介质不均匀性和断层倾角对同震位移场影响的数值模拟
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摘要
利用三维有限元数值模拟方法,定量研究了介质不均匀性和断层倾角变化对同震位移场的影响。模拟结果显示:1)在均匀及纵向分层介质模型中,对于垂直走滑断层地震,水平位移场分量与介质的泊松比呈较弱的负相关,垂直位移场与介质的泊松比呈正相关,水平位移场与剪切模量呈正相关,垂直位移场与剪切模量呈负相关;2)模型介质的横向变化对同震位移场有较大影响,剪切模量的横向变化对地震位移场影响最大,且两者呈负相关,在垂直走滑断层地震中,保持断层一侧块体的介质参数不变、减半另一侧块体的剪切模量,剪切模量减半的块体中的最大垂直位移分量增大55.6%;3)倾角对同震位移场有重要影响。断层附近,倾角对位移场起控制作用,对于高倾角逆冲断层(60°～90°),上盘断层附近区域的水平位移场出现反向,反向区域的范围随倾角的增大而增大,当倾角为90°时,上盘水平位移场全部反向;断层倾角增大时,断层附近下盘的水平位移场的增大幅度较大。
In order to quantify the effect of medium heterogeneities and the dip of the fault on the coseismic displacement,three-dimensional finite element numerical method was applied.The selected slip distribution models including finite rectangular strike,normal and reverse fault.The numerical simulation has given following results.1) For the vertical strike earthquake in the homogeneous and vertically layed mediums,the coseismic displacement slightly depends on the Poisson's ratio,the relation between horizontally displacements and Poisson's ratio is negative,and it is positive for the vertical displacements.The relation between horizontally displacements and shear modulus is positive,and it is negtive for the vertical displacements;2) In horizontally heterogeneous medium,the shear modulus plays a significant role on the surface displacements,the relation between shear modulus and displacement field is negative,in the case of the medium parameters on the right block of fault remain unchanged,the increase extent of maximum vertical displacements on the left block of fault reaches 55.6% and the shear modulus of the left block of fault halved.3)In the neighborhood of fault,the dip angle of fault dominate the coseismic displacements,as for the reverse fault earthquake with high dip(60°-90°),opposite direction region appears in the horizontal displacements on the hanging wall,the range of opposite direction region increase with dip-angle;and the increase extent of coseismic displacements on the foot wall is obvious.
In order to quantify the effect of medium heterogeneities and the dip of the fault on the coseismic displacement,three-dimensional finite element numerical method was applied.The selected slip distribution models including finite rectangular strike,normal and reverse fault.The numerical simulation has given following results.1) For the vertical strike earthquake in the homogeneous and vertically layed mediums,the coseismic displacement slightly depends on the Poisson's ratio,the relation between horizontally displacements and Poisson's ratio is negative,and it is positive for the vertical displacements.The relation between horizontally displacements and shear modulus is positive,and it is negtive for the vertical displacements;2) In horizontally heterogeneous medium,the shear modulus plays a significant role on the surface displacements,the relation between shear modulus and displacement field is negative,in the case of the medium parameters on the right block of fault remain unchanged,the increase extent of maximum vertical displacements on the left block of fault reaches 55.6% and the shear modulus of the left block of fault halved.3)In the neighborhood of fault,the dip angle of fault dominate the coseismic displacements,as for the reverse fault earthquake with high dip(60°-90°),opposite direction region appears in the horizontal displacements on the hanging wall,the range of opposite direction region increase with dip-angle;and the increase extent of coseismic displacements on the foot wall is obvious.
引文
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9楼海,等.2008年汶川Ms8.0级地震的深部构造环境———远震P波接收函数和布格重力异常的联合解释[J].中国科学D辑(地球科学),2008,38(10):1 207-1 220.(Lou Hai,et al.Deep tectonic setting of the 2008Wenchuan Ms8.0 earthquake in southwest China———Jointanalysis of teleseismic P-wave veceiver functions and Bougu-er gravity anomalies[J].Science in China(series D),2008,38(10):1 207-1 220))
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14王栋,谢礼立.断层倾角对上/下盘效应的影响[J].地震工程与工程振动,2007,27(5):1-6.(Wang Dongand Xie Lili.The influence of the fault dtp angle on the onthe hanging wall/footwall effect[J].Journal of EarthquakeEngineering and Engineering Vibration,2007,27(5):1-6)
15张国宏,等.基于GPS和InSAR反演汶川Mw7.9地震断层滑动分布[J].大地测量与地球动力学,2010,(4):19-24.(Zhang Guohong,et al.Inversion of slip distribu-tion of 2008 Wenchuan Mw7.9 earthquake constrainedjointly by InSAR and GPS measurements[J].Journal of Ge-odesy and Geodynamics,2010,(4):19-24)
16 Li F and Huang J.Three-dimensional numerical simulationon the coseismic deformation of the 2008 Ms8.0 Wenchuanearthquake in China[J].Earthquake Science,2010,23:191-200.
17 Ji C and Hayes G.Preliminary result of the 12 May 2008Mw7.9 eastern Sichuan[B/OL].http://earthquake.usgs.gov/earthquakes/eqinthenews/2008/us2008ryan/finite_fault.php.2008.
18 Nishimuru N and Yaji Y.Rupture process for may 12,2008Sichuan earthquake[B/OL].http://www.geol.tsukuba.ac.jp/～nisimura/20080512/.2008.
