甘肃北山南缘俄博庙断裂的新活动特征及活动速率

doi:10.3969/j.issn.0253-4967.2020.02.013

摘要/Abstract

摘要： 通常认为甘肃北山是构造稳定区, 不发育活动断裂, 近年来新发现的俄博庙活动断裂挑战了这一传统认识, 深入研究该断裂的新活动特征和活动速率, 对于重新认识北山地区的新构造活动以及青藏高原和阿拉善块体的相互作用等问题具有重要意义。文中基于卫星影像解译、探槽开挖、差分GPS和无人机摄影测量、光释光测年等成熟的活动构造研究方法, 定量研究了俄博庙断裂的新活动特征, 得到以下认识: 首先, 文中完善了俄博庙断裂的几何展布, 将断裂长度由约20km延长至45km, 根据破裂长度与震级的经验关系推断俄博庙断裂具有发生7级地震的能力; 其次, 查明了断层陡坎的形态和成因, 发现正向陡坎和反向陡坎交替发育, 反向陡坎的高度为(0.22±0.02)~(1.32±0.1)m, 正向陡坎的高度为(0.33±0.1)~(0.64±0.1)m, 反向陡坎受由南向北低角度逆冲的断层控制, 断层倾角为23°~86°, 正向陡坎受倾向S的高角度正断层控制, 断层倾角为60°~81°; 另外, 断层的左旋走滑比倾滑更显著, 西段19条冲沟的左旋位移为(3.8±0.5)~(105±25)m, 根据其中最典型的一条冲沟的阶地陡坎的左旋位移量(16.7±0.5)m和上阶地年龄(11.2±1.5)ka, 得到俄博庙断裂晚更新世末以来的左旋滑动速率为(1.52±0.25)mm/a。晚新生代以来, 在青藏高原NE向扩展的构造背景下, 俄博庙断裂的新活动特征可能响应了青藏高原与阿拉善块体之间的相对剪切分量。

关键词: 俄博庙断裂, 甘肃北山, 左旋走滑, 金塔盆地, 青藏高原, 阿拉善块体

Abstract: The Ebomiao Fault is a newly discovered active fault near the block boundary between the Tibetan plateau and the Alashan Block. This fault locates in the southern margin of the Beishan Mountain, which is generally considered to be a tectonically inactive zone, and active fault and earthquake are never expected to emerge, so the discovery of this active fault challenges the traditional thoughts. As a result, studying the new activity of this fault would shed new light on the neotectonic evolution of the Beishan Mountain and tectonic interaction effects between the Tibetan plateau and the Alashan Block. Based on some mature and traditional research methods of active tectonics such as satellite image interpretation, trenches excavation, differential GPS measurement, Unmanned Aircraft Vehicle Photogrammetry(UAVP), and Optical Stimulated Luminescence(OSL)dating, we quantitatively study the new activity features of the Ebomiao Fault.
    Through this study, we complete the fault geometry of the Ebomiao Fault and extend the fault eastward by 25km on the basis of the 20km-fault trace identified previously, the total length of the fault is extened to 45km, which is capable of generating magnitude 7 earthquake calculated from the empirical relationships between earthquake magnitude and fault length. The Ebomiao Fault is manifested as several segments of linear scarps on the land surface, the scarps are characterized by poor continuity because of seasonal flood erosion. Linear scarps are either north- or south-facing scarps that emerge intermittently. Fourteen differential GPS profiles show that the height of the north-facing scarps ranges from (0.22±0.02)m to (1.32±0.1)m, and seven differential GPS profiles show the height of south-facing scarps ranging from (0.33±0.1)m to (0.64±0.1)m. To clarify the causes of the linear scarps with opposite-facing directions, we dug seven trenches across these scarps, the trench profiles show that the south-dipping reverse faults dominate the north-facing scarps, the dipping angles range from 23° to 86°. However, the south-facing scarps are controlled by south-dipping normal faults with dipping angles spanning from 60° to 81°.
    The Ebomiao Fault is dominated by left-lateral strike-slip activity, with a small amount of vertical-slip component. From the submeter-resolution digital elevation models(DEM)constructed by UAVP, the measured left-lateral displacement of 19 gullies in the western segment of the Ebomiao Fault are(3.8±0.5)~(105±25)m, while the height of the north-facing scarps on this segment are(0.22±0.02)~(1.32±0.10)m(L₃-L₇), the left-lateral displacement is much larger than the scarp height. In this segment, there are three gullies preserving typical left-lateral offsets, one gully among them preserves two levels of alluvial terraces, the terrace riser between the upper terrace and the lower terrace is clear and shows horizontal offset. Based on high-resolution DEM interpretation and displacement restoration by LaDiCaoz software, the left-lateral displacement of the terrace riser is measured to be(16.7±0.5)m. The formation time of the terrace riser is approximated by the OSL age of the upper terrace, which is (11.2±1.5)ka BP at (0.68±0.03)m beneath the surface, and(11.4±0.6)ka at (0.89±0.03)m beneath the surface, the OSL age (11.2±1.5)ka BP at (0.68±0.03)m beneath the surface is more close to the formation time of the upper terrace because of a nearer distance to sediment contact between alluvial fan and eolian sand silt. Taking the (16.7±0.5)m left-lateral displacement of the terrace riser and the upper terrace age (11.2±1.5)ka, we calculate a left-lateral strike-slip rate of(1.52±0.25)mm/a for the Ebomiao Fault. The main source for the slip rate error is that the terrace risers on both walls of the fault are not definitely corresponded. The north wall of the fault is covered by eolian sand, we can only presume the location of terrace riser by geomorphic analysis. In addition, the samples used to calculate slip rate before were collected from the aeolian sand deposits on the north side of the fault, they are not sediments of the fan terraces, so they could not accurately define the formation age of the upper terrace. This study dates the upper terrace directly on the south wall of the fault.
    Since the late Cenozoic, the new activity of the Ebomiao Fault may have responded to the shear component of the relative movement between the Tibetan plateau and the Alashan Block under the macroscopic geological background of the northeastern-expanding of the Tibetan plateau. The north-facing fault scarps are dominated by south-dipping low-angle reverse faults, the emergence of this kind of faults(faults overthrusting from the Jinta Basin to the Beishan Mountain)suggests the far-field effect of block convergence between Tibetan plateau and Alashan Block, which results in the relative compression and crustal shortening. As for whether the Ebomiao Fault and Qilianshan thrust system are connected in the deep, more work is needed.

