PRELIMINARY STUDY ON FAULTED LANDFORMS AND AGES OF RECENT STRONG EARTHQUAKE ACTIVITY ON THE KARAKORUM FAULT IN NGARI, TIBET

doi:10.3969/j.issn.0253-4967.2022.04.007

Abstract

Abstract:

The Karakoram Fault is located in the west of the Qinghai-Tibet Plateau and crosses Kashmir, Xinjiang and Tibet in China. It is a large normal dextral strike-slip fault in the middle of the Asian continent. As a boundary fault dividing the Qinghai-Tibet Plateau and the Pamir Plateau-Karakoram Mountains, the Karakoram Fault plays a role in accommodating the collision deformation between the Indian plate and the Eurasian plate and in the tectonic evolution of the western Qinghai-Tibet Plateau. The fault trace in Ngari area is clear and the faulted landforms are obvious, which show strong activity characteristics in late Quaternary. As a large active fault, only one earthquake of magnitude 7 has been recorded on the Karakoram Fault since the recorded history, namely, the Tashkurgan earthquake of 1895 at its north end. There are no records of strong earthquakes of magnitude≥7 along the rest of the fault, and no paleo-seismic research has been carried out. Ages of recent strong earthquake activity and earthquake recurrence intervals are not clear, which greatly limit the accuracy of seismic risk assessment. In this study, we investigated the fault geometry and faulted landforms in Ngari area, collected OSL samples of the faulted landforms and sag ponds in Zhaxigang, Menshi and Baga towns and preliminarily discussed the ages of recent strong earthquake activity.

Study shows that the fault can be divided into three sections by Zhaxigang town and Suoduo village, and the structure and properties of each section are significantly different. In west Zhaxigang town section, the fault is dominated by dextral strike-slip with certain vertical movement, it is almost straight on the surface, with river terraces, alluvial-proluvial fans and water system faulted ranging from tens to hundreds of meters. In Zhaxigang town to Suoduo village section, the normal faulting is remarkable, the main fault constitutes the boundary fault between Ayilari Mountain and Gar Basin; fault facets and fault scarps are common along the fault line, there are also secondary faults with the same or opposite dip as the main fault developed near the piedmont basin. In east Suoduo village section, the main part of the fault is located at the south foot of Gangdise Mountain, and in addition to the piedmont fault, several approximately parallel faults are also developed on the southern alluvial-proluvial fans and moraine fans which are mainly dextrally faulted with certain vertical component.

According to the analysis of the faulted landforms and dating of the OSL samples collected from the sag ponds and faulted landforms in the west of Zhaxigang town, the east of Menshi town and the east of Baga town, the ages of recent strong earthquake activity on the fault are analyzed as follows. In the west of Zhaxigang town, the age of recent strong earthquake activity of the fault is constrained to be close to 2.34kaBP according to the average OSL dating results of KKF-3 and KKF-4. In the east of Menshi town, the recent earthquake activity age of fault f₂ is 4.67~3.01kaBP, but closer to 3.01kaBP according to the OSL dating results of KKF-11 of the youngest faulted geomorphic surface and average OSL dating results of KKF-6 and KKF-13 collected from sag ponds. In the area near Angwang village, Baga town, it is inferred that the recent strong earthquake activity age of the fault is close to 2.54kaBP according to the OSL dating results of KKF-2 collected from sag pond. If the faults of above three places are active at the same time, the age of recent strong earthquake activity of the fault is close to 2.63kaBP. The Karakorum Fault in Ngari area has obvious segment boundaries, and the activity of each segment and in its internal branch faults is most likely to be independent.

The earthquake recurrence interval on the fault is estimated to be 2.8ka according to the slip rate and the amount of displacement. From the above analysis, it can be seen the time since the last strong earthquake activity of Karakorum Fault may have been very close to the interval of earthquake recurrence. If the fault is characterized by a quasi-periodic in-situ recurrence, the energy accumulation in the fault may have reached a very high degree and the risk of recurrence of strong earthquake events of the fault may be very high, so more attention should be paid and more detailed research on the paleo-earthquake events and recurrence intervals should be carried out as quickly as possible.

