甘孜-玉树断裂东南段晚第四纪活动特征及古地震破裂行为
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摘要
甘孜-玉树断裂是1条全新世强烈活动的左旋走滑断裂带,与鲜水河断裂共同构成了巴颜喀拉地块和羌塘地块、川滇菱形地块的边界断裂,研究其晚第四纪活动特征及大地震复发行为是认识甘孜-玉树断裂未来7级以上大地震危险性的重要基础工作。文中通过野外地质调查、微地貌测量等方法揭示出甘孜段和邓柯段除左旋运动性质外,还具有明显的拉张作用,而马尼干戈段运动性质则以左旋走滑兼逆冲性质为主,全新世地层最大垂直位移量>2m。结合断裂的几何展布特征、古地震破裂行为和历史地震地表破裂分布范围等方面的研究结果,可以将垭口和邓柯盆地2个阶区作为甘孜-玉树断裂东南段的分段边界。由于垭口附近的山脊及邓科盆地的障碍体规模均较小,阶区宽度仅1~2km左右,为非持久性障碍体,在未来大地震的破裂中可能会被突破。文中在马尼干戈段上的竹庆乡进行了探槽开挖,通过样品年代学测试共识别出3次古地震事件,分别为3875~3455BC之间、晚于775BC和最新1次断错地表事件。通过与前人在甘孜段和邓柯段的古地震研究结果进行对比,揭示出马尼干戈段与甘孜段、邓柯段的古地震破裂事件具有明显的不同,但限于甘孜-玉树断裂东南段的古地震研究仍缺乏足够的数据支撑,各几何分段之间是否存在级联破裂仍需要进一步的探讨。
The Ganzi-Yushu Fault,the boundary of Bayan Har active tectonic block,Qiantang active tectonic block and Sichuan-Yunan active tectonic block,is a sinistral strike-slip fault zone with intensive Holocene activity. Thus, the study of activity characteristics and rupture behavior of paleoearthquakes in the late Quaternary on the Ganzi-Yushu Fault is of fundamental importance for understanding the future seismic risk of this fault. The southeast section of Ganzi-Yushu Fault is made up of three segments of Ganzi,Manigange and Dengke,where a MS7. 3 earthquake in 1866,a MS7. 7 earthquake in 1854 and a MS7. 3 in 1896 occurred,respectively. There is still lack of in-depth study on the active features and the cascading rupture possibility of these segments,which hindered the evaluation of seismic risk for the southeast section of Ganzi-Yushu Fault. By the means of field geological survey and micro topography measurement, this paper studied the geological and geomorphological features of the southeast section of the Ganzi-Yushu Fault. The results show that the Ganzi and Dengke segments show obvious extension movement, in addition to the left-lateral movement. For Manigange segment,the characteristics of the movement are mainly left-lateral strikeslip and thrusting,and the maximum vertical displacement of the Holocene strata is greater than 2 m.In part areas,the movement is normal faulting,which perhaps relates to the left stepping zone in the local stress environment. Therefore,combining the research results such as the fracture distribution in different motion characteristics, rupture behavior of paleoearthquakes, and the distribution of historical earthquake surface ruptures,we divide the southeast section of Ganzi Yushu Fault into Ganzi,Manigange and Dengke segment,and consider the Yakou and the Dengke Basin as the stepovers and the segments' boundaries. As the small scale of impermanent barriers including Dengke Basin and the ridge near Yakou,of which the width is about 1 ~ 2 km,they may be broken through in great earthquake rupture in future. A trench was excavated in Zhuqing township to investigate the paleoearthquakes on the Manigange segment,radiocarbon dating was employed and 3 paleoseismic events were revealed in the Zhuqing trench,which are the seismic events occurring respectively at3875 ~ 3455 BC,after 775 BC,and the latest one that ruptured the surface. Compared with the previous results of paleoseismology in the southeast section of Ganzi-Yushu Fault,it is found that the paleoseismic events in the Manigange segment are obviously different with that in Ganzi segment and Dengke segment. Due to the lack of sufficient data on the southeast section of the Ganzi-Yushu Fault,it still needs further discussion whether the cascade-rupturing between these segments exists.
