汶川地震形成位移场的空间分布
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摘要
采用Yoshimitsu Okada及Steketee的断裂位错模型和汶川地震现有成果,通过坐标转换和合成矢量的方法将断裂位错模型用于映秀—北川断裂、灌县—安县断裂和北川—青川断裂组成的断裂系统的错动研究中,理论上计算龙门山近断裂地区的水平位移场(包括沿走向和垂直走向方向)和垂直位移场从震源到地表的分布.模型参数源于现有的研究成果和野外实地考察,计算得到的地表位移场与先前研究成果,包括GPS实测数据,具有的近似性表明了模型的正确性.但GPS只能测定地表水平和垂直变形,对于地下变形情况及其分布却无法描述;目前对于地下变形的研究主要基于对大量仪器记录的地震资料进行反演或通过野外观测进行推测;但是反演多集中于空间较大范围,这样虽可阐述断裂运动引起的大范围位移趋势,而对于震源附近空间介质位移的描述却略显粗糙;同时,野外观测误差较大.本文通过理论模型计算汶川地震中近断裂区域(距断裂50km)内的位移及分布.由计算发现在近断裂区域内垂直位移场和垂直走向方向位移场变化趋势一样,幅值都是从震源到地表逐渐减小;沿断裂走向方向的水平位移场从震源到地表逐渐变大,同时计算还表明位移场的变化在断裂上盘比下盘剧烈,余震分布主要集中于断裂上盘,这说明余震分布和位移剧烈程度存在某种相关性.
Basing on the Yoshimitsu Okada or Steketee's dislocation model and achievements of present researches on Wenchuan earthquake,through the coordination transform and vector composition,we apply dislocation model to fault system and make the dislocation model of Yingxiu-Beichuan fault Guanxian-Anxian fault and Beichuan-Qingchuan fault.We calculate theoretically the evolvement of region displacement fields including horizontal and vertical displacement from the source to the ground surface in the region near the faults.In the computation,the model parameters are from the present research achievement and field scientific research.Compared the computational result with GPS data achievements,we prove the validity of model.In fact,GPS can only measure the horizontal and vertical displacement along the ground surface,but it can not depict the deformation fields of underground.Through the much data from the seismic instrument or field survey,people mainly compute the large area underground deformation now.Although this computation can give the trend of displacement due to the motion of fault in large zone,it can not depict the displacement near the source nicely.In addition,field survey has relatively large error.This paper,we will apply the dislocation model to compute the displacement fields near the fault.The computation results show that vertical displacement field and horizontal displacement field vertical to strike direction have the same variation trend which change gradually small from the underground to ground surface.At the same time,horizontal displacement field along the strike direction varies gradually larges from the underground to ground surface.Furthermore,our computational results also show displacement fields vary stronger in hanging wall of fault than that of foot wall.The distribution of aftershock mainly focusing on the hanging wall of fault shows that the distribution of aftershock has the some correlation to the strong deformation displacement of strata.
Basing on the Yoshimitsu Okada or Steketee's dislocation model and achievements of present researches on Wenchuan earthquake,through the coordination transform and vector composition,we apply dislocation model to fault system and make the dislocation model of Yingxiu-Beichuan fault Guanxian-Anxian fault and Beichuan-Qingchuan fault.We calculate theoretically the evolvement of region displacement fields including horizontal and vertical displacement from the source to the ground surface in the region near the faults.In the computation,the model parameters are from the present research achievement and field scientific research.Compared the computational result with GPS data achievements,we prove the validity of model.In fact,GPS can only measure the horizontal and vertical displacement along the ground surface,but it can not depict the deformation fields of underground.Through the much data from the seismic instrument or field survey,people mainly compute the large area underground deformation now.Although this computation can give the trend of displacement due to the motion of fault in large zone,it can not depict the displacement near the source nicely.In addition,field survey has relatively large error.This paper,we will apply the dislocation model to compute the displacement fields near the fault.The computation results show that vertical displacement field and horizontal displacement field vertical to strike direction have the same variation trend which change gradually small from the underground to ground surface.At the same time,horizontal displacement field along the strike direction varies gradually larges from the underground to ground surface.Furthermore,our computational results also show displacement fields vary stronger in hanging wall of fault than that of foot wall.The distribution of aftershock mainly focusing on the hanging wall of fault shows that the distribution of aftershock has the some correlation to the strong deformation displacement of strata.
