唐山余震区中小地震震源机制解分区特征的初步研究
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摘要
利用2002~2006年数字化地震资料,分析了该时段发生的中小地震空间分布特征,并采用网格密集值计算方法将唐山余震区细分为5个区域。在每一分区内利用格点尝试法求解小震综合节面解。结果表明:各分区小震震源机制节面解有所不同,P轴方位角存在一定的转向变化。宁河6.9级地震所在的一区以及唐山7.8级主震所在的二区的P轴方位角呈北东东-南西西方向,三区、四区P轴方位角沿中小地震的分布呈东西向,此后五区再次转为北东向。各分区小震综合解的P波初动方向矛盾比也呈现出较大的差异。唐山7.8级主震所在的二区矛盾比最高,达0.41,而没有发生强余震的夏官营一带所在的五区矛盾比较低,仅为0.23。分区研究小震综合节面解,显示出应力场的细微差异,具体勾划了唐山余震区应力场的复杂性。
With the digital seismic data from 2002 to 2006, we analyzed the spatial distribution of small and moderate earthquakes. We divided the Tangshan aftershock region into five seismic density zones by calculating seismic density at each grid node. Grid points test method is used to compute composite nodal-plane solution of small and moderate earthquakes in each density zone. The result shows that focal mechanism solution of small and moderate earthquakes as well as azimuth angle of P axis have some differences in each zone. Azimuth angle of P axis is NEE direction in both the first zone where Ninghe earthquake (MS=6.9) occurred and the second where the Tangshan earthquake (MS=7.8) took place, then it turns to East-West direction along the distribution of small and moderate earthquakes. Finally azimuth angle of P axis turns to NE direction. The ratios of contradiction signs vary with different zones. It is the highest 0.41 in the second zone where the Tangshan MS7.8 earthquake occurred, whereas it is lower 0.23 in the zone where no strong aftershock happened. The research of composite nodal-plane solution of small and moderate earthquakes shows slight difference in stress field and tectonic stress field's complexity in Tangshan aftershock region.
With the digital seismic data from 2002 to 2006, we analyzed the spatial distribution of small and moderate earthquakes. We divided the Tangshan aftershock region into five seismic density zones by calculating seismic density at each grid node. Grid points test method is used to compute composite nodal-plane solution of small and moderate earthquakes in each density zone. The result shows that focal mechanism solution of small and moderate earthquakes as well as azimuth angle of P axis have some differences in each zone. Azimuth angle of P axis is NEE direction in both the first zone where Ninghe earthquake (MS=6.9) occurred and the second where the Tangshan earthquake (MS=7.8) took place, then it turns to East-West direction along the distribution of small and moderate earthquakes. Finally azimuth angle of P axis turns to NE direction. The ratios of contradiction signs vary with different zones. It is the highest 0.41 in the second zone where the Tangshan MS7.8 earthquake occurred, whereas it is lower 0.23 in the zone where no strong aftershock happened. The research of composite nodal-plane solution of small and moderate earthquakes shows slight difference in stress field and tectonic stress field's complexity in Tangshan aftershock region.
引文
高阿甲、许忠淮、黄雨蕊,1998,华北地区地震震源机制的分区跟踪监测,地震地磁观测与研究,19(1A),56~61。
高阿甲,1999,1998年华北地区地震震源机制,地震地磁观测与研究,20(1A),75~81。
高原、郑斯华、孙勇,1995,唐山地区地壳裂隙各向异性,地震学报,17(3),283~293。
李钦祖,1980,华北地壳应力场的基本特征,地球物理学报,23(4),376~388。
李钦祖、于利民、刁桂苓等,1997,中国地震科学的特色,见:陈运泰主编,中国地震学研究进展———庆贺谢毓寿教授八十寿辰,76~86,北京:地震出版社。
许忠淮、阎明、赵仲和,1983,由多个小地震推断的华北地区构造应力场的方向,地震学报,5(3),268~279。
鄢家全、时振梁、汪素云等,1979,中国及邻区现代构造应力场的区域特征,地震学报,1(1),9~24。
阎明,1991,区域小震平均节面解的时空分析,地震学报,13(1),9~20。
王健,2001,地震活动性图象处理的网格点密集值计算方法,地震学报,23(3),262~267。
Aki.K,1966,Earthquake generating stress in Japan for the years1961to1963obtained by smoothing the first motion patterns,Bull.Earthq.Res.Inst.,44,447~471.
Bulter,R.,G.S.Stewart,and H.Kanamori,1979,The July27,1976Tangshan,China earthquake———Acomplex sequence of intraplateevents,Bull.Seismol.Soc.Am.,69,207~220.
高阿甲,1999,1998年华北地区地震震源机制,地震地磁观测与研究,20(1A),75~81。
高原、郑斯华、孙勇,1995,唐山地区地壳裂隙各向异性,地震学报,17(3),283~293。
李钦祖,1980,华北地壳应力场的基本特征,地球物理学报,23(4),376~388。
李钦祖、于利民、刁桂苓等,1997,中国地震科学的特色,见:陈运泰主编,中国地震学研究进展———庆贺谢毓寿教授八十寿辰,76~86,北京:地震出版社。
许忠淮、阎明、赵仲和,1983,由多个小地震推断的华北地区构造应力场的方向,地震学报,5(3),268~279。
鄢家全、时振梁、汪素云等,1979,中国及邻区现代构造应力场的区域特征,地震学报,1(1),9~24。
阎明,1991,区域小震平均节面解的时空分析,地震学报,13(1),9~20。
王健,2001,地震活动性图象处理的网格点密集值计算方法,地震学报,23(3),262~267。
Aki.K,1966,Earthquake generating stress in Japan for the years1961to1963obtained by smoothing the first motion patterns,Bull.Earthq.Res.Inst.,44,447~471.
Bulter,R.,G.S.Stewart,and H.Kanamori,1979,The July27,1976Tangshan,China earthquake———Acomplex sequence of intraplateevents,Bull.Seismol.Soc.Am.,69,207~220.
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