青藏块体东北缘6次中强地震前地震相关长度增长现象
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摘要
为研究大震前地震空间相关长度的变化特征,分析了青藏块体东北缘6次中强地震前的地震活动的时空演变.在计算空间相关长度过程中,采用长轴与孕震区主要断裂走向一致的椭圆形空间窗,并设计了优化程序.比较椭圆形和圆形空间窗的结果,表明对所研究的6次中强地震前都观测到了增长的地震空间相关长度.椭圆形空间窗的结果比圆形的结果更好,相关长度增长幅度较大,曲率参数值较小.利用3种合成地震目录对结果进行了显著性检验.3种随机数据的检验结果都否定了零假设,表明观察到的模型不是由随机数据干扰造成的,这一观点的置信水平被证实为99%以上.最后得出主震震级与临界区的尺度(等效半径)关系为logRe～0.46(±0.02)M,与理论值符合得较好.
For studying the characteristics of seismic correlation length before great earthquakes,the temporal-spatial change of seismicity prior to 6 moderate strong earthquakes(ML>5.5)in the boundaries along the northeast margin of Tibet block have been analyzed.We use ellipse,whose long axis is coincident with the strike of main fault belt in the source area,as the spatial window to analyze growing correlation length prior to main-shock and design the corresponding optimization procedure.Comparison between the results from elliptical and circular spatial windows shows that the growing correlation length prior to 6 moderate strong earthquakes studied have been observed in both two spatial windows.The results from ellipse are better than that from circular,and the growth ranges of correlation length in former are larger than those in later yet the smaller curvature parameter values of C are obtained in elliptical spatial windows.Three types of random synthetic catalog are used to test the significance of the results.The results reject the null hypothesis for three types of random synthetic catalog and show that the observed patterns are not consequences of random fluctuations.That theory is found to be of above 99% confidence levels.The scaling relation we found,log Re～0.46M between the main-shock magnitude M and the equivalent radius Re of the critical region is in good agreement with theoretical values.
For studying the characteristics of seismic correlation length before great earthquakes,the temporal-spatial change of seismicity prior to 6 moderate strong earthquakes(ML>5.5)in the boundaries along the northeast margin of Tibet block have been analyzed.We use ellipse,whose long axis is coincident with the strike of main fault belt in the source area,as the spatial window to analyze growing correlation length prior to main-shock and design the corresponding optimization procedure.Comparison between the results from elliptical and circular spatial windows shows that the growing correlation length prior to 6 moderate strong earthquakes studied have been observed in both two spatial windows.The results from ellipse are better than that from circular,and the growth ranges of correlation length in former are larger than those in later yet the smaller curvature parameter values of C are obtained in elliptical spatial windows.Three types of random synthetic catalog are used to test the significance of the results.The results reject the null hypothesis for three types of random synthetic catalog and show that the observed patterns are not consequences of random fluctuations.That theory is found to be of above 99% confidence levels.The scaling relation we found,log Re～0.46M between the main-shock magnitude M and the equivalent radius Re of the critical region is in good agreement with theoretical values.
引文
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Epstein,B.,Lomnitz,C.,1966.A model for the occurrenceof large earthquakes.Nature,211(5052):954-956.
Frohlich,C.,Davis,S.D.,1990.Single-link cluster analysisas a method to evaluate spatial and temporal propertiesof earthquake catalogues.Geophys.J.Int.,100(1):19-32.
Gaudemer,Y.,Tapponnier,P.,Meyer,B.,et al.,1995.Par-titioning crustal slip between linked,active faults in theeastern Qilian Shan,and evidence for a major seismicgap,the“Tianzhu gap”,on the western Haiyuan fault,Gansu(China).Geophys.J.Int.,120(3):599-645.
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Kanamori,H.,Anderson,D.L.,1975.Theoretical basis ofsome empirical relations in seismology.Bull.Seismol.Soc.Am.,65,1073-1095.
Lasserre,C.,Bukchin,B.,Bernard,P.,et al.,2001.Sourceparameters and tectonic origin of the1996June1Tianzhu(Mw=5.2)and1995July21Yongden(Mw=5.6)earthquakes near the Haiyuan fault(Gansu,Chi-na).Geophys.J.Int.,144(1):206-220.
Liu,B.C.,Cao,J.J.,Yuan,D.Y.,et al.,2008.Quantitative data of active faults within the active tectonic block inNorth Qinghai-Xizang plateau.Seismology and Geolo-gy,30(1):161-175(in Chinese with English ab-stract).
