日本东北9.0级地震的同震与震后滑动
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摘要
大部分强震都发生在海沟,那里是海洋板块向大陆板块俯冲的地方。大量矩震级MW9.0以上的地震发生在若干区域,包括智利,阿拉斯加,堪察加半岛和苏门答腊岛等。位于太平洋板块俯冲鄂霍茨克板块的日本海沟,历史记载上没有发生过MW9.0地震,除了至今震级还有争议的公元869年Jogan大地震[1](可能超过MW9.0)。然而,根据最新的大地测量资料估算的应变积累速率比已发生的板块间地震的平均释放速率要高[2~6]。这一发现又引发了这样的疑问:这些区域如何释放积累的应变。2011年3月11日发生的逆冲型MW9.0强震(下文中均称为日本东北大地震),撕裂了日本东北部的太平洋海岸板块边界。我们报道根据GPS网络监测到的地表位移确定的同震与震后滑动特征。同震滑移区域沿日本海沟方向长约400 km,与震前闭锁区域基本吻合[4]。震后滑动不仅覆盖了同震滑移区域,而且扩展到了其邻区,甚至其影响已经达到100 km深度区域,引起2011年3月25日的MW8.3地震。由于东北地震释放了积累数百年的应变,之前提到的应变积累与释放不平衡的问题可能得到部分解释。这次东北地震同时也提醒我们,即使在过去没有发生过强震的其它海沟地区,也有发生MW9.0强震的潜在危险。因此,利用空间对地形变观测技术监测应变积累,以确定强震潜在危险区是非常重要的。
Most large earthquakes occur along an oceanic trench,where anoceanic plate subducts beneath a continental plate.Massive earthquakes with a moment magnitude,MW,of nine have been known to occur in only a few areas,including Chile,Alaska,Kamchatka and Sumatra.No historical records exist of a MW=9 earthquake along the Japan trench,where the Pacific plate subducts beneath the Okhotsk plate,with the possible exception of the AD 869 Jogan earthquake[1],the magnitude of which has not been well constrained.However,the strain accumulation rate estimated there from recent geodetic observations is much higher than the average strain rate released in previous interplate earthquakes.This finding raises the question of how such areas release the accumulated strain.A megathrust earthquake with MW=9.0(hereafter referred to as the Tohoku-Oki earthquake) occurred on 11 March 2011,rupturing the plate boundary off the Pacific coast of northeastern Japan.Here we report the distributions of the coseismic slip and postseismic slip as determined from ground displacement detected using a network based on the Global Positioning System.The coseismic slip area extends approximately 400 km along the Japan trench,matching the area of the pre-seismic locked zone 4.The afterslip has begun to overlap the coseismic slip area and extends into the surrounding region.In particular,the afterslip area reached a depth of approximately 100 km,with MW=8.3,on 25 March 2011.Because the Tohoku-Oki earthquake released the strain accumulated for several hundred years,the paradox of the strain budget imbalance may be partly resolved.This earthquake reminds us of the potential for MW≈9 earthquakes to occur alongother trench systems,even if no past evidence of such events exists.Therefore,it is imperative that strain accumulation be monitored using a space geodetic technique to assess earthquake potential.
Most large earthquakes occur along an oceanic trench,where anoceanic plate subducts beneath a continental plate.Massive earthquakes with a moment magnitude,MW,of nine have been known to occur in only a few areas,including Chile,Alaska,Kamchatka and Sumatra.No historical records exist of a MW=9 earthquake along the Japan trench,where the Pacific plate subducts beneath the Okhotsk plate,with the possible exception of the AD 869 Jogan earthquake[1],the magnitude of which has not been well constrained.However,the strain accumulation rate estimated there from recent geodetic observations is much higher than the average strain rate released in previous interplate earthquakes.This finding raises the question of how such areas release the accumulated strain.A megathrust earthquake with MW=9.0(hereafter referred to as the Tohoku-Oki earthquake) occurred on 11 March 2011,rupturing the plate boundary off the Pacific coast of northeastern Japan.Here we report the distributions of the coseismic slip and postseismic slip as determined from ground displacement detected using a network based on the Global Positioning System.The coseismic slip area extends approximately 400 km along the Japan trench,matching the area of the pre-seismic locked zone 4.The afterslip has begun to overlap the coseismic slip area and extends into the surrounding region.In particular,the afterslip area reached a depth of approximately 100 km,with MW=8.3,on 25 March 2011.Because the Tohoku-Oki earthquake released the strain accumulated for several hundred years,the paradox of the strain budget imbalance may be partly resolved.This earthquake reminds us of the potential for MW≈9 earthquakes to occur alongother trench systems,even if no past evidence of such events exists.Therefore,it is imperative that strain accumulation be monitored using a space geodetic technique to assess earthquake potential.
