利用三维孔隙弹性模型探讨紫坪铺水库对汶川地震的影响
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摘要
本文基于三维孔隙弹性理论,建立了紫坪铺水库及周边地区的有限元模型.根据紫坪铺水库开始蓄水到汶川地震发震时刻的水位变化情况,计算了整个区域的孔隙压力和库仑应力.详细讨论了断层及周围地层的弹性模量和扩散系数对计算结果的影响.计算结果表明:从弹性角度看,断层的弹性模量对汶川地震震源处的库仑应力影响很小;震源处的库仑应力随着断层和周围地层的扩散系数增大而增大.当给定弹性模量和扩散系数代表性值的时候,计算结果表明在汶川地震发震时刻,震源处的库仑应力变化量为+1kPa左右,这表明紫坪铺水库使得汶川地震发震断层更加危险.是否这个量级的库仑应力就能够触发汶川地震还需要进一步探讨.通过分析库区周边小震的分布,发现小震分布区域均是库仑应力增加的地区,因此紫坪铺水库周边的小震应该与紫坪铺水库蓄水有直接关系.
Some large reservoirs are known to induce earthquakes.After occurrence of the Wenchuan earthquake,some studies suggest that it was induced by the Zipingpu reservoir which is not far from the Longmenshan fault.In this paper,based on the poroelastic theory,a 3D finite element model of the Zipingpu area is constructed.According to the water level of the Zipingpu reservoir from the beginning of the impoundment to the occurrence of the 2008 Wenchuan earthquake,we calculate the pore pressure and the change of Coulomb stress with the model.Furthermore,we discuss the effects of elastic modulus and diffusivity of faults and around medium on the results.The results show that the elastic modulus of faults and around medium has little effect on the Coulomb stress in the hypocenter of the Wenchuan earthquake.With the increase of diffusivity of the fault or around medium,the Coulomb stress in the hypocenter increases.If we give the representative values of elastic modulus and diffusivity,the change of Coulomb stress in the hypocenter reaches 1 kPa when the Wenchuan earthquake occurred.The Zipingpu reservoir enhanced the seismic activity of the Longmenshan fault.But it needs further investigation whether increasing 1 kPa of Coulomb stress can trigger the occurrence of the Wenchuan earthquake.The analysis of the distribution of small earthquakes in the Zipingpu area before the Wenchuan earthquake reveals that most of the small earthquakes are located in the increasing region of Coulomb stress.So it indicates that the small earthquakes in the Zipingpu area should have a direct relationship with the impoundment of the Zipingpu reservoir.
Some large reservoirs are known to induce earthquakes.After occurrence of the Wenchuan earthquake,some studies suggest that it was induced by the Zipingpu reservoir which is not far from the Longmenshan fault.In this paper,based on the poroelastic theory,a 3D finite element model of the Zipingpu area is constructed.According to the water level of the Zipingpu reservoir from the beginning of the impoundment to the occurrence of the 2008 Wenchuan earthquake,we calculate the pore pressure and the change of Coulomb stress with the model.Furthermore,we discuss the effects of elastic modulus and diffusivity of faults and around medium on the results.The results show that the elastic modulus of faults and around medium has little effect on the Coulomb stress in the hypocenter of the Wenchuan earthquake.With the increase of diffusivity of the fault or around medium,the Coulomb stress in the hypocenter increases.If we give the representative values of elastic modulus and diffusivity,the change of Coulomb stress in the hypocenter reaches 1 kPa when the Wenchuan earthquake occurred.The Zipingpu reservoir enhanced the seismic activity of the Longmenshan fault.But it needs further investigation whether increasing 1 kPa of Coulomb stress can trigger the occurrence of the Wenchuan earthquake.The analysis of the distribution of small earthquakes in the Zipingpu area before the Wenchuan earthquake reveals that most of the small earthquakes are located in the increasing region of Coulomb stress.So it indicates that the small earthquakes in the Zipingpu area should have a direct relationship with the impoundment of the Zipingpu reservoir.
引文
[1]滕吉文,白登海,杨辉等.2008汶川Ms8.0地震发生的深层过程和动力学响应.地球物理学报,2008,51(5):1385-1402.Teng J W,Bai D H,Yang H,et al.Deep processes anddynamic responses associated with the Wenchuan Ms8.0earthquake of 2008.Chinese J.Geophys.(in Chinese),2008,51(5):1385-1402.
