用改进的相对幅值法反演震源机制及其在核爆炸地震事件识别中的应用
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摘要
与波形反演方法相比,相对幅值法在利用短周期地震波反演震源机制时不需要高分辨率的地球模型,因此更适合于低震级地震事件的震源机制反演.本文以Pearce的传统相对幅值法为基础,引入一种新目标函数以量化特定震源机制解模型的直达P波与地表反射pP和sP波的理论相对幅值与实际观测之间的不吻合程度,由此提高了相对幅值法的容错能力.利用改进的相对幅值法,反演了吉尔吉斯斯坦伊赛克湖地区震级分别为mb4.9和mb3.8的两次天然地震震源断层面解.对于较大的地震,利用5个远震台阵上观测的pP/P和sP/P相对幅值得到的震源断层面解,与哈佛大学的CMT断层面解非常接近;对于哈佛大学没有给出CMT解的较小地震,利用同样方法得到的震源断层面解的走向与震中位置处主要断层的走向一致,而且利用该断层面解可以拟合和解释区域台站上的长周期波形和P波初动方向.最后,为了说明相对幅值法在地下核爆炸地震事件识别中的应用,利用改进的相对幅值法分析了朝鲜2006年10月9日核试验的远震P波波形,发现没有断层面解与远震台站上的P波波形特征相吻合.
In comparison with the inversion methods based on waveform modeling,the relative amplitude method(RAM)is more suitable for finding focal mechanisms of low magnitude earthquakes,as precise modeling of short period seismic signals requires a high resolution earth model,which is unavailable in most practical cases.Based on the method originally presented by Pearce,we introduced a new method to quantify the fitness between predictive and observed relative amplitudes among direct P,surface reflected pP and sP for a given focal mechanism and improved the method's robustness.We have applied the improved RAM to constraining fault plane solutions of the mb 4.9 and mb 3.8 Issyk-Kul lake earthquakes,Kyrgyzstan.For the larger earthquake,its fault plane solution derived mainly from pP/P and sP/P measurements at 5 teleseismic array stations by improved RAM is well consistent with the Harvard CMT solution.As to the smaller event for which CMT solution is unavailable,the strike of result is similar to the strike of a major fault near its epicenter.Both long period synthetics and first-motion polarities predicted by the obtained fault plane solution are basically consistent with the observations recorded at regional stations.Finally,to demonstrate its applicability in identifying underground explosions,we also applied the improved RAM method to the underground nuclear explosion detonated by DPRK on October 9,2006.The result shows that there is no fault plane solutions matching the overall P waveform characteristics at teleseismic stations.
In comparison with the inversion methods based on waveform modeling,the relative amplitude method(RAM)is more suitable for finding focal mechanisms of low magnitude earthquakes,as precise modeling of short period seismic signals requires a high resolution earth model,which is unavailable in most practical cases.Based on the method originally presented by Pearce,we introduced a new method to quantify the fitness between predictive and observed relative amplitudes among direct P,surface reflected pP and sP for a given focal mechanism and improved the method's robustness.We have applied the improved RAM to constraining fault plane solutions of the mb 4.9 and mb 3.8 Issyk-Kul lake earthquakes,Kyrgyzstan.For the larger earthquake,its fault plane solution derived mainly from pP/P and sP/P measurements at 5 teleseismic array stations by improved RAM is well consistent with the Harvard CMT solution.As to the smaller event for which CMT solution is unavailable,the strike of result is similar to the strike of a major fault near its epicenter.Both long period synthetics and first-motion polarities predicted by the obtained fault plane solution are basically consistent with the observations recorded at regional stations.Finally,to demonstrate its applicability in identifying underground explosions,we also applied the improved RAM method to the underground nuclear explosion detonated by DPRK on October 9,2006.The result shows that there is no fault plane solutions matching the overall P waveform characteristics at teleseismic stations.