Key words: Karakorum Fault, late Quaternary, faulted landform, ages of recent strong earthquake activity

摘要：

喀喇昆仑断裂是青藏高原西部一条大型边界断裂, 调节了印度板块与欧亚板块的碰撞变形, 在青藏高原西部构造演化过程中扮演着重要角色。阿里地区断裂迹线清晰, 断错地貌显著, 显示出晚第四纪强烈活动的特征。目前, 断裂最近的强震活动时代、复发间隔等地震活动性参数尚不清楚, 极大地限制了地震危险性评估的准确性。文中对阿里地区的断裂几何结构、断错地貌进行了调查, 在扎西岗乡、门士乡、巴嘎乡等地对断错地貌面及断塞塘进行了光释光年代样品采集。研究结果表明, 断裂以扎西岗乡、索多村为界分可为3段, 各段断裂结构及性质差异显著; 断裂最近的强震活动在扎西岗乡西、门士乡东以及巴嘎乡一带, 时间分别约为2.34kaBP、 3.01kaBP及2.54kaBP。断裂最近的强震活动距今的时间可能已非常接近地震复发间隔, 其能量积累或已达到了非常高的程度, 再次发生强震事件的危险性很大, 需引起足够重视, 尽快对断裂的古地震事件、复发间隔等地震活动性参数开展细致的研究。

关键词: 喀喇昆仑断裂, 晚第四纪, 断错地貌, 最近强震活动时代

CLC Number:

P315.2

XU Wei, LIU Zhi-cheng, WANG Ji, GAO Zhan-wu, YIN Jin-hui. PRELIMINARY STUDY ON FAULTED LANDFORMS AND AGES OF RECENT STRONG EARTHQUAKE ACTIVITY ON THE KARAKORUM FAULT IN NGARI, TIBET[J]. SEISMOLOGY AND GEOLOGY, 2022, 44(4): 925-943.

徐伟, 刘志成, 王继, 高战武, 尹金辉. 西藏阿里地区喀喇昆仑断裂断错地貌及最近强震活动时代的初步研究[J]. 地震地质, 2022, 44(4): 925-943.

Figures/Tables 12

Fig. 1 Regional tectonic framework of Karakorum Fault( modified from Cowgill, 2010)

Fig. 2 Distribution characteristics of Karakorum Fault in Ngari Prefecture.

Fig. 3 Satellite image and typical faulted landforms of the west Zhaxigang town section.

Fig. 4 Typical fault distribution, fault facets and fault scarps of Zhaxigang town to Suoduo village section.

Fig. 5 Typical fault distribution satellite image and faulted landforms of the east Suoduo village section.

Fig. 6 Sampling locations(a, b)and profiles(c, d)in sag pond west of Zhaxigang town.

Fig. 7 DEM image(a), typical topographic elevation lines(b), river offset and geomorphic surface interpretation(c)along the fault east of Yaerqin River.

Fig. 8 Sampling location S3 and S4 in sag pond P1 and P2, and corresponding sampling profiles.

Fig. 9 Fault trace and sag pond distribution(a), DEM image(b), and typical topographic elevation line(c)south of Angwang village.

Fig. 10 Photos showing the sampling at site S6 and S7, and corresponding sampling profiles.

Table 1 OSL test parameters and age of samples

样品编号	埋深 /m	U /μg·g^-1	Th /μg·g^-1	K /%	含水量 /%	环境剂量率 /Gy·ka^-1	等效剂量 /Gy	年龄 /ka
KKF-1	0.28	4.04±0.08	16.5±0.26	3.00±0.02	14.09	5.83±0.38	74.93±10.88	12.84±2.04
KKF-2	0.34	1.7±0.01	18.5±0.14	2.14±0.01	7.39	4.84±0.32	12.3±1.15	2.54±0.29
KKF-3	0.21	1.67±0.03	19.5±0.30	2.74±0.01	22.86	4.74±0.28	13.35±1.00	2.82±0.27
KKF-4	0.24	2.36±0.03	28.8±0.29	2.81±0.01	26.37	5.59±0.31	10.39±0.56	1.86±0.15
KKF-6	0.18	3.38±0.06	20.2±0.26	2.61±0.01	6.37	6.09±0.42	19.93±1.56	3.27±0.34
KKF-11	0.25	2.26±0.04	15.7±0.20	1.76±0.01	4.93	4.51±0.31	21.07±1.69	4.67±0.49
KKF-12	0.17	2.27±0.04	14±0.16	1.67±0.01	2.52	4.39±0.30	12.01±0.78	2.74±0.26

Fig. 11 Comparison of ages of recent strong earthquake activity in different parts of the fault.

