断层破裂面倾角变化对断陷盆地强地面运动的影响
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摘要
地震事件中,断层破裂面的倾角大小直接影响到地表强地震动的分布状态,尤其在断陷盆地中,强地面运动特征还可能受到盆地结构及盆地内多条围限断层的影响.本文模拟了银川断陷盆地内的活动断层———银川隐伏断层南段发生Mw6.5特征地震时,断层破裂面倾角在30°～85°范围内变化时引起的强地面运动,探讨了断层破裂面倾角变化对盆地内强地面运动分布特征和强度的影响.结果表明:破裂面倾角较缓时,银川盆地内的强地面运动分布区域不仅仅决定于发震断层的产状,同时还受到断层上盘距离最近的芦花台断层的影响,致使强地面运动集中于两条断层所围限的区域;随着发震断层破裂面的倾角逐渐增大,强地面运动以发震断层产状的影响为主,强震集中区向发震断层靠近并分布于发震断层上盘,且沿断层走向方向出现了强度不同的地震动反射区;尤其是发震断层破裂面倾角接近垂直时,受银川盆地"西陡东缓"结构和盆地西边界贺兰山东麓断裂反射作用的影响,竖向地震动反射区强度在远离发震断层的西北方向明显增大,致使芦花台断层附近区域与银川断层南段上盘区域成为地震发生时可能遭受震害最严重的地区.本文探讨结果提醒我们在类似区域的活动断层附近进行建(构)筑规划和地震工程设计时,有必要考虑发震断层破裂面倾角大小和盆地内其它断层构造的共同影响,综合评价潜在地震对盆地内近断层地表及各类建(构)筑物的危害性.
For a large-size faulted basin with many active faults developed,the strong ground motion in basin will be influenced by the following several factors,the fault dips,the activity modes,the expand shape of faults inside basin or along basin edges.In order to research the relations between the fault dip angles and strong ground motion characters in faulted basin,Yinchuan basin and Yinchuan buried fault are suitable for us to carry out our plans.In Yinchuan faulted basin,there are two major faults inside and two enormous faults stretching along west and east sides.Yinchuan buried fault,a Late Pleistocene epoch-Holocene active fault,is a major one of those activity faults which perhaps affect the urban planning and development and earthquake resistance of Yinchuan City seriously.In our research,according to the earthquake risk evaluation results of southern segment of Yinchuan Fault,we defined the characteristic earthquake magnitude Mw6.5 and assume different dip angles(30°,45°,60°,66°,75°,and 85°) for simulations of strong ground motion.By an improved Finite-Element Method,we computed all above cases of ground motion and draw following conclusions.For a gently dipping fault,the intensive distribution of ground motion appeared in the area between the southern segment of Yinchuan buried fault and the Luhuatai fault which means that the Luhuatai fault blocks the spreading of seismic wave.With the increasing of the fault dip angle,the strong ground motion mainly distribute on the hanging-wall close to the fault which shows that the fault angle of inclination is the major factor controlling the ground motion distribution.Furthermore,along the direction of the trend of Yinchuan buried fault,several areas of weaker ground motion formed gradually.When the fault dip became larger and larger until 85°,influenced by edge faults of Yinchuan basin with the occurrence of "steep in west edge and gentle in east edge",special reflection region of strong ground motion in UD component become stronger and stronger in the southwest area far away from the Yinchuan buried fault which makes the regions near Yinchuan fault and Luhuatai fault become two major possible risk zones if potential earthquake occurred.All above results remind us that it is quite necessary to consider the combined action of active fault dip angle and reflected waves from edge faults in faulted basin when we undertake the seismic safety evaluation and resistance for buildings and constructions in the near-field region.
