逆冲断层错动形成变形场及应力场的有限元模型——以映秀-青川断层为例
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摘要
为了研究逆断层受到垂直于断层走向的应力作用下发生逆冲构造运动时造成的变形以及相应的应力场分布,以龙门山中央断层映秀—青川段为例建立了逆冲断层的有限元模型。该模型为单个逆冲断层有限元模型,计算了汶川地震过程中龙门山中央断层逆冲错动引起的地表变形场和断层附近应力场的变化。模拟中对断层面采用的是摩擦接触单元,且断层面设为曲面的几何形状;模拟给出断层错动形成的地表沿垂直走向和垂直地表的变形以及相应的应力分量场的变化情况。为得到计算模型边界处的应力值,采用了断层静态位错模型进行计算。结果发现,在不施加沿断层走向的载荷时,沿断层走向上存在变形,这可能是断层在受到挤压后发生的横向变形,但该变形较小;逆冲断层构造运动引起沿垂直断层走向方向上的变形并不是在近断层处达到最大,而是沿垂直地表向上的变形在断层处达到最大;逆冲断层在挤压构造应力下的变形要大于逆冲构造附近的隆升变形,同时断层面上的挤压应力大于垂直地表方向的应力;断层面上的应力场沿断层面的变化主要集中在断层面倾角发生变化以及震源区域附近。
This paper mainly studies the distribution of structural deformation and stress under the motion of thrust fault due to the effect of stress normal to the strike direction. As an example,we build the finite element model of central fault of Longmen Shan Fault zone,the Yingxiu-Qingchuan Fault. The finite element model is the model of single inverse fault. During the study,we compute the variations of surface deformation and stress fields near to the fault due to the thrust motion of Yingxiu-Qingchuan Fault in the process of Wenchuan earthquake. In the computation,we apply the frictional contact element and curved surface geometry to simulating the fault plane to obtain the variations of stress components and displacement field which are normal to strike direction and ground surface. In order to get the stress value of the hanging fall of the Yingxiu-Qingchuan Fault,we also apply the static dislocation model to the computation. Through the computation,we find that the displacement field along the strike direction can exist even if there is no initial stress load along the strike,but the value of this deformation is tiny. So we believe the displacement field along the strike may stem from the transverse deformation due to the extrusion of thrust fault; The structure deformation normal to the strike direction resulting from the thrust motion of inverse fault does not reach to maximum value at the zone near the fault,but the structure deformation normal to the ground surface can reach the maximum at the zone near to the fault; Generally,under the compression stress effect,the amount of crustal shortening is much bigger than that of uplift deformation at the zone near to the inverse fault,and the value of compression stress is much bigger than that of stress normal to ground surface along the fault plane.Furthermore,variation of stress on the inverse fault plane occurs mainly at the area where the dip angle of fault plane changes.
This paper mainly studies the distribution of structural deformation and stress under the motion of thrust fault due to the effect of stress normal to the strike direction. As an example,we build the finite element model of central fault of Longmen Shan Fault zone,the Yingxiu-Qingchuan Fault. The finite element model is the model of single inverse fault. During the study,we compute the variations of surface deformation and stress fields near to the fault due to the thrust motion of Yingxiu-Qingchuan Fault in the process of Wenchuan earthquake. In the computation,we apply the frictional contact element and curved surface geometry to simulating the fault plane to obtain the variations of stress components and displacement field which are normal to strike direction and ground surface. In order to get the stress value of the hanging fall of the Yingxiu-Qingchuan Fault,we also apply the static dislocation model to the computation. Through the computation,we find that the displacement field along the strike direction can exist even if there is no initial stress load along the strike,but the value of this deformation is tiny. So we believe the displacement field along the strike may stem from the transverse deformation due to the extrusion of thrust fault; The structure deformation normal to the strike direction resulting from the thrust motion of inverse fault does not reach to maximum value at the zone near the fault,but the structure deformation normal to the ground surface can reach the maximum at the zone near to the fault; Generally,under the compression stress effect,the amount of crustal shortening is much bigger than that of uplift deformation at the zone near to the inverse fault,and the value of compression stress is much bigger than that of stress normal to ground surface along the fault plane.Furthermore,variation of stress on the inverse fault plane occurs mainly at the area where the dip angle of fault plane changes.