[2]Kerr R A,Stone R.A human trigger for the great quake ofSichuan?Science,2009,323(5912):322.
[3]陈颙.汶川地震是由水库蓄水引起的吗?中国科学D辑(地球科学),2009,39(3):257-259.Chen Y.Did the reservoir impoundment trigger theWenchuan earthquake?Science China Earth Sciences,2009,52(4):431-433.
[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—以紫坪铺水库为例.地震地质,2008,30(4):1046-1064.Lei X L,Ma S L,Wen X Z,et al.Integrated analysis ofstress and regional seismicity by surface loading—a case studyof Zipingpu reservoir.Seismology and Geology(in Chinese),2008,30(4):1046-1064.
[5]Lei X.Possible roles of the Zipingpu Reservoir in triggeringthe 2008 Wenchuan earthquake.Journal of Asian EarthSciences,2010,40(4):844-854.
[6]Ge S,Liu M,Lu N,et al.Did the Zipingpu reservoir triggerthe 2008 Wenchuan earthquake?Geophysical ResearchLetters,2009,36(20):L20315.
[7]Deng K,Zhou S,Wang R,et al.Evidence that the 2008Mw7.9Wenchuan earthquake could not have been induced bythe Zipingpu reservoir.Bulletin of the Seismological Societyof America,2010,100(5B):2805-2814.
[8]Gahalaut K,Gahalaut V K.Effect of the Zipingpu reservoirimpoundment on the occurrence of the 2008 Wenchuanearthquake and local seismicity.GeophysicalJ ournal International,2010,183(1):277-285.
[9]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.地球物理学报,2010,53(11):2651-2670.Zhou B,Xue S F,Deng Z H,et al.Relationship between theevolution of reservoir induced seismicity in space-time and theprocess of reservoir water body load unloading and waterinfiltration—a case study of Zipingpu reservoir.Chinese J.Geophys.(in Chinese),2010,53(11):2651-2670.
[10]Talwani P.On the nature of reservoir-induced Seismicity.Pure and Applied Geophysics,1997,150(3-4):473-492.
[11]Bell M L,Nur A.Strength changes due to reservior-inducedpore pressure and stresses and application to Lake Oroville.J.Geophys.Res.,1978,83(B9):4469-4483.
[12]张贝,石耀霖.紫坪铺水库对附近断层稳定性影响的探讨.中国科学院研究生院学报,2010,27(6):755-762.Zhang B,Shi Y L.A discussion on how the Zipingpu reservoirinfluences the stability of faults in the neighborhood.Journal ofthe Graduate School of the Chinese Academy of Sciences(inChinese),2010,27(6):755-762.
[13]邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学.地震地质,1994,16(4):389-403.Deng Q D,Chen S F,Zhao X L.Tectonics,scismisity anddynamics of Longmenshan mountains and its adjacentregions.Seismology and Geology(in Chinese),1994,16(4):389-403.
[14]张培震,徐锡伟,闻学泽等.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,2008,51(4):1066-1073.Zhang P Z,Xu X W,Wen X Z,et al.Slip rates andrecurrence intervals of the Longmenshan active fault zone andtectonic implications for the mechanism of the May 12Wenchuan earthquake,2008,Sichuan,China.Chinese J.Geophysics(in Chinese),2008,51(4):1066-1073.
[15]王卫民,赵连锋,李娟等.四川汶川8.0级地震震源过程.地球物理学报,2009,51(5):1403-1410.Wang W M,Zhao L F,Li J,et al.Rupture process of Ms8.0Wenchuan earthquake of Sichuan,China.Chinese J.Geophys.(in Chinese),2008,52(5):1403-1410.
[16]胡先明,张永久,谢蓉华等.紫坪铺水库区小地震震源机制研究.地震地质,2009,31(4):676-685.Hu X M,Zhang Y J,Xie R H,et al.Research on focalmechanism of small earthquakes in Zipingpu reservoir area.Seismology and Geology(in Chinese),2009,31(4):676-685.
[17]张永久,张致伟.汶川8.0级地震前紫坪铺库区震源机制及应力场特征.地震地质,2010,32(4):614-627.Zhang Y J,Zhang Z W.The focal mechanisms andcharacteristic of stress field in Zipingpu area before Wenchuanearthquake.Seismology and Geology(in Chinese),2010,32(4):614-627.
