东日本大地震地震序列的震源机制解特征及其动力学意义
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摘要
日本本州及其邻近区域的应力状态以及弧后盆地的演化机制一直是人们所关注的问题.本文对2011年3月11日东日本大地震地震序列(2011年3月11日至2012年3月15日)的哈佛双力偶解进行了聚类分析,得到五种类型的震源机制解:与主震类型一致的低倾角逆断层型地震;主张应力方向垂直于日本海沟走向的正断层型地震;主张应力方向平行于日本海沟走向的正断层型地震;主压应力方向平行于日本海沟走向的逆断层型地震;包括走滑型地震在内的其他类型地震.东日本大地震地震序列中发生在弧前增生楔地震的震源机制解与大地震发生之前地震的震源机制解特征有显著区别,反映出该地区的应力状态与震前相比有较大改变.东日本大地震及其前震释放了附近区域的累积弹性应力,主震破裂区附近太平洋板块和其上覆板块接近完全解耦,降低了日本海盆地、中国东北地区的近东西向挤压应力水平.不过,整个本州岛东部区域太平洋板块和其上覆板块并没有完全解耦,但应力水平并不高.我们认为,日本海及中国东北应力水平的降低会使该区域的近东西向挤压型地震的危险性降低,而使NNE-SSW走向的走滑型地震活动性增强.同时,火山活动性也会增强.尤其是本州岛地区,存在近期火山爆发的可能性.东日本大地震地震序列的震源机制解特征还提示我们,日本海的应力状态及日本海的演化可能在一定程度上取决于太平洋板块和上覆板块的耦合状态.持续的弱耦合将不仅使得弧后大范围的地区保持岩浆上涌所必须的拉伸应力环境,而且还会因弧前隆起区发育大量正断层型地震而向深部提供促使岩浆生成所必须的水,因而造成日本海的再次扩张.
The stress state of Japan Sea region and its evolution are both concerned greatly by geoscientists.In this paper,we study Harvard CMT solutions of the March 11,2011 Tohoku-Oki Earthquake sequence from March 11th,2011 to March 15th,2012 by cluster analysis and find that they might be roughly sorted to four groups.The first group are low-angle thrust events,which are the same as the main shock and are mostly interplate events.The second group events are normal-fault earthquakes with principal extensional direction roughly pointing to E-W direction.Most of these earthquakes were located in the fore-arc uplift region of the Pacific plate,while some others occurred in the fore-arc accretionary wedge.The third group events are also normal-fault events mainly occurred in the fore-arc accretionary wedge though their principal extensional directions roughly parallel the Japan Trench.The forth group are reverse earthquakes with principal compressional directions roughly along N-S direction.We observe that Harvard CMT solutions of 2011 Tohoku-Oki earthquake sequence are obviously different from before.They show that Tohoku-Oki Earthquake sequence have released most of elastic energy in the main shock area.As a result,Pacific Plate and North America Plate have decoupled in the main rupture zone,which lowered the E-W compressional stress in Japan Sea and Northeastern China.However,Japan Sea Subduction Zone has not completely decoupled with North American Plate,even though the stress level in this region is lowered now.We claim that releasing of accumulated stress in the region of Japan Sea and Northeast China could lower the seismic hazard of roughly E-W direction compressive events,while tend to increase the activity of NNE-SSW strike-slip events as well as the volcanism,especially in Honshu.The characteristics of the Focal Mechanism Solutions of the Tohoku-Oki Earthquake Sequence remind us that stress state as well as evolution of Japan Sea might depend to some extent on coupling state between Pacific Plate and North American Plate.Long-lasting weak coupling might lead to re-opening of Japan Sea Basin because it will not only guarantee a relatively extensional environment,but also provide necessary water to deep depth.
