利用重力观测约束2011日本Tohoku大地震的震源机制
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摘要
2011年3月11日,日本东北部(Tohoku)太平洋海域发生Mw9.0特大地震.一些国际学术机构用不同的震相和反演方法,计算了大地震的震源机制解.但这些结果存在一定的差异.地球长周期自由振荡的振幅主要依赖于地震矩的大小及地震断层的破裂方式,可以约束地震的震源机制、地震大小及持续时间.本文利用地球自由振荡0S0简正模对Tohoku大地震的震源机制解进行分析和约束.0S0振幅大小与地震断层的倾角(dip)、滑动方向角(slip)、震源深度及地震断层的破裂时间有关.我们利用震源机制解得到大地震后自由振荡模拟值,利用超导重力仪得到自由振荡的高精度重力观测值.二者比较后的结果显示:由GCMT震源机制解得到的0S0振幅与观测值符合较好,而由USGS CMT震源机制解模拟的结果明显大于观测值.2011Tohoku地震为逆冲型浅源大地震.进一步的分析表明:逆冲型浅源大地震的断层倾角对0S0振幅的影响很大,而滑动方向角以及震源深度对0S0振幅的影响较小.USGS CMT震源机制解中较大的断层倾角是导致其0S0振幅显著偏离观测值的主要原因.
An Mw9.0 earthquake occurred near the Pacific coast of Tohoku,Japan on March 11,2011.Some seismic research institutes,using different phases and inversion methods,provided different focal mechanism solutions.Mainly depended on seismic scalar moment and the pattern of the fault rupture,the Earth′s free oscillations can constrain the focal mechanism solution,size and duration of an earthquake.In this paper,we use the radial mode 0S0 to analyze and constrain the focal mechanism solutions of the Tohoku earthquake.The 0S0 amplitude is related to the fault dip angle,slip azimuth,depth and duration of the fault rupture.Based on the focal mechanism solutions,we calculated the synthetic normal modes and compared with the high-precision superconductor gravity observations.The comparison indicates an excellent agreement between the observations and the GCMT synthetics while a significant discrepancy between the observations and USGS CMT synthetics.Our studies indicate that,for a megathrust-shallow event,the influence of fault dip on the 0S0 amplitude is significant but that of the slip and the depth are minor.The large dip is the main reason for the significant discrepancy between the observations and USGS CMT synthetics.
An Mw9.0 earthquake occurred near the Pacific coast of Tohoku,Japan on March 11,2011.Some seismic research institutes,using different phases and inversion methods,provided different focal mechanism solutions.Mainly depended on seismic scalar moment and the pattern of the fault rupture,the Earth′s free oscillations can constrain the focal mechanism solution,size and duration of an earthquake.In this paper,we use the radial mode 0S0 to analyze and constrain the focal mechanism solutions of the Tohoku earthquake.The 0S0 amplitude is related to the fault dip angle,slip azimuth,depth and duration of the fault rupture.Based on the focal mechanism solutions,we calculated the synthetic normal modes and compared with the high-precision superconductor gravity observations.The comparison indicates an excellent agreement between the observations and the GCMT synthetics while a significant discrepancy between the observations and USGS CMT synthetics.Our studies indicate that,for a megathrust-shallow event,the influence of fault dip on the 0S0 amplitude is significant but that of the slip and the depth are minor.The large dip is the main reason for the significant discrepancy between the observations and USGS CMT synthetics.
引文
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[16]Lay T,Kanamori H,Ammon C J,et al.The great Sumatra-Andaman earthquake of 26December 2004.Science,2005,308(5725):1127-1133.
[17]Giardini D,Li X D,Woodhouse J H.Three-dimensionalstructure of the Earth from splitting in free-oscillationspectra.Nature,1987,325(6103):405-411.
[18]Laske G,Masters G.Limits on differential rotation of theinner core from an analysis of the Earth′s free oscillations.Nature,1999,402(6757):66-69.
[19]Ishii M,Tromp J.Normal-mode and free-air gravityconstraints on lateral variations in velocity and density ofEarth′s mantle.Science,1999,285(5431):1231-1236.
[20]Hu X G,Liu L T,Sun H P,et al.Wavelet filter analysis ofsplitting and coupling of seismic normal modes below 1.5mHz with superconducting gravimeters after the December26,2004Sumatra earthquake.Science in China Series D:Earth Sciences,2006,49(12):1259-1269.