References 41

[1]	陈杰, 李涛, 李文巧, 等. 2011. 帕米尔构造结及邻区的晚新生代构造与现今变形[J]. 地震地质, 33(2): 241-259. doi: 10.3969/j.issn.0253-4967.2011.02.001. DOI
	CHEN Jie, LI Tao, LI Wen-qiao, et al. 2011. Late Cenozoic and present tectonic deformation in the Pamir salient, northwestern China[J]. Seismology and Geology, 33(2): 241-259. (in Chinese)
[2]	陈杰, 李涛, 孙建宝, 等. 2016. 2016年11月25日新疆阿克陶 M_W6.6 地震发震构造与地表破裂[J]. 地震地质, 38(4): 1161-1174. doi: 10.3969/j.issn.0253-4967.2016.04.028. DOI
	CHEN Jie, LI Tao, SUN Jian-bao, et al. 2016. Coseismic surface ruptures and seismogenic Muji Fault of the 25 November 2016 Arketao M_W6.6 earthquake in northern Pamir[J]. Seismology and Geology, 38(4): 1161-1174. (in Chinese)
[3]	邓起东. 2005. 活动构造研究及其应用: 谨以此文深切悼念先师陈国达院士[J]. 大地构造与成矿学, 29(1): 17-23.
	DENG Qi-dong. 2005. Studies and applications of active tectonics: Mourning for Academician CHEN Guo-da, the great master of Chinese geology[J]. Geotectonica et Metallogenia, 29(1): 17-23. (in Chinese)
[4]	邓起东, 闻学泽. 2008. 活动构造研究: 历史、进展与建议[J]. 地震地质, 30(1): 1-30.
	DENG Qi-dong, WEN Xue-ze. 2008. A review on the research of active tectonics: History, progress and suggestions[J]. Seismology and Geology, 30(1): 1-30. (in Chinese)
[5]	付碧宏, 时丕龙, 贾营营. 2009. 青藏高原大型走滑断裂带晚新生代构造地貌生长及水系响应[J]. 地质科学, 44(4): 1343-1363.
	FU Bi-hong, SHI Pi-long, JIA Ying-ying. 2009. Late Cenozoic tectono-geomorphic growth and drainage response along the large-scale strike-slip fault system, Tibetan plateau[J]. Chinese Journal of Geology, 44(4): 1343-1363. (in Chinese)
[6]	顾功叙. 1983. 中国地震目录(公元前1831-公元1969年)[Z]. 北京: 科学出版社.
	GU Gong-xu. 1983. Catalogue of Chinese Earthquakes(1831BC-1969AD)[Z]. Science Press, Beijing. (in Chinese)
[7]	雷东宁, 蔡永建, 李媛. 2018. 西藏喀喇昆仑断裂东南段晚第四纪活动的地质地貌特征[J]. 科学技术与工程, 18(32): 152-156.
	LEI Dong-ning, CAI Yong-jian, LI Yuan. 2018. Geological and topographical features of Karakorum Fault in southeastern segment, western Tibet Plateau at Late Quaternary[J]. Science Technology and Engineering, 18(32): 152-156. (in Chinese)
[8]	李传友, 张培震, 袁道阳, 等. 2010. 活动走滑断裂上断塞塘沉积特征及其构造含义: 以西秦岭北缘断裂带断塞塘为例[J]. 地质学报, 84(1): 90-105.
	LI Chuan-you, ZHANG Pei-zhen, YUAN Dao-yang, et al. 2010. Sedimentary characteristics of sag-pond on the active strike-slip fault and its tectonic implications: An example from sag pond along the West Qinling Fault[J]. Acta Geologica Sinica, 84(1): 90-105. (in Chinese)
[9]	李海兵, Valli F, 刘敦一, 等. 2007. 喀喇昆仑断裂的形成时代: 锆石SHRIMP U-Pb年龄的制约[J]. 科学通报, 52(4): 438-447.
	LI Hai-bing, Valli F, LIU Dun-yi, et al. 2007. Initial movement of the Karakorum Fault in western Tibet: Constraints from SHRIMP U-Pb dating of zircons[J]. Chinese Science Bulletin, 52(8): 1089-1100. DOI URL
[10]	李海兵, Valli F, 许志琴, 等. 2006. 喀喇昆仑断裂的变形特征及构造演化[J]. 中国地质, 33(2): 239-255.
	LI Hai-bing, Valli F, XU Zhi-qin, et al. 2006. Deformation and tectonic evolution of the Karakorum Fault, western Tibet[J]. Geology in China, 33(2): 239-255. (in Chinese)
[11]	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. DOI
	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)
[12]	王世锋, 江万, 王超. 2016. 喀喇昆仑断裂沿雅鲁藏布江缝合带活动的构造地貌特征[J]. 地球科学与环境学报, 38(4): 483-493.