The Ganzi-Yushu Fault,the boundary of Bayan Har active tectonic block,Qiantang active tectonic block and Sichuan-Yunan active tectonic block,is a sinistral strike-slip fault zone with intensive Holocene activity. Thus, the study of activity characteristics and rupture behavior of paleoearthquakes in the late Quaternary on the Ganzi-Yushu Fault is of fundamental importance for understanding the future seismic risk of this fault. The southeast section of Ganzi-Yushu Fault is made up of three segments of Ganzi,Manigange and Dengke,where a MS7. 3 earthquake in 1866,a MS7. 7 earthquake in 1854 and a MS7. 3 in 1896 occurred,respectively. There is still lack of in-depth study on the active features and the cascading rupture possibility of these segments,which hindered the evaluation of seismic risk for the southeast section of Ganzi-Yushu Fault. By the means of field geological survey and micro topography measurement, this paper studied the geological and geomorphological features of the southeast section of the Ganzi-Yushu Fault. The results show that the Ganzi and Dengke segments show obvious extension movement, in addition to the left-lateral movement. For Manigange segment,the characteristics of the movement are mainly left-lateral strikeslip and thrusting,and the maximum vertical displacement of the Holocene strata is greater than 2 m.In part areas,the movement is normal faulting,which perhaps relates to the left stepping zone in the local stress environment. Therefore,combining the research results such as the fracture distribution in different motion characteristics, rupture behavior of paleoearthquakes, and the distribution of historical earthquake surface ruptures,we divide the southeast section of Ganzi Yushu Fault into Ganzi,Manigange and Dengke segment,and consider the Yakou and the Dengke Basin as the stepovers and the segments' boundaries. As the small scale of impermanent barriers including Dengke Basin and the ridge near Yakou,of which the width is about 1 ~ 2 km,they may be broken through in great earthquake rupture in future. A trench was excavated in Zhuqing township to investigate the paleoearthquakes on the Manigange segment,radiocarbon dating was employed and 3 paleoseismic events were revealed in the Zhuqing trench,which are the seismic events occurring respectively at3875 ~ 3455 BC,after 775 BC,and the latest one that ruptured the surface. Compared with the previous results of paleoseismology in the southeast section of Ganzi-Yushu Fault,it is found that the paleoseismic events in the Manigange segment are obviously different with that in Ganzi segment and Dengke segment. Due to the lack of sufficient data on the southeast section of the Ganzi-Yushu Fault,it still needs further discussion whether the cascade-rupturing between these segments exists.
引文
国家地震局.1977.中国地震简目[M].北京:地震出版社.
China Earthquake Administration.1977.Brief Earthquake Catalogue of China[M].Seismological Press,Beijing(in Chinese).
黄学猛,田坤,杜义,等.2015.玉树巴塘断裂晚第四纪滑动速率及其构造意义[J].北京大学学报(自然科学版),51(1):65-78.
HUANG Xue-meng,TIAN Kun,DU Yi,et al.2015.Late Quaternary slip rate of the Yushu Batang Fault and its tectonic significance[J].Acta Scientiarum Naturalium Universitatis Pekinensis,51(1):65-78(in Chinese).
李闽峰,邢成起,蔡长星,等.1995.玉树断裂活动性研究[J].地震地质,17(3):218-224.
LI Min-feng,XING Cheng-qi,CAI Chang-xing,et al.1995.Research on activity of Yushu Fault[J].Seismology and Geology,17(3):218-224(in Chinese).
李正芳,肖海波,周本刚.2015.阶区对走滑型地震地表破裂带传播与终止行为的影响[J].地震地质,37(1):126-138.doi:10.3969/j.issn.0253-4967.2015.01.010.
LI Zheng-fang,XIAO Hai-bo,ZHOU Ben-gang.2015.Effect of fault steps on propagation and termination behavior of strike-slip earthquake surface ruptures[J].Seismology and Geology,37(1):126-138(in Chinese).
刘静,徐锡伟,李岩峰,等.2007.以海原断裂甘肃老虎山段为例浅析走滑断裂古地震记录的完整性:兼论古地震研究中的若干问题[J].地质通报,26(6):650-660.
LIU Jing,XU Xi-wei,LI Yan-feng,et al.2007.On the completeness of paleoseismic records of strike-slip faults:An example from the Laohushan segment of the Haiyuan Fault in Gansu,China,with a discussion of several problemsin the paleoearthquake study[J].Geological Bulletin of China,26(6):650-660(in Chinese).
彭华,马秀敏,白嘉启,等.2006.甘孜玉树断裂带第四纪活动特征[J].地质力学学报,12(3):295-304.
PENG Hua,MA Xiu-min,BAI Jia-qi,et al.2006.Characteristics of Quaternary activities of the Garzê-Yushu fault zone[J].Journal of Geomechanics,12(3):295-304(in Chinese).
冉勇康,王虎,李彦宝,等.2012.中国大陆古地震研究的关键技术与案例解析(1):走滑活动断裂的探槽地点、布设与事件识别标志[J].地震地质,34(2):197-210.doi:10.3969/j.issn.0253-4967.2012.02.001.
RAN Yong-kang,WANG Hu,LI Yan-bao,et al.2012.Key techniques and several cases analysis in paleoseismic studies in mainland China(1):Trenching sites,layouts and paleoseismic indicators on active strike-slip faults[J].Seismology and Geology,34(2):197-210(in Chinese).
