STUDY ON PALEOEARTHQUAKES ALONG THE JINGHE SECTION OF BOLOKENU-AQIKEKUDUKE FAULT

doi:10.3969/j.issn.0253-4967.2020.04.001

Abstract

Abstract: The Bolokenu-Aqikekuduk fault zone(B-A Fault)is a 1 000km long right-lateral strike-slip active fault in the Tianshan Mountains. Its late Quaternary activity characteristics are helpful to understand the role of active strike-slip faults in regional compressional strain distribution and orogenic processes in the continental compression environment, as well as seismic hazard assessment. In this paper, research on the paleoearthquakes is carried out by remote sensing image interpretation, field investigation, trench excavation and Quaternary dating in the Jinghe section of B-A Fault. In this paper, two trenches were excavated on in the pluvial fans of Fan2b in the bulge and Fan3a in the fault scarp. The markers such as different strata, cracks and colluvial wedges in the trenches are identified and the age of sedimentation is determined by means of OSL dating for different strata. Four most recent paleoearthquakes on the B-A Fault are revealed in trench TC1 and three most recent paleoearthquakes are revealed in trench TC2. Only the latest event was constrained by the OSL age among the three events revealed in the trench TC2. Therefore, when establishing the recurrence of the paleoearthquakes, we mainly rely on the paleoearthquake events in trench TC1, which are labeled E1-E4 from oldest to youngest, and their dates are constrained to the following time ranges: E1(19.4±2.5)~(19.0±2.5)ka BP, E2(18.6±1.4)~(17.3±1.4)ka BP, E3(12.2±1.2)~(6.6±0.8)ka BP, and E4 6.9~6.2ka BP, respectively. The earthquake recurrence intervals are(1.2±0.5)ka, (8.7±3.0)ka and(2.8±3)ka, respectively. According to the sedimentation rate of the stratum, it can be judged that there is a sedimentary discontinuity between the paleoearthquakes E2 and E3, and the paleoearthquake events between E2 and E3 may not be recorded by the stratum. Ignoring the sedimentary discontinuous strata and the earthquakes occurring during the sedimentary discontinuity, the earthquake recurrence interval of the Jinghe section of B-A Fault is ~1~3ka. This is consistent with the earthquake recurrence interval(~2ka)calculated from the slip rate and the minimum displacement. The elapsed time of the latest paleoearthquake recorded in the trench is ~6.9~6.2ka BP. The magnitude of the latest event defined by the single event displacement on the fault is ~M_W7.4, and a longer earthquake elapsed time indicates the higher seismic risk of the B-A Fault.

Key words: strike-slip structure, paleoearthquake, B-A Fault, Tian Shan

摘要： 博罗可努-阿齐克库都克断裂(简称博-阿断裂)是天山内部一条长约1 000km的右旋走滑活动断裂, 研究其晚第四纪的活动特征有助于理解大陆内挤压环境下活动走滑断裂在区域构造应变分配和造山过程中的作用并评价其地震危险性。文中选取博-阿断裂精河段作为研究对象, 利用遥感影像解译、野外调查、探槽开挖以及第四纪测年等方法进行了古地震研究。博-阿断裂精河段断错了多期洪积扇, 在Fan2和Fan3洪积扇上开挖了2个探槽。通过识别探槽内的地层与断层的切盖关系、裂缝、崩积楔等标志, 结合沉积层的光释光定年结果, 共识别出4次古地震事件。地震的发震时间分别为: E1(19.4±2.5)~(19.0±2.5)ka BP; E2(18.6±1.4)~(17.3±1.4)ka BP; E3(12.2±1.2)~(6.6±0.8)ka BP; E4 6.9~6.2ka BP。地震的复发间隔分别为(1.2±0.5)ka、 (8.7±3.0)ka和(2.8±3)ka。探槽内记录的最新一次古地震的离逝时间为6.2~6.9ka, 由断裂上单次事件的位移限定的最新一次地震的震级为M_W7.4。较长的古地震离逝时间揭示了博-阿断裂精河段可能存在较强的地震风险。

关键词: 走滑断裂, 古地震, 博-阿断裂, 天山山脉

CLC Number:

P315.2

HU Zong-kai, YANG Xiao-ping, YANG Hai-bo, WU Guo-dong, LI Jun, ZHOU Ben-gang. STUDY ON PALEOEARTHQUAKES ALONG THE JINGHE SECTION OF BOLOKENU-AQIKEKUDUKE FAULT[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(4): 773-790.

胡宗凯, 杨晓平, 杨海波, 吴国栋, 李军, 周本刚. 北天山博罗可努-阿齐克库都克断裂精河段的古地震事件[J]. 地震地质, 2020, 42(4): 773-790.

