THE NEW FINDINGS OF SURFACE RUPTURE ZONES AND ITS SEISMOLOGICAL SIGNIFICANCE OF THE EASTERN MARGIN OF YUMUSHAN FAULT, NORTHEASTERN MARGIN OF QINGZANG PLATEAU

doi:10.3969/j.issn.0253-4967.2024.03.005

Abstract

Abstract:

The Hexi Corridor in northwest China has obvious structural deformation and complex fracture image. With the development of several NW thrust fault zones accompanied by a large number of ancient earthquakes and historical seismic events, the earthquake disaster is relatively serious. The eastern margin of Yumushan fault is one of them. The fault is mainly developed in the east site of Yumushan Mountain, with the exposed fault plane striking NW330° and dipping about 41°~85° to the southwest as a whole. Previous research data show that the Eastern Margin of the Yumushan fault is an important part of the Qilian Mountain active thrust fault system in the northeast margin of the Tibet Plateau. It also constitutes the boundary structure between Hexi Corridor and Yumushan Uplift. Its late Quaternary tectonic deformation and recent activity characteristics reflect the northward extension process of the Qilian Mountains and the remote collision effect of the northward extrusion of the Indian Plate. However, there are still some controversies in the study of the latest activity age and deformation characteristics of the eastern Margin of the Yumushan fault zone, which directly affect the seismic risk assessment along the fault line and the Hexi Corridor, as well as the in-depth understanding of the active structural characteristics of the northeast margin of the Tibetan plateau.

Combined with remote sensing image interpretation, paleoseismologic excavations, aerial photogrammetry of unmanned aerial vehicles and late Quaternary dating, this study carried out field investigations and newly discovered the surface rupture zone of The Eastern Margin of Yumushan Fault and its activity characteristics. The results show that The Eastern Margin of the Yumushan Fault strikes NW330° combined with obvious thrust movement, which is manifested as a fault scarp landform. That’s revealing than the kinematics property of The eastern margin of Yumushan fault is dominated by thrust. The fault forms the dividing line between the Yumushan uplift and Zhangye Basin, and also the dividing line between pre-quaternary strata and Quaternary strata. The southwest side of the fault is dominated by pre-quaternary bedrock which constitutes a mountain landform. Late Quaternary sediments are exposed on the northeast side, and the Holocene strata are widely distributed around the Heihe River. The results show that there are obvious differences in the activity habits of the faults. With the Heihe River as the boundary, the fault activity difference is obvious on the south and north sides of the Heihe River. The latest surface fracture zone in the late Holocene was found along the Heiheokou segment(F_1-1). And the Hongshahesegment(F_1-2)showed pre-quaternary fault. It can be seen that the Miocene fine sandstone is in fault contact with the early Pleistocene glutenite and late Ordovician metamorphic andesite, and the fault gouge develops near the fault, which is gray-green and yellow-green with moderate hardness and easy to be wet when encountering water.

The Heihekou segment(F_1-1)starts from Daciyaohe River in the north, passes Xiaociyaokou, and reaches Heihekou in the south. The fracture zone moves towards NW330° and tends to SW, with a length of about 10km and a width of 3~10m. For river terraces, gullies, and platforms with young surface faults, the maximum height of the surface scarp is based on the DEM data generated by UAVs. The height of the T1 terrace fault scarp measured by two profile lines is(1.7±0.1)m to(3.3±0.2)m. In the excavating trenches, obvious evidence of fault activity such as traction bending of strata and directional arrangement of gravel can be seen. The strata consist of late Quaternary alluvial sand, gravel layer, loess layer, and silty layer. The optically stimulated luminescence dating results show that the latest surface rupture event occurred at(0.6±0.07)ka BP.