For a large-size faulted basin with many active faults developed,the strong ground motion in basin will be influenced by the following several factors,the fault dips,the activity modes,the expand shape of faults inside basin or along basin edges.In order to research the relations between the fault dip angles and strong ground motion characters in faulted basin,Yinchuan basin and Yinchuan buried fault are suitable for us to carry out our plans.In Yinchuan faulted basin,there are two major faults inside and two enormous faults stretching along west and east sides.Yinchuan buried fault,a Late Pleistocene epoch-Holocene active fault,is a major one of those activity faults which perhaps affect the urban planning and development and earthquake resistance of Yinchuan City seriously.In our research,according to the earthquake risk evaluation results of southern segment of Yinchuan Fault,we defined the characteristic earthquake magnitude Mw6.5 and assume different dip angles(30°,45°,60°,66°,75°,and 85°) for simulations of strong ground motion.By an improved Finite-Element Method,we computed all above cases of ground motion and draw following conclusions.For a gently dipping fault,the intensive distribution of ground motion appeared in the area between the southern segment of Yinchuan buried fault and the Luhuatai fault which means that the Luhuatai fault blocks the spreading of seismic wave.With the increasing of the fault dip angle,the strong ground motion mainly distribute on the hanging-wall close to the fault which shows that the fault angle of inclination is the major factor controlling the ground motion distribution.Furthermore,along the direction of the trend of Yinchuan buried fault,several areas of weaker ground motion formed gradually.When the fault dip became larger and larger until 85°,influenced by edge faults of Yinchuan basin with the occurrence of "steep in west edge and gentle in east edge",special reflection region of strong ground motion in UD component become stronger and stronger in the southwest area far away from the Yinchuan buried fault which makes the regions near Yinchuan fault and Luhuatai fault become two major possible risk zones if potential earthquake occurred.All above results remind us that it is quite necessary to consider the combined action of active fault dip angle and reflected waves from edge faults in faulted basin when we undertake the seismic safety evaluation and resistance for buildings and constructions in the near-field region.
引文
[1]丁海平,宋贞霞.震源参数对地震动相干函数的影响.振动与冲击,2010,29(7):16-18,74.Ding H P,Song Z X.Effects of source parameters oncoherency function of ground motion.Journal of Vibrationand Shock(in Chinese),2010,29(7):16-18,74.
[2]Aagaard B T,Hall J F,Heaton T H.Effects of fault dip andslip rake angles on near-source ground motions:why rupturedirectivity was minimal in the 1999 Chi-Chi,Taiwan,Earthquake.Bulletin of the Seismological Society ofAmerica,2004,94(1):155-170.
[3]Wald D J.Slip History of the 1995Kobe,Japan,earthquakedetermined from strong motion,teleseismic,and geodeticdata.Journal of Physics of the Earth,1996,44(5):489-503.
[4]许力生,陈运泰.从全球长周期波形资料反演2001年11月14日昆仑山口地震时空破裂过程.中国科学D辑,2004,34(3):256-264.Xu L S,Chen Y T.Temporal and spatial rupture process ofthe great Kunlun Mountain pass earthquake of November 14,2001from the GDSN long period waveform data.Science inChina Ser.D Earth Sciences(in Chinese),2004,34(3):256-264.
[5]Parsons T,Ji C,Kirby E.Stress changes from the 2008Wenchuan Earthquake and increased hazard in the Sichuanbasin.Nature,2008,454(7203):509-510.
[6]张勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学D辑,2008,38(10):1186-1194.Zhang Y,Feng W P,Xu L S,et al.Temporal and spatialrupture process of 2008 Wenchuan Earthquake,China.Science in China Ser.D Earth Sciences(in Chinese),2008,38(10):1186-1194.
[7]Graves R W.Three-dimensional finite-difference modeling ofthe San Andreas fault:source parameterization and ground-motion levels.Bulletin of the Seismological Society ofAmerica,1998,88(4):881-897.
[8]Ripperger J,Mai P M,Ampuero J P.Variability of near-fieldground motion from dynamic earthquake rupture simulations.Bulletin of the Seismological Society of America,2008,98(3):1207-1228.
[9]姜慧,沈钧,俞言祥等.逆断层地震近场地震动影响场和地表形变模拟.地震工程与工程振动,2006,26(1):11-17.Jiang H,Shen J,Yu Y X,et al.Dynamic simulation of effectfield of strong ground motions and deformation of ground nearreverse fault.Earthquake Engineering and EngineeringVibration(in Chinese),2006,26(1):11-17.
[10]刘启方,金星,丁海平.复杂场地条件下震源参数对断层附近长周期地震动的影响.地球物理学报,2008,51(1):186-196.Liu Q F,Jin X,Ding H P.Effects of the source parameterson long period near-fault ground motion in the case ofcomplex site condition.Chinese Journal of Geophysics(inChinese),2008,51(1):186-196.
[11]Frankel A D,Stephenson W J,Carver D L,et al.Seismichazard maps for seattle,Washington,incorporating 3Dsedimentary basin effects.Nonlinear Site Response,andRupture Directivity.U.S.Geological Survey Open-FileReport 2007.2007,1175,77p.,3pls.
