基于Lg波识别判据的特性分析
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摘要
Lg波是检测、识别地下核爆炸的重要震相.通常情况下,地下核爆炸的低频段Lg波能量相对较强,基于Lg波的识别判据在高频段表现较好.然而在低频范围内却表现出难以用球对称爆炸源模式解释的现象,如Lg/Pg判据在1Hz附近失效等现象.本文利用理论地震图方法,分析了伴随层裂过程产生的重要辅助源——CLVD源对Lg波低频成分的调制作用,给出了基于Lg波的识别判据成功及失效的原因,并将层裂过程视为输入扰动,利用振型叠加原理,进一步解释了基于Lg波识别判据特性的物理机制.这对于更好地利用Lg波识别地下核爆炸,具有较好的参考意义.
Lg wave characteristic is widely used to discriminate underground nuclear explosions from earthquakes.In contrast,the high-frequency Lg/Pg discriminant appears to perform very well,but fails around 1 Hz.This phenomenon can not be explained by pure explosion source model,but the CLVD source appears to take a key role to explain it.In this paper,the effect of CLVD source on the performance of the discriminants based on Lg wave is studied by means of theoretical seismogram analysis.Considering the spall as an input of disturbance with special frequency,we proposed a physical mechanism of the performance of Lg/Pg based on the normal mode method.An understanding of the effect on Lg caused by CLVD source can be useful not only for improving the performance of existing regional discriminants,but also for exploring new discriminants.
Lg wave characteristic is widely used to discriminate underground nuclear explosions from earthquakes.In contrast,the high-frequency Lg/Pg discriminant appears to perform very well,but fails around 1 Hz.This phenomenon can not be explained by pure explosion source model,but the CLVD source appears to take a key role to explain it.In this paper,the effect of CLVD source on the performance of the discriminants based on Lg wave is studied by means of theoretical seismogram analysis.Considering the spall as an input of disturbance with special frequency,we proposed a physical mechanism of the performance of Lg/Pg based on the normal mode method.An understanding of the effect on Lg caused by CLVD source can be useful not only for improving the performance of existing regional discriminants,but also for exploring new discriminants.
引文
韩绍卿,李夕海,安跃文,刘代志.2010.核爆、化爆、地震识别综述[J].地球物理学进展,25(4):1206-1218.
何永锋,陈晓非,张海明.2005a.层裂对区域震相Lg波的影响[J].地震学报,27(3):309-316.
何永锋,陈晓非,张海明.2005b.地下核爆炸Rg波低谷点的激发机理[J].地球物理学报,48(3):643-650.
靳平,徐国明,楼沩涛.1997.受低频动态正压力加载的椭球腔的地震矩表示及其在无限介质中辐射的地震波[J].地震学报,19(5):2-11.
靳平,徐国明,楼沩涛.1998.点力源在横向各向同性介质中激发的弹性波[J].地球物理学报,41(4):525-536.
靳平.1999.中国地下核爆炸近区地震观测与总结[R].西安:西北核技术研究所:25-58.
潘常周,靳平,王红春.2007.P/S震相幅值比判据对低震级事件的适用性检验[J].地震学报,29(5):521-528.
Barker T G,Day S.1990.An analysis of the effects of spall on regional and teleseismic waveforms using two-dimensionalnumerical modeling of underground explosions[C]∥System Science and Software(Report No:SSS-TR-90-11536).Washington:88-100.
Blandford R R.1977.Discrimination between earthquakes and underground explosions[J].Ann Rev Earth Planet Soc,5:111-122.
Bowers D,Selby N D.2009.Forensic seismology and the Comprehensive Nuclear-Test-Ban Treaty[J].Ann Rev EarthPlanet Soc,37:209-236.
Chen X F.1993.A systematic and efficient method of computing normal modes for multilayered half-space[J].GeophysJ Int,115:391-409.
Chen X F.1999.Seismogram synthesis in multi-layered half-space part I.Theor etical formulations[J].Earthquake Re-search in China,13(2):149-174.
Dahlman O.1977.Monitoring Underground Nuclear Explosions[M].Amsterdam:Elsevier Scientific Publishing Com-pany:134-149.
Douglas A,Rivers D W.1988.An explosion that looks like an earthquake[J].Bull Seism Soc Amer,78(2):1011-1019.
Gibson R L.1994.Radiation from seismic sources in cylindrical cavities[C]∥16th Seismic Research Symposium.Thorn-wood,New York.
Gupta I N,Chan W W,Wagner R A.2005.Regional source discrimination of small events based on the use of Lg wave-train[J].Bull Seism Soc Amer,95(1):341-346.
Gupta I N,Chan W W,Wanger R A.1992.A comparison of regional phases from underground nuclear explosions at East Kazakh and Nevada Test Sites[J].Bull Seism Soc Amer,82(1):352-382.
Masse P R.1981.Review of seismic source models for underground nuclear explosions[J].Bull Seism Soc Amer,71(4):1249-1268.
Mclaughlin K L,Barker T G,Day S M.1988.Effects of depth of burial on explosion and earthquake regional seismo-grams:Regional discrimination and yield estimation(Report No:SSS-R-88-9844)[R]∥S-CUBED Report.Califor-nia:Jolla.
Patton H J.1988.Source models of the Harzer explosion from regional observations of fundamental-mode and highermode surface waves[J].Bull Seism Soc Amer,78(3):1133-1157.
Patton H J,Taylor R S.1995.Analysis of Lg spectral ratios from NTS explosions:Implications for the source mecha-nisms of spall and the generation of Lg waves[J].Bull Seism Soc Amer,85(1):220-236.