The stress state of Japan Sea region and its evolution are both concerned greatly by geoscientists.In this paper,we study Harvard CMT solutions of the March 11,2011 Tohoku-Oki Earthquake sequence from March 11th,2011 to March 15th,2012 by cluster analysis and find that they might be roughly sorted to four groups.The first group are low-angle thrust events,which are the same as the main shock and are mostly interplate events.The second group events are normal-fault earthquakes with principal extensional direction roughly pointing to E-W direction.Most of these earthquakes were located in the fore-arc uplift region of the Pacific plate,while some others occurred in the fore-arc accretionary wedge.The third group events are also normal-fault events mainly occurred in the fore-arc accretionary wedge though their principal extensional directions roughly parallel the Japan Trench.The forth group are reverse earthquakes with principal compressional directions roughly along N-S direction.We observe that Harvard CMT solutions of 2011 Tohoku-Oki earthquake sequence are obviously different from before.They show that Tohoku-Oki Earthquake sequence have released most of elastic energy in the main shock area.As a result,Pacific Plate and North America Plate have decoupled in the main rupture zone,which lowered the E-W compressional stress in Japan Sea and Northeastern China.However,Japan Sea Subduction Zone has not completely decoupled with North American Plate,even though the stress level in this region is lowered now.We claim that releasing of accumulated stress in the region of Japan Sea and Northeast China could lower the seismic hazard of roughly E-W direction compressive events,while tend to increase the activity of NNE-SSW strike-slip events as well as the volcanism,especially in Honshu.The characteristics of the Focal Mechanism Solutions of the Tohoku-Oki Earthquake Sequence remind us that stress state as well as evolution of Japan Sea might depend to some extent on coupling state between Pacific Plate and North American Plate.Long-lasting weak coupling might lead to re-opening of Japan Sea Basin because it will not only guarantee a relatively extensional environment,but also provide necessary water to deep depth.
引文
[1]Honda H,Masatsuka A.On the mechanisms of theearthquakes and the stresses producing them in Japan and itsvicinity.Ibid,1952,4:42-60.
[2]Honda H,Masatsuka A,Emura K.On the mechanism of theearthquakes and the stresses producing them in Japan and itsvicinity(second paper):Tohoku Univ.Sci.Rept.,Ser.5.Geophys.,1957,8:186-205.
[3]Nakamura K,Uyeda S.Stress gradient in arc-back arcregions and plate subduction.J.Geophys.Res.,1980,85(B11):6419-6428.
[4]Uyeda S,Kanamori H.Back-arc opening and the mode ofsubduction.J.Geophys.Res.,1979,84(B3):1049-1061.
[5]宁杰远,臧绍先.日本海及中国东北地震的深度分布及其应力状态.地震地质,1987,9(2):49-61.Ning J Y,Zang S X.The distribution of earthquakes andstress state in the Japan Sea and the northeast China.Seismology and Geology(in Chinese),1987,9(2):49-61.
[6]谢富仁,崔效锋,赵建涛等.中国大陆及邻区现代构造应力场分区.地球物理学报,2004,47(4):654-662.Xie F R,Cui X F,Zhao J T,et al.Regional division of therecent tectonic stress field in China and adjacent areas.Chinese J.Geophys.(in Chinese),2004,47(4):654-662.
[7]俞春泉,陶开,崔效锋等.用格点尝试法求解P波初动震源机制解及解的质量评价.地球物理学报,2009,52(5):1402-1411.Yu C Q,Tao K,Cui X F,et al.P-wave first-motion focalmechanism solutions and their quality evaluation.Chinese J.Geophys.(in Chinese),2009,52(5):1402-1411.
[8]Zheng X F,Yao Z X,Liang J H,et al.The role played andopportunities provided by IGP DMC of China national seismicnetwork in Wenchuan earthquake disaster relief and researches.Bull.Seism.Soc.Am.,2010,100(5B):2866-2872,doi:10.1785/0120090257.
[9]Obana K,Fujie G,Takahashi T,et al.Normal-faultingearthquakes beneath the outer slope of the Japan trench afterthe 2011 Tohoku earthquake:Implications for the stressregime in the incoming Pacific plate.Geophysical ResearchLetters,2012,39(7),doi:10.1029/2011GL050399.
