GEOLOGICAL AND GEOMORPHIC EVIDENCES FOR THE HOLOCENE ACTIVITY OF THE NW ZHEDUOTANG BRANCH WITHIN THE XIANSHUIHE FAULT SYSTEM

doi:10.3969/j.issn.0253-4967.2020.05.001

Abstract

Abstract: Xianshuihe Fault is an active fault which originated from the eastern margin of the Tibetan plateau and formed by the orogenic events in Songpang-Ganzi area. The origin of Xianshuihe Fault is discovered in the NW of Ganzi, then it extends to the SE, passing through Luhuo, Daofu, Qianning, Kangding, Luding, Moxi and disappears after passing through Shimian. Based on previous studies, Xianshihe Fault is a sinistral strike-slip fault. According to GPS and InSAR data, the horizontal component of average slip rate for Xianshuihe Fault is approximately 7.5~16.7mm/a. As a crucial member of the regional earthquake zone, Xianshuihe Fault separates Sichuan-Yunnan block and Bayankala block. More importantly, Xianshuihe Fault is responsible for a great number of large magnitude earthquakes especially in the Qianning-Kangding segment, a segment of Xianshuihe Fault which consists of three branches. From east to west, they are Yalahe Fault, Selaha Fault and Zheduotang Fault which are all active since Holocene. Yalahe Fault is responsible for a M7 earthquake that occurred around 1700AD. Selaha Fault is responsible for another M7 earthquake which occurred around 1725AD. Around 1955AD, a M7.5 earthquake occurred which was related to Zheduotang Fault.
According to the 1:50k Xianshihe Active Faults Map(1995) and relevant researches, it is discovered that, from north to south, the Holocene active Zheduotang segment starts from Kangding airport to Zheduotang village. The total length of Zheduotang segment is around 30km which includes the surface rupture zone of the 1955 M7.5 earthquake. Due to the absence of researches, the northern part of the Zheduotang Fault, which is to the north of the Kangding airport, remains unstudied. Based on satellite image, we discovered that there are signs of faults to the north of Kangding airport. Therefore, we selected four sites to carry out field investigations and trench analysis. The first site is to the NW of the Duoriagamo village. Based on satellite image and DEM data, many typical faulted geomorphologic features are discovered. To the NW of this site, both the fan and the terrace are offset. By analyzing the DEM data, the offset of T1 terrace is around 7.8m and the offset of Fan1 is around 15.6m. To the SE of this site, the fan is also offset by sinistral movement which has an offset value of 21.7m. The second site is to the NW of the Muyazuqing school where 2.6m of sinistral offset between the fan and the T1 terrace are measured. To the SE of this site, obvious offset of fan and floodplain are observed which both have sinistral offset of 2.5m. The third site is to the south of first Duoriagamo village. The fault here shows two parallel branches. The fourth site is near the Tonglilongba and there are 37.5m of horizontal offset of the fan.
Based on trench analysis, 17 stratigraphic units are defined from which carbon samples are acquired for geochronological analysis. By constraining the age of each stratigraphic unit, the age of four deformation events are defined. Event 1 is the youngest which occurred between 5 821~3 148a BP. Event 2 occurred between 13 060~10 745a BP, Event 3 occurred between 13 687~11 420a BP and Event 4 occurred between 41 443~13 715a BP. According to the integration results of our analysis, the location of northwestern segment of Zheduotang Fault is defined. It is discovered that, the NW segment of Zheduotang Fault is located between the Kangding airport and Duoriagamo village with a total length of 15km. The trace of Zheduotang Fault is also defined. From north to south, Zheduotang Fault passes through Duoriagamo village, Tonglilongba, Kangding airport, Zheduoshan nek, Ertaizidaoban and disappears near Zheduotang village. Moreover, after Holocene, the Zheduotang Fault is dominated sinistral slip movement along with minor vertical component. Different from previous researches, we believe that the Holocene active Zheduotang segment extends 15km further to the NW. This discovery provides some basis for perfecting the plane geometric images of the three active faults in Qianning-Kangding segment of Xianshuihe fault zone, such as Zheduotang Fault, Selaha Fault and Yalahe Fault, and is of great significance for understanding the strain distribution and strong earthquake rupture mode of each branch fault in Qianning-Kangding segment of Xianshuihe fault zone.