引文
马淑田,姚振兴,纪晨.1997.1996年3月19日新疆伽师MS6.9地震的震源机制以及相关问题研究[J].地球物理学报,40(6):782-790.
马淑田,姚振兴,纪晨.1998.1996年2月3日云南丽江地震双重破裂的初步估计及相关问题研究[J].地震学报,20(1):18-28.
马淑田,姚振兴,纪晨.1999.用长周期面波波形拟合及P波初动方向估计中等地震的震源机制[J].地球物理学报,42(6):785-799.
任纪舜.1999.从全球看中国大地构造:中国及邻区大地构造图简要说明[M].北京:地质出版社:22-23.
赵翠萍,陈章立,郑斯华,刘杰.2005.2003年9月27日中、俄、蒙边界MS7.9地震震源机制及破裂过程研究[J].地震学报,27(3):237-249.
Aki K,Richards P G.1980.Quantitative Seismology:Theoryand Methods[M].California:San Francisco:W HFree-man:109-155.
Bowers D,Hudson J A.1999.Defining the scalar moment of a seismic source with a general moment tensor[J].BullSeism Soc Amer,89:1390-1394.
Clark R A,Pearce R G.1988.Identification of multiple underground explosions usingthe relative amplitude method[J].Bull Seism Soc Amer,78:885-897.
Douglas A.1997.Bandpass filtering to reduce noise on seismograms:Is there a better way-[J].Bull SeismSoc Amer,87:770-777.
Douglas A,Bowers D,Marshall P D,Young J B,Porter D,Walis NJ.1999.Putting nuclear-test monitoringto the test[J].Nature,398:474-475.
Dreger D S,Hel mberger D V.1991.Source parameter of the Sierra Madre Earthquake from regional and local bodywaves[J].Geophys Res Lett,98:8107-8125.
Dreger D S,Hel mberger D V.1993.Determination of source parameters at regional distances with three-componentsparse network data[J].J Geophys Res,98:8107-8125.
Dziewonski A M,Chou T A,Woodhouse J H.1981.Determination of earthquake source parameters from waveformda-ta for studies of global and regional seismicity[J].J Geophys Res,86:2825-2852.
Ford S R,Dreger D S,Walter WR.2007.Identifyingisotropic events using animproved regional moment tensor inver-sion technique[C]∥Proceedings ofthe29th Monitoring Research Review:Ground-Based Nuclear Explosion Moni-toring Technologies.LA-UR-07-5613,561-570.
Kuge K,Kawakatsu H.1990.Analysis of a deep“non double couple”earthquake using very broadband data[J].Geo-phys Res Lett,17:227-230.
Langston C A,Hel mberger D V.1975.Aprocedure for modeling shallowdislocations[J].Geophys J R astr Soc,42:117-130.
Marshall P D,Stewart R C,Lil wall R C.1989.The seismic disturbances on1986August1near Novaya Zemlya:Asource of concern-[J].Geophys J,98:565-573.
Marson-Pidgeon K,Kennett B L N.2000.Flexible computation of teleseismic synthetics for source and structural studies[J].Geophys J Int,143:689-699.
Stevens J L.1986.Estimation of scalar moments fromexplosion-generated surface waves[J].Bull SeismSoc Amer,76:123-151.
Pearce R G.1977.Fault plane solutions using relative amplitudes of P and pP[J].Geophys J R astr Soc,50:381-394.
Pearce R G.1980.Fault plane solutions using relative amplitudes of P and surface reflections:further studies[J].Geo-phys J R astr Soc,60:459-487.
Pearce R G,Hudson J A,Douglas A.1988.On the use of P-wave seismograms to identify a double-couple source[J].Bull Seism Soc Amer,78:651-671.
Rogers R M,Pearce P G.1992.Use of the relative amplitude method to compute“best fit”earthquake moment tensors[J].J Geophys Res,97:14083-14095.