[10]Ammon C J,Lay T,Kanamori H,et al.A rupture model ofthe 2011off the Pacific coast of Tohoku earthquake.EarthPlanets Space,2011,63(7):693-696.
[11]Fujii Y,Satake K,Sakai S,et al.Tsunami source of the2011off the Pacific coast of Tohoku earthquake.EarthPlanets Space,2011,63(7):815-820.
[12]Hayes G P.Rapid source characterization of the 2011 Mw9.0off the Pacific coast of Tohoku earthquake.Earth PlanetsSpace,2011,63(7):529-534.
[13]陈为涛,甘卫军,肖根如等.3.11日本大地震对中国东北部地区地壳形变态势的影响.地震地质,2012,34(3):425-439.Chen W T,Gan W J,Xiao G R,et al.The impact of 2011Tohoku-Oki earthquake in Japan on crustal deformation ofnortheastern region in China.Seismology and Geology(inChinese),2012,34(3):425-439.
[14]王敏,李强,王凡等.全球定位系统测定的2011年日本宫城MW9.0级地震远场同震位移.科学通报,2011,56(20):1593-1596.Wang M,Li Q,Wang F,et al.Far-field coseismicdisplacements associated with the 2011Tohoku-oki earthquake inJapan observed by Global Positioning System.Chinese Sci.Bull.,2011,56(23):2419-2424.
[15]王凡,沈正康,王阎昭等.2011年3月11日日本宫城Mw9.0级地震对其周边地区火山活动的影响.科学通报,2011,56(14):1080-1083.Wang F,Shen Z K,Wang Y Z,et al.Influence of the March11,2011 Mw9.0Tohoku-oki earthquake on regional volcanicactivities.Chinese Sci.Bull.,2011,56(20):2077-2081.
[16]Lallemand S,Jolivet L.Japan Sea:apull-apart basin?Earthand Planetary Science Letters,1986,76(3-4):375-389.
[17]Nakamura K.Possible nascent trench along the eastern Japansea as the convergent boundary between Eurasian and NorthAmerican plates.Bull.Earthquake Res.Inst.Univ.Tokyo(in Japanese with English abstract),1983,58:721-732.
[18]Kobayashi Y.Incipient subduction of a lithospheric plateunder the eastern margin of the Japan Sea.The EarthMonthly(in Japanese),1983,5:510-514.
[19]Seno T.A consideration on the“Japan sea subductionhypothesis”seismic slip vector along the Japan trench.Jishin(J.Geol.Soc.Jpn.)(in Japanese),1983,36:227-273.
[20]Jolivet L,Tamaki K.Neogene kinematics in the Japan Searegion and volcanic activity of the northeast Japan arc.∥Proc.Ocean Drill.Program Sci.Results,1992,127-128:1311-1331.
[21]Tamaki K.Two modes of back-arc spreading.Geology,1985,13(7):475-478.
[22]Otofuji Y I,Matsuda T,Nohda S.Paleomagnetic evidencefor the Miocene counter-clockwise rotation of northeastJapan-rifting process of the Japan arc.Earth Planet.Sci.Lett.,1985,75(2-3):265-277.
[23]Tatsumi Y,Otofuji Y I,Matsuda T,et al.Opening of thesea of Japan back-arc basin by asthenospheric injection.Tectonophysics,1989,166(4):317-329.
[24]Liu J Q,Han J T,Fyfe W S.Cenozoic episodic volcanismand continental rifting in northeast China and possible link toJapan Sea development as revealed from K-Ar geochronology.Tectonophysics,2001,339(3-4):385-401.
[25]Nelson T H,Temple P G.Mainstream mantle convection:Ageologic analysis of plate motion.Amer.Assoc.Petrol.Geol.Bull.,1972,56(2):226-246.
[26]Minster J B,Jordan T H,Molnar P,et al.Numericalmodelling of instantaneous plate tectonics.Geophys.J.Int.,1974,36(3):541-576.