引文
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[12]雷建设,赵大鹏,苏金蓉等.龙门山断裂带地壳精细结构与汶川地震发震机理.地球物理学报,2009,52(2):339-345.Lei J S,Zhao D P,Su J R,et al.Fine seismic structureunder the Longmenshan fault zone and the mechanism of thelarge Wenchuan earthquake.Chinese J.Geophysics.(inChinese),2009,52(2):339-345.
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[15]李延兴,张静华,周伟等.汶川MS8.0地震孕育发生的机制与动力学问题.地球物理学报,2009,52(2):519-530.Li Y X,Zhang J H,Zhou W,et al.The mechanism anddynamics of the generation and occurrence for Wenchuan Ms8.0earthquake.Chinese J.Geophys.(in Chinese),2009,52(2):519-530.
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[19]Mansinha L,Smylie D E.Effect of earthquakes on theChandler wobble and the secular polar shift.J.Geophys.Res.,1967,72(18):4731-4743.
[20]Mansinha L,Smylie D E.The displacement fields of inclinedfaults.Bull.Seism.Soc.Am.,1971,61(5):1433-1440.
[21]Converse G.Equations for the displacements and displacementderivatives due to a rectangulardislocation in a three-dimensional elastic half-space.User’s Manual For DIS3D,US Geological Survey,Menlo Park,1973:119-148.
[22]Iwasaki T,Sato R.Strain field in a semi-infinite medium dueto an inclined rectangular fault.J.Phys.Earth,1979,27(4):285-314.
[23]Okada Y.Surface deformation due to shear and tensile faultsin a half-space.Bul1.Seism.Soc.Am.,1985,75(4):1135-1154.
[24]Okada Y.Internal deformation due to shear and tensile faultsin a half-space.Bull.Seism.Soc.Am.,1992,82(2):1018-1040.
[25]陈运泰,林邦慧,林中洋等.根据地面形变的观测研究1966年邢台地震的震源过程.地球物理学报,1975,18(3):164-180.Chen Y T,Lin B H,Lin Z Y,et al.The focal mechanism ofthe 1966 Hsingtai earthquake as inferred from the grounddeformation observations.Chinese J.Geophys.(inChinese),1975,18(3):164-182.
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[27]张永志,赵大江,王卫东.断层走滑不均匀性对地面变形的影响.地球物理学报,2009,52(8):2113-2118.Zhang Y Z,Zhao D J,Wang W D.Effects on the earthsurface deformation by asymmetric strike slip on fault plane.Chinese J.Geophys.(in Chinese),2009,52(8):2113-2118.
[28]唐荣昌,文德华,黄祖智等.松潘-龙门山地区主要活动断裂带第四纪活动特征.中国地震,1991,7(3):64-71.Tang R C,Wen D H,Huang Z Z,et al.The Quaternaryactivity characteristics of several major active faults in theSongpan-Longmenshan region.Earthquake Research in China(in Chinese),1991,7(3):64-71.
[29]陈国光,计凤桔,周荣军等.龙门山断裂带晚第四纪活动性分段的初步研究.地震地质,2007,29(3):657-673.Chen G G,Ji F J,Zhou R J,et al.Primary research ofactivity segmentation of Longmenshan Fault zone since late-Quaternary.Seismology and Geology(in Chinese),2007,29(3):657-673.
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[2]刘静,张智慧,文力等.汶川8级大地震同震破裂的特殊性及构造意义——多条平行断裂同时活动的反序型逆冲地震事件.地质学报,2008,82(12):1707-1722.Liu J,Zhang Z H,Wen L,et al.The Ms8.0 WenchuanEarthquake co-seismic rupture and its tectonic implications—anout-of-sequence thrusting event with slip partitioned onmultiple faults.Acta Geologica Sinica(in Chinese),2008,82(12):1707-1722.
