中国数字地震台网记录的苏门答腊—安达曼地震激发的地球球型自由振荡的检测
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摘要
利用中国数字地震台网(CDSN)改造后的7个台站的VHZ波形资料,提取了2004年12月26日苏门答腊-安达曼地震激发的0S2~0S54地球球型自由振荡,并与地球初步参考模型(PREM)的理论自由振荡频率进行了对比,发现与PREM模型预测的球型自由振荡周期符合得很好.观测的该地震激发的0S2,0S3,0S4,2S1和1S2振型自由振荡有明显的频谱分裂现象.特别是2S1振型,是继Rosat等之后的第二次报道不叠加的情况下观测到的这种振型.根据该地震的总体震源机制,试算了不同的地震矩,模拟了该地震0S2振型在CDSN7个台上的自由振荡振幅,并与记录资料进行了比较,得到该地震的地震矩可达1023N·m;本文发现地球自由振荡记录包含了大量震源机制和地震位置的信息,可用于地震震源破裂参数的精细研究.
The 0S2~0S54 spheroidal modes of Earth's free oscillations, triggered by the great Sumatra-Andaman earthquake of 26 December 2004 are retrieved from VHZ data recorded by seven upgraded stations of China Digital Seismograph Network (CDSN). We compare these spheroidal modes with theoretical free oscillation spectra calculated from the Preliminary Reference Earth Model (PREM) and find a coincidence between their periods. Spectral splitting phenomenon is observed obviously in 0S2, 0S3, 0S4, 2S1 and 1S2 free oscillation modes. What is most noticeable is that the oscillation mode 2S1 is reported for the second time (the first time by Rosat et al) without any data stacking. We simulated the split singlet of 0S2 mode on seven CDSN stations based on general focal mechanism and seismic moment of the earthquake. The result shows that seismic moment of the earthquake can reach 1023 N·m. We also find that the recording of Earth′s free oscillations carries abundant information of source mechanism and earthquake location, which is applicable to the detailed study of source rupture parameters.
The 0S2~0S54 spheroidal modes of Earth's free oscillations, triggered by the great Sumatra-Andaman earthquake of 26 December 2004 are retrieved from VHZ data recorded by seven upgraded stations of China Digital Seismograph Network (CDSN). We compare these spheroidal modes with theoretical free oscillation spectra calculated from the Preliminary Reference Earth Model (PREM) and find a coincidence between their periods. Spectral splitting phenomenon is observed obviously in 0S2, 0S3, 0S4, 2S1 and 1S2 free oscillation modes. What is most noticeable is that the oscillation mode 2S1 is reported for the second time (the first time by Rosat et al) without any data stacking. We simulated the split singlet of 0S2 mode on seven CDSN stations based on general focal mechanism and seismic moment of the earthquake. The result shows that seismic moment of the earthquake can reach 1023 N·m. We also find that the recording of Earth′s free oscillations carries abundant information of source mechanism and earthquake location, which is applicable to the detailed study of source rupture parameters.
引文
[1]Depart ment of Earth and Planetary Sciences,Division of Engineering and Applied Science,Harvard University.2005.[2006-03-20].http:∥www.seismology.harvard.edu.
傅承义,陈运泰,祁贵仲.1985.地球物理学基础[M].北京:科学出版社:347-368.
高原,Van der Lee S,Giardini D,等.2001.应用振型叠加方法研究1997年11月8日中国西藏玛尼地震震源机制[J].地球物理学报,44(增刊):98-106.
雷湘鄂,许厚泽,孙和平.2002.利用超导重力观测资料检测地球自由振荡[J].科学通报,47(18):1432-1436.
雷湘鄂,许厚泽,孙和平.2004.由5个国际超导重力仪台站资料检测到的秘鲁8.2级大地震所激发的球型自由振荡现象[J].中国科学(D辑),34(5):483～491.
马淑田,郝建国.1997.1995年7月12日中缅边界MS=7.3地震的震源机制解[J].地震学报,19(1):107-109.
万永革,周公威,郭燕平.2005.中国数字地震台网记录的昆仑山口西地震的球型自由振荡[J].地震,25(1):31-40.
Ammon C J,Chen J,Thio H K,et al.2005.Rupture process of the2004Sumatra-Andaman earthquake[J].Science,308:1133-1139.
Benioff H,Press F,Smith S.1961.Excitation of the free oscillations of the earth by earthquakes[J].J Geophys Res,66:605-619.
Beroza G C,Jordan T H.1990.Searchingfor slowand silent earthquakes usingfree oscillations[J].J Geophys Res,95:2485-2510.
Courtier N,Ducarme B,Goodkind J,et al.2000.Global superconducting gravi meter observations and the searchfor thetranslational modes of the inner core[J].Phys Earth Planet Interi,117:3-20.
Dahlen F A,Sailor R V.1979.Rotational and elliptical splitting of the free oscillations of the earth[J].Geophys J RastrSoc,58:609-623.
Derr J S.1969.Internal structure of the earthinferred fromfree oscillations[J].J Geophys Res,74:5202-5219.
