisotropy-I.P,SV,and SH travel-times[J].Geophysical Journal of the Royal Astronomical Society,1987,91:461-484.
[16]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 Z Y,Huang F G,Jin Zh L.1970Tonghai earthquake[M].Beijing:Seismological Press,1990.(in Chinese)
[17]刘恢先.唐山大地震震害[M].北京:地震出版社,1985.Liu H X.Earthquake damage of Tangshan earthquake[M].Beijing:Seismological Press,1985.(in Chinese)
[18]姜葵.1988年云南澜沧-耿马地震[M].昆明:云南大学出版社,1993.Jiang K.1988 Lancang-Dima earthquake[M].Kunming:Yunnan University Press,1993.(in Chinese)
[19]Jongmans D,Malin P E.Microearthquake S-wave observations from 0 to 1 km in the Varian Well at Parkfield,California[J].Bulletin of the Seismological Society of America,1995,85:1805-1820.
[20]Sieh K E,Jones L M,Hauksson E,et al.Near-field investigations of the Landers earthquake sequence,April to July 1992[J].Science,1993,260:171-176.
[21]Michael A J,Eberhart-Phillips D M.Relations among fault behavior,subsurface geology,and three-dimensional velocity models[J].Science,1991,253:651-654.
[22]Thurber C H,Roecker S,Ellsworth W,et al.Twodimensional 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.
[23]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 B D,Wang W,Li X J,et al.Isolation effect of Xianshuihe fault zone in Wenchuan earthquake[J].Technology for Earthquake Disaster Prevention,2014,9(4),855-861.(in Chinese)
[2]周锡元,王广军,苏经宇.场地地基设计地震[M].北京:地震出版社,1990.Zhou X Y,Wang G J,Su J Y.Site foundation design earthquake[M].Beijing:Seismological Press,1990.(in Chinese).
[3]通海地震影响场调查组.通海地震的烈度分布与场地影响[R].哈尔滨:中国科学院工程力学研究所,1977.Field Investigation Group of Tonghai Earthquake.The intensity distribution and site effect of Tonghai earthquake[R].Harbin:Institute of Engineering Mechanics,Chinese Academy of Sciences,1977.(in Chinese)
[4]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 B D.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)
[5]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 B D,Wang W,Yu M.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)
[6]Li Y G,Leary P C.Fault zone trapped seismic waves[J].Bulletin of the Seismological Society of America,1990,80:1245-1271.
[7]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.
[8]Wang C.On the constitution of the San Andreas fault zone in Central California[J].Journal of Geophysical Research Atmospheres,1984,89:5858-5866.
[9]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.
[10]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 F,Song Ch K,Meng Q X,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)
[11]Michelini A,McEvilly T V.Seismological studies at Parkfield I.Simultaneous inversion for velocity structure and hypocentersusing cubic B-splines parameterization[J].Bulletin of the Seismological Society of America,1991,81:524-552.
[12]Mooney W D,Ginzburg A.Seismic measurements of theinternal properties of fault zones[J].Pure&Applied Geophysics,1986,124:141-157.
[13]Scholz C H.The mechanics of earthquakes and faulting[M].Cambridge:Cambridge University Press,1990.
[14]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.
[15]Leary P C,Li Y G,Aki K.Observation and modeling of fault zone fracture seismic anisotropy-I.P,SV,and SH travel-times[J].Geophysical Journal of the Royal Astronomical Society,1987,91:461-484.
[16]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 Z Y,Huang F G,Jin Zh L.1970Tonghai earthquake[M].Beijing:Seismological Press,1990.(in Chinese)
[17]刘恢先.唐山大地震震害[M].北京:地震出版社,1985.Liu H X.Earthquake damage of Tangshan earthquake[M].Beijing:Seismological Press,1985.(in Chinese)
[18]姜葵.1988年云南澜沧-耿马地震[M].昆明:云南大学出版社,1993.Jiang K.1988 Lancang-Dima earthquake[M].Kunming:Yunnan University Press,1993.(in Chinese)
[19]Jongmans D,Malin P E.Microearthquake S-wave observations from 0 to 1 km in the Varian Well at Parkfield,California[J].Bulletin of the Seismological Society of America,1995,85:1805-1820.
[20]Sieh K E,Jones L M,Hauksson E,et al.Near-field investigations of the Landers earthquake sequence,April to July 1992[J].Science,1993,260:171-176.
[21]Michael A J,Eberhart-Phillips D M.Relations among fault behavior,subsurface geology,and three-dimensional velocity models[J].Science,1991,253:651-654.
[22]Thurber C H,Roecker S,Ellsworth W,et al.Twodimensional 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.
[23]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 B D,Wang W,Li X J,et al.Isolation effect of Xianshuihe fault zone in Wenchuan earthquake[J].Technology for Earthquake Disaster Prevention,2014,9(4),855-861.(in Chinese)