[3]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:地球科学,2008,38(10):1186-1194.Zhang Y,Feng W P,Xu L S,et al.Spatio-temporal ruptureprocess of the 2008great Wenchuan earthquake.Science China(Ser D-Earth Sci)(in Chinese),2008,38(10):1186-1194.
[4]王卫民,赵连锋,李娟等.四川汶川8.0级地震震源过程.地球物理学报,2008,51(5):1403-1410.Wang W M,Zhao L F,Li J,et al.Rupture process of the Ms8.0 Wenchuan earthquake of Sichuan,China.Chinese J.Geophys.(in Chinese),2008,51(5):1403-1410.
[5]朱守彪,张培震.2008年汶川Ms8.0地震发生过程的动力学机制研究.地球物理学报,2009,52(2):418-427.Zhu S B,Zhang P Z.A study on the dynamical mechanisms ofthe Wenchuan Ms8.0earthquake,2008.Chinese J.Geophys.(in Chinese),2009,52(2):418-427.
[6]陈章立,赵翠萍,王勤彩等.汶川Ms8.0级地震发生背景与过程的研究.地球物理学报,2009,52(2):456-463.Chen Z L,Zhao C P,Wang Q C,et al.A study on theoccurrence background and process of Wenchuan Ms8.0earthquake.Chinese J.Geophys.(in Chinese),2009,52(2):456-463.
[7]王绪本,朱迎堂,赵锡奎等.青藏高原东缘龙门山逆冲构造深部电性结构特征.地球物理学报,2009,52(2):464-471.Wang X B,Zhu Y T,Zhao X K,et al.Deep conductivitycharacteristics of the Longmen Shinto,Eastern Qinghai-TibetPlateau.Chinese J.Geophys.(in Chinese),2009,52(2):464-471.
[8]申重阳,李辉,谈洪波.汶川8.0级地震同震重力与形变效应模拟.大地测量与地球动力学,2008,28(5):6-12.Shen C Y,Li H,Tan H B.Simulation of coseismic gravitychanges and deformation effect of Wenchuan MS8.0earthquake.Journal of Geodesy and Geodynamics(inChinese),2008,28(5):6-12.
[9]张国宏,屈春燕,宋小刚等.基于InSAR同震形变场反演汶川Mw7.9地震断层滑动分布.地球物理学报,2010,53(2):269-279.Zhang G H,Qu C Y,Song X G,et al.Slip distribution andsource parameters Inverted from co-seismic deformationderived by InSAR technology of Wenchuan Mw 7.9earthquake.Chinese J.Geophysics.(in Chinese),2010,53(2):269-279.
[10]赵国泽,陈晓斌,肖骑彬等.汶川Ms8.0级地震成因三“层次”分析—基于深部电性结构.地球物理学报,2009,52(2):553-563.Zhao G Z,Chen X B,Xiao Q B,et al.Generationmechanism of Wenchuan strong earthquake of Ms8.0inferredfrom EM measurements in three levers.Chinese J.Geophysics.(in Chinese),2009,52(2):553-563.
[11]闻学泽,张培震,杜方等.2008年汶川8.0级地震发生的历史与现今地震活动背景.地球物理学报,2009,52(2):444-454.Wen X Z,Zhang P Z,Du F,et al.The background ofhistorical and modern seismic activities of the occurrence ofthe 2008Ms8.0Wenchuan,Sichuan,earthquake.Chinese J.Geophysics.(in Chinese),2009,52(2):444-454.
[12]雷建设,赵大鹏,苏金蓉等.龙门山断裂带地壳精细结构与汶川地震发震机理.地球物理学报,2009,52(2):339-345.Lei J S,Zhao D P,Su J R,et al.Fine seismic structureunder the Longmenshan fault zone and the mechanism of thelarge Wenchuan earthquake.Chinese J.Geophysics.(inChinese),2009,52(2):339-345.