[18]Biot M A.General theory of three-dimensional consolidation.J.Appl.Phys,1941,12(2):155-164.
[19]Rice J R,Cleary M P.Some basic stress diffusion solutionsfor fluid-saturated elastic porous media with compressibleconstituents.Rev.Geophys.Space Phys.,1976,14(2):227-241.
[20]Roeloffs E A.Fault stability changes induced beneath areservoir with cyclic variations in water level.J.Geophys.Res,1988,93(B3):2107-2124.
[21]Harris R A.Introduction to special section:Stress triggers,stress shadows,and implications for seismic harzard.JournalofGeophysicalResearch,1998,103(B10):24347-24358.
[22]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.地球物理学报,2010,53(1):102-110.Shi Y L,Cao J L.Some aspects in static stress changecalculation—case study on Wenchuan earthquake.Chinese J.Geophysics(in Chinese),2010,53(1):102-110.
[23]张勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学D辑(地球科学),2008,38(10):1186-1194.Zhang Y,Feng W P,Xu L S,et al.Spatio-temporal ruptureprocess of the 2008 great Wenchuan earthquake.ScienceChina Earth Sciences,2009,52(2):145-154
[24]陈建业,杨晓松,党嘉祥等.汶川地震断层带结构及渗透率.地球物理学报,2011,54(7):1805-1816.Chen J Y,Yang X S,Dang J X,et al.Internal structure andpermeability of Wenchuan earthquake fault.Chinese J.Geophysics(in Chinese),2011,54(7):1805-1816.
[25]Talwani P,Chen L,Gahalaut K.Seismogenic permeability,ks.J.Geophys.Res,2007,112:B07309,doi:10.1029/2006JB004665.
[26]雷建设,赵大鹏,苏金蓉等.龙门山断裂带地壳精细结构与汶川地震发震机理.地球物理学报,2009,52(2):339-345.Lei J S,Zhao D P,Su J R,et al.Fine seismic structureunder the Longmenshan fault zone and the mechanism of thelarge Wenchuan earthquake.Chinese J.Geophys.(in Chinese),2009,52(2):339-345.
[2]Kerr R A,Stone R.A human trigger for the great quake ofSichuan?Science,2009,323(5912):322.
[3]陈颙.汶川地震是由水库蓄水引起的吗?中国科学D辑(地球科学),2009,39(3):257-259.Chen Y.Did the reservoir impoundment trigger theWenchuan earthquake?Science China Earth Sciences,2009,52(4):431-433.
[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—以紫坪铺水库为例.地震地质,2008,30(4):1046-1064.Lei X L,Ma S L,Wen X Z,et al.Integrated analysis ofstress and regional seismicity by surface loading—a case studyof Zipingpu reservoir.Seismology and Geology(in Chinese),2008,30(4):1046-1064.
[5]Lei X.Possible roles of the Zipingpu Reservoir in triggeringthe 2008 Wenchuan earthquake.Journal of Asian EarthSciences,2010,40(4):844-854.
[6]Ge S,Liu M,Lu N,et al.Did the Zipingpu reservoir triggerthe 2008 Wenchuan earthquake?Geophysical ResearchLetters,2009,36(20):L20315.
[7]Deng K,Zhou S,Wang R,et al.Evidence that the 2008Mw7.9Wenchuan earthquake could not have been induced bythe Zipingpu reservoir.Bulletin of the Seismological Societyof America,2010,100(5B):2805-2814.
[8]Gahalaut K,Gahalaut V K.Effect of the Zipingpu reservoirimpoundment on the occurrence of the 2008 Wenchuanearthquake and local seismicity.GeophysicalJ ournal International,2010,183(1):277-285.
[9]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.地球物理学报,2010,53(11):2651-2670.Zhou B,Xue S F,Deng Z H,et al.Relationship between theevolution of reservoir induced seismicity in space-time and theprocess of reservoir water body load unloading and waterinfiltration—a case study of Zipingpu reservoir.Chinese J.Geophys.(in Chinese),2010,53(11):2651-2670.
[10]Talwani P.On the nature of reservoir-induced Seismicity.Pure and Applied Geophysics,1997,150(3-4):473-492.
[11]Bell M L,Nur A.Strength changes due to reservior-inducedpore pressure and stresses and application to Lake Oroville.J.Geophys.Res.,1978,83(B9):4469-4483.