引文
白玉柱,徐杰,徐锡伟,等.2010.2008年汶川8.0级地震地表位移场的模拟:映秀-北川断裂逆冲兼右旋走滑错动形成的地表位移场[J].地震地质,32(1):16—27.doi:10.3969/j.issn.0253-4967.2010.01.002.BAI Yu-zhu,XU Jie,XU Xi-wei,et al.2010.Simulations on displacement fields of ground surface in 2008 Wenchuan earthquake:The case of inverse and right-lateral motion of Yingxiu-Beichuan Fault[J].Seismology and Geology,32 (1):16—27(in Chinese).
白玉柱,徐锡伟,徐杰,等.2011.2008年汶川地震近断裂区域变形场的空间分布[J].地球物理学报,54(7):1798—1804.BAI Yu-zhu,XU Xi-wei,XU Jie,et al.2011.A research on the distribution of deformation fields near the fault of 2008Wenchuan earthquake[J].Chinese J Geophys,54(7):1798—1804(in Chinese).
白玉柱,徐杰,周本刚.2009.2008年汶川8.0级地震地表垂直和水平位移场模拟计算分析[J].震灾防御技术,(3):256—265.BAI Yu-zhu,XU Jie,ZHOU Ben-gang.2009.Simulation of vertical and level displacement fields in 2008 Wenchuan earthquake[J].Technology for Earthquake Disaster Prevention,(3):256—265(in Chinese).
白玉柱,周庆,徐锡伟,等.2012.汶川地震形成位移场的空间分布[J].地球物理学进展,27(1):29—37.BAI Yu-zhu,ZHOU Qing,XU Xi-wei,et al.2012.The spatial distribution of displacement fields in 2008 Wenchuan earthquake[J].Progress in Geophysics,27(1):29—37(in Chinese).
陈连旺,张培震,陆远忠,等.2008.川滇地区强震序列库伦破裂应力加卸载效应的数值模拟[J].地球物理学报,51(5):1411—1421.CHEN Lian-wang,ZHANG Pei-zhen,LU Yuan-zhong,et al.2008.Numerical simulation of loading/unloading effect on Coulomb failure stress among strong earthquakes in Sichuan-Yunnan area[J].Chinese Journal of Geophysics,51(5):1411—1421(in Chinese).
杜晨晓,谢富仁,张扬,等.2010.1976年M S7 .8唐山地震断层动态破裂及近断层强地面运动特征[J].地球物理学报,53(2):293—304.DU Chen-xiao,XIE Fu-ren,ZHANG Yang,et al.2010.3D modeling of dynamic fault rupture and strong ground motion of the 1976 M S7 .8 Tangshan earthquake[J].Chinese Journal of Geophysics,53(2):293—304(in Chinese).
焦龙,吴云,张跃刚.2010.用边界元法研究川西地区的形变场与应变场[J].大地测量与地球动力学,30(3):35 —38.JIAO Long,WU Yun,ZHANG Yue-gang.2010.Research on deformation field and strain field in western Sichuan area by BEM[J].J Geodesy and Geodynamics,30(3):35—38(in Chinese).
李红,陈连旺,李玉江.2008.广州地区活动断裂的数值模拟[J].大地测量与地球动力学,28(2):39—44.LI Hong,CHEN Lian-wang,LI Yu-jiang.2008.Numerical simulation of active faults in Guangzhou area[J].Journal of Geodesy and Geodynamics,28(2):39—44(in Chinese).
申重阳,李辉,谈洪波.2008.汶川8.0级地震同震重力与形变效应模拟[J].大地测量与地球动力学,28(5):6 —12.SHEN Chong-yang,LI Hui,TAN Hong-bo.2008.Simulation of coseismic gravity changes and deformation effect of Wenchuan M S8 .0 earthquake[J].Journal of Geodesy and Geodynamics,28(5):6—12(in Chinese).
