龙门山中央断裂北川-邓家—带古地震初步研究
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摘要
龙门山断裂带是否存在类似汶川5.12大地震的地质记录,是地震科学工作者所关注的科学问题之。处于中央断裂带中段和北段分界地区的北川-邓家一带,古地震研究对认识整个龙门山断裂带的大地震复发特征有重要意义。沿北川-邓家地震地表破裂带,可能有过早期活动,并兼顾是否有较多细粒第四纪沉积物,以便能较清晰地分析、判断古地震事件以及采集测年样品,所以我们在沙坝1组、和尚坪和邓家海光6组等3个地点开挖了4个探槽,并进行了断错地貌的实测,发现了该地区明显的古地震遗迹,以及该地区特殊的正断层地表破裂样式。通过探槽和实测地貌情况与前人在龙门山中央和前山断裂带的古地震研究结果的对比分析,结果显示该地区至少发生过两次地震事件(包括5.12地震事件在内),与龙门山中央和前山断裂大部分地点已揭露的古地震事件相吻合。而通过对该地区地貌侵蚀特征与地震陡坎的高度变化分析,可以得出该地区之前的地震事件与5.12地震的大小相近。
Whether there was an earthquake similar to the May 12, 2008 Wenchuan Eearthquake in the Longmen Mountain Fault zone in the geological records is one of the questions seismologists are trying to answer. Paleoearthquake study in the Beichuan -Dengjia area, the boundary area between the north and the middle segments along the Central Fault zone is important for understanding the characteristics of earthquake recurrence in the Longmen Mountain Fault zone. Paleoearthquake events may be recognized and estimated through observation on surface rupture and through analyses of fine grain Quaternary sediments in Beichuan - Dengjia area. The authors excavated 4 trenches and measured the geomorphologic features of deformation in the 1 st Tribe of Shaba Village,the Heshangping(the 5th Tribe of Haiguang Village), and the 6th Tribe of Haiguang Village. Paleoearthquake traces and special surface rupture pattern of normal fault were discovered in the area. Based on our results and previous investigation on the center of the Longmen Mountain as well as its front fault,we conclude that there have been at least 2 serious earthquakes in the area(including the May 12, 2008 Wenchuan Eearthquake). This is consistent with the revealed paleoearthquakes of Longmen Mountain central and range-front faults. Through analyzing the erosional characteristics and heights of earthquake scarps, the authors suggest that the magnitude of the paleo- earthquake is close to the May 12, 2008 Wenchuan Eearthquake.
Whether there was an earthquake similar to the May 12, 2008 Wenchuan Eearthquake in the Longmen Mountain Fault zone in the geological records is one of the questions seismologists are trying to answer. Paleoearthquake study in the Beichuan -Dengjia area, the boundary area between the north and the middle segments along the Central Fault zone is important for understanding the characteristics of earthquake recurrence in the Longmen Mountain Fault zone. Paleoearthquake events may be recognized and estimated through observation on surface rupture and through analyses of fine grain Quaternary sediments in Beichuan - Dengjia area. The authors excavated 4 trenches and measured the geomorphologic features of deformation in the 1 st Tribe of Shaba Village,the Heshangping(the 5th Tribe of Haiguang Village), and the 6th Tribe of Haiguang Village. Paleoearthquake traces and special surface rupture pattern of normal fault were discovered in the area. Based on our results and previous investigation on the center of the Longmen Mountain as well as its front fault,we conclude that there have been at least 2 serious earthquakes in the area(including the May 12, 2008 Wenchuan Eearthquake). This is consistent with the revealed paleoearthquakes of Longmen Mountain central and range-front faults. Through analyzing the erosional characteristics and heights of earthquake scarps, the authors suggest that the magnitude of the paleo- earthquake is close to the May 12, 2008 Wenchuan Eearthquake.