According to the empirical formula between maximum vertical displacement(D_max)and magnitude(M), the magnitude of the latest seismic event is estimated. The magnitude and potential seismic risk of the latest rupture event are evaluated. The results reveal that the maximum vertical displacement of the latest surface rupture event is(3.3±0.2)m. Based on the empirical relationship between magnitude and vertical displacement, it is concluded that a large earthquake rupture occurred in the eastern margin of the Yumushan fault in the late Holocene and the corresponding magnitude is estimated to be M7.5.

Derived from the analysis of existing data, the fault in the eastern margin of the Yumushan fault may conform to the quasiperiodic earthquake recurrence behavior. And the recurrence interval of strong earthquakes may exceed 1 600a. The time interval between the latest event revealed in this paper and its last seismic event is about 1 800a, which is consistent with the time interval under the fault quasiperiodic earthquake recurrence model.

The results show that the eastern margin of the Yumushan fault has intensive tectonic deformation in the late Quaternary and a large seismic background of M7 or above. The current kinematic mode of the fault is compressive shortening. Its geodynamic process may be mainly controlled by the northward extension of the Qilian Mountains and the remote collision effect of the northward extrusion of the Indian Plate. The deformation process of the fault may be in line with pre-spreading imbricate thrust deformation and the latest deformation has gradually extended from the basin-mountain boundary to the interior of Zhangye Basin, which provides new data to support the seismic risk assessment of the interior of the basin. At the same time, the latest deformation achievement of the eastern margin of the Yumushan fault has important scientific significance for improving the active tectonic image of the northeastern margin of the Qingzang plateau and discussing the kinematics model of the Qingzang plateau.

Key words: The eastern margin of Yumushan fault, the late Quaternary activity of the fault, the latest surfacerupture, seismic hazard of great earthquakes

摘要：

榆木山东缘断裂的晚第四纪构造变形及最新的活动特征反映了祁连山的向N扩展过程及印度板块向N挤压的远程碰撞效应。文中结合遥感影像解译、探槽古地震、无人机航空摄影测量和晚第四纪测年等方法, 调查并新发现了榆木山东缘断裂的地表破裂带及其活动特征。结果表明, 榆木山东缘断裂整体走向NW330°, 现今的运动学特征以逆冲为主。以黑河为界, 断裂的活动习性存在明显差异。在黑河口段(F_1-1)发现了全新世晚期最新强震活动的地表破裂带。破裂带整体走向NW330°, 倾向SW, 长约10km, 宽3~10m。地表破裂断错年轻的河流阶地、冲沟及台地, 地表陡坎的最大高度为(3.3±0.2)m。光释光年代学结果显示, 最新的地表破裂事件发生于(0.6±0.07)ka BP, 经验公式估算其震级约为M7.5。研究结果表明榆木山东缘断裂的变形特征为前展式逆冲推覆, 其最新前缘的变形已经到达盆地内部。

关键词: 榆木山东缘断裂, 晚第四纪活动性, 最新地表破裂, 强震危险性

CHEN Bai-xu, YU Zhong-yuan, XIAO Peng, DAI Xun-ye, ZHANG Shi-long, ZHENG Rong-ying. THE NEW FINDINGS OF SURFACE RUPTURE ZONES AND ITS SEISMOLOGICAL SIGNIFICANCE OF THE EASTERN MARGIN OF YUMUSHAN FAULT, NORTHEASTERN MARGIN OF QINGZANG PLATEAU[J]. SEISMOLOGY AND GEOLOGY, 2024, 46(3): 589-607.

陈柏旭, 余中元, 肖鹏, 戴训也, 张世龙, 郑荣荧. 青藏高原东北缘榆木山东缘断裂地表破裂带的新发现及其地震地质意义[J]. 地震地质, 2024, 46(3): 589-607.