[27]Kanamori H.Seismic and aseismic slip along subductionzones and their tectonic implications.//Talwani M,PitmanW C eds.Island Arcs,Deep Sea Trenches and Back-ArcBasins.American Geophysical Union,Washington,D.C.1977,doi:10.1029/ME001p0163.
[28]Nishimura S.Why are there no back-arc basins around theeastern Pacific margin?Revista Mexicana de CienciasGeologicas,2002,19(3):170-174.
[29]Kimura G,Tamaki K.Collision,rotation and back-arcspreading in the region of the Okhotsk and Japan Seas.Tectonics,1986,5(3):389-401.
[30]Jolivet L,Huchon P,Ragin C.Tectonic setting of WesternPacific marginal basins.Tectonophysics,1989,160(1-4):23-47.
[31]Tamaki K,Honza E.Global tectonics and formation ofmarginal basins:role of the western Pacific.Episodes,1991,14(3):224-230.
[32]许浚远,张凌云.欧亚板块东缘新生代盆地成因:右行剪切拉分作用.石油与天然气地质,1999,20(3):187-191.Xu J Y,Zhang L Y.Genesis of Cenozoic basins in the easternmargin of Eurasia plate:dextral pulling apart.Oil&GasGeology(in Chinese),1999,20(3):187-191.
[33]许浚远,张凌云.西北太平洋边缘新生代盆地成因(上):成盆机制述评.石油与天然气地质,2000,21(2):93-98.Xu J Y,Zhang L Y.Genesis of Cenozoic basins in NorthwestPacific Ocean margin(1):comments on basin-formingmechanism.Oil&Gas Geology(in Chinese),2000,21(2):93-98.
[34]许浚远,张凌云.西北太平洋边缘新生代盆地成因(中):连锁右行拉分裂谷系统.石油与天然气地质,2000,21(3):185-190.Xu J Y,Zhang L Y.Genesis of Cenozoic basins in NorthwestPacific margin(2):linked dextral pull-apart basin system.Oil&Gas Geology(in Chinese),2000,21(3):185-190.
[35]许浚远,张凌云.西北太平洋边缘新生代盆地成因(下):后裂谷期构造演化.石油与天然气地质,2000,21(4):287-292.Xu J Y,Zhang L Y.Genesis of cenozoic basins in NorthwestPacific margin(3):tectonic evlution of post rifting period.Oil&Gas Geology(in Chinese),2000,21(4):287-292.
[36]Karig D E.Origin and development of marginal basins in thewestern Pacific.Journal of Geophysical Research,1971,76(11):2542-2561.
[37]Maruyama S,Hasegawa A,Santosh M,et al.The dynamicsof Big Mantle Wedge,Magma Factory,and metamorphic-metasomatic factory in subduction zones.Gondwana Res.,2009,16(3-4):414-430.
[38]Grove T L,Till C B,Lev E,et al.Kinematic variables andwater transport control the formation and location of arcvolcanoes.Nature,2009,459(7247):694-697.
[2]Honda H,Masatsuka A,Emura K.On the mechanism of theearthquakes and the stresses producing them in Japan and itsvicinity(second paper):Tohoku Univ.Sci.Rept.,Ser.5.Geophys.,1957,8:186-205.
[3]Nakamura K,Uyeda S.Stress gradient in arc-back arcregions and plate subduction.J.Geophys.Res.,1980,85(B11):6419-6428.
[4]Uyeda S,Kanamori H.Back-arc opening and the mode ofsubduction.J.Geophys.Res.,1979,84(B3):1049-1061.
[5]宁杰远,臧绍先.日本海及中国东北地震的深度分布及其应力状态.地震地质,1987,9(2):49-61.Ning J Y,Zang S X.The distribution of earthquakes andstress state in the Japan Sea and the northeast China.Seismology and Geology(in Chinese),1987,9(2):49-61.
[6]谢富仁,崔效锋,赵建涛等.中国大陆及邻区现代构造应力场分区.地球物理学报,2004,47(4):654-662.Xie F R,Cui X F,Zhao J T,et al.Regional division of therecent tectonic stress field in China and adjacent areas.Chinese J.Geophys.(in Chinese),2004,47(4):654-662.
