水平分层孔隙介质中点源激发的震电波场数值模拟及分析
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摘要
为认识地震波诱导的电磁场的特性,本文研究地震波在孔隙介质中由于动电效应引起的电磁场.基于Pride弹性-电磁耦合方程组推导了双力偶震源对应的位移-应力-电磁场间断向量的表达式,模拟了双力偶源激发的震电波场.作为比较,还模拟了爆炸点源激发的震电波场.结果表明:存在伴随纵波的电场,其各分量的波形与固相位移对应分量的波形相似,但相位相反;存在伴随横波的磁场,其波形与固相位移波形相似;双力偶震源还激发出了独立传播的辐射电磁场,其速度比纵波至少高一个数量级,几乎是"瞬间同时"到达了每个接收器,但是其强度比伴随电磁场小得多,且随着源距增大而迅速减小.本文研究还表明:伴随纵波的电场强度不仅与地震纵波幅度和动电耦合系数有关,还与由介质孔隙结构决定的流-固两相动力协调性有关,存在一种动力协调介质,纵波在这种介质中不引起电场.
To understand the characteristics of the electromagnetic(EM)fields during an earthquake,we studied the EM fields induced by the seismic waves in a porous medium due to the electrokinetie effect.Using the Pride's equations for the coupled poroelastic and electromagnetic fields,we derived the displacement-stress-EM-discontinuity vector for a double couple source, and then calculated the full waveforms generated by such a double couple source.As a comparison,waveforms generated by an explosion source are also simulated.The result shows that a P wave can induce an accompanying electric field,of which each component has a similar but opposite-phased waveform with the corresponding component of the solid displacement; an Swave can induce accompanying a magnetic field,which has similar waveform with the solid displacement.The double couple source also generates a kind of radiating EM wave,which propagates independently.Such EM wave is at least one order of magnitude faster than the p- wave,thus arrives at all receivers almost at the same time.However,its amplitude is much weaker than that of the accompanying electric and magnetic fields,and decreases rapidly when offset increases.It is also shown that the amplitude of the accompanying electric field induced by the P-wave not only depends on the amplitude of the P-wave and the electrokinetic coupling coefficient,but also depends on the fluid-solid dynamic compatibility,which is determined by the pore structure.There exists a special kind of porous medium,in which the P-wave cannot induce any accompanying electric field.
To understand the characteristics of the electromagnetic(EM)fields during an earthquake,we studied the EM fields induced by the seismic waves in a porous medium due to the electrokinetie effect.Using the Pride's equations for the coupled poroelastic and electromagnetic fields,we derived the displacement-stress-EM-discontinuity vector for a double couple source, and then calculated the full waveforms generated by such a double couple source.As a comparison,waveforms generated by an explosion source are also simulated.The result shows that a P wave can induce an accompanying electric field,of which each component has a similar but opposite-phased waveform with the corresponding component of the solid displacement; an Swave can induce accompanying a magnetic field,which has similar waveform with the solid displacement.The double couple source also generates a kind of radiating EM wave,which propagates independently.Such EM wave is at least one order of magnitude faster than the p- wave,thus arrives at all receivers almost at the same time.However,its amplitude is much weaker than that of the accompanying electric and magnetic fields,and decreases rapidly when offset increases.It is also shown that the amplitude of the accompanying electric field induced by the P-wave not only depends on the amplitude of the P-wave and the electrokinetic coupling coefficient,but also depends on the fluid-solid dynamic compatibility,which is determined by the pore structure.There exists a special kind of porous medium,in which the P-wave cannot induce any accompanying electric field.