Figures/Tables 16

References 21

[1]	艾晟, 张波, 樊春, 等. 2017. 武威盆地南缘断裂晚第四纪活动地表形迹与活动速率[J]. 地震地质, 39(2): 408—422. doi: 10.3969/j.issn.0253-4967.2017.02.010.
	AI Sheng, ZHANG Bo, FAN Chun, et al. 2017. Surface tracks and slip rate of the fault along the southern margin of the Wuwei Basin in the late Quaternary[J]. Seismology and Geology, 39(2): 408—422 (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. Research on relationship between surface rupture parameters and magnitude of earthquake [G]∥Institute of Geology, China Earthquake Administration. Active Fault Research(2), Seismological Press, Beijing: 247—264 (in Chinese).
[3]	国家地震局地质研究所. 1993. 祁连山-河西走廊活动断裂系[M]. 北京: 地震出版社.
	China Earthquake Administration. 1993. Qilian Mountain-Hexi Corridor Active Fault System[M]. Seismological Press, Beijing (in Chinese).
[4]	郭鹏. 2019. 北祁连山冷龙岭断裂大震复发行为与危险性研究[D]. 北京: 中国地震局地质研究所.
	GUO Peng. 2019. Earthquake recurrence behavior and seismic hazards of the Lenglongling Fault, Northern Qilian Shan[D]. Institute of Geology, China Earthquake Administration, Beijing (in Chinese).
[5]	金卿. 2011. 榆木山断裂带晚第四纪构造活动与大震危险性评价[D]. 兰州: 中国地震局兰州地震研究所.
	JIN Qing. 2011. Study on activity in late Quaternary and the earthquake risk assessment of the Yumu Mountain fault zone[D]. Lanzhou Institute of Seismology, CEA, Lanzhou (in Chinese).
[6]	李有利, 李保俊, 杨景春. 1995. 甘肃张掖黑河口断层晚更新世晚期以来的活动[J]. 北京大学学报(自然科学版), 31(3): 351—357.
	LI You-li, LI Bao-jun, YANG Jing-chun. 1995. Late Quaternary movement on the Heihekou Fault, West Gansu, China[J]. Acta Scientiarum Naturalium Universitatis Pekinesis, 31(3): 351—357 (in Chinese).
[7]	李有利, 杨景春, 李保俊, 等. 1997. 河西走廊榆木山边缘断层构造地貌研究[J]. 地质力学学报, 3(4): 20—26.
	LI You-li, YANG Jing-chun, LI Bao-jun, et al. 1997. On the tectonic landform of the Yumu Mountain, Hexi Corridor, Gansu Province[J]. Journal of Geomechanics, 3(4): 20—26 (in Chinese).
[8]	李玉龙, 邢成起. 1988. 河西走廊地质构造基本特征以及榆木山北麓与黑河口上龙王活断层研究[J]. 西北地震学报, 10(2): 35—47.
	LI Yu-long, XING Cheng-qi. 1988. Research on the fundamental characteristics of the geological structures of the Hexi Corridor and the active faults of the northern and eastern flank of the Yumushan mountain[J]. Northwestern Seismological Journal, 10(2): 35—47 (in Chinese).
[9]	潘家伟, 李海兵, Chevalier M L, 等. 2022. 2022年青海门源 M_S6.9 地震地表破裂带及发震构造研究[J]. 地质学报, 96(1): 215—231.
	PAN Jia-wei, LI Hai-bing, Chevalier M L, et al. 2022. Coseismic surface rupture and seismogenic structure of the 2022 M_S6.9 Menyuan earthquake, Qinghai Province, China[J]. Acta Geologica Sinica, 96(1): 215—231 (in Chinese).
[10]	庞炜. 2015. 祁连山前逆冲断裂带古地震识别的关键技术研究[D]. 兰州: 中国地震局兰州地震研究所.
	PANG Wei. 2015. Key techniques in paleoearthquake studies of reverse faults on Qilian Mountain piedmont[D]. Lanzhou Institute of Seismology, CEA, Lanzhou (in Chinese).
[11]	齐若男. 2017. 河西走廊黑河、梨园河河流阶地对新构造运动的响应[D]. 北京: 中国地质大学.
	QI Ruo-nan. 2017. The characteristics of river terraces of Heihe and Liyuan Rivers in Hexi Corridor and the respinse of its neotectonic movement[D]. China University of Geosciences, Beijing (in Chinese).
[12]	冉勇康, 李志义, 尤惠川, 等. 1988. 河西走廊黑河口断层上的古地震及年代研究[J]. 地震地质, 10(4): 118—126.
	RAN Yong-kang, LI Zhi-yi, YOU Hui-chuan, et al. 1988. The study and dating of paleoearthquake along Heihekou Fault in Hexi Corridor[J]. Seismology and Geology, 10(4): 118—126 (in Chinese).
[13]	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).
[14]	张宁, 郑文俊, 刘兴旺, 等. 2016. 河西走廊西端黑山断裂运动学特征及其在构造转换中的意义[J]. 地球科学与环境学报, 38(2): 245—257.
	ZHANG Ning, ZHENG Wen-jun, LIU Xing-wang, et al. 2016. Kinematics characteristics of Heishan Fault in the Western Hexi Corridor and its implications for regional tectonic transformation[J]. Journal of Earth Sciences and Environment, 38(2): 245—257 (in Chinese).
[15]	张培震, 张会平, 郑文俊, 等. 2014. 东亚大陆新生代构造演化[J]. 地震地质, 36(3): 574—585.
	ZHANG Pei-zhen, ZHANG Hui-ping, ZHENG Wen-jun, et al. 2014. Cenozoic tectonic evolution of continental Eastern Asia[J]. Seismology and Geology, 36(3): 574—585 (in Chinese).
[16]	郑文俊, 张博譞, 袁道阳, 等. 2021. 阿拉善地块南缘构造活动特征与青藏高原东北缘向外扩展的最新边界[J]. 地球科学与环境学报, 43(2): 224—236.
	ZHENG Wen-jun, ZHANG Bo-xuan, YUAN Dao-yang, et al. 2021. Tectonic activity in the southern Alashan Block and the latest boundary of outward expansion on the northeastern Tibetan plateau in China[J]. Journal of Earth Sciences and Environment, 43(2): 224—236 (in Chinese).
[17]	Hetzel R, Tao M X, Stokes S, et al. 2004. Late Pleistocene/Holocene slip rate of the Zhangye thrust(Qilian Shan, China)and implications for the active growth of the northeastern Tibetan plateau[J]. Tectonics, 23(6): 1—17.
[18]	Molnar P, Stock J M. 2009. Slowing of India’s convergence with Eurasia since 20Ma and its implications for Tibetan mantle dynamics[J]. Tectonics, 28(3): 1—11.
[19]	Ren J J, Xu X W, Zhang S M, et al. 2019. Late Quaternary slip rates and Holocene paleoearthquakes of the eastern Yumu Shan Fault, northeast Tibet: Implications for kinematic mechanism and seismic hazard[J]. Journal of Asian Earth Sciences, 32: 42—56.
[20]	Tapponnier P, Meyer B, Avouac J P, et al. 1990. Active thrusting and folding in the Qilian Shan, and decoupling between upper crust and mantle in northeastern Tibet[J]. Earth and Planetary Science Letters, 97: 382—403.
[21]	Tapponnier P, Xu Z Q, Roger F, et al. 2001. Oblique stepwise rise and growth of the Tibet Plateau[J]. Science, 294(5547): 1671—1677.