[7]俞春泉,陶开,崔效锋等.用格点尝试法求解P波初动震源机制解及解的质量评价.地球物理学报,2009,52(5):1402-1411.Yu C Q,Tao K,Cui X F,et al.P-wave first-motion focalmechanism solutions and their quality evaluation.Chinese J.Geophys.(in Chinese),2009,52(5):1402-1411.
[8]Zheng X F,Yao Z X,Liang J H,et al.The role played andopportunities provided by IGP DMC of China national seismicnetwork in Wenchuan earthquake disaster relief and researches.Bull.Seism.Soc.Am.,2010,100(5B):2866-2872,doi:10.1785/0120090257.
[9]Obana K,Fujie G,Takahashi T,et al.Normal-faultingearthquakes beneath the outer slope of the Japan trench afterthe 2011 Tohoku earthquake:Implications for the stressregime in the incoming Pacific plate.Geophysical ResearchLetters,2012,39(7),doi:10.1029/2011GL050399.
[10]Ammon C J,Lay T,Kanamori H,et al.A rupture model ofthe 2011off the Pacific coast of Tohoku earthquake.EarthPlanets Space,2011,63(7):693-696.
[11]Fujii Y,Satake K,Sakai S,et al.Tsunami source of the2011off the Pacific coast of Tohoku earthquake.EarthPlanets Space,2011,63(7):815-820.
[12]Hayes G P.Rapid source characterization of the 2011 Mw9.0off the Pacific coast of Tohoku earthquake.Earth PlanetsSpace,2011,63(7):529-534.
[13]陈为涛,甘卫军,肖根如等.3.11日本大地震对中国东北部地区地壳形变态势的影响.地震地质,2012,34(3):425-439.Chen W T,Gan W J,Xiao G R,et al.The impact of 2011Tohoku-Oki earthquake in Japan on crustal deformation ofnortheastern region in China.Seismology and Geology(inChinese),2012,34(3):425-439.
[14]王敏,李强,王凡等.全球定位系统测定的2011年日本宫城MW9.0级地震远场同震位移.科学通报,2011,56(20):1593-1596.Wang M,Li Q,Wang F,et al.Far-field coseismicdisplacements associated with the 2011Tohoku-oki earthquake inJapan observed by Global Positioning System.Chinese Sci.Bull.,2011,56(23):2419-2424.
[15]王凡,沈正康,王阎昭等.2011年3月11日日本宫城Mw9.0级地震对其周边地区火山活动的影响.科学通报,2011,56(14):1080-1083.Wang F,Shen Z K,Wang Y Z,et al.Influence of the March11,2011 Mw9.0Tohoku-oki earthquake on regional volcanicactivities.Chinese Sci.Bull.,2011,56(20):2077-2081.
[16]Lallemand S,Jolivet L.Japan Sea:apull-apart basin?Earthand Planetary Science Letters,1986,76(3-4):375-389.
[17]Nakamura K.Possible nascent trench along the eastern Japansea as the convergent boundary between Eurasian and NorthAmerican plates.Bull.Earthquake Res.Inst.Univ.Tokyo(in Japanese with English abstract),1983,58:721-732.
[18]Kobayashi Y.Incipient subduction of a lithospheric plateunder the eastern margin of the Japan Sea.The EarthMonthly(in Japanese),1983,5:510-514.
[19]Seno T.A consideration on the“Japan sea subductionhypothesis”seismic slip vector along the Japan trench.Jishin(J.Geol.Soc.Jpn.)(in Japanese),1983,36:227-273.
[20]Jolivet L,Tamaki K.Neogene kinematics in the Japan Searegion and volcanic activity of the northeast Japan arc.∥Proc.Ocean Drill.Program Sci.Results,1992,127-128:1311-1331.
[21]Tamaki K.Two modes of back-arc spreading.Geology,1985,13(7):475-478.