Key words: Ebomiao Fault, Gansu Beishan, left-lateral strike-slip, Jinta Basin, Tibetan plateau, Alashan Block

中图分类号:

P315.2

张波, 何文贵, 刘炳旭, 高效东, 庞炜, 王爱国, 袁道阳. 甘肃北山南缘俄博庙断裂的新活动特征及活动速率[J]. 地震地质, 2020, 42(2): 455-471.

ZHANG Bo, HE Wen-gui, LIU Bing-xu, GAO Xiao-dong, PANG Wei, WANG Ai-guo, YUAN Dao-yang. NEW ACTIVITY CHARACTERISTICS AND SLIP RATE OF THE EBOMIAO FAULT IN THE SOUTHERN MARGIN OF BEISHAN, GANSU PROVINCE[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(2): 455-471.

参考文献

[1] 陈涛, 刘玉刚, 闵伟, 等. 2012. 塔尔湾断裂活动时代厘定及地貌陡坎成因分析[J]. 地震地质, 34(3): 401—414. doi: 10.3969/j.issn.0253-4967.2012.03.002.
CHEN Tao, LIU Yu-gang, MIN Wei, et al.2012. The activity age of Tarwan Fault and genesis of the topographic scarp[J]. Seismology and Geology, 34(3): 401—414(in Chinese).
[2] 邓起东, 于贵华, 叶文华. 1992. 地震地表破裂参数与震级关系的研究 [G]∥国家地震局地质研究所. 活动断裂研究(2). 北京: 地震出版社: 247—264.
DENG Qi-dong, YU Gui-hua, YE Wen-hua.1992. Relationship between earthquake magnitude and parameters of surface ruptures associated with historical earthquake [G]∥Institute of Geology, State Seismological Bureau. Research of Active Fault (2). Seismological Press, Beijing: 247—264(in Chinese).
[3] 国家地震局地质研究所, 国家地震局兰州地震研究所. 1993. 祁连山-河西走廊活动断裂系 [M]. 北京: 地震出版社: 1—340.
Institute of Geology and Lanzhou Institute of Seismology, State Seismological Bureau. 1993. The Qilianshan-Hexi Corridor Active Fault System [M]. Seismological Press, Beijing: 1—340(in Chinese).
[4] 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, State Seismological Bureau. 1995. Catalogue of Chinese Historical Strong Earthquakes [Z]. Seismological Press, Beijing(in Chinese).
[5] 何文贵, 雷中生, 袁道阳, 等. 2010. 1785年玉门惠回堡地震的震灾特点与发震构造[J]. 西北地震学报, 32(1): 47—53.
HE Wen-gui, LEI Zhong-sheng, YUAN Dao-yang, et al.2010. Disaster characteristics of Huihuipu earthquake in 1785 in Yumen, Gansu Province, and discussion on its seismogenic structure[J]. Northwestern Seismological Journal, 32(1): 47—53(in Chinese).
[6] 何文贵, 袁道阳, 王爱国, 等. 2012. 酒泉盆地北侧金塔南山北缘断裂西段全新世活动特征[J]. 地震, 32(3): 59—66.
HE Wen-gui, YUAN Dao-yang, WANG Ai-guo, et al.2012. Active faulting features in Holocene of the west segment of the Jintananshan north margin fault at the north of Jiuquan Basin[J]. Earthquake, 32(3): 59—66(in Chinese).
[7] 刘兴旺, 雷中生, 袁道阳, 等. 2011. 1609年甘肃红崖堡7¼级地震考证[J]. 西北地震学报, 33(2): 143—148.
LIU Xing-wang, LEI Zhong-sheng, YUAN Dao-yang, et al.2011. Textual research on the Hongyapu M7.25 earthquake in 1609[J]. Northwestern Seismological Journal, 33(2): 143—148(in Chinese).
[8] 刘兴旺, 袁道阳, 邹小波, 等. 2018. 青藏高原北缘三危山断裂晚更新世活动特征[J]. 地震地质, 40(1): 121—132. doi: 10.3969/j.issn.0253-4967.2018.01.010.