石峰,李安,杨晓平,等.2013.甘孜-玉树断裂带东南段晚第四纪活动性研究[J].地震地质,35(1):50-63.doi:10.3969/j.issn.0253-4967.2013.01.004.
SHI Feng,LI An,YANG Xiao-ping,et al.2013.Research on late Quaternary activity of the southeastern segment of Ganzi-Yushu fault zone[J].Seismology and Geology,35(1):50-63(in Chinese).
闻学泽,黄圣睦,江在雄.1985.甘孜-玉树断裂带的新构造特征与地震危险性估计[J].地震地质,7(3):23-32.
WEN Xue-ze,HUANG Sheng-mu,JIANG Zai-xiong.1985.Neotectonic features of the Ganzi-Yushu fault zone and assessment of its earthquake risk[J].Seismology and Geology,7(3):23-32(in Chinese).
闻学泽,徐锡伟,郑荣章,等.2003.甘孜-玉树断裂的平均滑动速率与近代大地震破裂[J].中国科学(D辑),33(S1):199-208.
WEN Xue-ze,XU Xi-wei,ZHENG Rong-zhang,et al.2003.Average slip-rate and recent large earthquake ruptures along the Garzê-Yushu Fault[J].Science in China(Ser D):46(S2):276-288.
徐锡伟,闻学泽,郑荣章,等.2003.川滇地区活动块体最新构造变动样式及其动力来源[J].中国科学(D辑),33(S1):151-162.
XU Xi-wei,WEN Xue-ze,ZHENG Rong-zhang,et al.2003.Pattern of latest tectonic motion and its dynamics for active blocks in Sichuan-Yunnan region,China[J].Science in China(Ser D),46(S2):210-226.
周荣军,马声浩,蔡长星.1996.甘孜-玉树断裂带的晚第四纪活动特征[J].中国地震,12(3):250-260.
ZHOU Rong-jun,MA Sheng-hao,CAI Chang-xing.1996.Late Quaternary active features of the Ganzi-Yushu fault zone[J].Earthquake Research in China,12(3):250-260(in Chinese).
周荣军,闻学泽,蔡长星,等.1997.甘孜-玉树断裂带的近代地震与未来地震趋势估计[J].地震地质,19(2):115-124.
ZHOU Rong-jun,WEN Xue-ze,CAI Chang-xing,et al.1997.Recent earthquakes and assessment of seismic tendency on the Ganzi-Yushu fault zone[J].Seismology and Geology,19(2):115-124(in Chinese).
Huang X M,Du Y,He Z T,et al.2015.Late Pleistocene-Holocene paleoseismology of the Batang Fault(central Tibet Plateau,China)[J].Geomorphology,239:127-141.
Shi F,He H L,Densmore A L,et al.2016.Active tectonics of the Ganzi-Yushu Fault in the southeastern Tibetan plateau[J].Tectonophysics,676:112-124.
Wang Y Z,Wang M,Shen Z K,et al.2013.Inter-seismic deformation field of the Ganzi-Yushu Fault before the 2010MW6.9 Yushu earthquake[J].Tectonophysics,584:138-143.
Zhou R J,Li Y,Liang M J,et al.2014.Determination of mean recurrence interval of large earthquakes on the Garzê-Yushu Fault(Dengke segment)on the eastern margin of the Qinghai-Tibetan plateau[J].Quaternary International,333:179-187.
(1)本文中所有14C测年样品结果均由美国BETA实验室测定
China Earthquake Administration.1977.Brief Earthquake Catalogue of China[M].Seismological Press,Beijing(in Chinese).
黄学猛,田坤,杜义,等.2015.玉树巴塘断裂晚第四纪滑动速率及其构造意义[J].北京大学学报(自然科学版),51(1):65-78.
HUANG Xue-meng,TIAN Kun,DU Yi,et al.2015.Late Quaternary slip rate of the Yushu Batang Fault and its tectonic significance[J].Acta Scientiarum Naturalium Universitatis Pekinensis,51(1):65-78(in Chinese).
李闽峰,邢成起,蔡长星,等.1995.玉树断裂活动性研究[J].地震地质,17(3):218-224.
LI Min-feng,XING Cheng-qi,CAI Chang-xing,et al.1995.Research on activity of Yushu Fault[J].Seismology and Geology,17(3):218-224(in Chinese).
李正芳,肖海波,周本刚.2015.阶区对走滑型地震地表破裂带传播与终止行为的影响[J].地震地质,37(1):126-138.doi:10.3969/j.issn.0253-4967.2015.01.010.
LI Zheng-fang,XIAO Hai-bo,ZHOU Ben-gang.2015.Effect of fault steps on propagation and termination behavior of strike-slip earthquake surface ruptures[J].Seismology and Geology,37(1):126-138(in Chinese).
刘静,徐锡伟,李岩峰,等.2007.以海原断裂甘肃老虎山段为例浅析走滑断裂古地震记录的完整性:兼论古地震研究中的若干问题[J].地质通报,26(6):650-660.