孙卫涛,杨慧珠.2004.各向异性介质弹性波传播的三维不规则网格有限差分方法[J].地球物理学报,47(2):332 —337.SUN Wei-tao,YANG Hui-zhu.2004.A 3-D finite difference method using irregular grids for elastic wave propagation in anisotropic media[J].Chinese J Geophys,47(2):332—337(in Chinese).
王卫民,赵连锋,李娟,等.2008.四川汶川8.0级地震震源过程[J].地球物理学报,51(5):1403—1410.WANG Wei-ming,ZHAO Lian-feng,LI Juan,et al.2008.Rupture process of the M S8 .0 Wenchuan earthquake of Sichuan,China[J].Chinese J Geophys,51(5):1403—1410(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川M S8 .0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629 .XU Xi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.The M S8 .0 Wenchuan earthquake surface ruptures and its seismogenic structure[J].Seismology and Geology,30(3):597—629(in Chinese).
杨晓平,冯希杰,戈天勇,等.2008.龙门山断裂带北段第四纪活动的地质地貌证据[J].地震地质,30(3):644 —657.YANG Xiao-ping,FENG Xi-jie,GE Tian-yong,et al.2008.Geological and geomorphic evidence for the Quaternary activity on the northeast segment of Longmenshan Fault zone[J].Seismology and Geology,30(3):644—657(in Chinese).
张勇,冯万鹏,许力生,等.2008.2008年汶川大地震的时空破裂过程[J].中国科学(D),38(10):1186—1194.ZHANG Yong,FENG Wan-peng,XU Li-sheng,et al.2008.The fault process of 2008 Wenchuan earthquake[J].Science in China(Ser D),38(10):1186—1194(in Chinese).
张永志,赵大江,王卫东.2009.断层走滑不均匀性对地表变形的影响[J].地球物理学报,52(8):2113—2118.ZHANG Yong-zhi,ZHAO Da-jiang,WANG Wei-dong.2009.Effects on the earth surface deformation by asymmetric strike slip on fault plane[J].Chinese J Geophys,52(8):2113—2118(in Chinese).
MA Shuo,LIU Peng-cheng.2006.Modeling of the perfectly matched layer absorbing boundaries and intrinsic attenuation in explicit finite-element methods[J].Bull Seism Soc Am,96:1779—1794.
Okada Y.1992.Internal deformation due to shear and tensile faults in a half-space[J].Bull Seism Soc Am,82:1018—1040.
白玉柱,徐锡伟,徐杰,等.2011.2008年汶川地震近断裂区域变形场的空间分布[J].地球物理学报,54(7):1798—1804.BAI Yu-zhu,XU Xi-wei,XU Jie,et al.2011.A research on the distribution of deformation fields near the fault of 2008Wenchuan earthquake[J].Chinese J Geophys,54(7):1798—1804(in Chinese).
白玉柱,徐杰,周本刚.2009.2008年汶川8.0级地震地表垂直和水平位移场模拟计算分析[J].震灾防御技术,(3):256—265.BAI Yu-zhu,XU Jie,ZHOU Ben-gang.2009.Simulation of vertical and level displacement fields in 2008 Wenchuan earthquake[J].Technology for Earthquake Disaster Prevention,(3):256—265(in Chinese).
白玉柱,周庆,徐锡伟,等.2012.汶川地震形成位移场的空间分布[J].地球物理学进展,27(1):29—37.BAI Yu-zhu,ZHOU Qing,XU Xi-wei,et al.2012.The spatial distribution of displacement fields in 2008 Wenchuan earthquake[J].Progress in Geophysics,27(1):29—37(in Chinese).
陈连旺,张培震,陆远忠,等.2008.川滇地区强震序列库伦破裂应力加卸载效应的数值模拟[J].地球物理学报,51(5):1411—1421.CHEN Lian-wang,ZHANG Pei-zhen,LU Yuan-zhong,et al.2008.Numerical simulation of loading/unloading effect on Coulomb failure stress among strong earthquakes in Sichuan-Yunnan area[J].Chinese Journal of Geophysics,51(5):1411—1421(in Chinese).