Durek J J,Romanowicz B.1999.Inner core anisotropyinferred by direct inversion of normal model spectra[J].GeophysJInt,139:599-622.
Dziewonski A M,Anderson D L.1981.Preli minary reference Earth model(PREM)[J].Phys Earth Planet Interi,25:297-356.
Geller RJ,Stein S.1977.Split free oscillation amplitudesfor the1960Chilean and1964Alaskan earthquakes[J].BullSeism Soc Amer,67(3):651-660.
Haddon R A W,Bullen K E.1969.An earth model incorporating free oscillation data[J].Phys Earth Planet Interi,2:35-49.
Kedar S,Watada S,Tani moto T.1994.The1989Macquarie Ridge earthquake:Seismic moment esti mation fromlongperiod free oscillations[J].J Geophys Res,99:17893-17908.
Lamb H.1882.On the vibrations of an elastic sphere[J].London Mathematical Society,14:50-56.
Love A E H.1911.Some Problemof Geodynamics[M].London:Cambridge University Press:176-181.
Masters G,Gilbert F.1981.Structure of theinner coreinferredfromobservations of its spheroidal shear modes[J].Geo-phys Res Lett,8:569-571.
Morrelli A,Dziewonski A M,Woodhouse J H.1986.Anisotropy of inner core inferred from PKIKP travel ti mes[J].Geophys Res Lett,13:1545-1548.
Ness N R,Harrison C T,Slichter L B.1961.Observation of the free oscillation of the earth[J].J Geophys Res,66:621-629.
Nowroozi A A.1972.Characteristic periods of fundamental and overtone oscillations of the earth following a deep-focusearthquake[J].Bull Seism Soc Amer,62:247-274.
Park J,Song T-R A,Tromp J,et al.2005.Earth's free oscillations excited by the26December2004Sumatra-Andamanearthquake[J].Science,308:139-143.
Resovsky J S,Pestana R.2003.I mproved normal mode constraints on lower mantlevPfrom generalized spectral fitting[J].Geophys Res Lett,30(7):1383,doi:10.1029/2002GL015790.
Resovsky J S,Ritzwoller M H.1998.New and refined constraints on three-di mensional earth structure from normalmodes below3mHz[J].J Geophys Res,103:783-810.
Resovsky J S,Ritzwoller M H.1999.A degree8mantle shear velocity model from normal mode observations below3mHz[J].J Geophys Res,104:993-1014.
Rosat S,Sato T,I manishi Y,et al.2005.High-resolution analysis of the gravest seismic normal modes after the2004MW=9Sumatra earthquake using superconducting gravi meter data[J].Geophys Res Lett,32:L133304,doi:10.1029/2005GL023128.
Shearer P M.1994.Constraints oninner core anisotropy from PKP(DF)travel ti mes[J].J Geophys Res,99:19647-19657.
Shibata N,Suda N,Fukao Y.1991.Use of apparent complexfrequencies of free oscillations to esti mate aspherical struc-ture of the earth[J].Geophys Res Lett,18:905-908.
Song X D,Hel mberger D V.1995.Depth dependence of anisotropy of the Earth′s inner core[J].J Geophys Res,100:9805-9816.
Stein S,Geller RJ.1977.Amplitudes of the Earth′s split normal modes[J].J Phys Earth,25:117-142.
Stein S,Okal E A.2005a.Speed and size of the Sumatra earthquake[J].Nature,434:581-582.
Stein S,Okal E A.2005b.The2004Sumatra earthquake and India ocean tsunami:What happened and why[J].TheEarth′s Scientist,XXXI(2):6-11.
Subarya C,Chlieh M,Prawirodirjo L,et al.2006.Plate-boundary deformation associated withthe great Sumatra-Anda-man earthquake[J].Nature,440:46-51.
Van Camp M.1999.Measuring seismic normal modes with the GWRC021 superconducting gravi meter[J].Phys EarthPlanet Interi,116:81-92.
Widmer-Schnidrig R.1999.Free oscillations illuminate the mantle[J].Nature,398:292-293.
Woodhouse J H,Giardini D,Li X D.1986.Evidence for inner core anisotropy fromfree oscillations[J].Geophys ResLett,13:1549-1552.
傅承义,陈运泰,祁贵仲.1985.地球物理学基础[M].北京:科学出版社:347-368.
高原,Van der Lee S,Giardini D,等.2001.应用振型叠加方法研究1997年11月8日中国西藏玛尼地震震源机制[J].地球物理学报,44(增刊):98-106.
雷湘鄂,许厚泽,孙和平.2002.利用超导重力观测资料检测地球自由振荡[J].科学通报,47(18):1432-1436.
雷湘鄂,许厚泽,孙和平.2004.由5个国际超导重力仪台站资料检测到的秘鲁8.2级大地震所激发的球型自由振荡现象[J].中国科学(D辑),34(5):483～491.
马淑田,郝建国.1997.1995年7月12日中缅边界MS=7.3地震的震源机制解[J].地震学报,19(1):107-109.
万永革,周公威,郭燕平.2005.中国数字地震台网记录的昆仑山口西地震的球型自由振荡[J].地震,25(1):31-40.