References

[1] 邓起东, 冯先岳, 张培震, 等. 2000. 天山活动构造 [M]. 北京: 地震出版社.
DENG Qi-dong, FENG Xian-yue, ZHANG Pei-zhen, et al. 2000. Active Tectonics of the Tian Shan Mountains [M]. Seismology Press, Beijing(in Chinese).
[2] 国家地震局震害防御司. 1995. 中国历史强震目录 [Z]. 北京: 地震出版社.
Department of Earthquake Disaster Prevention, SSB. 1995. Catalogue of Chinese Strong Historical Earthquakes [Z]. Seismological Press, Beijing(in Chinese).
[3] 胡宗凯, 杨晓平, 杨海波, 等. 2019. 博罗可努-阿齐克库都克断裂精河段晚更新世以来的断错地貌和走滑速率[J]. 地震地质, 41(2): 266—280. doi: 10.3969/j.issn.0253-4967.2019.02.002.
HU Zong-kai, YANG Xiao-ping, YANG Hai-bo, et al. 2019. Faulted landform and slip rate of the Jinghe section of the Bolokenu-Aqikekuduke Fault since the late Pleistocene[J]. Seismology and Geology, 41(2): 266—280(in Chinese).
[4] 毛凤英, 张培震. 1995. 古地震研究中的逐次限定法与新疆北部主要断裂带的古地震研究 [A]//国家地震局地质研究所. 活动断裂研究(4). 北京: 地震出版社: 153—164.
MAO Feng-ying, ZHANG Pei-zhen. 1995. progressive constraining method in paleoseismic study and paleoearthquakes along the major active faults in northern Xinjiang [A]// Institute of Geology, State Seismological Bureau. Research of Active Fault (4). Seismological Press, Beijing: 153—164(in Chinese).
[5] 冉勇康, 李彦宝, 杜鹏, 等. 2014. 中国大陆古地震研究的关键技术与案例解析(3): 正断层破裂特征、环境影响与古地震识别[J]. 地震地质, 36(2): 287—301. doi: 10.3969/j.issn.0253-4967.2014.02.001.
RAN Yong-kang, LI Yan-bao, DU Peng, et al. 2014. Key techniques and several cases analysis in paleoseismic studies in mainland China(3): Rupture characteristics, environment impact and paleoseismic indicators on normal faults[J]. Seismology and Geology, 36(2): 287—301(in Chinese).
[6] 沈军, 杨小平. 1998. 博洛科努断裂西北段古地震形变带初步研究[J]. 内陆地震, 12(3): 248—255.
SHEN Jun, YANG Xiao-ping. 1998. A preliminary study on the paleoearthquake rupture belt on the northwestern section of Bolohkenu Fault[J]. Inland Earthquake, 12(3): 248—255(in Chinese).
[7] 杨晓平, 邓起东, 张培震, 等. 2008. 天山山前主要推覆构造区的地壳缩短[J]. 地震地质, 30(1): 111—131.
YANG Xiao-ping, DENG Qi-dong, ZHANG Pei-zhen, et al.2008. Crustal shortening of major nappe structures on the front margins of the Tianshan[J]. Seismology and Geology, 30(1): 111—131(in Chinese).
[8] 杨晓平, 沈军. 2000. 天山内部博罗科努断裂精河—阿拉山口段晚更新世以来的活动特征[J]. 地震地质, 22(3): 305—315.
YANG Xiao-ping, SHEN Jun. 2000. Late Quaternary activity of Jinghe-Alashankou section of the Boluokenu Fault, interior Tianshan[J]. Seismology and Geology, 22(3): 305—315(in Chinese).
[9] 张培震, 邓起东, 徐锡伟, 等. 1994. 盲断裂、褶皱地震与新疆1906年玛纳斯地震[J]. 地震地质, 16(3): 193—204.
ZHANG Pei-zhen, DENG Qi-dong, XU Xi-wei, et al.1994. Blind thrust, folding earthquake, and the 1906 Manas earthquake, Xinjiang[J]. Seismology and Geology, 16(3): 193—204(in Chinese).
[10] Abdrakhmatov K E, Walker R T, Campbell G E, et al. 2016. Multisegment rupture in the 11 July 1889 Chilik earthquake(M_W8.0~8.3), Kazakh Tien Shan, interpreted from remote sensing, field survey, and paleoseismic trenching[J]. Journal of Geophysical Research: Solid Earth, 121(6): 4615—4640.
[11] Abdrakhmatov K Y, Aldazhanov S A, Hager B H, et al. 1996. Relatively recent construction of the Tien Shan inferred from GPS measurements of present-day crustal deformation rates[J]. Nature, 384(6608): 450—453.
[12] Arrowsmith J R, Crosby C J, Korzhenkov A M, et al. 2016. Surface rupture of the 1911 Kebin(Chon-Kemin)earthquake, northern Tien Shan, Kyrgyzstan[J]. Geological Society, London, Special Publications, 432(1): 233—253.
[13] Avouac J P, Tapponnier P, Bai M, et al. 1993. Active thrusting and folding along the northern Tien Shan and Late Cenozoic rotation of the Tarim relative to Dzungaria and Kazakhstan[J]. Journal of Geophysical Research: Solid Earth, 98(B4): 6755—6804.
[14] Burtman V S. 1975. Structural geology of Variscan Tien Shan, USSR[J]. American Journal of Science, 275:157—186.
[15] Campbell G E, Walker R T, Abdrakhmatov K, et al. 2013. The Dzhungarian Fault: Late Quaternary tectonics and slip rate of a major right-lateral strike-slip fault in the northern Tien Shan region[J]. Journal of Geophysical Research: Solid Earth, 118(10): 5681—5698.