地层单元编号	地层特征描述
U₁	土黄色含砾腐殖层。厚约10cm,断层陡坎处尖灭,夹青褐色砾石,砾石直径3~8cm,局部最大可达30cm,磨圆较好,多为圆状、次圆状。
U₂	灰白色含细砂砾石层。厚约1.4m,向两侧尖灭,偶见草根,砾石多为棱角状和次棱角状,粒径7~15cm。顶部砾石较大,局部可达40cm。底部为砾石夹漫洪相灰黄色含黏土细砂,发育的层理受断层的牵引作用向SW倾斜。
U₃	冲洪积相浅灰色含细砂砾石层。砾石的粒径普遍较大,较大的为30~60cm,部分砾石的粒径为5~20cm,多为次圆状和次棱角状,无分选。其间夹漫洪相黄灰色细砂,砾石与砂土混杂堆积,未发育层理。
U₄	灰黄色黄土,厚约0.8m,向NE延伸至断层F₃处尖灭,底部被F₃断错。
U₅	灰白色含细砂砾石层。厚约0.6m,砾石粒径多为5~20cm,局部可达40cm,多为次棱角状,与少量细砂混杂堆积。向NE延伸并被F₃错断。
U₆	灰黄色黄土,厚约1m,向SW逐渐减薄,向NE延伸并被F₃错断,为充填楔W₂的形成提供空间。
U₇	灰黄色含砂砾石层。厚约3m,砾石粒径多为5~20cm,局部可达0.5m,磨圆一般,多为次圆状和次棱角状,其间夹深黄色细砂层,发育水平层理。被F₃错断。
U₈	灰黄色砾石层。厚约1.2m,相较于上覆的U₃层, U₈层砾石普遍较小,多为2~5cm,局部可达10cm,多为次棱角状,位于底部的砾石长轴方向沿断层呈顺时针定向偏转。U₈层与下伏U₉层呈沉积接触。断层的牵引作用使U₈层整体向SW倾斜。
U₉	土黄色粉砂层。厚约2m,以土黄色粉砂为主,含少量砾石,粒径为3~7cm,磨圆较好,多为圆状和次圆状,与U₈层呈断层接触。距地表30cm处取光释光样品ZYFZ-OSL-2,测年结果为(0.6±0.07)ka。
W₁	充填楔,以黄土为主,偶夹砾石,粒径2~5cm,多为圆状和次圆状,无分选,无层理。
W₂	充填楔,近断层处的砾石层发生拖曳变形,粒径2~5cm,顶部砾石层近水平排列,粒径15~25cm。

