基于唐山7.8级地震探讨动态应力作用
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摘要
运用三维非线性动态有限元方法(Non-linear Dynamic FEM)仿真模拟研究了菱形模型的动态应力作用,分析了1976年唐山7.8级地震.结果表明:(1)唐山地震前增强的中强地震产生的冲击力形成的应力波反射后发生半波损失,成为动态的拉伸应力,通过减小内摩擦而引起岩石产生裂纹、局部破裂并发生串通,一方面触发地震,另一方面为孕育唐山地震积累能量,表现为正反馈过程.(2)唐山地震产生的冲击力加卸载存在时间差,造成加卸载冲击波相位不同,结果产生的动应力和围压叠加致使围压波动和下降,导致抗剪切强度降低,使初始破裂分别向北东、西南方向传播.(3)冲击力的卸载,相对于产生拉伸性的应力波,反射后发生半波损失,成为动态的压缩应力,致使围压增大并导致破裂停止;而动态应力在传播过程中衰减.因此,余震的发生是一个负反馈过程.
We use the three-dimensional non-linear dynamic finite element method to perform a modeling study on dynamical stress effects with a rhombic model and analyze the Tangshan M7.8 earthquake in 1976.The result shows that stress wave is generated by shock force which is produced by strengthened moderately strong earthquakes before the Tangshan earthquake, when this wave encounters a fault, the reflected stress wave, becomes tensile due to half-wavelength loss, which causes cracks, local rupture and crack linkage in the rock by reducing rock friction. On the one hand, other earthquakes are triggered.On the other hand, energy for the Tangshan earthquake is accumulated.This is a process of positive feedback.The shock force from the Tangshan earthquake during processes of loading and unloading has a time difference, this forms the different phase of shock waves.The dynamical stress produced by stress wave, superposed on the confining pressure, makes confining pressure reduce and change at low values.These effects can reduce shear strength and make the initial fracture of the Tangshan earthquake propagate toward northeast and southwest respectively.The unloading of shock force generated by the Tangshan earthquake is equal to producing the effect of tensile stress wave, the reflected tensile stress waves, having lost half-wavelength, become compressive ones which cause confining pressure increase and rupture stop.Meanwhile during the process of dynamical stress propagation, its amplitude decays.So the aftershock occurrence of the Tangshan earthquake is a negative feedback process.
We use the three-dimensional non-linear dynamic finite element method to perform a modeling study on dynamical stress effects with a rhombic model and analyze the Tangshan M7.8 earthquake in 1976.The result shows that stress wave is generated by shock force which is produced by strengthened moderately strong earthquakes before the Tangshan earthquake, when this wave encounters a fault, the reflected stress wave, becomes tensile due to half-wavelength loss, which causes cracks, local rupture and crack linkage in the rock by reducing rock friction. On the one hand, other earthquakes are triggered.On the other hand, energy for the Tangshan earthquake is accumulated.This is a process of positive feedback.The shock force from the Tangshan earthquake during processes of loading and unloading has a time difference, this forms the different phase of shock waves.The dynamical stress produced by stress wave, superposed on the confining pressure, makes confining pressure reduce and change at low values.These effects can reduce shear strength and make the initial fracture of the Tangshan earthquake propagate toward northeast and southwest respectively.The unloading of shock force generated by the Tangshan earthquake is equal to producing the effect of tensile stress wave, the reflected tensile stress waves, having lost half-wavelength, become compressive ones which cause confining pressure increase and rupture stop.Meanwhile during the process of dynamical stress propagation, its amplitude decays.So the aftershock occurrence of the Tangshan earthquake is a negative feedback process.
