利用DEMETER卫星数据分析汶川地震前的电离层异常
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摘要
DEMETER卫星由法国于2004年6月发射,高度约为665km,圆轨道且经过极区,其主要目的是研究与地震有关的电离层异常.2008年5月12日6∶28(世界时)在四川省汶川县(31.02°N,103.37°E)发生了Ms8.0级的特大地震.本文分析了在震前一周内DEMETER卫星观测到的电离层异常.这些异常主要包括:(1)卫星在震前4天和5天经过震中附近时,记录到电子浓度、电子温度和氧离子浓度出现剧烈变化(变化率均超过20%);(2)在震前3天和7天,卫星探测到增强的电磁辐射.同时利用ELF频段(0～1250Hz)的三分量电场和磁场数据,对异常电磁辐射作了进一步的分析(计算了电场功率谱、磁场功率谱、波矢方向和极化特性等).另外,考查了观测期间的地磁指数,由此得出观测到的异常现象不大可能由地磁活动引起.最后,对震前出现的这些电离层异常的可能的物理机理进行了讨论.
The French micro-satellite DEMETER was launched on June 29,2004 in a polar and circular orbit with an altitude of about 665 km.The main objective of the satellite is to research ionospheric disturbance related to seismic activities.This paper reports the ionospheric anomalies observed by DEMETER within one week before the Ms 8.0 Wenchuan earthquake(31.02°N,103.37°E)which occurred at 0628UT on May 12,2008.The observation results include:(1)Electron density,electron temperature and oxygen ion density changed sharply(greater than 20%)near the epicenter four and five days prior to the shock.(2)Increased electromagnetic emissions were registered when the satellite passed the epicenter three and seven days before the shock.A further analysis(calculations of electric and magnetic power spectra,the wave vector direction and polarization sense)of the increased electromagnetic emissions is carried out based on the three-component electric and magnetic ELF(extremely low frequency,0~1250 Hz)data.In addition,the geophysical conditions are also investigated and it can be inferred that the observed anomalies are not likely due to geomagnetic activity.Finally,a possible mechanism which could account for these pre-earthquake ionospheric perturbations is discussed.
The French micro-satellite DEMETER was launched on June 29,2004 in a polar and circular orbit with an altitude of about 665 km.The main objective of the satellite is to research ionospheric disturbance related to seismic activities.This paper reports the ionospheric anomalies observed by DEMETER within one week before the Ms 8.0 Wenchuan earthquake(31.02°N,103.37°E)which occurred at 0628UT on May 12,2008.The observation results include:(1)Electron density,electron temperature and oxygen ion density changed sharply(greater than 20%)near the epicenter four and five days prior to the shock.(2)Increased electromagnetic emissions were registered when the satellite passed the epicenter three and seven days before the shock.A further analysis(calculations of electric and magnetic power spectra,the wave vector direction and polarization sense)of the increased electromagnetic emissions is carried out based on the three-component electric and magnetic ELF(extremely low frequency,0~1250 Hz)data.In addition,the geophysical conditions are also investigated and it can be inferred that the observed anomalies are not likely due to geomagnetic activity.Finally,a possible mechanism which could account for these pre-earthquake ionospheric perturbations is discussed.
引文
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[19]Danilov A D,Lastovika J.Effects of geomagnetic storms on the ionosphere and at mosphere.Int.J.Geomagn.Aeron.,2001,2(3):209～224
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[21]Gonzalez W D,Joselyn J A,Kamide Y,et al.What is a geomagnetic storm-J.Geophys.Res.,1994,99:5771～5792
[22]Santolik O,Parrot M,Lefeuvre F.Singular value decomposition methods for wave propagation analysis.Radio.Sci.,2003,38(1):1010.doi:10.1029/2000RS002523
[23]Santolik O,Nemec F,Parrot M,et al.Analysis methods for multi-component wave measurements on board the DEMETER spacecraft.Planet.Space Sci.,2006,54:512～527
[24]Molchanov O A,Hayakawa M,Rafalsky V A.Penetration characteristics of electromagnetic emissions froman underground seismic source into the at mosphere,ionosphere,and magnetosphere.J.Geophys Res.,1995,100:1691～1712
[25]Hayakawa M,Molchanov O A,NASDA/UEC team.Summary report of NASDA's earthquake remote sensing frontier project.Phys.Chem.Earth,2004,29:617～625
[26]Shklyar D R,Nagano I.On VLF wave scattering in plasma with density irregularities.J.Geophys.Res.,1998,103:29515～29526
[2]Warwick J W,Stoker C,Meye T R.Radio emission associated withrockfracture:possible applicationtothe great Chilean earthquake of May22,1960.J.Geophys.Res.,1982,87:2851～2859