[22]Otofuji Y I,Matsuda T,Nohda S.Paleomagnetic evidencefor the Miocene counter-clockwise rotation of northeastJapan-rifting process of the Japan arc.Earth Planet.Sci.Lett.,1985,75(2-3):265-277.
[23]Tatsumi Y,Otofuji Y I,Matsuda T,et al.Opening of thesea of Japan back-arc basin by asthenospheric injection.Tectonophysics,1989,166(4):317-329.
[24]Liu J Q,Han J T,Fyfe W S.Cenozoic episodic volcanismand continental rifting in northeast China and possible link toJapan Sea development as revealed from K-Ar geochronology.Tectonophysics,2001,339(3-4):385-401.
[25]Nelson T H,Temple P G.Mainstream mantle convection:Ageologic analysis of plate motion.Amer.Assoc.Petrol.Geol.Bull.,1972,56(2):226-246.
[26]Minster J B,Jordan T H,Molnar P,et al.Numericalmodelling of instantaneous plate tectonics.Geophys.J.Int.,1974,36(3):541-576.
[27]Kanamori H.Seismic and aseismic slip along subductionzones and their tectonic implications.//Talwani M,PitmanW C eds.Island Arcs,Deep Sea Trenches and Back-ArcBasins.American Geophysical Union,Washington,D.C.1977,doi:10.1029/ME001p0163.
[28]Nishimura S.Why are there no back-arc basins around theeastern Pacific margin?Revista Mexicana de CienciasGeologicas,2002,19(3):170-174.
[29]Kimura G,Tamaki K.Collision,rotation and back-arcspreading in the region of the Okhotsk and Japan Seas.Tectonics,1986,5(3):389-401.
[30]Jolivet L,Huchon P,Ragin C.Tectonic setting of WesternPacific marginal basins.Tectonophysics,1989,160(1-4):23-47.
[31]Tamaki K,Honza E.Global tectonics and formation ofmarginal basins:role of the western Pacific.Episodes,1991,14(3):224-230.
[32]许浚远,张凌云.欧亚板块东缘新生代盆地成因:右行剪切拉分作用.石油与天然气地质,1999,20(3):187-191.Xu J Y,Zhang L Y.Genesis of Cenozoic basins in the easternmargin of Eurasia plate:dextral pulling apart.Oil&GasGeology(in Chinese),1999,20(3):187-191.
[33]许浚远,张凌云.西北太平洋边缘新生代盆地成因(上):成盆机制述评.石油与天然气地质,2000,21(2):93-98.Xu J Y,Zhang L Y.Genesis of Cenozoic basins in NorthwestPacific Ocean margin(1):comments on basin-formingmechanism.Oil&Gas Geology(in Chinese),2000,21(2):93-98.
[34]许浚远,张凌云.西北太平洋边缘新生代盆地成因(中):连锁右行拉分裂谷系统.石油与天然气地质,2000,21(3):185-190.Xu J Y,Zhang L Y.Genesis of Cenozoic basins in NorthwestPacific margin(2):linked dextral pull-apart basin system.Oil&Gas Geology(in Chinese),2000,21(3):185-190.
[35]许浚远,张凌云.西北太平洋边缘新生代盆地成因(下):后裂谷期构造演化.石油与天然气地质,2000,21(4):287-292.Xu J Y,Zhang L Y.Genesis of cenozoic basins in NorthwestPacific margin(3):tectonic evlution of post rifting period.Oil&Gas Geology(in Chinese),2000,21(4):287-292.
[36]Karig D E.Origin and development of marginal basins in thewestern Pacific.Journal of Geophysical Research,1971,76(11):2542-2561.
[37]Maruyama S,Hasegawa A,Santosh M,et al.The dynamicsof Big Mantle Wedge,Magma Factory,and metamorphic-metasomatic factory in subduction zones.Gondwana Res.,2009,16(3-4):414-430.
[38]Grove T L,Till C B,Lev E,et al.Kinematic variables andwater transport control the formation and location of arcvolcanoes.Nature,2009,459(7247):694-697.
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