引文
[1] 国家地震局《一九七六年唐山地震》编辑组.一九七六年唐山地震.北京:地震出版社,1982 Editing Group of Tangshan Earthquake on 1976,State Seismological Bureau.Tangshan Earthquake on 1976(in Chinese).Beijing:Seismological Press,1982
[2] 张之立,李钦祖,谷继成等.唐山地震的破裂过程及其力学分析.地震学报,1980,2(2) :111～129 Zhang Z L,Li Q Z,Gu J C,et al.The fracture processes of the Tangshan earthquake and its mechanical analysis.Acta Seismologia Sinica(in Chinese),1980,2(2) :111～129
[3] 陈运泰,黄立人,林邦慧等.用大地测量结果反演唐山7． 8级主震位错模型.地球物理学报,1979,22(2) :201～217 Chen Y T,Huang L R,Lin B H,et al.A dislocation model of the Tangshan earthquake of 1976 from the inversion of geodetic data.Chinese J.Geophys.(in Chinese),1979,22(3) :201～217
[4] 国家地震局科研处.唐山地震考察与研究.北京:地震出版社,1981． 410～415 Office of Scientific Research,State Seismological Bureau.Inspect and Study on Tangshan Earthquake(in Chinese).Beijing:Seismological Press,1981． 410～415
[5] 刘桂萍,傅征祥.1976年7月28日唐山7． 8级地震触发的区域地震活动和静态应力场变化.地震学报,2000,22(1) :17～26 Liu G P,Fu Z X.Regional seismicity triggered by the M_s= 7． 8 Tangshan event of July 28,1976 and the static stress field change.Acta Seismologia Sinica(in chinese),2000,22(1) :17～26
[6] Harris R A,Simpson R W.Suppression of large earthquake by stress shadows:A comparison of Coulomb and rate-and state.J.Geophys.Res.,1998,103:24439～24451
[7] Hill D P,Reasenberg P A,Michael A,et al.Seismicity remotely triggered by the magnitude 7． 3 Landers,California earthquake.Science,1993,260． 1617～1623
[8] Pollitz F F,Sacks I S.The 1995 Kobe,Japan earthquake:a long delayed aftershock of the offshore 1994 Tonankai and 1946 Nankaido earthquakes.Bull.Seism.Soc.Am.,1997,87:1～10
[9] Mohamad R,Darkal A N,Seber D,et al.Remote earthquake triggering along the Dead Sea fault in Syria following the 1995 Gulf of Aqaba earthquake(M_s = 7． 3) .Seismol.Res.Lett., 2000,71:47～52
[10] Cotton F,Coutant O.Dynamic stress variations due to shear faults in a plane layered medium.Geophys.J.Int.,1997,128:676～688
[11] Kilb D,Gomberg J,Bodin P.Earthquake triggering by dynamic stresses.Nature,2000,408:570～574
[12] Rigobert T,Douglas A W,Hiroshi I.Remote triggering of deep earthquakes in the 2002 Tonga sequences.Nature,2003,424(6951) :921～925
[13] Byerlee J.Model for episodic flow of high presure water in fault zones before earthquakes.Geology,1993,21:303～306
[14] Gomberg J.The failure of earthquake failure models.J.Geophys.Res.,2001,106(B8) :16253～16263
[15] Sturtevant B,Kanamori H,Brodsky E E.Seismic triggering by rectified diffusion in geothermal systems.J.Geophys.Res.,1996,101:25269～25282
[16] 陆明勇,郑文衡.地壳块体动应力演化特征及其与地震关系的初步研究.地震学报,2005,27(3) :282～291 Lu M Y,Zheng W H.Preliminary study on variation characteristics of ocean tide dynamic stress in crust and its relationship with earthquakes.Acta Seismologia Sinica,2005,18(3) :303～312
[17] 陆明勇,郑文衡,胡志奇.动态应力作用与地震机制的初步研究.地球物理学报,2006,49(1) :170～179 Lu M Y,Zheng W H,Hu Z Q.A preliminary study on effects of dynamical stress in relation to earthquake mechanism.Chinese J.Geophys.(in Chinese),2006,49(1) :170～179
[18] 万永革,吴忠良,周公威等.地震应力触发研究.地震学报,2002,24(5) :533～551 Wan Y G,Wu Z L,Zhou G W,et al.Research on seismic stress triggering.Acta Seimologica Sinica(in Chinese),2002,24(5) :533～551
[19] 陆明万,罗学富.弹性理论基础.北京:清华大学出版社,1990． 410～415 Lu M W,Luo X F.Basic Theory of Elasticity(in Chinese).Beijing:Tsinghua University Press,1990． 410～415
[20] Harris R A.Introduction to special session:stress triggers,stress shadows,and implications for seismic hazard.J.Geophys.Res.,1998,103(24) :24347～24358