[3]Parrot M,Achache J,Berthelier J J,et al.High-frequency seismo-electromagnetic effects.Phys.Earth Planet.Int.,1993,77:65～83
[4]Pulinets S A,Boyarchuk K A.Ionoshperic Precursors of Earthquakes.New York:Springer,2004
[5]Rios V H,Kim VP,Hegai V V.Abnormal perturbationsin the F2regionionosphere observed prior to the great San Juan earthquake of23November1977.Adv.Spa.Res.,2004,33:323～327
[6]Liu J Y,Chen YI,Pulinets S A,et al.Seismo-ionospheric signatures prior toM≥6.0Tai wan earthquake.Geophys.Res.Lett.,2000,27:3113～3116
[7]Chuo Y J,Chen Y I,Liu J Y,et al.IonosphericfoF2variations prior to strong earth-quakes in Tai wan area.Adv.Space Res.,2001,27(6-7):1305～1310
[8]Hayakawa M,Molchanov O A,Kodama T,et al.Plasma density variations observed on a satellite possibly related to seismicity.Adv.Space Res.,2000,26(8):1277～1280
[9]Sarkar S,Gwal A K,Parrot M.Ionospheric variations observed by the DEMETER satellite in the mid-latitude region during strong earthquakes.J.At mos.Solar-Terr.Phys.,2007,69:1524～1540
[10]Molchanov O,Rozhnoi1A,Solovieva M,et al.Global diagnostics of the ionospheric perturbations related to the seismic activity using the VLF radio signals collected on the DEMETER satellite.Nat.Hazards Earth Syst.Sci.,2006,6:745～753
[11]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):1086～1073Zhang P Z,Xu X W,Wen X Z,et al.Slip rates and recurrence intervals of the Longmen Shan active fault zone,and tectonic implications for the mechanism of the May12Wenchuan earthquake,2008,Sichuan,China.Chinese J.Geophys.(in Chinese),2008,51(4):1086～1073
[12]滕吉文,白登海,杨辉等.2008Ms8.0汶川地震发生的深层过程和动力学响应.地球物理学报,2008,51(5):1385～1402Teng J W,Bai D H,Yang H,et al.Deep processes and dynamics responses associated with the WenchuanMs8.0earthquake of2008.Chinese J.Geophys.(in Chinese),2008,51(5):1385～1402
[13]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,2008,51(5):1403～1410Wang W M,Zhao L F,Li J,et al.Rupture process of the Ms8.0Wenchuan earthquake of Sichuan,China.Chinese J.Geophys.(in Chinese),2008,51(5):1403～1410
[14]Zhao B Q,Wang M,Wan W X,et al.Unusual large enhancement of ionospheric electron density link with the2008great wenchuan earthquake-J.Geophys.Res.,2008,113,A11304,doi:10.1029/2008JA013613
[15]余涛,毛田,王云冈.汶川特大地震前电离层变化.科学通报,2008,in press Yu T,Mao T,Wang Y G.The ionospheric disturbances before the great Wenchuan earthquake.Chinese Sci.Bull.,2008,in press
[16]Berthelier J J,Godefroy M,Leblanc F,et al.ICE,The electric field experiment on DEMETER.Planet.Space Sci.,2006,54:456～471
[17]Parrot M,Benoist D,Berthelier J J,et al.The magnetic field experiment I MSC and its data processing onboard DEMETER:scientific objectives,description and first results.Planet.Space Sci.,2006,54:441～455
[18]Lebreton J P,Stverak S,Travnicek P,et al.The ISL Langmuir Probe experiment and its data processing onboard DEMETER:scientific objectives,description and first results.Planet.Space Sci.,2006,54:472～486
[19]Danilov A D,Lastovika J.Effects of geomagnetic storms on the ionosphere and at mosphere.Int.J.Geomagn.Aeron.,2001,2(3):209～224
[20]Hattori K,Akinaga Y,Hayakawa M,et al.ULF magnetic anomaly preceding the1997Kagoshima earthquakes.In:Hayakawa M,Molchanov O A eds.Seismo-electromagne-tics:Lithosphere-At mosphere-Ionosphere Coupling.Tokyo:Terr.Sc.Pub.,2002.19～28
[21]Gonzalez W D,Joselyn J A,Kamide Y,et al.What is a geomagnetic storm-J.Geophys.Res.,1994,99:5771～5792
[22]Santolik O,Parrot M,Lefeuvre F.Singular value decomposition methods for wave propagation analysis.Radio.Sci.,2003,38(1):1010.doi:10.1029/2000RS002523
[23]Santolik O,Nemec F,Parrot M,et al.Analysis methods for multi-component wave measurements on board the DEMETER spacecraft.Planet.Space Sci.,2006,54:512～527
[24]Molchanov O A,Hayakawa M,Rafalsky V A.Penetration characteristics of electromagnetic emissions froman underground seismic source into the at mosphere,ionosphere,and magnetosphere.J.Geophys Res.,1995,100:1691～1712
[25]Hayakawa M,Molchanov O A,NASDA/UEC team.Summary report of NASDA's earthquake remote sensing frontier project.Phys.Chem.Earth,2004,29:617～625
[26]Shklyar D R,Nagano I.On VLF wave scattering in plasma with density irregularities.J.Geophys.Res.,1998,103:29515～29526
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