引文
[1] Matsushima M,Honkura Y,Oshiman N,et al.Seismoelectromagnetic effect associated with the Izmit earthquake and its aftershocks.Bulletin of the Seismological Society of America,2002,92:350～360
[2] 汤吉,詹艳,王立凤等.5月12日汶川8． 0级地震强余震观测的电磁同震效应.地震地质,2008,30(3) :739～745Tang J,Zhan Y,Wang L F,et al.Coseismic signal associated with aftershock of the M_s8． 0 Wenchuan earthquake.Seismology and Geology(in Chinese),2008,30(3) :739～745
[3] Ivanov A G.Effect of electrization of earth layers by elastic waves passing through them:Dokl.Akad.Nauk.SSSR,1939,24:42～45
[4] Frenkel J.On the theory of seismic and seismoelectric phenomena in a mosit soil.J.Physics(Russian),1944,8(4) :230～241
[5] Thompson A H,Gist G A.Geophysical application of electrokinetic conversion.The Leading Edge,12:1169～1173
[6] Butler K E,Russel R D,Kepic A W,et al.Measurement of the seismoelectric response from a shallow boundary.Geophysics,1996,61:1769～1778
[7] Mikhailov O V,Haartsen M W,Toksoz M N.Eelectroseismic investigation of the shallow subsurface-field measurements and numerical modeling.Geophysics,1997,62:97～105
[8] Biot M A.Theory of propagation of elastic waves in a fluid saturated porous solid:I.Low-frequency range.J.Acoust.Soc.Am.,1956,28:168～178
[9] Biot M A.Mechanics of deformation and acoustic propagation in porous media.J.Appl.Phys.,1962,33:1482～1498
[10] Pride S R.Governing equations for the coupled electromagnetics and acoustics of porous media.Phys.Rev.B,1994,50:15678～15696
[11] Pride S R,Haartsen M W.Electroseimic wave properties.J.Acous.Soc.Am.,1996,100:1301～1315
[12] Haartsen M W,Pride S R.Electroseismic waves from point sources in layered media.J.Geophys.Res.,1997,102:24745～24769
[13] 胡恒山,王克协.井孔周围轴对称声电耦合波:(1) 理论.测井技术.1999,23(6) :427～432Hu H S,Wang K X.Coupled acoustic and electromanetic waves around a borehole embedded in a porous formation:Part 1． theory.Well Logging Technology(in Chinese),1999,23(6) :427～432
[14] 胡恒山.声电效应测井的理论、数值与实验研究[博士论文].长春:吉林大学,2000 Hu H S.Study of the acoustic and electromagnetic fields around a borehole in acousto-electric well logging[Ph.D.thesis](in Chinese).Changchun:Jilin University,2000
[15] 胡恒山,刘家琦,王洪滨等.基于简化的Pride理论模拟声电效应测井响应.地球物理学报,2003,46(2) :259～264Hu H S,Liu J Q,Wang H B.Simulation of acousto-electric well logging based on simplified Pride equations.Chinese J.Geophys.(in Chinese),2003,46(2) :259～264
[16] Garambois S,Dietrich M.Seismoelectric wave conversions in porous media:field measurements and transfer function analysis.Geophysics,2001,66:1417～1430
[17] Garambois S,Dietrich M.Full waveform numerical simulations of seismoelectromagnetic wave conversions in fluid-saturated stratified porous media.Journal of Geophysical Research,2002,107(B7) :2148,10． 1029/2001JB000316
[18] White B S,Zhou M Y.Electroseismic prospecting in layered media.Society for Industrial and Applied Mathematics,2006,67(1) :69～98
[19] 陈运泰.多层弹性半空间中的地震波(一).地球物理学报,1974,17(1) :20～43Chen Y T.Seismic wave in multilayered elastic half-space.Acta Geophysica Sinica(in Chinese),1974,17(1) :20～43
[20] Kennett B L N.Seismic Wave Propagation in Stratified Media.New York:Cambridge University Press,1983
[21] Hanks T C,Kanamori H.A moment magnitude scale.J.Geophys.Res.,1979,84(B5) :2348～2350
[22] 李山有,金星,马强等.地震预警系统与智能应急控制系统研究.世界地震工程,2001,20(4) :21～26Li S Y,Jin X,Ma Q,et al.Study on earthquake early warning system and intelligent emergency controlling system.World Earthquake Engineering(in Chinese),2001,20(4) :21～26
[23] 胡恒山,王克协,刘家琦.孔隙介质中快纵波的衰减特性和动力协调现象.计算物理,2002,19(3) :203～207Hu H S,Wang K X,Liu J Q.Attenuation and dynamic compatibility of the fast compressional wave in porous medium.Chinese J.Computation Physics(in Chinese),2002,19(3) :203～207