[13]单建新,屈春燕,宋小刚等.汶川Ms8.0级地震InSAR同震形变场观测与研究.地球物理学报,2009,52(2):496-504.Shan J X,Qu C Y,Song X G,et al.Coseismic surfacedeformation caused by the Wenchuan Ms8.0earthquake fromInSAR data analysis.Chinese J.Geophysics.(in Chinese),2009,52(2):496-504.
[14]张培震.GPS测定的2008年汶川MS8.0级地震的同震位移场.中国科学D辑(地球科学),2008,38(10):1195-1206.Zhang P Z.The coseismic displacement fields of WenchuanMS8.0earthquake 2008.Science China(Ser D-Earth Sci)(inChinese),2008,38(10):1195-1206.
[15]李延兴,张静华,周伟等.汶川MS8.0地震孕育发生的机制与动力学问题.地球物理学报,2009,52(2):519-530.Li Y X,Zhang J H,Zhou W,et al.The mechanism anddynamics of the generation and occurrence for Wenchuan Ms8.0earthquake.Chinese J.Geophys.(in Chinese),2009,52(2):519-530.
[16]Steketee J A.On Volterra's dislocations in a semi-infiniteelastic medium.Can.J.Phys.,1958,36(2):192-205.
[17]Chinnery M A.The deformation of the ground around surfacefaults.Bull.Seism.Soc.Am.,1961,51(3):355-372.
[18]Chinnery M A.The stress changes that accompany strike-slipfaulting.Bull.Seism.Soc.Am.,1963,53(5):921-931.
[19]Mansinha L,Smylie D E.Effect of earthquakes on theChandler wobble and the secular polar shift.J.Geophys.Res.,1967,72(18):4731-4743.
[20]Mansinha L,Smylie D E.The displacement fields of inclinedfaults.Bull.Seism.Soc.Am.,1971,61(5):1433-1440.
[21]Converse G.Equations for the displacements and displacementderivatives due to a rectangulardislocation in a three-dimensional elastic half-space.User’s Manual For DIS3D,US Geological Survey,Menlo Park,1973:119-148.
[22]Iwasaki T,Sato R.Strain field in a semi-infinite medium dueto an inclined rectangular fault.J.Phys.Earth,1979,27(4):285-314.
[23]Okada Y.Surface deformation due to shear and tensile faultsin a half-space.Bul1.Seism.Soc.Am.,1985,75(4):1135-1154.
[24]Okada Y.Internal deformation due to shear and tensile faultsin a half-space.Bull.Seism.Soc.Am.,1992,82(2):1018-1040.
[25]陈运泰,林邦慧,林中洋等.根据地面形变的观测研究1966年邢台地震的震源过程.地球物理学报,1975,18(3):164-180.Chen Y T,Lin B H,Lin Z Y,et al.The focal mechanism ofthe 1966 Hsingtai earthquake as inferred from the grounddeformation observations.Chinese J.Geophys.(inChinese),1975,18(3):164-182.
[26]黄建梁,李辉,李瑞浩.点源位错引起的重力、位势及其梯度变化.地震学报,1995,17(1):72-80.Huang J L,Li H,Li R H.The variation of gravity potentialand gradient due to source dislocation.Acta SeismologicaSinca(in Chinese),1995,17(1):72-80.
[27]张永志,赵大江,王卫东.断层走滑不均匀性对地面变形的影响.地球物理学报,2009,52(8):2113-2118.Zhang Y Z,Zhao D J,Wang W D.Effects on the earthsurface deformation by asymmetric strike slip on fault plane.Chinese J.Geophys.(in Chinese),2009,52(8):2113-2118.
[28]唐荣昌,文德华,黄祖智等.松潘-龙门山地区主要活动断裂带第四纪活动特征.中国地震,1991,7(3):64-71.Tang R C,Wen D H,Huang Z Z,et al.The Quaternaryactivity characteristics of several major active faults in theSongpan-Longmenshan region.Earthquake Research in China(in Chinese),1991,7(3):64-71.
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