水库触发地震研究中二维与三维有限元模拟结果比较
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摘要
紫坪铺水库蓄水载荷引起的库仑应力变化以及是否可以触发汶川MS8.0地震是地学界关注的一个热点问题。已有较多研究均建立在二维有限元模拟基础上,然而二维与三维结果存在较大差异,本文定量给出了该差异的大小。首先比较了有限元方法与解析方法求解半无限空间点载荷下弹性问题结果,确认了三维有限元计算在百万网格下具有足够的计算精度;然后数值计算并比较了二维、三维模型中紫坪埔水库蓄水的弹性力学及渗流效应。结果表明,总体上弹性加载会造成逆断层更趋安全,而水压渗透使其趋于危险,两者叠加仍然没有导致增加汶川地震危险性;但现有的二维有限元模拟夸大了真实结果,在汶川震源位置三维计算的应力大小仅为二维计算的1/3到1/4,因此在严格的讨论中必须使用三维建模。
It has been widely discussed in geoscience community whether Coulomb stress change caused by Zipingpu reservoir loading activities has triggered the 2008 Wenchuan MS 8.0 earthquake.Many conclusions have come from 2D finite element simulations,which are quite different with the 3D results.In this paper,we quantitatively discussed the difference of the 2D and the 3D results.First,a comparison of the 3D finite element solutions and the analytic solutions was given to ensure the enough precision of the 3D finite element simulation with 1million grid points.Then,the 2D and the 3D numerical solutions of the elastic effect and the seepage effect caused by Zipingpu reservoir were compared.The simulation results show that elastic load caused the thrust fault to be more secure,while the water pressure caused it to be more dangerous.The superimposed effect,however,didn't result an increase in the risk of Wenchuan earthquake.The comparison of the 2D and the 3D results show the 2D result exaggerated the truth.At the hypocenter of the Wenchuan earthquake,the computed stress of the 3D result is only 1/3 to 1/4 of the 2D result,thus in a serious study,3D modeling is necessary.
It has been widely discussed in geoscience community whether Coulomb stress change caused by Zipingpu reservoir loading activities has triggered the 2008 Wenchuan MS 8.0 earthquake.Many conclusions have come from 2D finite element simulations,which are quite different with the 3D results.In this paper,we quantitatively discussed the difference of the 2D and the 3D results.First,a comparison of the 3D finite element solutions and the analytic solutions was given to ensure the enough precision of the 3D finite element simulation with 1million grid points.Then,the 2D and the 3D numerical solutions of the elastic effect and the seepage effect caused by Zipingpu reservoir were compared.The simulation results show that elastic load caused the thrust fault to be more secure,while the water pressure caused it to be more dangerous.The superimposed effect,however,didn't result an increase in the risk of Wenchuan earthquake.The comparison of the 2D and the 3D results show the 2D result exaggerated the truth.At the hypocenter of the Wenchuan earthquake,the computed stress of the 3D result is only 1/3 to 1/4 of the 2D result,thus in a serious study,3D modeling is necessary.
引文
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[14]陈章立,赵翠萍,王勤彩,等.汶川MS8.0地震发生背景与过程的研究[J].地球物理学报,2009,52(2):455-463.
[15]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[J].地球物理学报,2009,52(2):444-454.
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[18]张贝,石耀霖.紫坪铺水库对附近断层稳定性影响的探讨[J].中国科学院研究生院学报,2010,27(6):754-760.
[19]Deng K,Zhou S,Wang R,et al.Evidence that the 2008 MW7.9 Wenchuan Earthquake Could NotHave Been Induced by the Zipingpu Reservoir[J].Bull Seism Soc Am,2010,100(5B):2 805-2 814.
[20]石耀霖,曹建玲.库仑应力计算及应用过程中若干问题的讨论——以汶川地震为例[J].地球物理学报,2010,53(1):102-110.
[21]Harris R A.Introduction to special section:Stress triggers,stress shadows,and implications forseismic hazard[J].Journal of Geophysical Research,1998,103(B10):24 347-24 358.
[22]Stein R S.The role of stress transfer in earthquake occurrence[J].Nature,1999,402:605-609.
[23]Rice J R,Cleary M P.Some Basic Stress Diffusion Solutions for Fluid-Saturated Elastic PorousMedia With Compressivle Consituents[J].Review of Geophysics and Space physics,1976,14(2):227-241.
[24]Talwani P,Chen L,Gahalaut K.Seismogenic permeability,ks[J].Journal of Geophysical Re-search,2007,112(B07309).