LIU Xing-wang, YUAN Dao-yang, ZOU Xiao-bo, et al.2018. Active characteristics of the Sanweishan Fault in the northern margin of the Tibetan plateau during late Pleistocene[J]. Seismology and Geology, 40(1): 121—132(in Chinese).
[9] 袁道阳, 张培震, 刘百篪, 等. 2004. 青藏高原东北缘晚第四纪活动构造的几何图像与构造转换[J]. 地质学报, 78(2): 270—278.
YUAN Dao-yang, ZHANG Pei-zhen, LIU Bai-chi, et al.2004. Geometrical imagery and tectonic transformation of late Quaternary active tectonics in northeastern margin of Qinghai-Xizang Plateau[J]. Acta Geologica Sinica, 78(2): 270—278(in Chinese).
[10] 云龙, 张进, 徐伟, 等. 2019. 甘肃北山南缘断裂的活动特征及其意义[J]. 地质论评, 65(4): 825—838.
YUN Long, ZHANG Jin, XU Wei, et al.2019. The active characteristics and its significance of the southern margin fault of Beishan area in Gansu Province[J]. Geological Review, 65(4): 825—838(in Chinese).
[11] 云龙, 张进, 徐伟, 等. 2020. 河西走廊西段花海断裂几何学、运动学及区域构造意义[J]. 地球科学, 待刊.
YUN Long, ZHANG Jin, XU Wei, et al.2020. Geometry, kinematics and regional tectonic significance of the Huahai Fault in the western Hexi Corridor, NW China[J]. Earth Science, in press(in Chinese).
[12] 张波, 何文贵, 庞炜, 等. 2016. 青藏块体北部金塔南山断裂晚第四纪走滑活动的地质地貌特征[J]. 地震地质, 38(1): 1—21. doi: 10.3969/j.issn.0253-4967.2016.01.001.
ZHANG Bo, HE Wen-gui, PANG Wei, et al.2016. Geological and geomorphic expressions of late Quaternary strike-slip activity on Jinta Nanshan Fault in northern edge of Qing-Zang block[J]. Seismology and Geology, 38(1): 1—21(in Chinese).
[13] 张辉, 王熠熙. 2012. 2012年5月3日金塔-阿拉善盟5.4级地震震源机制解[J]. 西北地震学报, 34(2): 205—206.
ZHANG Hui, WANG Yi-xi.2012. Focal mechanism of the Jinta-Alashanmeng M5.4 earthquake on May 3^rd, 2012[J]. Northwestern Seismological Journal, 34(2): 205—206(in Chinese).
[14] 张培震, 邓起东, 张国民, 等. 2003. 中国大陆的强震活动与活动地块[J]. 中国科学(D辑), 33(S1): 12—20.
ZHANG Pei-zhen, DENG Qi-dong, ZHANG Guo-min, et al.2003. Strong earthquake activity and active block in mainland China[J]. Science in China(Ser D), 33(S1): 12—20(in Chinese).
[15] 张培震, 邓起东, 张竹琪, 等. 2013. 中国大陆的活动断裂、地震灾害及其动力过程[J]. 中国科学(D辑), 43(10): 1607—1620.
ZHANG Pei-zhen, DENG Qi-dong, ZHANG Zhu-qi, et al.2013. Active faults, earthquake disasters and their dynamic processes in mainland China[J]. Science in China(Ser D), 43(10): 1607—1620(in Chinese).
[16] 郑文俊. 2009. 河西走廊及其邻区活动构造图像及构造变形模式 [D]. 北京: 中国地震局地质研究所: 1—209.
ZHENG Wen-jun.2009. Geometric pattern and active tectonics of the Hexi Corridor and its adjacent regions [D]. Institute of Geology, China Earthquake Administration, Beijing: 1—209(in Chinese).
[17] 郑文俊, 张培震, 袁道阳, 等. 2009. 甘肃高台合黎山南缘发现地震地表破裂带[J]. 地震地质, 31(2): 247—255. doi: 10.3969/j.issn.0253-4967.2009.02.005.