Press F,Dewart G,Gilman R.1962.Release of tectonic strain by underground explosions[J].J Geophys Res,67(1):337-343.
Taylor S R.1989.Regional discrimination between NTS-explosions and earthquakes[J].Bull Seism Soc Amer,79(4):1142-1176.
Taylor S R.1996.Analysis of high-frequency Pg/Lg ratiofrom NTS explosions and western U S earthquakes[J].BullSeism Soc Amer,86(4):1042-1053.
Walter W R,Myeda K M,Patton H J.1995.Phase and spectral ratio discrimination between NTS earthquakes and ex-plosions.Part1:Empirical observations[J].Bull Seism Soc Amer,85(4):1050-1067.
Xie X B,Lay T.1994.The excitation of Lg wavs by explosions:A fine difference investigation[J].Bull Seism SocAmer,84(2):324-342.
Yao Z X,Harkrider D G.1983.A generalized reflection-transmission coeffici ent matrix and discrete wavenumber methodfor synthetic seismograms[J].Bull Seism Soc Amer,73(6):1685-1699.
何永锋,陈晓非,张海明.2005a.层裂对区域震相Lg波的影响[J].地震学报,27(3):309-316.
何永锋,陈晓非,张海明.2005b.地下核爆炸Rg波低谷点的激发机理[J].地球物理学报,48(3):643-650.
靳平,徐国明,楼沩涛.1997.受低频动态正压力加载的椭球腔的地震矩表示及其在无限介质中辐射的地震波[J].地震学报,19(5):2-11.
靳平,徐国明,楼沩涛.1998.点力源在横向各向同性介质中激发的弹性波[J].地球物理学报,41(4):525-536.
靳平.1999.中国地下核爆炸近区地震观测与总结[R].西安:西北核技术研究所:25-58.
潘常周,靳平,王红春.2007.P/S震相幅值比判据对低震级事件的适用性检验[J].地震学报,29(5):521-528.
Barker T G,Day S.1990.An analysis of the effects of spall on regional and teleseismic waveforms using two-dimensionalnumerical modeling of underground explosions[C]∥System Science and Software(Report No:SSS-TR-90-11536).Washington:88-100.
Blandford R R.1977.Discrimination between earthquakes and underground explosions[J].Ann Rev Earth Planet Soc,5:111-122.
Bowers D,Selby N D.2009.Forensic seismology and the Comprehensive Nuclear-Test-Ban Treaty[J].Ann Rev EarthPlanet Soc,37:209-236.
Chen X F.1993.A systematic and efficient method of computing normal modes for multilayered half-space[J].GeophysJ Int,115:391-409.
Chen X F.1999.Seismogram synthesis in multi-layered half-space part I.Theor etical formulations[J].Earthquake Re-search in China,13(2):149-174.
Dahlman O.1977.Monitoring Underground Nuclear Explosions[M].Amsterdam:Elsevier Scientific Publishing Com-pany:134-149.
Douglas A,Rivers D W.1988.An explosion that looks like an earthquake[J].Bull Seism Soc Amer,78(2):1011-1019.
Gibson R L.1994.Radiation from seismic sources in cylindrical cavities[C]∥16th Seismic Research Symposium.Thorn-wood,New York.
Gupta I N,Chan W W,Wagner R A.2005.Regional source discrimination of small events based on the use of Lg wave-train[J].Bull Seism Soc Amer,95(1):341-346.
Gupta I N,Chan W W,Wanger R A.1992.A comparison of regional phases from underground nuclear explosions at East Kazakh and Nevada Test Sites[J].Bull Seism Soc Amer,82(1):352-382.
Masse P R.1981.Review of seismic source models for underground nuclear explosions[J].Bull Seism Soc Amer,71(4):1249-1268.
Mclaughlin K L,Barker T G,Day S M.1988.Effects of depth of burial on explosion and earthquake regional seismo-grams:Regional discrimination and yield estimation(Report No:SSS-R-88-9844)[R]∥S-CUBED Report.Califor-nia:Jolla.
Patton H J.1988.Source models of the Harzer explosion from regional observations of fundamental-mode and highermode surface waves[J].Bull Seism Soc Amer,78(3):1133-1157.
Patton H J,Taylor R S.1995.Analysis of Lg spectral ratios from NTS explosions:Implications for the source mecha-nisms of spall and the generation of Lg waves[J].Bull Seism Soc Amer,85(1):220-236.
Press F,Dewart G,Gilman R.1962.Release of tectonic strain by underground explosions[J].J Geophys Res,67(1):337-343.
Taylor S R.1989.Regional discrimination between NTS-explosions and earthquakes[J].Bull Seism Soc Amer,79(4):1142-1176.
Taylor S R.1996.Analysis of high-frequency Pg/Lg ratiofrom NTS explosions and western U S earthquakes[J].BullSeism Soc Amer,86(4):1042-1053.
Walter W R,Myeda K M,Patton H J.1995.Phase and spectral ratio discrimination between NTS earthquakes and ex-plosions.Part1:Empirical observations[J].Bull Seism Soc Amer,85(4):1050-1067.
Xie X B,Lay T.1994.The excitation of Lg wavs by explosions:A fine difference investigation[J].Bull Seism SocAmer,84(2):324-342.
Yao Z X,Harkrider D G.1983.A generalized reflection-transmission coeffici ent matrix and discrete wavenumber methodfor synthetic seismograms[J].Bull Seism Soc Amer,73(6):1685-1699.
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