[25]Farr T G,Rosen P A,Caro E,et al.The shuttle radar topography mission[J].Reviews of Geo-physics,2007,45(2):RG2004.
[2]Gupta H K.A review of recent studies of triggered earthquakes by artificial water reservoirs withspecial emphasis on earthquakes in Koyna,India[J].Earth-Science Reviews,2002,58:279-310.
[3]陈颙.汶川地震是由水库蓄水引起的吗[J].中国科学D辑:地球科学,2009,39(3):257-259.
[4]雷兴林,马胜利,闻学泽,等.地表水体对断层应力与地震时空分布影响的综合分析[J].地震地质,2008,30(4):1 046-1 064.
[5]Ge S,Liu M,Lu N.Did the Zipingpu Reservoir trigger the 2008 Wenchuan earthquake[J].Geo-physical Research Letters,2009,36(L20315).
[6]周斌,薛世峰,邓志辉,等.水库诱发地震时空演化与库水加卸载及渗透过程的关系——以紫坪铺水库为例[J].地球物理学报,2010,53(11):2 651-2 670.
[7]Zhou S,Deng K,Zhao C,et al.Discussion on‘Was the 2008 Wenchuan earthquake triggered byZipingpu Reservoir?’[J].Earthquake Science,2010,23:577-581.
[8]Gahalaut K,Gahalaut V K.Effect of the Zipingpu reservoir impoundment on the occurrence of the2008Wenchuan earthquake and local seismicity[J].Geophysical Journal International,2010,183:277-285.
[9]程万正,张致伟,阮祥.紫坪铺水库区不同蓄水阶段的地震活动及成因分析[J].地球物理学进展,2010,25(3):759-767.
[10]韦伟,孙若昧,石耀霖.青藏高原东南缘地震层析成像及汶川地震成因探讨[J].中国科学D辑:地球科学,2010,40(7):831-839.
[11]Royden L H,Burchfiel B C,King R W,et al.Surface Deformation and Lower Crustal Flow in East-ern Tibet[J].Science,1997,276:788-790.
[12]Royden L H,Burchfiel B C,van der Hilst R D.The Geological Evolution of the Tibetan Plateau[J].Science,2008,321:1 054-1 058.
[13]张培震.青藏高原东缘川西地区的现今构造变形、应变分配与深部动力过程[J].中国科学D辑:地球科学,2008,38(9):1 041-1 056.
[14]陈章立,赵翠萍,王勤彩,等.汶川MS8.0地震发生背景与过程的研究[J].地球物理学报,2009,52(2):455-463.
[15]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[J].地球物理学报,2009,52(2):444-454.
[16]Hainzl S,Ogata Y.Detecting fluid signals in seismicity data through statistical earthquake modeling[J].Journal of Geophysical Research,2005,110(B05S07).
[17]Lei X,Yu G,Ma S,et al.Earthquakes induced by water injection at 3km depth within theRongchang gas field,Chongqing,China[J].Journal of Geophysical Research,2008,113(B10310).
[18]张贝,石耀霖.紫坪铺水库对附近断层稳定性影响的探讨[J].中国科学院研究生院学报,2010,27(6):754-760.
[19]Deng K,Zhou S,Wang R,et al.Evidence that the 2008 MW7.9 Wenchuan Earthquake Could NotHave Been Induced by the Zipingpu Reservoir[J].Bull Seism Soc Am,2010,100(5B):2 805-2 814.
[20]石耀霖,曹建玲.库仑应力计算及应用过程中若干问题的讨论——以汶川地震为例[J].地球物理学报,2010,53(1):102-110.
[21]Harris R A.Introduction to special section:Stress triggers,stress shadows,and implications forseismic hazard[J].Journal of Geophysical Research,1998,103(B10):24 347-24 358.
[22]Stein R S.The role of stress transfer in earthquake occurrence[J].Nature,1999,402:605-609.
[23]Rice J R,Cleary M P.Some Basic Stress Diffusion Solutions for Fluid-Saturated Elastic PorousMedia With Compressivle Consituents[J].Review of Geophysics and Space physics,1976,14(2):227-241.
[24]Talwani P,Chen L,Gahalaut K.Seismogenic permeability,ks[J].Journal of Geophysical Re-search,2007,112(B07309).
[25]Farr T G,Rosen P A,Caro E,et al.The shuttle radar topography mission[J].Reviews of Geo-physics,2007,45(2):RG2004.
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