杜晨晓,谢富仁,张扬,等.2010.1976年M S7 .8唐山地震断层动态破裂及近断层强地面运动特征[J].地球物理学报,53(2):293—304.DU Chen-xiao,XIE Fu-ren,ZHANG Yang,et al.2010.3D modeling of dynamic fault rupture and strong ground motion of the 1976 M S7 .8 Tangshan earthquake[J].Chinese Journal of Geophysics,53(2):293—304(in Chinese).
焦龙,吴云,张跃刚.2010.用边界元法研究川西地区的形变场与应变场[J].大地测量与地球动力学,30(3):35 —38.JIAO Long,WU Yun,ZHANG Yue-gang.2010.Research on deformation field and strain field in western Sichuan area by BEM[J].J Geodesy and Geodynamics,30(3):35—38(in Chinese).
李红,陈连旺,李玉江.2008.广州地区活动断裂的数值模拟[J].大地测量与地球动力学,28(2):39—44.LI Hong,CHEN Lian-wang,LI Yu-jiang.2008.Numerical simulation of active faults in Guangzhou area[J].Journal of Geodesy and Geodynamics,28(2):39—44(in Chinese).
申重阳,李辉,谈洪波.2008.汶川8.0级地震同震重力与形变效应模拟[J].大地测量与地球动力学,28(5):6 —12.SHEN Chong-yang,LI Hui,TAN Hong-bo.2008.Simulation of coseismic gravity changes and deformation effect of Wenchuan M S8 .0 earthquake[J].Journal of Geodesy and Geodynamics,28(5):6—12(in Chinese).
孙卫涛,杨慧珠.2004.各向异性介质弹性波传播的三维不规则网格有限差分方法[J].地球物理学报,47(2):332 —337.SUN Wei-tao,YANG Hui-zhu.2004.A 3-D finite difference method using irregular grids for elastic wave propagation in anisotropic media[J].Chinese J Geophys,47(2):332—337(in Chinese).
王卫民,赵连锋,李娟,等.2008.四川汶川8.0级地震震源过程[J].地球物理学报,51(5):1403—1410.WANG Wei-ming,ZHAO Lian-feng,LI Juan,et al.2008.Rupture process of the M S8 .0 Wenchuan earthquake of Sichuan,China[J].Chinese J Geophys,51(5):1403—1410(in Chinese).
徐锡伟,闻学泽,叶建青,等.2008.汶川M S8 .0地震地表破裂带及其发震构造[J].地震地质,30(3):597—629 .XU Xi-wei,WEN Xue-ze,YE Jian-qing,et al.2008.The M S8 .0 Wenchuan earthquake surface ruptures and its seismogenic structure[J].Seismology and Geology,30(3):597—629(in Chinese).
杨晓平,冯希杰,戈天勇,等.2008.龙门山断裂带北段第四纪活动的地质地貌证据[J].地震地质,30(3):644 —657.YANG Xiao-ping,FENG Xi-jie,GE Tian-yong,et al.2008.Geological and geomorphic evidence for the Quaternary activity on the northeast segment of Longmenshan Fault zone[J].Seismology and Geology,30(3):644—657(in Chinese).
张勇,冯万鹏,许力生,等.2008.2008年汶川大地震的时空破裂过程[J].中国科学(D),38(10):1186—1194.ZHANG Yong,FENG Wan-peng,XU Li-sheng,et al.2008.The fault process of 2008 Wenchuan earthquake[J].Science in China(Ser D),38(10):1186—1194(in Chinese).
张永志,赵大江,王卫东.2009.断层走滑不均匀性对地表变形的影响[J].地球物理学报,52(8):2113—2118.ZHANG Yong-zhi,ZHAO Da-jiang,WANG Wei-dong.2009.Effects on the earth surface deformation by asymmetric strike slip on fault plane[J].Chinese J Geophys,52(8):2113—2118(in Chinese).
MA Shuo,LIU Peng-cheng.2006.Modeling of the perfectly matched layer absorbing boundaries and intrinsic attenuation in explicit finite-element methods[J].Bull Seism Soc Am,96:1779—1794.
Okada Y.1992.Internal deformation due to shear and tensile faults in a half-space[J].Bull Seism Soc Am,82:1018—1040.