Key words: Tibetan plateau, Qianning-Kangding segment of Xianshuihe fault zone, the NW branch of Zheduotang Fault, fault activity, paleoseismicity

摘要： NW向的鲜水河断裂带乾宁—康定段由3条分支断裂组成, 自东向西分别为雅拉河断裂、色拉哈断裂和折多塘断裂, 这3条断裂自全新世以来均有明显的活动。雅拉河断裂、色拉哈断裂和折多塘断裂南段分别发生过1700年7级、 1725年7级和1955年7.5级地震。 1︰50 000的鲜水河活动断裂带地质图(1995)及现有相关研究结果表明, 折多塘断裂全新世活动段南起折多塘村附近, 向N至康定机场附近, 全长约30km, 该段也是1955年7.5级地震地表破裂带展布的位置, 而康定机场以北的西北段没有全新世活动的报道。文中通过影像解译, 结合野外地质调查, 发现折多塘断裂西北段全新世活动的新证据。经实地调查与探槽开挖等工作核实, 该活动段自SE起于康定机场北侧, 向NW延伸到多日阿嘎莫村, 呈NW向展布, NW端邻近色拉哈断裂北段。文中结果表明折多塘断裂在全新世的活动范围较前人的研究成果向NW延伸了15km。该发现为完善鲜水河断裂带乾宁—康定段的折多塘断裂、色拉哈断裂以及雅拉河断裂这3支活动断裂的平面几何图像提供了一些依据, 对深入认识鲜水河断裂带康定段在各分支断裂上的应变分配、强震破裂模式等方面具有重要意义。

关键词: 青藏高原, 鲜水河断裂带乾宁—康定段, 折多塘断裂西北段, 断裂活动性, 古地震

CLC Number:

P315.2

MA Jun, ZHOU Ben-gang, WANG Ming-ming, AN Li-ke. GEOLOGICAL AND GEOMORPHIC EVIDENCES FOR THE HOLOCENE ACTIVITY OF THE NW ZHEDUOTANG BRANCH WITHIN THE XIANSHUIHE FAULT SYSTEM[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(5): 1021-1038.

马骏, 周本刚, 王明明, 安力科. 鲜水河断裂带折多塘断裂西北段全新世活动的地质地貌依据[J]. 地震地质, 2020, 42(5): 1021-1038.