Ogata,Y.,1989.Statistical model for standard seismicity anddetection of anomalies by residual analysis.Tectono-physics,169(1-3):159-174.
Sykes,L.R.,Jaume,S.C.,1990.Seismic activity on neigh-bouring faults as a long-term precursor to large earth-quakes in the San Francisco Bay area.Nature,348(6302):595-599.
Z ller,G.,Hainzl,S.,Kurths,J.,2001.Observation ofgrowing correlation length as an indicator for criticalpoint behavior prior to large earthquakes.J.Geophys.Res.,106(B2):2167-2175.
崔效锋,谢富仁,赵建涛,2005.中国及邻区震源机制解的分区特征.地震地质,27(2):298-307.
郭增建,秦保燕,徐文耀,等,1973.震源孕育模式的初步讨论.地球物理学报,16:43-48.
刘百篪,曹娟娟,袁道阳,等,2008.青藏高原北部活动地块内部的活断层定量资料.地震地质,30(1):161-175.
Bruce,A.,Wallace,D.,1992.Critical point phenomena:Uni-versal physics at large length scales.In:Davis,P.,ed.,The new physics.Cambridge Univ.Press,NewYork,236-267.
Cui,X.F.,Xie,F.R.,Zhao,J.T.,2005.The regional charac-teristics of focal mechanism solutions in China and itsadjacent areas.Seismology and Geology,27(2):298-307(in Chinese with English abstract).
Epstein,B.,Lomnitz,C.,1966.A model for the occurrenceof large earthquakes.Nature,211(5052):954-956.
Frohlich,C.,Davis,S.D.,1990.Single-link cluster analysisas a method to evaluate spatial and temporal propertiesof earthquake catalogues.Geophys.J.Int.,100(1):19-32.
Gaudemer,Y.,Tapponnier,P.,Meyer,B.,et al.,1995.Par-titioning crustal slip between linked,active faults in theeastern Qilian Shan,and evidence for a major seismicgap,the“Tianzhu gap”,on the western Haiyuan fault,Gansu(China).Geophys.J.Int.,120(3):599-645.
Guo,Z.J.,Qin,B.Y.,Xu,W.Y.,et al.,1973.Preli minarystudy on a model for the development of the focus of anearthquake.Acta Geophysica Sinica,16:43-48(inChinese with English abstract).
Gutenberg,B.,Richter,C.F.,1956.Earthquake magnitude,intensity,energy,and acceleration(Second paper).Bull.Seismol.Soc.Am.,46,105-145.
Hardebeck,J.L.,Felzer,K.R.,Michael,A.J.,2008.I m-proved tests reveal that the accelerating moment releasehypothesis is statistically insignificant.J.Geophys.Res.,113,B08310,doi:10.1029/2007JB005410.
Kanamori,H.,Anderson,D.L.,1975.Theoretical basis ofsome empirical relations in seismology.Bull.Seismol.Soc.Am.,65,1073-1095.
Lasserre,C.,Bukchin,B.,Bernard,P.,et al.,2001.Sourceparameters and tectonic origin of the1996June1Tianzhu(Mw=5.2)and1995July21Yongden(Mw=5.6)earthquakes near the Haiyuan fault(Gansu,Chi-na).Geophys.J.Int.,144(1):206-220.
Liu,B.C.,Cao,J.J.,Yuan,D.Y.,et al.,2008.Quantitative data of active faults within the active tectonic block inNorth Qinghai-Xizang plateau.Seismology and Geolo-gy,30(1):161-175(in Chinese with English ab-stract).
Ogata,Y.,1989.Statistical model for standard seismicity anddetection of anomalies by residual analysis.Tectono-physics,169(1-3):159-174.
Sykes,L.R.,Jaume,S.C.,1990.Seismic activity on neigh-bouring faults as a long-term precursor to large earth-quakes in the San Francisco Bay area.Nature,348(6302):595-599.
Z ller,G.,Hainzl,S.,Kurths,J.,2001.Observation ofgrowing correlation length as an indicator for criticalpoint behavior prior to large earthquakes.J.Geophys.Res.,106(B2):2167-2175.
崔效锋,谢富仁,赵建涛,2005.中国及邻区震源机制解的分区特征.地震地质,27(2):298-307.
郭增建,秦保燕,徐文耀,等,1973.震源孕育模式的初步讨论.地球物理学报,16:43-48.
刘百篪,曹娟娟,袁道阳,等,2008.青藏高原北部活动地块内部的活断层定量资料.地震地质,30(1):161-175.
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