汶川余震序列北川以北段的震源分布特性与破裂复杂性研究
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摘要
在采用HYPODD方法对汶川地震序列精确定位的基础上,利用CAP方法反演了龙门山断裂带北川以北段5级以上余震的震源机制解,讨论了该段的震源分布特征和强余震的破裂复杂性。结果显示,汶川余震序列的震源深度沿龙门山断裂带走向从汶川映秀至平武南坝有逐渐变浅的趋势,且震中沿映秀-北川-南坝地震地表破裂带分布;在该断裂带的北川以北段,余震序列具有更次级的分段活动特点,5.5级以上强余震发生在余震带走向的端部或者拐折、错位的部位;7次5.5级以上强余震中有4次以逆冲破裂为主,3次以走滑破裂为主,可能是北川-青川断裂、平武-青川等4条断裂参与了余震活动过程。
On the basis of precise locations of the Wenchuan earthquake sequence by using the HYPODD method,the focal mechanisms of the aftershocks(M≥5.0) occurred on the Longmenshan fault zone north to Beichuan were inversed by using the CAP method and the characteristics of hypocenter distribution and rupture complexity of strong aftershocks are discussed.The results are that the focal depth of Wenchuan aftershock sequence decreased gradually from Yingxiu of Wenchuan to Nanba of Pingwu along Longmen Shan fault zone,which beyond the segment boundary located in Beichuan,and the epicenters were distributed along the Yingxiu-Beichuan-Nanba coseismic surface rupture zone in the Central Fault.The aftershock sequence was characterized as less secondary segmented activity in Central Fault Zone north to Beichuan.The aftershocks(M≥5.5) were occurred on the end,transition or dislocation of the aftershocks zone.According to the focal mechanism,four of the seven stronger aftershocks are thrust and the others are strike-slip,it may suggest that the process of the aftershock activity was related to the Beichuan-Qingchuan Fault,Pingwu-Qingchuan Fault etc.
On the basis of precise locations of the Wenchuan earthquake sequence by using the HYPODD method,the focal mechanisms of the aftershocks(M≥5.0) occurred on the Longmenshan fault zone north to Beichuan were inversed by using the CAP method and the characteristics of hypocenter distribution and rupture complexity of strong aftershocks are discussed.The results are that the focal depth of Wenchuan aftershock sequence decreased gradually from Yingxiu of Wenchuan to Nanba of Pingwu along Longmen Shan fault zone,which beyond the segment boundary located in Beichuan,and the epicenters were distributed along the Yingxiu-Beichuan-Nanba coseismic surface rupture zone in the Central Fault.The aftershock sequence was characterized as less secondary segmented activity in Central Fault Zone north to Beichuan.The aftershocks(M≥5.5) were occurred on the end,transition or dislocation of the aftershocks zone.According to the focal mechanism,four of the seven stronger aftershocks are thrust and the others are strike-slip,it may suggest that the process of the aftershock activity was related to the Beichuan-Qingchuan Fault,Pingwu-Qingchuan Fault etc.
引文
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2李传友,宋方敏,冉勇康.龙门山断裂带晚第四纪活动性讨论[J].地震地质,2004,26(2):248-258.(Li Chuany-ou,Song Fangmin and Ran Yongkang.Late quaternary activi-ty and age constraint of the northern Longmenshan fault zone[J].Seismology and Geology,2004,26(2):248-258)
3陈运泰,等.2008年5月12日汶川特大地震震源特性分析报告[J/OL].http://www.csi.ac.cn/Si-chuan/chenyun-tai.pdf,2008.(Chen Yuntai,et al.Report on the great Wen-chuan earthquake source of May 12,2008[J/OL].http://www.csi.ac.cn/Sichuan/chenyuntai.pdf,2008)
4 Ji C and Hayes G.Preliminary result of the May 12,2008Mw7.9 eastern Sichuan,China.Earthquake[J/OL].ht-tp://earthquake.usgs.gov/eqcenter/eqinrhenews/2008/us2008ryan/finite_fault.php,2008)
5王卫民,等.四川汶川8.0级地震震源过程[J].地球物理学报,2008,51(5):1403-1410.(Wang Weimin,et al.Rupture process of the MS8.0 Wenchuan earthquake in Si-chuan,China[J].Chinese Journal of Geophysics,2008,51(5):1403-1410)
6 Li Zhixiong,et al.Uneven aftershock distribution of Wen-chuan Ms8.0 earthquake and possible mechanism[J].Ge-odesy and Geodynamics,2011,2(3):7-12.