[12]张贝,石耀霖.紫坪铺水库对附近断层稳定性影响的探讨.中国科学院研究生院学报,2010,27(6):755-762.Zhang B,Shi Y L.A discussion on how the Zipingpu reservoirinfluences the stability of faults in the neighborhood.Journal ofthe Graduate School of the Chinese Academy of Sciences(inChinese),2010,27(6):755-762.
[13]邓起东,陈社发,赵小麟.龙门山及其邻区的构造和地震活动及动力学.地震地质,1994,16(4):389-403.Deng Q D,Chen S F,Zhao X L.Tectonics,scismisity anddynamics of Longmenshan mountains and its adjacentregions.Seismology and Geology(in Chinese),1994,16(4):389-403.
[14]张培震,徐锡伟,闻学泽等.2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,2008,51(4):1066-1073.Zhang P Z,Xu X W,Wen X Z,et al.Slip rates andrecurrence intervals of the Longmenshan active fault zone andtectonic implications for the mechanism of the May 12Wenchuan earthquake,2008,Sichuan,China.Chinese J.Geophysics(in Chinese),2008,51(4):1066-1073.
[15]王卫民,赵连锋,李娟等.四川汶川8.0级地震震源过程.地球物理学报,2009,51(5):1403-1410.Wang W M,Zhao L F,Li J,et al.Rupture process of Ms8.0Wenchuan earthquake of Sichuan,China.Chinese J.Geophys.(in Chinese),2008,52(5):1403-1410.
[16]胡先明,张永久,谢蓉华等.紫坪铺水库区小地震震源机制研究.地震地质,2009,31(4):676-685.Hu X M,Zhang Y J,Xie R H,et al.Research on focalmechanism of small earthquakes in Zipingpu reservoir area.Seismology and Geology(in Chinese),2009,31(4):676-685.
[17]张永久,张致伟.汶川8.0级地震前紫坪铺库区震源机制及应力场特征.地震地质,2010,32(4):614-627.Zhang Y J,Zhang Z W.The focal mechanisms andcharacteristic of stress field in Zipingpu area before Wenchuanearthquake.Seismology and Geology(in Chinese),2010,32(4):614-627.
[18]Biot M A.General theory of three-dimensional consolidation.J.Appl.Phys,1941,12(2):155-164.
[19]Rice J R,Cleary M P.Some basic stress diffusion solutionsfor fluid-saturated elastic porous media with compressibleconstituents.Rev.Geophys.Space Phys.,1976,14(2):227-241.
[20]Roeloffs E A.Fault stability changes induced beneath areservoir with cyclic variations in water level.J.Geophys.Res,1988,93(B3):2107-2124.
[21]Harris R A.Introduction to special section:Stress triggers,stress shadows,and implications for seismic harzard.JournalofGeophysicalResearch,1998,103(B10):24347-24358.
[22]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.地球物理学报,2010,53(1):102-110.Shi Y L,Cao J L.Some aspects in static stress changecalculation—case study on Wenchuan earthquake.Chinese J.Geophysics(in Chinese),2010,53(1):102-110.
[23]张勇,冯万鹏,许力生等.2008年汶川大地震的时空破裂过程.中国科学D辑(地球科学),2008,38(10):1186-1194.Zhang Y,Feng W P,Xu L S,et al.Spatio-temporal ruptureprocess of the 2008 great Wenchuan earthquake.ScienceChina Earth Sciences,2009,52(2):145-154
[24]陈建业,杨晓松,党嘉祥等.汶川地震断层带结构及渗透率.地球物理学报,2011,54(7):1805-1816.Chen J Y,Yang X S,Dang J X,et al.Internal structure andpermeability of Wenchuan earthquake fault.Chinese J.Geophysics(in Chinese),2011,54(7):1805-1816.
[25]Talwani P,Chen L,Gahalaut K.Seismogenic permeability,ks.J.Geophys.Res,2007,112:B07309,doi:10.1029/2006JB004665.
[26]雷建设,赵大鹏,苏金蓉等.龙门山断裂带地壳精细结构与汶川地震发震机理.地球物理学报,2009,52(2):339-345.Lei J S,Zhao D P,Su J R,et al.Fine seismic structureunder the Longmenshan fault zone and the mechanism of thelarge Wenchuan earthquake.Chinese J.Geophys.(in Chinese),2009,52(2):339-345.
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