引文
[1]Minoura,K.,Imamura,F.,Sugawara,D.,Kono,Y.&Iwashita,T.The 869 Jogan tsunami deposit andrecurrence interval of large-scale tsunami on the Pacific coast of northeast Japan.J.Nat.Disaster Sci.23,83-88(2001).
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[5]Hashimoto,C.,Noda,A.,Sagiya,T.&Matsu'ura,M.Interplate seismogenic zones along the Kuril-Japan trenchfromGPS data inversion.Nature Geosci.2,141-144(2009).
[6]Suwa,Y.,Miura,S.,Hasegawa,A.,Sato,T.&Tachibana,K.Interplate coupling beneath NE Japan inferredfromthree-dimensional displacement field.J.Geophys.Res.111,B04402(2006).
[7]Sella,G.F.,Dixon,T.H.&Mao,A.REVEL:a model for recent plate velocities from space geodesy.J.Geophys.Res.107,2081(2002).
[8]Apel,E.V.et al.Independent activemicroplate tectonics ofnortheastAsia from GPS velocities and blockmodeling.Geophys.Res.Lett.33,L11303(2006).
[9]Utsu,T.Chronological table of earthquakes in Japan with a moment magnitude larger than 6.0 and disastrousearthquakes from 1885 to 1980.Bull.Earthq.Res.Inst.57,401-463(1983).
[10]Heki,K.,Miyazaki,S.&Tsuji,H.Silent fault slip following an interplate thrust earthquake at the JapanTrench.Nature 386,595-597(1997).
[11]Sagiya,T.,Miyazaki,S.&Tada,T.Continuous GPS array and present-day crustal deformation of Japan.PureAppl.Geophys.157,2303-2322(2000).
[12]Yabuki,T.&Matsu'ura,M.Geodetic data inversion using a Bayesian information criterion for spatialdistribution of fault slip.Geophys.J.Int.109,363-375(1992).
[13]Igarashi,T.,Matsuzawa,T.,Umino,N.&Hasegawa,A.Spatial distribution of focal mechanisms for andintraplate earthquakes associated with the subducting Pacific plate beneath the northeastern Japan arc:atriple-planed deep seismic zone.J.Geophys.Res.106,2177-2191(2001).
[14]Nakajima,J.&Matsuzawa,T.Hasegawa,A.&Zhao,D.Seismic imaging of arc magma and fluids under thecentral part of northeast Japan.Tectonophysics 341,1-17(2001).
[15]Global CMT Web Page.Global Centroid Moment Tensor Project http://www.globalcmt.org/?(accessed 30March 2011).
[16]Shearer,P.&Burgmann,R.Lessons learned from the 2004 Sumatra-Andaman megathrust rupture.Annu.Rev.Earth Planet.Sci.38,103-131(2010).
[17]Pollitz,F.Gravitational viscoelastic postseismic relaxation on a layered spherical earth.J.Geophys.Res.102,17921-17941(1997).
[18]Ozawa,S.,Kaidzu,M.,Murakami,M.,Imakiire,T.&Hatanaka,Y.Coseismic and postseismic crustaldeformation after the Mw 8 Tokachi-oki earthquake in Japan.Earth Planets Space 56,675-680(2004).
[19]Hsu,Y.et al.Frictional afterslip following the 2005 Nias-Simeulue earthquake,Sumatra.Science 312,1921-1926(2006).