19国家重大科学工程“中国地壳运动观测网络”项目组.GPS测定的2008年汶川Ms8.0地震的同震位移场[J].中国科学D辑(地球科学),2008,38(10):1 195-1 206.(CMONOC Group.Cosesmic displacements of the2008 Wenchuan Ms8.0 earthquake from GPS observation[J].Science in China(series D),2008,38(10):1 195-1 206)
2 Okada Y.Internal deformation due to shear and tensile faultsin a half-space[J].Bulletin of the Seismological Society ofAmerica,1992,82(2):1 018-1 040.
3 Wang R,et al.PSGRN/PSCMP-a new code for calculatingco-and post-seismic deformation,geoid and gravity changesbased on the viscoelastic-gravitational dislocation theory[J].Computer&Geosciences,2006,32(2006):527-541.
4袁旭东,等.同震变形中模型分层和重力影响研究[J].大地测量与地球动力学,2007,(1):69-76.(Yuan Xu-dong,et al.On influences of earth stracification and gravita-tion on co-seismic deformation[J].Journal of Geodesy andGeodynamics,2007,(1):69-76)
5谈洪波,等.地壳分层和地壳厚度对汶川地震同震效应的影响[J].大地测量与地球动力学,2010,(4):29-35.(Tan Hongbo,et al.Influence of crust layering and tick-ness on co-seismic effects of Wenchuan earthquake[J].Jour-nal of Geodesy and Geodynamics,2010,(4):29-35)
6雷建设,等.龙门山断裂带地壳精细结构与汶川地震发震机理[J].地球物理学报,2009,52(2):339-345.(LeiJianshe,et al.Fine seismic structure under the Longmenshanfault zone and the mechanism of the large Wenchuan earth-quake[J].Chinese J Geophys.,2009,52(2):339-345)
7 Wang C,et al.S-wave crustal and upper mantle’s velocitystructure in the eastern Tibetan Plateau-deep environment oflower crustal flow[J].Science in China Series D(Earth Sci-ences),2008,51(2):263-274.
8 Wang C,et al.P-wave crustal velocity structure in westernSichuan and eastern Tibetan region[J].Science in China(Series D),2003,46:254-265.
9楼海,等.2008年汶川Ms8.0级地震的深部构造环境———远震P波接收函数和布格重力异常的联合解释[J].中国科学D辑(地球科学),2008,38(10):1 207-1 220.(Lou Hai,et al.Deep tectonic setting of the 2008Wenchuan Ms8.0 earthquake in southwest China———Jointanalysis of teleseismic P-wave veceiver functions and Bougu-er gravity anomalies[J].Science in China(series D),2008,38(10):1 207-1 220))
10 Aagaard B,et al.Pylith:A finite-element code for model-ing quasi-static and dynamic crustal deformation[R].EosTrans.AGU.2008.
11 Aagaard B,et al.Pylith:A finite-element code for model-ing quasi-static and dynamic crustal deformation[R].EosTrans.AGU.2007.
12杨海燕,等.川西地区壳幔结构与汶川Ms8.0地震的孕震背景[J].地球物理学报,2009,52(2):356-364.(Yang Haiyan,et al.Crust-mantle structure and seismogen-ic background of Wenchuan Ms8.0 earthquake in westernSichuan area[J].Chinese J Geophys,2009,52(2):356-364)
13 Burchfiel B C,et al.A geological and geophysical contextfor the Wenchuan earthquake of 12 May 2008 Sichuan Peo-ple’s Republic of China[J].GSA Today,2008,18(7):4-11.
14王栋,谢礼立.断层倾角对上/下盘效应的影响[J].地震工程与工程振动,2007,27(5):1-6.(Wang Dongand Xie Lili.The influence of the fault dtp angle on the onthe hanging wall/footwall effect[J].Journal of EarthquakeEngineering and Engineering Vibration,2007,27(5):1-6)
15张国宏,等.基于GPS和InSAR反演汶川Mw7.9地震断层滑动分布[J].大地测量与地球动力学,2010,(4):19-24.(Zhang Guohong,et al.Inversion of slip distribu-tion of 2008 Wenchuan Mw7.9 earthquake constrainedjointly by InSAR and GPS measurements[J].Journal of Ge-odesy and Geodynamics,2010,(4):19-24)
16 Li F and Huang J.Three-dimensional numerical simulationon the coseismic deformation of the 2008 Ms8.0 Wenchuanearthquake in China[J].Earthquake Science,2010,23:191-200.
17 Ji C and Hayes G.Preliminary result of the 12 May 2008Mw7.9 eastern Sichuan[B/OL].http://earthquake.usgs.gov/earthquakes/eqinthenews/2008/us2008ryan/finite_fault.php.2008.
18 Nishimuru N and Yaji Y.Rupture process for may 12,2008Sichuan earthquake[B/OL].http://www.geol.tsukuba.ac.jp/～nisimura/20080512/.2008.
19国家重大科学工程“中国地壳运动观测网络”项目组.GPS测定的2008年汶川Ms8.0地震的同震位移场[J].中国科学D辑(地球科学),2008,38(10):1 195-1 206.(CMONOC Group.Cosesmic displacements of the2008 Wenchuan Ms8.0 earthquake from GPS observation[J].Science in China(series D),2008,38(10):1 195-1 206)
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