[24] Vernik L.Acoustic velocity and porosity systematics in siliciclastics.The Log Analyst,1998,39:27～35
[2] 汤吉,詹艳,王立凤等.5月12日汶川8． 0级地震强余震观测的电磁同震效应.地震地质,2008,30(3) :739～745Tang J,Zhan Y,Wang L F,et al.Coseismic signal associated with aftershock of the M_s8． 0 Wenchuan earthquake.Seismology and Geology(in Chinese),2008,30(3) :739～745
[3] Ivanov A G.Effect of electrization of earth layers by elastic waves passing through them:Dokl.Akad.Nauk.SSSR,1939,24:42～45
[4] Frenkel J.On the theory of seismic and seismoelectric phenomena in a mosit soil.J.Physics(Russian),1944,8(4) :230～241
[5] Thompson A H,Gist G A.Geophysical application of electrokinetic conversion.The Leading Edge,12:1169～1173
[6] Butler K E,Russel R D,Kepic A W,et al.Measurement of the seismoelectric response from a shallow boundary.Geophysics,1996,61:1769～1778
[7] Mikhailov O V,Haartsen M W,Toksoz M N.Eelectroseismic investigation of the shallow subsurface-field measurements and numerical modeling.Geophysics,1997,62:97～105
[8] Biot M A.Theory of propagation of elastic waves in a fluid saturated porous solid:I.Low-frequency range.J.Acoust.Soc.Am.,1956,28:168～178
[9] Biot M A.Mechanics of deformation and acoustic propagation in porous media.J.Appl.Phys.,1962,33:1482～1498
[10] Pride S R.Governing equations for the coupled electromagnetics and acoustics of porous media.Phys.Rev.B,1994,50:15678～15696
[11] Pride S R,Haartsen M W.Electroseimic wave properties.J.Acous.Soc.Am.,1996,100:1301～1315
[12] Haartsen M W,Pride S R.Electroseismic waves from point sources in layered media.J.Geophys.Res.,1997,102:24745～24769
[13] 胡恒山,王克协.井孔周围轴对称声电耦合波:(1) 理论.测井技术.1999,23(6) :427～432Hu H S,Wang K X.Coupled acoustic and electromanetic waves around a borehole embedded in a porous formation:Part 1． theory.Well Logging Technology(in Chinese),1999,23(6) :427～432
[14] 胡恒山.声电效应测井的理论、数值与实验研究[博士论文].长春:吉林大学,2000 Hu H S.Study of the acoustic and electromagnetic fields around a borehole in acousto-electric well logging[Ph.D.thesis](in Chinese).Changchun:Jilin University,2000
[15] 胡恒山,刘家琦,王洪滨等.基于简化的Pride理论模拟声电效应测井响应.地球物理学报,2003,46(2) :259～264Hu H S,Liu J Q,Wang H B.Simulation of acousto-electric well logging based on simplified Pride equations.Chinese J.Geophys.(in Chinese),2003,46(2) :259～264
[16] Garambois S,Dietrich M.Seismoelectric wave conversions in porous media:field measurements and transfer function analysis.Geophysics,2001,66:1417～1430
[17] Garambois S,Dietrich M.Full waveform numerical simulations of seismoelectromagnetic wave conversions in fluid-saturated stratified porous media.Journal of Geophysical Research,2002,107(B7) :2148,10． 1029/2001JB000316
[18] White B S,Zhou M Y.Electroseismic prospecting in layered media.Society for Industrial and Applied Mathematics,2006,67(1) :69～98
[19] 陈运泰.多层弹性半空间中的地震波(一).地球物理学报,1974,17(1) :20～43Chen Y T.Seismic wave in multilayered elastic half-space.Acta Geophysica Sinica(in Chinese),1974,17(1) :20～43
[20] Kennett B L N.Seismic Wave Propagation in Stratified Media.New York:Cambridge University Press,1983
[21] Hanks T C,Kanamori H.A moment magnitude scale.J.Geophys.Res.,1979,84(B5) :2348～2350
[22] 李山有,金星,马强等.地震预警系统与智能应急控制系统研究.世界地震工程,2001,20(4) :21～26Li S Y,Jin X,Ma Q,et al.Study on earthquake early warning system and intelligent emergency controlling system.World Earthquake Engineering(in Chinese),2001,20(4) :21～26
[23] 胡恒山,王克协,刘家琦.孔隙介质中快纵波的衰减特性和动力协调现象.计算物理,2002,19(3) :203～207Hu H S,Wang K X,Liu J Q.Attenuation and dynamic compatibility of the fast compressional wave in porous medium.Chinese J.Computation Physics(in Chinese),2002,19(3) :203～207
[24] Vernik L.Acoustic velocity and porosity systematics in siliciclastics.The Log Analyst,1998,39:27～35
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