引文
1 冉勇康,陈立春,陈桂华等.汶川M_S8． 0地震发震断裂大地震原地重复现象初析.地震地质,2008,30(3) :630～643 Ran Yongkang,Chen Lichun,Chen Guihua et al.Primary analyses of in-situ recurrence of large earthquake along seismogenic fault of the M_S8． 0 Wenchuan Earthquake.Seismology and Geology,2008,30(3) :630-643
2 郑文俊,李传友,王伟涛等.汶川8． 0级地震陡坎(北川以北段)探槽的记录特征.地震地质,2008,30(3) :697～709 Zheng Wenjun,Li Chuanyou,Wang Weitao et al.Trench logs of earthquake scarp of the M_S8． 0 Wenchuan in the segment north of Beichuan.Seismology and Geology,2008,30 (3) :697-709
3 张培震,徐锡伟,闻学泽等.2008年汶川8． 0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,2008,51(4) :1066-1073 Zhang Peizhen,Xu Xiwei,Wen Xueze et al.Slip rates and recurrence intervals of the Longmenshan active fault zone,and tectonics implications for the mechanism of the May 12 Wenchuan Earthquake,2008,Sichuan,China.Chinese Journal of Geophysics,2008,51(4) :1066-1073
4 邓起东,陈社发,赵小麟等.龙门山及其邻区的构造和地震活动及动力学.地震地质,1994,16(4) :389～403
Deng Qidong,Chen Shefa,Zhao Xiaolin et al.Tectonics,seismisity dynamics of Longmenshan Mountains and its adjacent regions.Seismology and Geology,1994,16 (4) :389-403
5 陈社发,邓起东,赵小麟等.龙门山中段推覆构造带及相关构造的演化历史和变形机制(一),(二).地震地质,1994,16(4) :404-421 Chen Shefa,Deng Qidong,Zhao Xiaolin et al.Deformational characteristics,Evolutionary history and deformation mechanism of the middle Longmenshan thrust-nappes and related tectonics.Seismology and Geology,1994,16 (4) :404-421
6 陈国光,计凤桔,周荣军等.龙门山断裂带晚第四纪活动性分段的初步研究.地震地质,2007,29(3) :657～673 Chen Guoguang,Ji Fengju,Zhou Rongjun et al.Primary research of activity segmentation of Longmenshan Fault zone since Late-Quarternary.Seismology and Geology,2007,29 (3) :657-673
7 徐锡伟,闻学泽,叶建青等.汶川M_S8． 0地震地表破裂带及其发 震构造.地震地质,2008,30(3) :597～629 Xu Xiwei,Wen Xueze,Ye Jianqing et al.The Ms8． 0 Wenchuan Earthquake surface ruptures and its seismogenic structure.Seismology and Geology,2008,30 (3) :597-629
8 李传友,叶建青,谢富仁等.汶川M_S8． 0地震地表破裂带北川以北段的基本特征.地震地质,2008,30(3) :683-696 Li Chuanyou,Ye Jianqing,Xie Furen et al.Characteristics of the surface rupture zone of the Ms8． 0 Wenchuan Earthquake,China along the segment north to Beichuan.Seismology and Geology,2008,30(3) :683-696
9 刘静,张智慧,文力等.汶川8级大地震同震破裂的特殊性及构造意义--多条平行断裂同时活动的反序型逆冲地震事 件.地质学报,2008,82(12) :1707-1722 Liu Jing,Zhang Zhihui,Wen Li et al.The M_S8． 0 Wenchuan earthquake co-seismic rupture and its tectonic implications--An out-of-sequence thrusting event with slip partitioned on multiple faults.Acta Geologica Sinica,2008,82,(12) :1707-1722
10 冉勇康,史翔,王虎等.汶川M_S8． 0地震最大地表同震垂直位移量及其地表变形样式.科学通报,2009(出版中) Ran Yongkang,Shi Xiang,Wang Hu et al.The maximum coseismic vertical surface displacement and surface deformation pattern accompanying the Ms8． 0 Wenchuan earthquake.Chinese Science Bulletin,2009(in press)