LIU Jing,XU Xi-wei,LI Yan-feng,et al.2007.On the completeness of paleoseismic records of strike-slip faults:An example from the Laohushan segment of the Haiyuan Fault in Gansu,China,with a discussion of several problemsin the paleoearthquake study[J].Geological Bulletin of China,26(6):650-660(in Chinese).
彭华,马秀敏,白嘉启,等.2006.甘孜玉树断裂带第四纪活动特征[J].地质力学学报,12(3):295-304.
PENG Hua,MA Xiu-min,BAI Jia-qi,et al.2006.Characteristics of Quaternary activities of the Garzê-Yushu fault zone[J].Journal of Geomechanics,12(3):295-304(in Chinese).
冉勇康,王虎,李彦宝,等.2012.中国大陆古地震研究的关键技术与案例解析(1):走滑活动断裂的探槽地点、布设与事件识别标志[J].地震地质,34(2):197-210.doi:10.3969/j.issn.0253-4967.2012.02.001.
RAN Yong-kang,WANG Hu,LI Yan-bao,et al.2012.Key techniques and several cases analysis in paleoseismic studies in mainland China(1):Trenching sites,layouts and paleoseismic indicators on active strike-slip faults[J].Seismology and Geology,34(2):197-210(in Chinese).
石峰,李安,杨晓平,等.2013.甘孜-玉树断裂带东南段晚第四纪活动性研究[J].地震地质,35(1):50-63.doi:10.3969/j.issn.0253-4967.2013.01.004.
SHI Feng,LI An,YANG Xiao-ping,et al.2013.Research on late Quaternary activity of the southeastern segment of Ganzi-Yushu fault zone[J].Seismology and Geology,35(1):50-63(in Chinese).
闻学泽,黄圣睦,江在雄.1985.甘孜-玉树断裂带的新构造特征与地震危险性估计[J].地震地质,7(3):23-32.
WEN Xue-ze,HUANG Sheng-mu,JIANG Zai-xiong.1985.Neotectonic features of the Ganzi-Yushu fault zone and assessment of its earthquake risk[J].Seismology and Geology,7(3):23-32(in Chinese).
闻学泽,徐锡伟,郑荣章,等.2003.甘孜-玉树断裂的平均滑动速率与近代大地震破裂[J].中国科学(D辑),33(S1):199-208.
WEN Xue-ze,XU Xi-wei,ZHENG Rong-zhang,et al.2003.Average slip-rate and recent large earthquake ruptures along the Garzê-Yushu Fault[J].Science in China(Ser D):46(S2):276-288.
徐锡伟,闻学泽,郑荣章,等.2003.川滇地区活动块体最新构造变动样式及其动力来源[J].中国科学(D辑),33(S1):151-162.
XU Xi-wei,WEN Xue-ze,ZHENG Rong-zhang,et al.2003.Pattern of latest tectonic motion and its dynamics for active blocks in Sichuan-Yunnan region,China[J].Science in China(Ser D),46(S2):210-226.
周荣军,马声浩,蔡长星.1996.甘孜-玉树断裂带的晚第四纪活动特征[J].中国地震,12(3):250-260.
ZHOU Rong-jun,MA Sheng-hao,CAI Chang-xing.1996.Late Quaternary active features of the Ganzi-Yushu fault zone[J].Earthquake Research in China,12(3):250-260(in Chinese).
周荣军,闻学泽,蔡长星,等.1997.甘孜-玉树断裂带的近代地震与未来地震趋势估计[J].地震地质,19(2):115-124.
ZHOU Rong-jun,WEN Xue-ze,CAI Chang-xing,et al.1997.Recent earthquakes and assessment of seismic tendency on the Ganzi-Yushu fault zone[J].Seismology and Geology,19(2):115-124(in Chinese).
Huang X M,Du Y,He Z T,et al.2015.Late Pleistocene-Holocene paleoseismology of the Batang Fault(central Tibet Plateau,China)[J].Geomorphology,239:127-141.
Shi F,He H L,Densmore A L,et al.2016.Active tectonics of the Ganzi-Yushu Fault in the southeastern Tibetan plateau[J].Tectonophysics,676:112-124.
Wang Y Z,Wang M,Shen Z K,et al.2013.Inter-seismic deformation field of the Ganzi-Yushu Fault before the 2010MW6.9 Yushu earthquake[J].Tectonophysics,584:138-143.
Zhou R J,Li Y,Liang M J,et al.2014.Determination of mean recurrence interval of large earthquakes on the Garzê-Yushu Fault(Dengke segment)on the eastern margin of the Qinghai-Tibetan plateau[J].Quaternary International,333:179-187.
(1)本文中所有14C测年样品结果均由美国BETA实验室测定
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