大震前显示的地震震源机制趋于一致的变化
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摘要
在构造应力场的制约下强震孕育过程中特定阶段,震源区中小地震震源机制与构造应力场的方向大体一致,根据这一特点,定义各个震源机制解的P轴,B轴,T轴和构造应力场的3个应力主轴在3维空间的夹角之和为一致性参数a,研究强震前应力场变化特征。对2006年11月15日千岛岛弧MW8.3地震和2001年6月23日秘鲁MW8.4地震研究表明,大震发生前孕震区一致性参数a比较低,震源机制与构造应力场的差异较小,说明这些前震受到了震源区应力场的统一作用,而主震发生之后震源机制解的一致性参数比较高,说明后续发生的地震的震源机制散乱,表明背景应力场的控制作用开始减弱。
At some stage of earthquake preparation,the focal mechanisms of small and medium-sized earthquake have roughly the same direction with the tectonic stress field.According to this feature,we define the angle between P,B,and T axises of focal mechanisms and three stress axises of tectonic stress field as the consistency parameter a,to research the dynamic changes of stress field in earthquake preparation area before strong earthquakes.In this paper,we mainly studied the changes of the consistency parameter a of the Kuril island arc MW8.3 earthquake and Peru MW8.4 earthquake.Our study found that before strong earthquake occurred,the focal mechanisms of a series of small and medium-sized earthquakes get small differences with the tectonic stress field,this indicates that those foreshocks are under the control of stress field,the focal mechanisms of shocks occurred at this time have the same direction with tectonic stress field;while the higher consistency means that the focal mechanisms of aftershocks are scattered,and have big difference with tectonic field,which means the control of background stress field start weakening.
At some stage of earthquake preparation,the focal mechanisms of small and medium-sized earthquake have roughly the same direction with the tectonic stress field.According to this feature,we define the angle between P,B,and T axises of focal mechanisms and three stress axises of tectonic stress field as the consistency parameter a,to research the dynamic changes of stress field in earthquake preparation area before strong earthquakes.In this paper,we mainly studied the changes of the consistency parameter a of the Kuril island arc MW8.3 earthquake and Peru MW8.4 earthquake.Our study found that before strong earthquake occurred,the focal mechanisms of a series of small and medium-sized earthquakes get small differences with the tectonic stress field,this indicates that those foreshocks are under the control of stress field,the focal mechanisms of shocks occurred at this time have the same direction with tectonic stress field;while the higher consistency means that the focal mechanisms of aftershocks are scattered,and have big difference with tectonic field,which means the control of background stress field start weakening.
引文
[1]陈连旺,陆远忠,等.华北地区三维构造应力场[J].地震学报,1999,21(2):140-149.
[2]Ellsworth W L,Xu Z H.Determination of the stress tensor fromfocal mechanism data[J].EOSTrans AGU,1980,61:11-17.
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[4]许忠淮,戈澍谟.用滑动方向拟合法反演富蕴地震断裂带应力场[J].地震学报,1984,6(4):395-404.
[5]许忠淮.用滑动方向拟合法反演唐山余震区的平均应力场[J].地震学报,1985,7(4):349-362.
[6]李钦祖,靳雅敏,于新昌.华北地区的震源机制与地壳应力场[J].地震学报,1982,4(1):55-61.
[7]陈顒.用震源机制一致性作为描述地震活动性的新参数[J].地球物理学报,1980,2(3):39-47.
[8]Fujita K,Kanamori H.Double seismic zones and stresses of intermediate depth earthquakes[J].Ge-ophysical Journal of the Royal Astronomical Societ,1981,66(1):131-156.
[9]吴忠良,臧绍先.千岛一鄂霍次克海地区的地震分布、震源机制及应力状态[J].地震地质,1989,11(2):85-95.
[10]Sykes L R.Seismicitty and deep structure of island arces[J].Geophyics Res,1966,71:2981-3006.
[11]Kao H,Rau R J.Detailed structures of the subduction Philippine Sea plate beneath northeast Tai-wan:A newtype of double seismic zone[J].Geophys Res,1999,104(B1):1015-1033.
[12]Veith K F.The nature of the dual zone of seismicity in the Kurils arc[J].Eos Trans AGU,1977,58:12-32.
[13]王俊国,刁桂苓.千岛岛弧地震前哈佛大学矩心矩张量(CMT)解一致性的预测意义[J].地震学报,2005,27(2):178-183.
[14]刁桂苓,赵英萍.大同晚期强余震前震源机制解的一致性特征[J].内陆地震,2004,18(3):202-206.
[15]赵英萍,刁桂苓.张北强余震前震源机制解的一致性特征[J].华北地震科学,2004,22(1):1-4.
[16]周荣茂,陈运泰.由矩张量反演得到的海南东方震群的震源机制[J].地震学报,1999,21(4):337-343.
[2]Ellsworth W L,Xu Z H.Determination of the stress tensor fromfocal mechanism data[J].EOSTrans AGU,1980,61:11-17.
[3]Gephart J W,Forsyth D W.An i mproved method for determining the regional stress tensor usingearthquake focal mechanismdata:Applicafion to the San Fernand earthquake sequence[J].GeophysRes,1984,89:9305-9320.
[4]许忠淮,戈澍谟.用滑动方向拟合法反演富蕴地震断裂带应力场[J].地震学报,1984,6(4):395-404.
[5]许忠淮.用滑动方向拟合法反演唐山余震区的平均应力场[J].地震学报,1985,7(4):349-362.
[6]李钦祖,靳雅敏,于新昌.华北地区的震源机制与地壳应力场[J].地震学报,1982,4(1):55-61.
[7]陈顒.用震源机制一致性作为描述地震活动性的新参数[J].地球物理学报,1980,2(3):39-47.
[8]Fujita K,Kanamori H.Double seismic zones and stresses of intermediate depth earthquakes[J].Ge-ophysical Journal of the Royal Astronomical Societ,1981,66(1):131-156.
[9]吴忠良,臧绍先.千岛一鄂霍次克海地区的地震分布、震源机制及应力状态[J].地震地质,1989,11(2):85-95.
[10]Sykes L R.Seismicitty and deep structure of island arces[J].Geophyics Res,1966,71:2981-3006.
[11]Kao H,Rau R J.Detailed structures of the subduction Philippine Sea plate beneath northeast Tai-wan:A newtype of double seismic zone[J].Geophys Res,1999,104(B1):1015-1033.
[12]Veith K F.The nature of the dual zone of seismicity in the Kurils arc[J].Eos Trans AGU,1977,58:12-32.
[13]王俊国,刁桂苓.千岛岛弧地震前哈佛大学矩心矩张量(CMT)解一致性的预测意义[J].地震学报,2005,27(2):178-183.
[14]刁桂苓,赵英萍.大同晚期强余震前震源机制解的一致性特征[J].内陆地震,2004,18(3):202-206.
[15]赵英萍,刁桂苓.张北强余震前震源机制解的一致性特征[J].华北地震科学,2004,22(1):1-4.
[16]周荣茂,陈运泰.由矩张量反演得到的海南东方震群的震源机制[J].地震学报,1999,21(4):337-343.
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