华北地区地震重新定位结果分析
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摘要
用双差地震定位法对华北地区(111°~120°E,35°~42°N)1993—2004年6771次地震(1.0≤M≤6.6)重新定位。重新定位后的结果显示:地震活动呈北东与北西向线性分布,与活动断裂关系密切;在新河断裂下方,存在两条走向北东、向西南倾斜的、不同深度的地震活动带,浅部的从地表向下延伸约20km,长60km,深部的从25km到34km,长约40km;83%的地震震源深度位于0~15km范围内,比由常规地震定位法给出的华北地区(7~21km)的震源深度要浅得多,说明华北地区的地震基本都集中在中上地壳中;约有92%的地震震源深度位于1~24km,表明24km是华北地震构造区震源深度的下界。
We relocuted epicenters of totally 6 771 earthquakes which occurred in North China region (35°~42°N, 111°~120°E) from 1993 to 2004. The relocation shows those formerly randomly-distributed earthquakes are clustered and are aligned tending to the North-East and North-West directions. It follows that there is a close relationship between the seismicity and known major active faults. From the cross sectional profile beneath the Xinhe fault, the relocated seismic sources reveal two seismic belts of different depths. One of them is around 60km long and in the direction of north-east, its depth varies from the surface downwards to 20 km underground. The other is about 40 km in length and is from 25km to 30 km in depth.At the same time, we found that the 83 percent relocated hypocenters vary from 0 km to 15 km in depth. This is certainly more shallow than that from the previous studies which are based on the roubine earthquake location, whose average focal depth is within a range of 7~21km. This result indicates that the contemporary seismicity in North China region is mainly concentrated in the upper and middle crusts. Furthermore, about 92 percent focal depth is ranged from 1 km to 24 km, which is in good agreement with the consensus that the lower bound of the focal depth in North China region is 24 km.
We relocuted epicenters of totally 6 771 earthquakes which occurred in North China region (35°~42°N, 111°~120°E) from 1993 to 2004. The relocation shows those formerly randomly-distributed earthquakes are clustered and are aligned tending to the North-East and North-West directions. It follows that there is a close relationship between the seismicity and known major active faults. From the cross sectional profile beneath the Xinhe fault, the relocated seismic sources reveal two seismic belts of different depths. One of them is around 60km long and in the direction of north-east, its depth varies from the surface downwards to 20 km underground. The other is about 40 km in length and is from 25km to 30 km in depth.At the same time, we found that the 83 percent relocated hypocenters vary from 0 km to 15 km in depth. This is certainly more shallow than that from the previous studies which are based on the roubine earthquake location, whose average focal depth is within a range of 7~21km. This result indicates that the contemporary seismicity in North China region is mainly concentrated in the upper and middle crusts. Furthermore, about 92 percent focal depth is ranged from 1 km to 24 km, which is in good agreement with the consensus that the lower bound of the focal depth in North China region is 24 km.
引文
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12 邵学钟,等.邢台地震区深部构造背景的地震转换波探测和研究[J].地球物理学报,1993,36(5),609-620.(Shao Xuezhong,et al.Study of deep tectonics in Xingtai earthquake area by method of converted waves of earth-quakes[J].Chinese J.Geophys,1993,36(5),609-620)
13 张家茹,等.邢台强震的深部三维构造背景和孕震条件[J].地震地质,1994,16(4):319-328.(Zhang Jiaru,et al.Background of3-D deep structure and dynamic condi-tions for occurrence of strong Xingtai earthquake[J].Seis-mology and Geology,1994,16(4),319-328)
14 尹京苑,梅世蓉,薛艳.邢台地震区地壳速度结构特征与强震孕育发生的关系[J].地球物理学报,1999,42(5),629-639.(Yin Jingyuan,Mei Shirong and Xue Yan.Relationship between the deep crustal features in ve-locity structure and the preparation of strong earthquakes in Xingtai area[J].Chinese J.Geophys,1999,42(5),629-639)
2 Waldhauser F and Ellsworth W.A double-difference earth-quake location algorithm:method and application to the northern Hayward fault,California[J].Bull.Seism.Soc.Am.,2000,90(6):1353-1368.