Ammon C J,Chen J,Thio H K,et al.2005.Rupture process of the2004Sumatra-Andaman earthquake[J].Science,308:1133-1139.
Benioff H,Press F,Smith S.1961.Excitation of the free oscillations of the earth by earthquakes[J].J Geophys Res,66:605-619.
Beroza G C,Jordan T H.1990.Searchingfor slowand silent earthquakes usingfree oscillations[J].J Geophys Res,95:2485-2510.
Courtier N,Ducarme B,Goodkind J,et al.2000.Global superconducting gravi meter observations and the searchfor thetranslational modes of the inner core[J].Phys Earth Planet Interi,117:3-20.
Dahlen F A,Sailor R V.1979.Rotational and elliptical splitting of the free oscillations of the earth[J].Geophys J RastrSoc,58:609-623.
Derr J S.1969.Internal structure of the earthinferred fromfree oscillations[J].J Geophys Res,74:5202-5219.
Durek J J,Romanowicz B.1999.Inner core anisotropyinferred by direct inversion of normal model spectra[J].GeophysJInt,139:599-622.
Dziewonski A M,Anderson D L.1981.Preli minary reference Earth model(PREM)[J].Phys Earth Planet Interi,25:297-356.
Geller RJ,Stein S.1977.Split free oscillation amplitudesfor the1960Chilean and1964Alaskan earthquakes[J].BullSeism Soc Amer,67(3):651-660.
Haddon R A W,Bullen K E.1969.An earth model incorporating free oscillation data[J].Phys Earth Planet Interi,2:35-49.
Kedar S,Watada S,Tani moto T.1994.The1989Macquarie Ridge earthquake:Seismic moment esti mation fromlongperiod free oscillations[J].J Geophys Res,99:17893-17908.
Lamb H.1882.On the vibrations of an elastic sphere[J].London Mathematical Society,14:50-56.
Love A E H.1911.Some Problemof Geodynamics[M].London:Cambridge University Press:176-181.
Masters G,Gilbert F.1981.Structure of theinner coreinferredfromobservations of its spheroidal shear modes[J].Geo-phys Res Lett,8:569-571.
Morrelli A,Dziewonski A M,Woodhouse J H.1986.Anisotropy of inner core inferred from PKIKP travel ti mes[J].Geophys Res Lett,13:1545-1548.
Ness N R,Harrison C T,Slichter L B.1961.Observation of the free oscillation of the earth[J].J Geophys Res,66:621-629.
Nowroozi A A.1972.Characteristic periods of fundamental and overtone oscillations of the earth following a deep-focusearthquake[J].Bull Seism Soc Amer,62:247-274.
Park J,Song T-R A,Tromp J,et al.2005.Earth's free oscillations excited by the26December2004Sumatra-Andamanearthquake[J].Science,308:139-143.
Resovsky J S,Pestana R.2003.I mproved normal mode constraints on lower mantlevPfrom generalized spectral fitting[J].Geophys Res Lett,30(7):1383,doi:10.1029/2002GL015790.
Resovsky J S,Ritzwoller M H.1998.New and refined constraints on three-di mensional earth structure from normalmodes below3mHz[J].J Geophys Res,103:783-810.
Resovsky J S,Ritzwoller M H.1999.A degree8mantle shear velocity model from normal mode observations below3mHz[J].J Geophys Res,104:993-1014.
Rosat S,Sato T,I manishi Y,et al.2005.High-resolution analysis of the gravest seismic normal modes after the2004MW=9Sumatra earthquake using superconducting gravi meter data[J].Geophys Res Lett,32:L133304,doi:10.1029/2005GL023128.
Shearer P M.1994.Constraints oninner core anisotropy from PKP(DF)travel ti mes[J].J Geophys Res,99:19647-19657.
Shibata N,Suda N,Fukao Y.1991.Use of apparent complexfrequencies of free oscillations to esti mate aspherical struc-ture of the earth[J].Geophys Res Lett,18:905-908.
Song X D,Hel mberger D V.1995.Depth dependence of anisotropy of the Earth′s inner core[J].J Geophys Res,100:9805-9816.
Stein S,Geller RJ.1977.Amplitudes of the Earth′s split normal modes[J].J Phys Earth,25:117-142.
Stein S,Okal E A.2005a.Speed and size of the Sumatra earthquake[J].Nature,434:581-582.
Stein S,Okal E A.2005b.The2004Sumatra earthquake and India ocean tsunami:What happened and why[J].TheEarth′s Scientist,XXXI(2):6-11.
Subarya C,Chlieh M,Prawirodirjo L,et al.2006.Plate-boundary deformation associated withthe great Sumatra-Anda-man earthquake[J].Nature,440:46-51.
Van Camp M.1999.Measuring seismic normal modes with the GWRC021 superconducting gravi meter[J].Phys EarthPlanet Interi,116:81-92.
Widmer-Schnidrig R.1999.Free oscillations illuminate the mantle[J].Nature,398:292-293.
Woodhouse J H,Giardini D,Li X D.1986.Evidence for inner core anisotropy fromfree oscillations[J].Geophys ResLett,13:1549-1552.
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