[12]Hruby C E,Beresnev I A.Empirical corrections for basineffects in stochastic ground-motion prediction,based on theLos Angeles basin analysis.Bulletin of the SeismologicalSociety of America,2003,93(4):1679-1690.
[13]张冬丽,张伟,徐锡伟等.断层破裂方式对银川盆地强地面运动的影响.地震工程与工程振动,2009,29(4):1-8.Zhang D L,Zhang W,Xu X W,et al.Influence of seismicsource rupture mode on strong ground motion in YinchuanBasin.Earthquake Engineering and Engineering Vibration(in Chinese),2009,29(4):1-8.
[14]宁夏地质局研究队《地质力学》编图组.宁夏回族自治区构造体系图(1∶50万).银川:宁夏人民出版社,1980.Geology Administration of Ninxia Hui Autonomous Region.Geological Structural System Map in Ninxia Hui AutonomousRegion(1∶500000)(in Chinese).Yinchuan:Ningxia People′sPress,1980.
[15]严烈宏,王利等著.银川盆地地热系统.银川:宁夏人民出版社,2002.Yan H L,Wang L,et al.Geothermal System in YinchuanBasin(in Chinese).Yinchuan:Ningxia People′s PublishingHouse,2002.
[16]方盛明,赵成彬,柴炽章等.银川断陷盆地地壳结构与构造的地震学证据.地球物理学报,2009,52(7):1768-1775.Fang S M,Zhao C B,Chai C Z,et al.Seismic evidence ofcrustal structures in the Yinchuan faulted basin.ChineseJournal of Geophysics(in Chinese),2009,52(7):1768-1775.
[17]柴炽章,孟广魁,杜鹏等.隐伏活动断层的多层次综合探测—以银川隐伏活动断层为例.地震地质,2006,28(4):536-546.Chai C Z,Meng G K,Du P,et al.Comprehensive multi-level exploration of buried active fault:an example ofYinchuan buried active fault.Seismology and Geology(inChinese),2006,28(4):536-546.
[18]Lei Q Y,Chai C Z,Du P,et al.Characteristics of lateQuaternary activity of the Luhuatai buried fault revealed bydrilling.Earthquake Research in China,2012,26(2):168-180.
[19]柴炽章,孟广魁,马贵仁等.银川市活动断层探测与地震危险性评价.北京:科学出版社,2011.Chai C Z,Meng G K,Ma G R,et al.Active Fault Surveyingand Seismic Hazard Evolution in Yinchuan Basin(inChinese).Beijing:Science Press,2011.
[20]丁国瑜,田勤俭,孔凡臣等.活断层分段—原则、方法及应用.北京:地震出版社,1993:39-76.Ding G Y,Tian Q J,Kong F C,et al.Principles andMethods for Segmentation of Active Faults and TheirApplications(in Chinese).Beijing:Seismological Press,1993:39-76.
[21]李孟銮,万自成.1739年平罗8.0级地震的发震构造及其孕育特征.地震地质,1984,6(3):23-28.Li M L,Wan Z C.Characteristics of the earthquakegenerating structures for magnitude 8.0earthquake of 1739and the process of its preparation.Seismology and Geology(in Chinese),1984,6(3):23-28.
[22]张冬丽,徐锡伟,赵伯明等.强地面运动数值模拟中三维物理模型的建立方法—以昆明盆地为例.地震学报,2007,29(2):187-196.Zhang D L,Xu X W,Zhao B M,et al.3-D physical model instrong ground motion numerical simulation:A case study ofKunming basin.Acta Seismologica Sinica(in Chinese),2007,29(2):187-196.
[23]Somerville P,Irikura K,Graves R,et al.Characterizingcrustal earthquake slip models for the prediction of strongground motion.Seis.Res.Lett.,1999,70(1):59-80.
[24]Wells D L,Coppersmith K H.New Empirical relationshipsamong magnitude,rupture length,rupture width,rupturearea,and surface displacement.Bulletin of the SeismologicalSociety of America,1994,84:974-1002.
[25]Wang H Y,Tao X X,Li J.Global source parameters offinite fault model for strong ground motion simulations orpredictions.//13th World Conference on EarthquakeEngineering.Vancouver,B.C.,Canada,2004:274.
[26]张伟.含地形起伏的三维非均匀介质中地震波传播的有限差分法及其在强地面运动模拟中的应用[博士论文].北京:北京大学,2006.Zhang W.Finite difference seismic wave modeling in 3Dheterogeneous media with surface topography and itsimplementation in strong ground motion study[Ph.D.thesis](in Chinese).Beijing:Beijing University,2006.