地层单元编号	地层特征描述
U₁	土黄色含砾腐殖层。厚约10cm,断层陡坎处尖灭,夹青褐色砾石,砾石直径3~8cm,局部最大可达30cm,磨圆较好,多为圆状、次圆状。
U₂	灰白色含细砂砾石层。厚约1.4m,向两侧尖灭,偶见草根,砾石多为棱角状和次棱角状,粒径7~15cm。顶部砾石较大,局部可达40cm。底部为砾石夹漫洪相灰黄色含黏土细砂,发育的层理受断层的牵引作用向SW倾斜。
U₃	冲洪积相浅灰色含细砂砾石层。砾石的粒径普遍较大,较大的为30~60cm,部分砾石的粒径为5~20cm,多为次圆状和次棱角状,无分选。其间夹漫洪相黄灰色细砂,砾石与砂土混杂堆积,未发育层理。
U₄	灰黄色黄土,厚约0.8m,向NE延伸至断层F₃处尖灭,底部被F₃断错。
U₅	灰白色含细砂砾石层。厚约0.6m,砾石粒径多为5~20cm,局部可达40cm,多为次棱角状,与少量细砂混杂堆积。向NE延伸并被F₃错断。
U₆	灰黄色黄土,厚约1m,向SW逐渐减薄,向NE延伸并被F₃错断,为充填楔W₂的形成提供空间。
U₇	灰黄色含砂砾石层。厚约3m,砾石粒径多为5~20cm,局部可达0.5m,磨圆一般,多为次圆状和次棱角状,其间夹深黄色细砂层,发育水平层理。被F₃错断。
U₈	灰黄色砾石层。厚约1.2m,相较于上覆的U₃层, U₈层砾石普遍较小,多为2~5cm,局部可达10cm,多为次棱角状,位于底部的砾石长轴方向沿断层呈顺时针定向偏转。U₈层与下伏U₉层呈沉积接触。断层的牵引作用使U₈层整体向SW倾斜。
U₉	土黄色粉砂层。厚约2m,以土黄色粉砂为主,含少量砾石,粒径为3~7cm,磨圆较好,多为圆状和次圆状,与U₈层呈断层接触。距地表30cm处取光释光样品ZYFZ-OSL-2,测年结果为(0.6±0.07)ka。
W₁	充填楔,以黄土为主,偶夹砾石,粒径2~5cm,多为圆状和次圆状,无分选,无层理。
W₂	充填楔,近断层处的砾石层发生拖曳变形,粒径2~5cm,顶部砾石层近水平排列,粒径15~25cm。