[20]Nishimura,T.et al.Distribution of seismic coupling on the subducting plateboundary in northeastern Japaninferred from GPS observations.Tectonophysics323,217-238(2000).
[21]Uchida,N.,Matsuzawa,T.,Nakajima,J.&Hasegawa,A.Subduction of a wedgeshaped Philippine Sea platebeneath Kanto,central Japan,estimated from converted waves and small repeating earthquakes.J.Geophys.Res.115,B07309(2010).
[22]Moreno,M.,Rosenau,M.&Oncken,O.2010 Maule earthquake slip correlates with pre-seismic locking ofAndean subduction zone.Nature 467,198-202(2010).
[23]Melbourn,T.I.,Webb,F.H.,Stock,J.M.&Reigbar,C.Rapid postseismic transientsin subduction zonesfrom continuous GPS.J.Geophys.Res.107,2241(2002).
[24]Chlieh,M.et al.Coseismic slip and afterslip of the great Mw 9.15 Sumatra-Andaman earthquake of 2004.Bull.Seismol.Soc.Am.97,S152-S173(2007).
[25]Kato,T.Secular and earthquake-related vertical crustal movements in Japan as deduced from tidal records(1951-1981).Tectonophysics 97,183-200(1983).
[26]Matsu'ura,T.,Furusawa,A.&Saomoto,H.Long-term and short-term vertical velocity profiles across theforearc in the NE Japan subduction zone.Quat.Res.71,227-238(2009).
[27]Suito,H.&Freymueller,J.T.A viscoelastic and afterslip postseismic deformationmodel for the1964 Alaskaearthquake.J.Geophys.Res.114,B11404(2009).
[28]Nakajima,J.&Hasegawa,A.Anomalous low-velocity zone and linear alignment of seismicity along it in thesubducted Pacific slabbeneathKanto,Japan:reactivation of subducted fracture zone?Geophys.Res.Lett.33,L16309(2006).
[29]Bird,P.An updated digitalmodel of plate boundaries.Geochem.Geophys.Geosyst.4,1027(2003).
[30]Savage,J.C.A dislocation model of strain accumulation and release at a subduction zone.J.Geophys.Res.88,4984-4996(1983).
[2]Peterson,E.T.&Seno,T.Factors affecting seismic moment release rates in subduction zones.J.Geophys.Res.89,10233-10248(1984).
[3]Pacheco,J.F.,Sykes,L.R.&Scholz,C.H.Nature of seismic coupling along simple plate boundaries of thesubduction type.J.Geophys.Res.98,14133-14159(1993).
[4]Nishimura,T.et al.Temporal change of interplate coupling in northeastern Japanduring 1995-2002 estimatedfrom continuous GPS observations.Geophys.J.Int.157,901-916(2004).
[5]Hashimoto,C.,Noda,A.,Sagiya,T.&Matsu'ura,M.Interplate seismogenic zones along the Kuril-Japan trenchfromGPS data inversion.Nature Geosci.2,141-144(2009).
[6]Suwa,Y.,Miura,S.,Hasegawa,A.,Sato,T.&Tachibana,K.Interplate coupling beneath NE Japan inferredfromthree-dimensional displacement field.J.Geophys.Res.111,B04402(2006).
[7]Sella,G.F.,Dixon,T.H.&Mao,A.REVEL:a model for recent plate velocities from space geodesy.J.Geophys.Res.107,2081(2002).
[8]Apel,E.V.et al.Independent activemicroplate tectonics ofnortheastAsia from GPS velocities and blockmodeling.Geophys.Res.Lett.33,L11303(2006).
[9]Utsu,T.Chronological table of earthquakes in Japan with a moment magnitude larger than 6.0 and disastrousearthquakes from 1885 to 1980.Bull.Earthq.Res.Inst.57,401-463(1983).
[10]Heki,K.,Miyazaki,S.&Tsuji,H.Silent fault slip following an interplate thrust earthquake at the JapanTrench.Nature 386,595-597(1997).