[27]Zhang W,Shen Y,Chen X F.Numerical simulation ofstrong ground motion for the Ms8.0Wenchuan earthquake of12 May 2008.Science in China Series D:Earth Science,2008,51(12):1673-1682.
[28]Aki K.Scaling law of seismic spectrum.J.Geophys.Res.,1967,72(4):1217-1231.
[29]陶夏新,王国新.近场强地震动模拟中对破裂的方向性效应和上盘效应的表达.地震学报,2003,25(2):191-198.Tao X X,Wang G X.Rupture directivity and hanging walleffect in near field strong ground motion simulation.ActaSeismologica Sinica(in Chinese),2003,25(2):191-198.
[2]Aagaard B T,Hall J F,Heaton T H.Effects of fault dip andslip rake angles on near-source ground motions:why rupturedirectivity was minimal in the 1999 Chi-Chi,Taiwan,Earthquake.Bulletin of the Seismological Society ofAmerica,2004,94(1):155-170.
[3]Wald D J.Slip History of the 1995Kobe,Japan,earthquakedetermined from strong motion,teleseismic,and geodeticdata.Journal of Physics of the Earth,1996,44(5):489-503.
[4]许力生,陈运泰.从全球长周期波形资料反演2001年11月14日昆仑山口地震时空破裂过程.中国科学D辑,2004,34(3):256-264.Xu L S,Chen Y T.Temporal and spatial rupture process ofthe great Kunlun Mountain pass earthquake of November 14,2001from the GDSN long period waveform data.Science inChina Ser.D Earth Sciences(in Chinese),2004,34(3):256-264.
[5]Parsons T,Ji C,Kirby E.Stress changes from the 2008Wenchuan Earthquake and increased hazard in the Sichuanbasin.Nature,2008,454(7203):509-510.
[6]张勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学D辑,2008,38(10):1186-1194.Zhang Y,Feng W P,Xu L S,et al.Temporal and spatialrupture process of 2008 Wenchuan Earthquake,China.Science in China Ser.D Earth Sciences(in Chinese),2008,38(10):1186-1194.
[7]Graves R W.Three-dimensional finite-difference modeling ofthe San Andreas fault:source parameterization and ground-motion levels.Bulletin of the Seismological Society ofAmerica,1998,88(4):881-897.
[8]Ripperger J,Mai P M,Ampuero J P.Variability of near-fieldground motion from dynamic earthquake rupture simulations.Bulletin of the Seismological Society of America,2008,98(3):1207-1228.
[9]姜慧,沈钧,俞言祥等.逆断层地震近场地震动影响场和地表形变模拟.地震工程与工程振动,2006,26(1):11-17.Jiang H,Shen J,Yu Y X,et al.Dynamic simulation of effectfield of strong ground motions and deformation of ground nearreverse fault.Earthquake Engineering and EngineeringVibration(in Chinese),2006,26(1):11-17.
[10]刘启方,金星,丁海平.复杂场地条件下震源参数对断层附近长周期地震动的影响.地球物理学报,2008,51(1):186-196.Liu Q F,Jin X,Ding H P.Effects of the source parameterson long period near-fault ground motion in the case ofcomplex site condition.Chinese Journal of Geophysics(inChinese),2008,51(1):186-196.
[11]Frankel A D,Stephenson W J,Carver D L,et al.Seismichazard maps for seattle,Washington,incorporating 3Dsedimentary basin effects.Nonlinear Site Response,andRupture Directivity.U.S.Geological Survey Open-FileReport 2007.2007,1175,77p.,3pls.
[12]Hruby C E,Beresnev I A.Empirical corrections for basineffects in stochastic ground-motion prediction,based on theLos Angeles basin analysis.Bulletin of the SeismologicalSociety of America,2003,93(4):1679-1690.
[13]张冬丽,张伟,徐锡伟等.断层破裂方式对银川盆地强地面运动的影响.地震工程与工程振动,2009,29(4):1-8.Zhang D L,Zhang W,Xu X W,et al.Influence of seismicsource rupture mode on strong ground motion in YinchuanBasin.Earthquake Engineering and Engineering Vibration(in Chinese),2009,29(4):1-8.
[14]宁夏地质局研究队《地质力学》编图组.宁夏回族自治区构造体系图(1∶50万).银川:宁夏人民出版社,1980.Geology Administration of Ninxia Hui Autonomous Region.Geological Structural System Map in Ninxia Hui AutonomousRegion(1∶500000)(in Chinese).Yinchuan:Ningxia People′sPress,1980.