[21]Hu X G,Liu L T,Hinderer J,et al.Wavelet filter analysisof local atmospheric pressure effects on gravity variations.J.Geodesy,2005,79(8):447-459.
[22]Hu X G,Liu L T,Hinderer J,et al.Wavelet filter analysisof atmospheric pressure effects in the long-period seismicmode band.Phys.Earth Planet.Inter.,2006,154(1):70-84.
[23]Aki K,Richards P G.Quantitative Seismology:Theory andMethods.San Francisco:W.H.Freeman,1980.
[24]Helffrich G R.How good are routinely determined focalmechanisms?Empirical statistics based on a comparison ofHarvard,USGS and ERI moment tensors.Geophys.J.Int.,1997,131(3):741-750.
[25]Kanamori H,Rivera L.Source inversion of W-phase:Speeding up seismic tsunami warning.Geophys.J.Int.,2008,175(1):222-238.
[26]Dziewonski A M,Anderson D L.Preliminary reference Earthmodel.Phys.Earth Planet.Inter.,1981,25(4):297-356.
[27]Kedar S,Watada S,Tanimoto T.The 1989Macquarie Ridgeearthquake:Seismic moment estimation from long-period freeoscillations.J.Geophys.Res.,1994,99(B9):17893-17907.
[28]Park J,Song T A,Tromp J,et al.Earth′s free oscillationsexcited by the 26 December 2004 Sumatra-Andamanearthquake.Science,2005,308(5725):1139-1144.
[29]Lambotte S,Rivera L,Hinderer J.Rupture length andduration of the 2004 Aceh-Sumatra earthquake from thephases of the Earth′s gravest free oscillations.Geophys.Res.Lett.,2006,33:L03307,doi:10.1029/2005GL024090.
[30]Shapiro N M,Ritzwoller M H.Monte-Carlo inversion for aglobal shear-velocity model of the crust and upper mantle.Geophys.J.Int.,2002,151(1):88-105.
[31]Tsai V C,Hayes G P,Duputel Z.Constraints on the long-period moment-dip tradeoff for the Tohoku earthquake.Geophys.Res.Lett.,2011,38:L00G17,doi:10.1029/2011GL049129.
[32]Banerjee P,Pollitz F F,Bürgmann R.The size and durationof the Sumatra-Andaman earthquake from far-field staticoffsets.Science,2005,308(5729):1769-1772.
[33]Pollitz F F,Bürgmann R,Banerjee P.Geodetic slip model ofthe 2011 M9.0Tohoku earthquake.Geophys.Res.Lett.,2011,38:L00G08,doi:10.1029/2011GL048632.
[34]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.
[2]Dziewonski A M,Chou T A,Woodhouse J H.Determinationof earthquake source parameters from waveform data forstudies of global and regional seismicity.J.Geophys.Res.,1981,86(B4):2825-2852.
[3]Arvidsson R,Ekstrom G.Global CMT analysis of moderateearthquake,Mw≥4.5,using intermediate-period surfacewaves.Bull.Seism.Soc.Am.,1998,88(4):1003-1013.
[4]Ekstrom G,Dziewoński A M,Maternovskaya N N,et al.Global seismicity of 2003:centroid-moment-tensor solutionsfor 1087earthquakes.Phys.Earth Planet.Inter.,2005,148(2-4):327-351.
[5]Hayes G P,Earle P S,Benz H M,et al.88Hours:The U.S.geological survey national earthquake information centerresponse to the 11 March 2011 Mw9.0Tohoku earthquake.Seismol.Res.Lett.,2011,82(4):481-493.
[6]Sipkin S A.Estimation of earthquake source parameters bythe inversion of waveform data:synthetic waveforms.Phys.Earth Planet.Inter.,1982,30(2-3):242-259.
[7]Sipkin S A.Estimation of earthquake source parameters bythe inversion of waveform data:Global seismicity,1981—1983.Bull.Seism.Soc.Am.,1986,76(6):1515-1541.
[8]Sipkin S A.Rapid determination of global moment-tensorsolutions.Geophys.Res.Lett.,1994,21(16):1667-1670.
[9]Duputel Z,Rivera L,Kanamori H,et al.Real-time W phaseinversion during the 2011off the Pacific coast of Tohokuearthquake.Earth Planets Space,2011,63(7):535-539.
[10]W Phase source inversion results 3/11/2011(Mw9.0),Tohoku-oki,Japan.http://eost.u-strasbg.fr/wphase/tohoku_oki_2011/UPDATED.