References

[1] 陈桂华, 徐锡伟, 闻学泽, 等. 2008. 川滇块体北—东边界活动构造带运动学转换与变形分解作用[J]. 地震地质, 30(1): 58—85.
CHEN Gui-hua, XU Xi-wei, WEN Xue-ze, et al. 2008. Kinematical transformation and slip partitioning of northern to eastern active boundary belt of Sichuan-Yunnan block[J]. Seismology and Geology, 30(1): 58—85(in Chinese).
[2] 胡朝忠, 杨攀新, 梁朋, 等. 2015. 2014年康定M_S6.3地震发震断裂的古地震[J]. 科学通报, 60(23): 2236—2244.
HU Chao-zhong, YANG Pan-xin, LIANG Peng, et al. 2015. The Holocene paleoearthquakes on the 2014 Kangding M_S6.3 earthquake faults[J]. Chinese Science Bulletin, 60(23): 2236—2244(in Chinese).
[3] 李天袑, 杜其方, 游泽李, 等. 1997. 鲜水河活动断裂带及强震危险性评估 [M]. 成都: 成都地图出版社: 128—129.
LI Tian-shao, DU Qi-fang, YOU Ze-li, et al. 1997. Risk Assessment of Xianshuihe Active Fault Zone and Strong Earthquake [M]. Chengdu Cartographic Publishing House, Chengdu: 128—129(in Chinese).
[4] 四川省地震局地震地质队鲜水河活动断裂带填图组. 2013. 鲜水河活动断裂带地质图(1︰50 000)[CM]. 北京: 地震出版社.
The Mapping Group of Xianshuihe Active Fault Zone of the Seismogeological Team of Sichuan Earthquake Administration. 2013. Geological Map of Xianshuihe Active Fault Zone(1︰50 000)specification[CM]. Seismological Press, Beijing(in Chinese).
[5] 唐荣昌, 韩渭宾. 1993. 四川活动断裂与地震 [M]. 北京: 地震出版社.
TANG Rong-chang, HAN Wei-bin. 1993. Active Faults and Earthquakes in Sichuan Province [M]. Seismological Press, Beijing(in Chinese).
[6] 王新民, 余河生, 裴锡瑜. 1996. 1955年康定折多塘 7$\frac{1}{2}$级地震灾情统计资料的应用及效果[J]. 四川地震, (3): 57—64.
WANG Xin-min, YU He-sheng, PEI Xi-yu.1996. Application and results of statistic hazard data about the 1955 M7.5 Kangding earthquake[J]. Earthquake Research in Sichuan, (3): 57—64(in Chinese).
[7] 王宗秀, 许志琴, 杨天南. 1997. 松潘-甘孜滑脱型山链变形构造演化模式[J]. 地质科学, 32(3): 327—336.
WANG Zong-xiu, XU Zhi-qin, YANG Tian-nan.1997. A model for deformation structure evolution of Songpan-Garze orogene[J]. Scientia Geologica Sinica, 32(3): 327—336(in Chinese).
[8] 闻学泽, Allen C R, 罗灼礼, 等. 1989. 鲜水河全新世断裂带的分段性、几何特征及其地震构造意义[J]. 地震学报, 11(4): 362—372.
WEN Xue-ze, Allen C R, LUO Zhuo-li, et al. 1989. Segmentation, geometric features, and their seismotectonic implications for the Holocene Xianshuihe fault zone[J]. Acta Seismologica Sinica, 11(4): 362—372(in Chinese).
[9] 吴婵, 许志琴, Webb A A G, 等. 2016. 松潘-甘孜造山带鲜水河断裂与雅拉雪山片麻岩穹窿的关系[J]. 地质学报, 90(11): 2982—2998.
WU Chan, XU Zhi-qin, Webb A A G, et al. 2016. The relationship between the Xianshuihe fault zone and Yala Snow Mountain gneiss dome in the Songpan￣Ganzi orogenic belt[J]. Acta Geologica Sinica, 90(11): 2982—2998(in Chinese).
[10] 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. A new tectonic style for active blocks of Sichuan-Yunnan region and its power source[J]. Science in China(Ser D), 33(S1): 151—162(in Chinese).
[11] 曾蒂. 2018. 鲜水河断裂带色拉哈段古地震研究与强震危险性预测[D]. 北京: 中国地震局地质研究所.
ZENG Di.2018. Investigation of paleoearthquakes and prediction of strong earthquake risk on the Selaha segment of Xianshuihe Fault[D]. Institute of Geology, China Earthquake Administration, Beijing(in Chinese).
[12] 周荣军, 何玉林, 黄祖智, 等. 2001. 鲜水河断裂带乾宁—康定段的滑动速率与强震复发间隔[J]. 地震学报, 23(3): 250—261.
ZHOU Rong-jun, HE Yu-lin, HUANG Zu-zhi, et al. 2001. The slip rate and strong earthquake recurrence interval on the Qianning-Kangding segment of the Xianshuihe fault zone[J]. Acta Seismologica Sinica, 23(3): 250—261(in Chinese).
[13] Allen C R, Luo Z, Qian H, et al. 1991. Field study of a highly active fault zone: The Xianshuihe Fault of southwestern China[J]. Geological Society of American Bulletin, 103(9): 1178—1199.
[14] Bai M, Chevalier M L, Pan J, et al. 2018. Southeastward increase of the late Quaternary slip-rate of the Xianshuihe Fault, eastern Tibet: Geodynamic and seismic hazard implications[J]. Earth and Planetary Science Letters, 485:19—31.
[15] Chen G, Xu X, Wen X, et al. 2016. Late Quaternary slip-rates and slip partitioning on the southeastern Xianshuihe fault system, eastern Tibetan plateau[J]. Acta Geologica Sinica(English Edition), 90(2): 537—554.
[16] Chevalier M L, Leloup P H, Replumaz A, et al. 2017. Temporally constant slip rate along the Ganzi Fault, NW Xianshuihe fault system, eastern Tibet[J]. Geological Society of America Bulletin, 130(3-4): 396—410.
[17] Wang H, Wright T J, Biggs J.2009. Interseismic slip rate of the northwestern Xianshuihe Fault from InSAR data[J]. Geophysical Research Letters, 36(3): 139—145.
[18] Wang S, Fan C, Wang G, et al. 2008. Late Cenozoic deformation along the northwestern continuation of the Xianshuihe fault system, eastern Tibetan plateau[J]. Geological Society of America Bulletin, 120(3): 312—328.
[19] Wen X, Ma S, Xu X, et al. 2008. Historical pattern and behavior of earthquake ruptures along the eastern boundary of the Sichuan-Yunnan faulted-block, southwestern China[J]. Physics of the Earth and Planetary Interiors, 168(1): 16—36.
[20] Xu X, Deng Q.1996. Nonlinear characteristics of paleoseismicity in China[J]. Journal of Geophysical Research: Solid Earth, 101(B3): 6209—6231.
[21] Zhang P.2013. A review on active tectonics and deep crustal processes of the western Sichuan region, eastern margin of the Tibetan plateau[J]. Tectonophysics, 584(2013): 7—22.
[22] Zhang Y, Yao X, Yu K, et al. 2016. Late-Quaternary slip rate and seismic activity of the Xianshuihe fault zone in southwest China[J]. Acta Seismologica Sinica(English Edition), 90(2): 525—536.
[23] Zheng G, Wang H, Wright T J, et al. 2017. Crustal deformation in the India-Eurasia collision zone from 25 years of GPS measurements: Crustal deformation in Asia from GPS[J]. Journal of Geophysical Research: Solid Earth, 122(11): 9290—9312.