7黄媛,等.汶川8.0级大地震及其余震序列重定位研究[J].中国科学(D辑),2008,38(10):1242-1249.(Huang Yuan,et al.Relocation of the M8.0 Wenchuanearthquake and its aftershock sequences[J].Science in Chi-na(Ser D),2008,51(12):1 703-1 711)
8吕鹏,丁志峰,朱露培.结合波形互相关的双差定位方法在2008年汶川地震余震序列中的应用[J].地震学报,2010,33(4):407-419.(LüPeng,Ding Zhifeng and ZhuLupei.Application of double-difference relocation techniqueto aftershocks of 2008 Wenchuan earthquake using waveformcross-correlation[J].Acta Seismologica Sinica,2010,33(4):407-419)
9王勤彩,陈章立,郑斯华.汶川大地震余震序列震源机制的空间分段特征[J].科学通报,2009,54:2348-2354.(Wang Qincai,Chen Zhangli and Zheng Sihua.Spatial seg-mentation characteristic of focal mechanism of aftershocksequence of Wenchuan earthquake[J].Chinese Sci Bull.,2009,54:2 263-2 270)
10吕坚,等.汶川8.0级地震序列重新定位及其发震构造初探[9].地震地质,2008,30(4):917-925.(LüJian,et al.Discussion on relocation and seismo-tectonics of theMs8.0 Wenchuan earthquake sequences[J].Seismologyand Geology,2008,30(4):917-925)
11张天中,等.近台资料对近震相对定位算法的影响[J].地球物理学报,2007,50(4):1123-1130.(ZhangTianzhong,et al.Effect of the data recorded at nearby sta-tions on earthquake relative location[J].Chinese Journal ofGeophysics,2007,50(4):1 123-1 130)
12吕坚,等.2005年11月26日九江-瑞昌Ms5.7、Ms4.8地震的震源机制解与发震构造研究[J].地球物理学报,2008,51(1):158-164.(LüJian,et al.Focal mechanismsand seismic fault of Ms5.7、Ms4.8 Jiujiang-Ruichang earth-quake on Nov.26,2005[J].Chinese Journal of Geophys-ics,2008,51(1):158-164)
13胡幸平,等.利用P波初动资料求解汶川地震及其强余震震源机制解[J].地球物理学报,2008,51(6):1 711-1 718.(Hu Xingping,et al.Focal mechanism solutions of Wenchuan earthquake and its strong aftershocks obtained from initial P wave polarity analysis[J].Chinese Journal of Geophysics,2008,51(6):1 711-1 718)
14郑勇,等.汶川地震强余震(Ms≥5.6)的震源机制解及其与发震构造的关系[J].中国科学(D辑),2009,39(4):413-426.(Zhen Yong,et al.Source mechanism of strong aftershocks(Ms≥5.6)of the2008-05-12Wen-chuan earthquake and the implication for seismo-tectonics[J].Science in China(Ser D),2009,39(4):413-426)
15李传友,等.汶川Ms8.0地震地表破裂带北川以北段的基本特征[J].地震地质,2008,30(3):683-696.(Li Chuanyou,et al.Characteristics of the surface rupture zone of the Ms8.0 Wenchuan earthquake,China along the segment north to Beichuan[J].Seismology and Geology,2008,30(3):683-696)
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