Sipkin S.1994.Rapid determination of global moment-tensor solutions[J].Geophys Res Lett,21:1667-1670.
马淑田,姚振兴,纪晨.1998.1996年2月3日云南丽江地震双重破裂的初步估计及相关问题研究[J].地震学报,20(1):18-28.
马淑田,姚振兴,纪晨.1999.用长周期面波波形拟合及P波初动方向估计中等地震的震源机制[J].地球物理学报,42(6):785-799.
任纪舜.1999.从全球看中国大地构造:中国及邻区大地构造图简要说明[M].北京:地质出版社:22-23.
赵翠萍,陈章立,郑斯华,刘杰.2005.2003年9月27日中、俄、蒙边界MS7.9地震震源机制及破裂过程研究[J].地震学报,27(3):237-249.
Aki K,Richards P G.1980.Quantitative Seismology:Theoryand Methods[M].California:San Francisco:W HFree-man:109-155.
Bowers D,Hudson J A.1999.Defining the scalar moment of a seismic source with a general moment tensor[J].BullSeism Soc Amer,89:1390-1394.
Clark R A,Pearce R G.1988.Identification of multiple underground explosions usingthe relative amplitude method[J].Bull Seism Soc Amer,78:885-897.
Douglas A.1997.Bandpass filtering to reduce noise on seismograms:Is there a better way-[J].Bull SeismSoc Amer,87:770-777.
Douglas A,Bowers D,Marshall P D,Young J B,Porter D,Walis NJ.1999.Putting nuclear-test monitoringto the test[J].Nature,398:474-475.
Dreger D S,Hel mberger D V.1991.Source parameter of the Sierra Madre Earthquake from regional and local bodywaves[J].Geophys Res Lett,98:8107-8125.
Dreger D S,Hel mberger D V.1993.Determination of source parameters at regional distances with three-componentsparse network data[J].J Geophys Res,98:8107-8125.
Dziewonski A M,Chou T A,Woodhouse J H.1981.Determination of earthquake source parameters from waveformda-ta for studies of global and regional seismicity[J].J Geophys Res,86:2825-2852.
Ford S R,Dreger D S,Walter WR.2007.Identifyingisotropic events using animproved regional moment tensor inver-sion technique[C]∥Proceedings ofthe29th Monitoring Research Review:Ground-Based Nuclear Explosion Moni-toring Technologies.LA-UR-07-5613,561-570.
Kuge K,Kawakatsu H.1990.Analysis of a deep“non double couple”earthquake using very broadband data[J].Geo-phys Res Lett,17:227-230.
Langston C A,Hel mberger D V.1975.Aprocedure for modeling shallowdislocations[J].Geophys J R astr Soc,42:117-130.
Marshall P D,Stewart R C,Lil wall R C.1989.The seismic disturbances on1986August1near Novaya Zemlya:Asource of concern-[J].Geophys J,98:565-573.
Marson-Pidgeon K,Kennett B L N.2000.Flexible computation of teleseismic synthetics for source and structural studies[J].Geophys J Int,143:689-699.
Stevens J L.1986.Estimation of scalar moments fromexplosion-generated surface waves[J].Bull SeismSoc Amer,76:123-151.
Pearce R G.1977.Fault plane solutions using relative amplitudes of P and pP[J].Geophys J R astr Soc,50:381-394.
Pearce R G.1980.Fault plane solutions using relative amplitudes of P and surface reflections:further studies[J].Geo-phys J R astr Soc,60:459-487.
Pearce R G,Hudson J A,Douglas A.1988.On the use of P-wave seismograms to identify a double-couple source[J].Bull Seism Soc Amer,78:651-671.
Rogers R M,Pearce P G.1992.Use of the relative amplitude method to compute“best fit”earthquake moment tensors[J].J Geophys Res,97:14083-14095.
Sipkin S.1994.Rapid determination of global moment-tensor solutions[J].Geophys Res Lett,21:1667-1670.
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