[2] 张之立,李钦祖,谷继成等.唐山地震的破裂过程及其力学分析.地震学报,1980,2(2) :111～129 Zhang Z L,Li Q Z,Gu J C,et al.The fracture processes of the Tangshan earthquake and its mechanical analysis.Acta Seismologia Sinica(in Chinese),1980,2(2) :111～129
[3] 陈运泰,黄立人,林邦慧等.用大地测量结果反演唐山7． 8级主震位错模型.地球物理学报,1979,22(2) :201～217 Chen Y T,Huang L R,Lin B H,et al.A dislocation model of the Tangshan earthquake of 1976 from the inversion of geodetic data.Chinese J.Geophys.(in Chinese),1979,22(3) :201～217
[4] 国家地震局科研处.唐山地震考察与研究.北京:地震出版社,1981． 410～415 Office of Scientific Research,State Seismological Bureau.Inspect and Study on Tangshan Earthquake(in Chinese).Beijing:Seismological Press,1981． 410～415
[5] 刘桂萍,傅征祥.1976年7月28日唐山7． 8级地震触发的区域地震活动和静态应力场变化.地震学报,2000,22(1) :17～26 Liu G P,Fu Z X.Regional seismicity triggered by the M_s= 7． 8 Tangshan event of July 28,1976 and the static stress field change.Acta Seismologia Sinica(in chinese),2000,22(1) :17～26
[6] Harris R A,Simpson R W.Suppression of large earthquake by stress shadows:A comparison of Coulomb and rate-and state.J.Geophys.Res.,1998,103:24439～24451
[7] Hill D P,Reasenberg P A,Michael A,et al.Seismicity remotely triggered by the magnitude 7． 3 Landers,California earthquake.Science,1993,260． 1617～1623
[8] Pollitz F F,Sacks I S.The 1995 Kobe,Japan earthquake:a long delayed aftershock of the offshore 1994 Tonankai and 1946 Nankaido earthquakes.Bull.Seism.Soc.Am.,1997,87:1～10
[9] Mohamad R,Darkal A N,Seber D,et al.Remote earthquake triggering along the Dead Sea fault in Syria following the 1995 Gulf of Aqaba earthquake(M_s = 7． 3) .Seismol.Res.Lett., 2000,71:47～52
[10] Cotton F,Coutant O.Dynamic stress variations due to shear faults in a plane layered medium.Geophys.J.Int.,1997,128:676～688
[11] Kilb D,Gomberg J,Bodin P.Earthquake triggering by dynamic stresses.Nature,2000,408:570～574
[12] Rigobert T,Douglas A W,Hiroshi I.Remote triggering of deep earthquakes in the 2002 Tonga sequences.Nature,2003,424(6951) :921～925
[13] Byerlee J.Model for episodic flow of high presure water in fault zones before earthquakes.Geology,1993,21:303～306
[14] Gomberg J.The failure of earthquake failure models.J.Geophys.Res.,2001,106(B8) :16253～16263
[15] Sturtevant B,Kanamori H,Brodsky E E.Seismic triggering by rectified diffusion in geothermal systems.J.Geophys.Res.,1996,101:25269～25282
[16] 陆明勇,郑文衡.地壳块体动应力演化特征及其与地震关系的初步研究.地震学报,2005,27(3) :282～291 Lu M Y,Zheng W H.Preliminary study on variation characteristics of ocean tide dynamic stress in crust and its relationship with earthquakes.Acta Seismologia Sinica,2005,18(3) :303～312
[17] 陆明勇,郑文衡,胡志奇.动态应力作用与地震机制的初步研究.地球物理学报,2006,49(1) :170～179 Lu M Y,Zheng W H,Hu Z Q.A preliminary study on effects of dynamical stress in relation to earthquake mechanism.Chinese J.Geophys.(in Chinese),2006,49(1) :170～179
[18] 万永革,吴忠良,周公威等.地震应力触发研究.地震学报,2002,24(5) :533～551 Wan Y G,Wu Z L,Zhou G W,et al.Research on seismic stress triggering.Acta Seimologica Sinica(in Chinese),2002,24(5) :533～551
[19] 陆明万,罗学富.弹性理论基础.北京:清华大学出版社,1990． 410～415 Lu M W,Luo X F.Basic Theory of Elasticity(in Chinese).Beijing:Tsinghua University Press,1990． 410～415
[20] Harris R A.Introduction to special session:stress triggers,stress shadows,and implications for seismic hazard.J.Geophys.Res.,1998,103(24) :24347～24358
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