[15]严烈宏,王利等著.银川盆地地热系统.银川:宁夏人民出版社,2002.Yan H L,Wang L,et al.Geothermal System in YinchuanBasin(in Chinese).Yinchuan:Ningxia People′s PublishingHouse,2002.
[16]方盛明,赵成彬,柴炽章等.银川断陷盆地地壳结构与构造的地震学证据.地球物理学报,2009,52(7):1768-1775.Fang S M,Zhao C B,Chai C Z,et al.Seismic evidence ofcrustal structures in the Yinchuan faulted basin.ChineseJournal of Geophysics(in Chinese),2009,52(7):1768-1775.
[17]柴炽章,孟广魁,杜鹏等.隐伏活动断层的多层次综合探测—以银川隐伏活动断层为例.地震地质,2006,28(4):536-546.Chai C Z,Meng G K,Du P,et al.Comprehensive multi-level exploration of buried active fault:an example ofYinchuan buried active fault.Seismology and Geology(inChinese),2006,28(4):536-546.
[18]Lei Q Y,Chai C Z,Du P,et al.Characteristics of lateQuaternary activity of the Luhuatai buried fault revealed bydrilling.Earthquake Research in China,2012,26(2):168-180.
[19]柴炽章,孟广魁,马贵仁等.银川市活动断层探测与地震危险性评价.北京:科学出版社,2011.Chai C Z,Meng G K,Ma G R,et al.Active Fault Surveyingand Seismic Hazard Evolution in Yinchuan Basin(inChinese).Beijing:Science Press,2011.
[20]丁国瑜,田勤俭,孔凡臣等.活断层分段—原则、方法及应用.北京:地震出版社,1993:39-76.Ding G Y,Tian Q J,Kong F C,et al.Principles andMethods for Segmentation of Active Faults and TheirApplications(in Chinese).Beijing:Seismological Press,1993:39-76.
[21]李孟銮,万自成.1739年平罗8.0级地震的发震构造及其孕育特征.地震地质,1984,6(3):23-28.Li M L,Wan Z C.Characteristics of the earthquakegenerating structures for magnitude 8.0earthquake of 1739and the process of its preparation.Seismology and Geology(in Chinese),1984,6(3):23-28.
[22]张冬丽,徐锡伟,赵伯明等.强地面运动数值模拟中三维物理模型的建立方法—以昆明盆地为例.地震学报,2007,29(2):187-196.Zhang D L,Xu X W,Zhao B M,et al.3-D physical model instrong ground motion numerical simulation:A case study ofKunming basin.Acta Seismologica Sinica(in Chinese),2007,29(2):187-196.
[23]Somerville P,Irikura K,Graves R,et al.Characterizingcrustal earthquake slip models for the prediction of strongground motion.Seis.Res.Lett.,1999,70(1):59-80.
[24]Wells D L,Coppersmith K H.New Empirical relationshipsamong magnitude,rupture length,rupture width,rupturearea,and surface displacement.Bulletin of the SeismologicalSociety of America,1994,84:974-1002.
[25]Wang H Y,Tao X X,Li J.Global source parameters offinite fault model for strong ground motion simulations orpredictions.//13th World Conference on EarthquakeEngineering.Vancouver,B.C.,Canada,2004:274.
[26]张伟.含地形起伏的三维非均匀介质中地震波传播的有限差分法及其在强地面运动模拟中的应用[博士论文].北京:北京大学,2006.Zhang W.Finite difference seismic wave modeling in 3Dheterogeneous media with surface topography and itsimplementation in strong ground motion study[Ph.D.thesis](in Chinese).Beijing:Beijing University,2006.
[27]Zhang W,Shen Y,Chen X F.Numerical simulation ofstrong ground motion for the Ms8.0Wenchuan earthquake of12 May 2008.Science in China Series D:Earth Science,2008,51(12):1673-1682.
[28]Aki K.Scaling law of seismic spectrum.J.Geophys.Res.,1967,72(4):1217-1231.
[29]陶夏新,王国新.近场强地震动模拟中对破裂的方向性效应和上盘效应的表达.地震学报,2003,25(2):191-198.Tao X X,Wang G X.Rupture directivity and hanging walleffect in near field strong ground motion simulation.ActaSeismologica Sinica(in Chinese),2003,25(2):191-198.
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