地震地质 ›› 2024, Vol. 46 ›› Issue (3): 547-569.DOI: 10.3969/j.issn.0253-4967.2024.03.003

• 研究论文 • 上一篇    下一篇

阿尔金断裂东段的河流阶地累积位错

李路瑶(), 丁锐*(), 姜大伟, 张世民   

  1. 应急管理部国家自然灾害防治研究院, 北京 100085
  • 收稿日期:2023-07-17 修回日期:2023-10-12 出版日期:2024-06-20 发布日期:2024-07-19
  • 通讯作者: *丁锐, 男, 1982年生, 助理研究员, 主要从事活动构造、 构造地貌方面的基础理论与应用研究, E-mail: ruiding@ninhm.ac.cn。
  • 作者简介:

    李路瑶, 女, 1998年生, 现为应急管理部国家自然灾害防治研究院地球物理学在读硕士研究生, 主要研究高分辨率遥感技术与机载雷达技术在地震断层与地质灾害定量研究中的应用, E-mail:

  • 基金资助:
    中央级公益性科研院所基本科研业务专项(ZDJ2020-12); 国家自然科学基金地震科学联合基金项目(U2039201)

CUMULATIVE DISLOCATIONS OF RIVER TERRACES IN THE EASTERN SEGMENT OF THE ALTYN TAGH FAULT

LI Lu-yao(), DING Rui*(), JIANG Da-wei, ZHANG Shi-min   

  1. National Institute of Natural Hazards, MEMC, Beijing 100085, China
  • Received:2023-07-17 Revised:2023-10-12 Online:2024-06-20 Published:2024-07-19

摘要:

阿尔金断裂带是青藏高原北缘的大型左旋走滑断裂, 其东段与NW走向的祁连山逆冲断裂带斜接。文中基于无人机摄影测量技术(SfM)获得的高分辨率影像数据, 对阿尔金断裂带东段长约127km的段落开展了详细解译, 并对其中9个典型河流阶地位错点进行测量与统计。沿阿尔金断裂带向E, 晚第四纪左旋累积位移总体呈衰减趋势, 且以断裂带东侧NW走向斜接逆冲断裂或逆冲走滑断裂为界, 其累积位错量在同一断裂段内大致相当, 但相邻断裂段之间表现为阶梯状递减, 指示了斜接断裂的构造转换关系及可能的地震破裂分段作用, 为阿尔金断裂带活动性分段研究与潜在发震能力评价提供了依据。

关键词: 阿尔金断裂带, 高分辨率地形数据, 累积位移, 断错地貌构造转换

Abstract:

The Altyn Tagh fault zone is a sizeable sinistral strike-slip fault on the northern margin of the Qinghai-Tibet Plateau, and its eastern section is obliquely connected with the northwest Qilian Mountain thrust fault zone. The left-lateral strike-slip action of the Altyn Tagh fault zone and the Qilian Mountain thrust belt constitute a structural transformation relationship. The activity behavior of this fault, especially the amount of sinistral dislocations, segmentation, and slip rate, has always been a hot topic of discussion among scholars. At present, based on geological methods and geodetic research, the slip rates of different sections of the Altyn Tagh Fault have been obtained, with a time scale ranging from tens of thousands of years to decades. The research results generally support the gradual attenuation of the slip rate of the Altyn Tagh fault zone from about 93°E to the east, indicating that its left-lateral attenuation is absorbed by a series of NW-trending thrust faults on its eastern side, and this trend has changed little for decades. The above work provides a framework for us to study the structural transformation relationship between the Altyn Tagh fault zone and the Qilian Mountains thrust belt in time and space. However, due to the limitations of previous observation points, especially the different methods of fault geomorphology measurement and dating used by various authors, there are significant differences in the obtained fault slip rates. Currently, it is not possible to analyze the segmented characteristics of the slip rate in the east section of the Altyn Tagh fault zone further and its spatial relationship with the Qilian Mountain thrust structural zone based on this. In recent years, the application of UAV aerial survey technology has allowed image data to be obtained at the centimeter to millimeter level, making the study of tectonic geomorphology more refined. Researchers can obtain the cumulative displacement or co-seismic displacement of several seismic cycles through micro-faulted landforms and reconstruct the dislocation accumulation process of active faults.

The transfixion terraces developed across the Altyn Tagh fault are mainly controlled by regional tectonic uplift and climate change, showing regional synchronization in time, which provides convenience for the comparison of regional landforms. Although there are differences in the grading standards of terraces at different sites and the dating methods are not completely consistent, the chronological sequence of the late Quaternary river terraces in the study area generally shows good consistency. From new to old, it is about 3-4ka BP, 6-8ka BP, 10-13ka BP, 20-21ka BP and 40-50ka BP, which provides a research basis for our subsequent comparison of the displacement amount of river terraces. Based on the high-resolution image data obtained by unmanned aerial vehicle photogrammetry(SfM), this paper carried out a detailed interpretation of the 127km section of the eastern section of the Altyn fault zone and measured and counted the dislocations of different levels of risers at 9 typical river terrace dislocation points. Based on the distribution of cumulative displacement of the same terrace, the kinematic segmentation characteristics and tectonic mechanism of the eastern section of the Altyn Tagh fault zone are discussed.

To define the displacement more accurately, we considered the following factors: 1)Usually, the riser is not a straight line but a curve formed by the free swing of the river bed; 2)Strictly speaking, a riser is a slope with a certain width, consisting of an upper edge, a lower edge, and a middle slope zone. When measuring displacement, we cannot only measure the upper edge or lower edge of the scarp but must consider it comprehensively. Based on the above prerequisites, this paper uses two envelope lines to surround the upper and lower edges of the riser and measures the distance between the corresponding envelope lines on both sides of the fault to obtain the displacement of different levels of scarp in the river terrace. Based on the above measurement methods, four dislocation values, A1-A4 and B1-B4, were obtained from the curve envelope of the upper and lower edge of the terrace scarp on both sides of the fault, respectively. After calculating the corresponding mean value, the standard deviation of the four measured values was estimated to reflect the dispersion degree of different measured values relative to the mean value, which was used as the error range of the measurement results.

The results show that the late Quaternary left-lateral cumulative displacement tends to decline along the Altyn fault zone eastward. The cumulative dislocations are roughly the same in the same fault segment, which may indicate the consistency of seismic ruptures within the segment. In addition, the dislocation amount of the same-level terrace scarp between adjacent fault segments shows a stepwise decrease, indicating the tectonic transformation relationship of the miter fault and the possible seismic rupture segmentation, which provides a basis for the active segmental research and potential earthquake-generating capacity evaluation of the Altyn fault zone. A horizontal dislocation of 2-3m occurred on the front scarp of the T1 terrace in the Gaoyangou area, indicating that the latest earthquake surface dislocation event may have occurred in the Hongliugou-Shaping section at the easternmost end of the Altyn Tagh fault zone.

Key words: Altyn Tagh Fault, High-Resolution Terrain Data, Cumulative displacement, Dislocation land form, Construction conversion