[11]Shao G F,Li X Y,Ji C,et al.Focal mechanism and sliphistory of the 2011 Mw9.1off the Pacific coast of Tohokuearthquake,constrained with teleseismic body and surfacewaves.Earth Planets Space,2011,63(7):559-564.
[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]陈运泰.地震参数:数字地震学在地震预测中的应用.北京:地震出版社,2003.Chen Y T.Parameters of Earthquake-Application of DigitalSeismology in Earthquake Prediction(in Chinese).Beijing:Seismological Press,2003.
[14]Stein S,Okal E A.Seismology:Speed and size of theSumatra earthquake.Nature,2005,434(7033):581-582.
[15]Ammon C J,Ji C,Thio H K,et al.Rupture process of the2004 Sumatra-Andaman earthquake.Science,2005,308(5725):1133-1139.
[16]Lay T,Kanamori H,Ammon C J,et al.The great Sumatra-Andaman earthquake of 26December 2004.Science,2005,308(5725):1127-1133.
[17]Giardini D,Li X D,Woodhouse J H.Three-dimensionalstructure of the Earth from splitting in free-oscillationspectra.Nature,1987,325(6103):405-411.
[18]Laske G,Masters G.Limits on differential rotation of theinner core from an analysis of the Earth′s free oscillations.Nature,1999,402(6757):66-69.
[19]Ishii M,Tromp J.Normal-mode and free-air gravityconstraints on lateral variations in velocity and density ofEarth′s mantle.Science,1999,285(5431):1231-1236.
[20]Hu X G,Liu L T,Sun H P,et al.Wavelet filter analysis ofsplitting and coupling of seismic normal modes below 1.5mHz with superconducting gravimeters after the December26,2004Sumatra earthquake.Science in China Series D:Earth Sciences,2006,49(12):1259-1269.
[21]Hu X G,Liu L T,Hinderer J,et al.Wavelet filter analysisof local atmospheric pressure effects on gravity variations.J.Geodesy,2005,79(8):447-459.
[22]Hu X G,Liu L T,Hinderer J,et al.Wavelet filter analysisof atmospheric pressure effects in the long-period seismicmode band.Phys.Earth Planet.Inter.,2006,154(1):70-84.
[23]Aki K,Richards P G.Quantitative Seismology:Theory andMethods.San Francisco:W.H.Freeman,1980.
[24]Helffrich G R.How good are routinely determined focalmechanisms?Empirical statistics based on a comparison ofHarvard,USGS and ERI moment tensors.Geophys.J.Int.,1997,131(3):741-750.
[25]Kanamori H,Rivera L.Source inversion of W-phase:Speeding up seismic tsunami warning.Geophys.J.Int.,2008,175(1):222-238.
[26]Dziewonski A M,Anderson D L.Preliminary reference Earthmodel.Phys.Earth Planet.Inter.,1981,25(4):297-356.
[27]Kedar S,Watada S,Tanimoto T.The 1989Macquarie Ridgeearthquake:Seismic moment estimation from long-period freeoscillations.J.Geophys.Res.,1994,99(B9):17893-17907.
[28]Park J,Song T A,Tromp J,et al.Earth′s free oscillationsexcited by the 26 December 2004 Sumatra-Andamanearthquake.Science,2005,308(5725):1139-1144.
[29]Lambotte S,Rivera L,Hinderer J.Rupture length andduration of the 2004 Aceh-Sumatra earthquake from thephases of the Earth′s gravest free oscillations.Geophys.Res.Lett.,2006,33:L03307,doi:10.1029/2005GL024090.
[30]Shapiro N M,Ritzwoller M H.Monte-Carlo inversion for aglobal shear-velocity model of the crust and upper mantle.Geophys.J.Int.,2002,151(1):88-105.
[31]Tsai V C,Hayes G P,Duputel Z.Constraints on the long-period moment-dip tradeoff for the Tohoku earthquake.Geophys.Res.Lett.,2011,38:L00G17,doi:10.1029/2011GL049129.
[32]Banerjee P,Pollitz F F,Bürgmann R.The size and durationof the Sumatra-Andaman earthquake from far-field staticoffsets.Science,2005,308(5729):1769-1772.
[33]Pollitz F F,Bürgmann R,Banerjee P.Geodetic slip model ofthe 2011 M9.0Tohoku earthquake.Geophys.Res.Lett.,2011,38:L00G08,doi:10.1029/2011GL048632.
[34]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.
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