ZHENG Wen-jun, ZHANG Pei-zhen, YUAN Dao-yang, et al.2009. Discovery of surface rupture zone on the south of Helishan in Gaotai, Gansu Province[J]. Seismology and Geology, 31(2): 247—255(in Chinese).
[18] Cunningham D, Zhang J, Li Y F.2016. Late Cenozoic transpressional mountain building directly north of the Altyn Tagh Fault in the Sanweishan and Nanjieshan, north Tibetan foreland, China[J]. Tectonophysics, 687:111—128.
[19] Hetzel R, Niedermann S, Tao M X, et al.2002. Low slip rates and long-term preservation of geomorphic features in central Asia[J]. Nature, 417:428—432.
[20] Liu R, Li A, Zhang S M, et al.2020. A NW-striking dextral strike-slip fault at the eastern end of the AltynTagh Fault and its tectonic implications for northeastward growth of the Tibetan plateau[J]. Journal of Asian Earth Sciences, 188:104069. doi: 10.1016/j.jseaes.2019.104069.
[21] Liu X W, Yuan D Y, Su Q.2017. Late Pleistocene slip rate of the northern Qilian Shan frontal thrust, western Hexi Corridor, China[J]. Terra Nova, 29(4): 238—244.
[22] 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.
[23] Xiao Q B, Zhao G Z, Dong Z Y.2011. Electrical resistivity structure at the northern margin of the Tibetan plateau and tectonic implications[J]. Journal of Geophysical Research: Solid Earth, 116(B12): 1—14.
[24] Yang H, Yang X P, Zhan Y, et al.2019. Quaternary activity of the Beihewan Fault in the southeastern Beishan wrench belt, western China: Implications for crustal stability and intraplate earthquake hazards north of Tibet[J]. Journal of Geophysical Research: Solid Earth, 124(12): 13286—13309.
[25] Yu J X, Zheng W J, Kirby E, et al.2016. Kinematics of late Quaternary slip along the Yabrai Fault: Implications for Cenozoic tectonics across the Gobi Alashan block, China[J]. Lithosphere, 8(3): 199—218.
[26] Yu J X, Zheng W J, Zhang P Z, et al.2017. Late Quaternary strike-slip along the Taohuala Shan-Ayouqi fault zone and its tectonic implications in the Hexi Corridor and the southern Gobi Alashan, China[J]. Tectonophysics, 721:28—44.
[27] Zhang B, Yuan D Y, He W G, et al.2018. First discovery of north-south striking normal faults near the potential eastern end of AltynTagh Fault[J]. Journal of Earth Science, 29(1): 182—192.
[28] Zheng W J, Zhang H P, Zhang P Z, et al.2013. Late Quaternary slip rates of the thrust faults in western Hexi Corridor(Northern Qilian Shan)and their implications for northeastward growth of the Tibetan plateau[J]. Geosphere, 9(2): 1—13.
[29] Zielke O, Arrowsmith J R.2012. LaDiCaoz and LiDARimager: MATLAB GUIs for LiDAR data handling and lateral displacement measurement[J]. Geosphere, 8(1): 206—221.