地层单元编号	地层特征描述
U₁	灰黄色地表粉砂层,厚约20cm,以粉砂为主,夹砾石,偶见植物根系。
U₂	含砾粉砂层,厚约1m,砾石颜色向SW由土黄色渐变为褐色,分选和磨圆极差。自U2层以下,地层向NE向倾斜,表明断层作用扰动了原始的地层沉积。
U₃	土黄色粉砂层,夹灰褐色砾石,厚约2.5m,粉砂含量比U₂层多,且砾石含量明显高于U₃层,含较多碎石,沿SW向可见砾石粒径逐渐变大。沉积厚度稳定,成层性较好,可观察到明显的分层现象,砾石磨圆度中等,分选一般,偶见粒径>5cm的巨砾,为冲洪积相堆积物。
U₄	青黄色砾石层,厚0.3~0.8m,砾石长轴沿NE向排列,成层性极好,同时具备较好的分选度,但磨圆较差,推测为冲洪积相沉积。
U₅	浅棕色坡积砾石层,厚0.3~1.1m,成层性较好,分选和磨圆适中,偶见棱角状砾石。
U₆	黄褐色砾石层,厚约0.7m,相较于U₅层,砾石粒径沿长轴方向较长,呈扁平状,分选性沿SW向逐渐变差,未见底。

地层单元编号	地层特征描述
U₁	灰黄色地表粉砂层,厚约20cm,以粉砂为主,夹砾石,偶见植物根系。
U₂	含砾粉砂层,厚约1m,砾石颜色向SW由土黄色渐变为褐色,分选和磨圆极差。自U2层以下,地层向NE向倾斜,表明断层作用扰动了原始的地层沉积。
U₃	土黄色粉砂层,夹灰褐色砾石,厚约2.5m,粉砂含量比U₂层多,且砾石含量明显高于U₃层,含较多碎石,沿SW向可见砾石粒径逐渐变大。沉积厚度稳定,成层性较好,可观察到明显的分层现象,砾石磨圆度中等,分选一般,偶见粒径>5cm的巨砾,为冲洪积相堆积物。
U₄	青黄色砾石层,厚0.3~0.8m,砾石长轴沿NE向排列,成层性极好,同时具备较好的分选度,但磨圆较差,推测为冲洪积相沉积。
U₅	浅棕色坡积砾石层,厚0.3~1.1m,成层性较好,分选和磨圆适中,偶见棱角状砾石。
U₆	黄褐色砾石层,厚约0.7m,相较于U₅层,砾石粒径沿长轴方向较长,呈扁平状,分选性沿SW向逐渐变差,未见底。

地层单元编号	地层特征描述
U₁	灰黑色变质安山岩。
U₂	根据颜色和粒径可细分为U_2-1、U_2-2、U_2-3、U_2-4 4个亚层,上覆为棕褐色薄层粉砂,下伏为灰色河床相砾石层,夹杂土黄色粉砂。U_2-1—U_2-4层粉砂含量依次增多且颜色变浅。
U₃	灰黄色黄土,在距地表1.3m处取光释光样品ZYFZ-OSL-1,结果为(5.08±0.53)ka。
U₄	可细分为U_4-1、U_4-2 2个亚层,上覆为薄层河漫滩相细砂层,下伏为灰色河床相砾石层。
U₅	E₁事件相关的崩积楔,顶部可见粉细砂薄层。
U₆	E₂事件相关的崩积楔。