	WANG Shi-feng, JIANG Wan, WANG Chao. 2016. Geomorphic evidence for recent right-lateral shear of Karakorum Fault along Indus-Yalu suture zone of Tibet[J]. Journal of Earth Sciences and Environment, 38(4): 483-493. (in Chinese)
[13]	许志琴, 李海兵, 杨经绥. 2006. 造山的高原: 青藏高原巨型造山拼贴体和造山类型[J]. 地学前缘, 13(4): 1-17.
	XU Zhi-qin, LI Hai-bing, YANG Jing-sui. 2006. An orogenic plateau: The orogenic collage and orogenic types of the Qinghai-Tibet plateau[J]. Earth Science Frontiers, 13(4): 1-17. (in Chinese)
[14]	赵一霖, 刘健, 姜科庆, 等. 2019. 喀喇昆仑断裂北段晚第四纪活动特征及其构造意义[J]. 地球学报, 40(4): 601-613.
	ZHAO Yi-lin, LIU Jian, JIANG Ke-qing, et al. 2019. Late Quaternary activity characteristics and tectonics significance of the northern Karakorum Fault[J]. Acta Geoscientica Sinica, 40(4): 601-613. (in Chinese)
[15]	中国地震局震害防御司. 1999. 中国近代地震目录(公元1912-1990年, M_S≥4.7)[Z]. 北京. 中国科学技术出版社.
	Department of Earthquake Disaster Prevention, China Earthquake Administration. 1999. Catalogue of Recent Chinese Earthquakes(1912-1990AD, M_S≥4.7)[Z]. China Science and Technology Press, Beijing. (in Chinese)
[16]	Boutonnet E, Leloup P H, Arnaud N, et al. 2012. Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike-slip shear zone: The case of the right-lateral Karakorum Fault[J]. Tectonics, 31(4): TC4012.
[17]	Brown E T, Bendick R, Bourlès D L, et al. 2002. Slip rates of the Karakorum Fault, Ladakh, India, determined using cosmic ray exposure dating of debris flows and moraines[J]. Journal of Geophysical Research: Solid Earth, 107(B9): ESE7-1-ESE7-13.
[18]	Burtman V S, Molnar P. 1993. Geological and geophysical evidence for deep subduction of continental crust beneath the Pamir [G]. Special Paper of the Geological Society of America, 281: 1-76.
[19]	Chevalier M L. 2019. Active tectonics along the Karakorum Fault, western Tibetan plateau: A review[J]. Acta Geoscientica Sinica, 40(1): 37-54.
[20]	Chevalier M L. 2005. Slip-rate measurements on the Karakorum Fault may imply secular variations in fault motion[J]. Science, 307(5708): 411-414. PMID
[21]	Chevalier M L, Li H, Pan J, et al. 2011. Fast slip-rate along the northern end of the Karakorum fault system, western Tibet[J]. Geophysical Research Letters, 38(22): L22309.
[22]	Chevalier M L, Pan J, Li H, et al. 2015. Quantification of both normal and right-lateral late Quaternary activity along the Kongur Shan extensional system, Chinese Pamir[J]. Terra Nova, 27(5): 379-391. DOI URL
[23]	Chevalier M L, Tapponnier P, van der Woerd J, et al. 2012. Spatially constant slip rate along the southern segment of the Karakorum Fault since 200ka[J]. Tectonophysics, 530-531: 152-179.
[24]	Chevalier M L, van der Woerd J, Tapponnier P, et al. 2016. Late Quaternary slip-rate along the central Bangong-Chaxikang segment of the Karakorum Fault, western Tibet[J]. Geological Society of America Bulletin, 128(42737): 284-314.
[25]	Cowgill E. 2010. Cenozoic right-slip faulting along the eastern margin of the Pamir salient, northwestern China[J]. Geological Society of America Bulletin, 122(1-2): 145-161. DOI URL
[26]	Lacassin R, Valli F, Arnaud N, et al. 2004. Large-scale geometry, offset and kinematic evolution of the Karakorum Fault, Tibet[J]. Earth and Planetary Science Letters, 219(3-4): 255-269. DOI URL