2 郑文俊,李传友,王伟涛等.汶川8． 0级地震陡坎(北川以北段)探槽的记录特征.地震地质,2008,30(3) :697～709 Zheng Wenjun,Li Chuanyou,Wang Weitao et al.Trench logs of earthquake scarp of the M_S8． 0 Wenchuan in the segment north of Beichuan.Seismology and Geology,2008,30 (3) :697-709
3 张培震,徐锡伟,闻学泽等.2008年汶川8． 0级地震发震断裂的滑动速率、复发周期和构造成因.地球物理学报,2008,51(4) :1066-1073 Zhang Peizhen,Xu Xiwei,Wen Xueze et al.Slip rates and recurrence intervals of the Longmenshan active fault zone,and tectonics implications for the mechanism of the May 12 Wenchuan Earthquake,2008,Sichuan,China.Chinese Journal of Geophysics,2008,51(4) :1066-1073
4 邓起东,陈社发,赵小麟等.龙门山及其邻区的构造和地震活动及动力学.地震地质,1994,16(4) :389～403
Deng Qidong,Chen Shefa,Zhao Xiaolin et al.Tectonics,seismisity dynamics of Longmenshan Mountains and its adjacent regions.Seismology and Geology,1994,16 (4) :389-403
5 陈社发,邓起东,赵小麟等.龙门山中段推覆构造带及相关构造的演化历史和变形机制(一),(二).地震地质,1994,16(4) :404-421 Chen Shefa,Deng Qidong,Zhao Xiaolin et al.Deformational characteristics,Evolutionary history and deformation mechanism of the middle Longmenshan thrust-nappes and related tectonics.Seismology and Geology,1994,16 (4) :404-421
6 陈国光,计凤桔,周荣军等.龙门山断裂带晚第四纪活动性分段的初步研究.地震地质,2007,29(3) :657～673 Chen Guoguang,Ji Fengju,Zhou Rongjun et al.Primary research of activity segmentation of Longmenshan Fault zone since Late-Quarternary.Seismology and Geology,2007,29 (3) :657-673
7 徐锡伟,闻学泽,叶建青等.汶川M_S8． 0地震地表破裂带及其发 震构造.地震地质,2008,30(3) :597～629 Xu Xiwei,Wen Xueze,Ye Jianqing et al.The Ms8． 0 Wenchuan Earthquake surface ruptures and its seismogenic structure.Seismology and Geology,2008,30 (3) :597-629
8 李传友,叶建青,谢富仁等.汶川M_S8． 0地震地表破裂带北川以北段的基本特征.地震地质,2008,30(3) :683-696 Li Chuanyou,Ye Jianqing,Xie Furen et al.Characteristics of the surface rupture zone of the Ms8． 0 Wenchuan Earthquake,China along the segment north to Beichuan.Seismology and Geology,2008,30(3) :683-696
9 刘静,张智慧,文力等.汶川8级大地震同震破裂的特殊性及构造意义--多条平行断裂同时活动的反序型逆冲地震事 件.地质学报,2008,82(12) :1707-1722 Liu Jing,Zhang Zhihui,Wen Li et al.The M_S8． 0 Wenchuan earthquake co-seismic rupture and its tectonic implications--An out-of-sequence thrusting event with slip partitioned on multiple faults.Acta Geologica Sinica,2008,82,(12) :1707-1722
10 冉勇康,史翔,王虎等.汶川M_S8． 0地震最大地表同震垂直位移量及其地表变形样式.科学通报,2009(出版中) Ran Yongkang,Shi Xiang,Wang Hu et al.The maximum coseismic vertical surface displacement and surface deformation pattern accompanying the Ms8． 0 Wenchuan earthquake.Chinese Science Bulletin,2009(in press)
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