[16] Charreau J, Saint-Carlier D, Dominguez S, et al. 2017. Denudation outpaced by crustal thickening in the eastern Tianshan[J]. Earth and Planetary Science Letters, 479:179—191.
[17] Huang W L, Yang X P, Li A, et al. 2015. Late Pleistocene shortening rate on the northern margin of the Yanqi Basin, southeastern Tian Shan, NW China[J]. Journal of Asian Earth Sciences, 112:11—24.
[18] Liu-Zeng J, Klinger Y, Xu X, et al. 2007. Millennial recurrence of large earthquakes on the Haiyuan Fault near Songshan, Gansu Province, China[J]. Bulletin of the Seismological Society of America, 97(1B): 14—34.
[19] Lu R Q, He D F, Xu X W, et al. 2018. Seismotectonics of the 2016 Hutubi M6.2 earthquake: Implications for the 1906 Manas M7.7 earthquake in the northern Tian Shan belt, China[J]. Seismological Research Letters, 89(1): 13—21.
[20] Molnar P, Tapponnier P. 1975. Cenozoic tectonics of Asia: Effects of a continental collision[J]. Science, 189(4201): 419—426.
[21] Molnar P, Brown E T, Burchfiel B C. 1994. Quaternary climate change and the formation of river terraces across growing anticlines on the north flank of the Tien Shan, China[J]. The Journal of Geology, 102(5): 583—602.
[22] Molnar P, Deng Q D. 1984. Faulting associated with large earthquakes and the average rate of deformation in central and eastern Asia[J]. Journal of Geophysical Research: Solid Earth, 89(B7): 6203—6227.
[23] Ran Y K, Chen L C, Chen J, et al. 2010. Paleoseismic evidence and repeat time of large earthquakes at three sites along the Longmenshan fault zone[J]. Tectonophysics, 491(1-4): 141—153.
[24] Rhodes E J. 2011. Optically stimulated luminescence dating of sediments over the past 200 000 years[J]. Annual Review of Earth and Planetary Sciences, 39(1): 461—488.
[25] Scharer K, Weldon R, Biasi G, et al. 2017. Ground-rupturing earthquakes on the northern Big Bend of the San Andreas Fault, California, 800AD to present[J]. Journal of Geophysical Research: Solid Earth, 122(3): 2193—2218.
[26] Shen J, Wang Y P, Li Y Z. 2011. Characteristics of the Late Quaternary right-lateral strike-slip movement of Bolokenu-Aqikekuduk Fault in northern Tianshan Mountains, NW China[J]. Geoscience Frontiers, 2(4): 519—527.
[27] Simpson D W, Hamburger M W, Pavlov V D, et al. 1981. Tectonics and seismicity of the Toktogul reservoir region, Kirgizia, USSR[J]. Journal of Geophysical Research: Solid Earth, 86(B1): 345—358.
[28] Tapponnier P, Molnar P. 1979. Active faulting and Cenozoic tectonics of the Tien Shan, Mongolia, and Baykal regions[J]. Journal of Geophysical Research: Solid Earth, 84(B7): 3425—3459.
[29] Thompson J A, Chen J, Yang H L, et al. 2018. Coarse-versus fine-grain quartz OSL and cosmogenic ¹⁰Be dating of deformed fluvial terraces on the northeast Pamir margin, northwest China[J]. Quaternary Geochronology, 46:1—15.
[30] Thompson S C, Weldon R J, Rubin C M, et al. 2002. Late Quaternary slip rates across the central Tien Shan, Kyrgyzstan, central Asia[J]. Journal of Geophysical Research: Solid Earth, 107(B9): ETG-7.
[31] Wells D L, Coppersmith K J. 1994. New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement[J]. Bulletin of the seismological Society of America, 84(4): 974—1002.
[32] Windley B F, Allen M B, Zhang C, et al. 1990. Paleozoic accretion and Cenozoic redeformation of the Chinese Tien Shan range, central Asia[J]. Geology, 18(2): 128—131.
[33] Yang S M, Li J, Wang Q. 2008. The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations[J]. Science in China(Ser D), 51(8): 1064—1080.
[34] Yin A. 2010. Cenozoic tectonic evolution of Asia: A preliminary synthesis[J]. Tectonophysics, 488(1-4): 293—325.
[35] Yuan Z D, Liu-Zeng J, Wang W, et al. 2018. A 6 000-year-long paleoseismologic record of earthquakes along the Xorkoli section of the Altyn Tagh Fault, China[J]. Earth and Planetary Science Letters, 497:193—203.