3 Waldhauser F and Ellsworth W.Fault structure and mechan-ics of the California,from double-difference earthquake loca-tions[J].J.Geophys.Res.,2002,107(B3):ESE3-1~3-14.
4 于湘伟,陈运泰,王培德.京津唐地区中上地壳三维P波速度结构[J].地震学报,2003,25(1):1-14.(Yu Xiang-wei,Chen Yuntai and Wang Peide.Three-dimensional P wave velocity structure in Beijing-Tianjin-Tangshan area[J].Acta Seismologica Sinica,2003,25(1):1-14)
5 滕吉文,等.北京、天津、唐山和张家口地区的地壳结构[J].地球物理学报,1979,22(3):218-236.(Teng Jiwen,et al.Crustal structure in the Beijing-Tianjin-Tangshan-Zhangjiakou region[J].Chinese J.Geophys,1979,22(3):218-236)
6 Kennett B L N,Engdahl E R and Buland R.Constraints on seismic velocities in the Earth from t ravel times[J].Geo-phys J Int,1995.122:108-124.
7 张国民,等.中国大陆地震震源深度及其构造含义[J].科学通报,2002,47(9):663-668.(Zhang Guomin,et al.Focal depth of the earthquakes in mainland China:implica-tion for tectonics[J].Chinese Science Bulletin,2002,47(9):663-668)
8 胡新亮,等.华北、西南一些地区地震发生在地壳浅部的证据[J].地震学报,2001,23(4):427-435.(Hu Xinlia-ng,et al.Some evidences for earthquake occurrence in the shallow crust in some area of North China and Southwest China[J].Acta Seismologica Sinica,2001,23(4):427-435)
9 张爱民,李强.双差定位法在三峡库区地震定位中的应用[J].大地测量与地球动力学,2006,(3):73-77.(Zhang Aimin and Li Qiang.Application of double-difference location method to earthquakes in Three Gorges reservoir aera[J].Journal of Geodesy and Geodynamics,2006,(3):73-77)
10 许桂林,范国胜.华北盆地北部断裂活动特征及其与地震的关系[J].华北地震科学,1986,4(1):37-47.(Xu Guilin and Fan Guosheng.Characteristics of fracturing in the northern part of the North China basin and its relation of earthquakes[J].North China Earthquake Sciences,1986,4(1):37-47)
11 徐杰,方仲景,杨理华.1966年邢台7.2级地震的构造背景和发震构造[J].地震地质,1988,10(4):51-59.(Xu Jie,Fang Zhongjing and Yang Lihua.Tectonic back-ground and causative fault of1966XingtaiMs7.2earth-quake[J].Seismology and Geology,1988,10(4):51-59)
12 邵学钟,等.邢台地震区深部构造背景的地震转换波探测和研究[J].地球物理学报,1993,36(5),609-620.(Shao Xuezhong,et al.Study of deep tectonics in Xingtai earthquake area by method of converted waves of earth-quakes[J].Chinese J.Geophys,1993,36(5),609-620)
13 张家茹,等.邢台强震的深部三维构造背景和孕震条件[J].地震地质,1994,16(4):319-328.(Zhang Jiaru,et al.Background of3-D deep structure and dynamic condi-tions for occurrence of strong Xingtai earthquake[J].Seis-mology and Geology,1994,16(4),319-328)
14 尹京苑,梅世蓉,薛艳.邢台地震区地壳速度结构特征与强震孕育发生的关系[J].地球物理学报,1999,42(5),629-639.(Yin Jingyuan,Mei Shirong and Xue Yan.Relationship between the deep crustal features in ve-locity structure and the preparation of strong earthquakes in Xingtai area[J].Chinese J.Geophys,1999,42(5),629-639)
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