[11]Sagiya,T.,Miyazaki,S.&Tada,T.Continuous GPS array and present-day crustal deformation of Japan.PureAppl.Geophys.157,2303-2322(2000).
[12]Yabuki,T.&Matsu'ura,M.Geodetic data inversion using a Bayesian information criterion for spatialdistribution of fault slip.Geophys.J.Int.109,363-375(1992).
[13]Igarashi,T.,Matsuzawa,T.,Umino,N.&Hasegawa,A.Spatial distribution of focal mechanisms for andintraplate earthquakes associated with the subducting Pacific plate beneath the northeastern Japan arc:atriple-planed deep seismic zone.J.Geophys.Res.106,2177-2191(2001).
[14]Nakajima,J.&Matsuzawa,T.Hasegawa,A.&Zhao,D.Seismic imaging of arc magma and fluids under thecentral part of northeast Japan.Tectonophysics 341,1-17(2001).
[15]Global CMT Web Page.Global Centroid Moment Tensor Project http://www.globalcmt.org/?(accessed 30March 2011).
[16]Shearer,P.&Burgmann,R.Lessons learned from the 2004 Sumatra-Andaman megathrust rupture.Annu.Rev.Earth Planet.Sci.38,103-131(2010).
[17]Pollitz,F.Gravitational viscoelastic postseismic relaxation on a layered spherical earth.J.Geophys.Res.102,17921-17941(1997).
[18]Ozawa,S.,Kaidzu,M.,Murakami,M.,Imakiire,T.&Hatanaka,Y.Coseismic and postseismic crustaldeformation after the Mw 8 Tokachi-oki earthquake in Japan.Earth Planets Space 56,675-680(2004).
[19]Hsu,Y.et al.Frictional afterslip following the 2005 Nias-Simeulue earthquake,Sumatra.Science 312,1921-1926(2006).
[20]Nishimura,T.et al.Distribution of seismic coupling on the subducting plateboundary in northeastern Japaninferred from GPS observations.Tectonophysics323,217-238(2000).
[21]Uchida,N.,Matsuzawa,T.,Nakajima,J.&Hasegawa,A.Subduction of a wedgeshaped Philippine Sea platebeneath Kanto,central Japan,estimated from converted waves and small repeating earthquakes.J.Geophys.Res.115,B07309(2010).
[22]Moreno,M.,Rosenau,M.&Oncken,O.2010 Maule earthquake slip correlates with pre-seismic locking ofAndean subduction zone.Nature 467,198-202(2010).
[23]Melbourn,T.I.,Webb,F.H.,Stock,J.M.&Reigbar,C.Rapid postseismic transientsin subduction zonesfrom continuous GPS.J.Geophys.Res.107,2241(2002).
[24]Chlieh,M.et al.Coseismic slip and afterslip of the great Mw 9.15 Sumatra-Andaman earthquake of 2004.Bull.Seismol.Soc.Am.97,S152-S173(2007).
[25]Kato,T.Secular and earthquake-related vertical crustal movements in Japan as deduced from tidal records(1951-1981).Tectonophysics 97,183-200(1983).
[26]Matsu'ura,T.,Furusawa,A.&Saomoto,H.Long-term and short-term vertical velocity profiles across theforearc in the NE Japan subduction zone.Quat.Res.71,227-238(2009).
[27]Suito,H.&Freymueller,J.T.A viscoelastic and afterslip postseismic deformationmodel for the1964 Alaskaearthquake.J.Geophys.Res.114,B11404(2009).
[28]Nakajima,J.&Hasegawa,A.Anomalous low-velocity zone and linear alignment of seismicity along it in thesubducted Pacific slabbeneathKanto,Japan:reactivation of subducted fracture zone?Geophys.Res.Lett.33,L16309(2006).
[29]Bird,P.An updated digitalmodel of plate boundaries.Geochem.Geophys.Geosyst.4,1027(2003).
[30]Savage,J.C.A dislocation model of strain accumulation and release at a subduction zone.J.Geophys.Res.88,4984-4996(1983).
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