[27]	Matte P, Tapponnier P, Arnaud N, et al. 1996. Tectonics of western Tibet, between the Tarim and the Indus[J]. Earth and Planetary Science Letters, 142(3-4): 311-330. DOI URL
[28]	McCarthy M R, Weinberg R F. 2010. Structural complexity resulting from pervasive ductile deformation in the Karakorum shear zone, Ladakh, NW India[J]. Tectonics, 29(3): TC3004.
[29]	Murphy M A, Burgess W P. 2006. Geometry, kinematics, and landscape characteristics of an active transtension zone, Karakorum fault system, southwest Tibet[J]. Journal of Structural Geology, 28(2): 268-283. DOI URL
[30]	Murphy M A, Yin A, Kapp P, et al. 2002. Structural evolution of the Gurla Mandhata detachment system, southwest Tibet: Implications for the eastward extent of the Karakorum fault system[J]. Geological Society of America Bulletin, 114(4): 428-447. DOI URL
[31]	Peltzer G, Tapponnier P. 1988. Formation and evolution of strike-slip faults, rifts, and basins during the India-Asia collision: An experimental approach[J]. Journal of Geophysical Research: Solid Earth, 93(B12): 15085-15117.
[32]	Phillips R J, Parrish R R, Searle M P. 2004. Age constraints on ductile deformation and long-term slip rates along the Karakorum fault zone, Ladakh[J]. Earth and Planetary Science Letters, 226(3-4): 305-319. DOI URL
[33]	Robinson A C. 2009. Evidence against Quaternary slip on the northern Karakorum Fault suggests kinematic reorganization at the western end of the Himalayan-Tibetan orogen[J]. Earth and Planetary Science Letters, 286(1-2): 158-170. DOI URL
[34]	Robinson A C, Owen L A, Chen J, et al. 2015. No late Quaternary strike-slip motion along the northern Karakoram Fault[J]. Earth and Planetary Science Letters, 49: 290-298.
[35]	Robinson A C, Yin A, Manning C E, et al. 2007. Cenozoic evolution of the eastern Pamir: Implications for strain-accommodation mechanisms at the western end of the Himalayan-Tibetan orogen[J]. Geological Society of America Bulletin, 119(7-8): 882-896. DOI URL
[36]	Rolland Y, Mahéo G, Pêcher A, et al. 2009. Syn-kinematic emplacement of the Pangong metamorphic and magmatic complex along the Karakorum Fault(N Ladakh)[J]. Journal of Asian Earth Sciences, 34(1): 10-25. DOI URL
[37]	Valli F, Arnaud N, Leloup P H, et al. 2007. Twenty million years of continuous deformation along the Karakorum Fault, western Tibet: A thermochronological analysis[J]. Tectonics, 26(4): TC4004.
[38]	Valli F, Leloup P H, Paquette J L, et al. 2008. New U-Th/Pb constraints on timing of shearing and long-term slip-rate on the Karakorum Fault[J]. Tectonics, 27(5): TC5007.
[39]	Wallace R E 1970. Earthquake recurrence intervals on the San Andreas Fault[J]. Geological Society of America Bulletin, 81(10): 2875-2890. DOI URL
[40]	Wright T J, Parsons B, England P C, et al. 2004. InSAR observations of low slip rates on the major faults of western Tibet[J]. Science, 305(5681): 236-239. PMID
[41]	Zhou Y, Ronghua X U, Yan Y, et al. 2001. Dating of the Karakorum strike-slip fault[J]. Acta Geologica Sinica, 75(1): 10-18. DOI URL