1. The Bend on the Haiyuan Strike‐Slip Fault Leads to Segmented Activity of the Minle‐Damaying Thrust Fault in the Qilian Shan, the Northeastern Tibetan Plateau.
- Author
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Liu, Qingri, Xiong, Jianguo, Zhang, Peizhen, Tao, Wei, Huang, Luyuan, Yang, Xuhang, Zhang, Yihui, Huang, Feipeng, Zhang, Xiuli, Zhang, Huiping, Li, Chuanyou, and Li, Youli
- Subjects
THRUST faults (Geology) ,PLATE tectonics ,DEFORMATIONS (Mechanics) ,STRAINS & stresses (Mechanics) - Abstract
The present tectonic regime of the Qilian Shan is dominated by large northeast and northwest striking strike‐slip faults and northwest striking thrust faults. Deformation distribution between the subparallel Haiyuan Strike‐slip Fault and the Minle‐Damaying Thrust Fault (MDF) is crucial for understanding the orogenic mechanism of the northeastern Tibetan Plateau. However, the uncertain kinematics of the MDF and the stress variation along the strike‐varying Haiyuan Fault inhibit further discussion of their relationship. Five key sites along the MDF were selected for analysis of terrace abandonment ages and vertical offsets to determine the slip rates. Two finite element models were constructed to calculate the stress‐strain relationship between the Haiyuan Fault and MDF. We find that the activity of the MDF can be divided into two segments by a stepover with less activity and lower terrain at the Xida River site. Shortening rates of the MDF vary between 0.2 and 2.4 mm/a since the late Pleistocene with trapezoidal trends on both fault segments. The two finite element models and GPS data reveal that the strain rates are lower at the Xida River site but higher at the Menyuan Bend on the Haiyuan Fault. We infer that long‐term strain accumulation at the Menyuan Bend may have mitigated the tectonic activity northeast to the bend under the northeastward stress field, including the activity of the MDF at the Xida River site, and resulted in the segmentation of the MDF. Plain Language Summary: The Haiyuan strike‐slip fault and the Minle‐Damaying thrust fault (MDF) are two important parallel faults that help us understand the growth of the Qilian Shan. The influence of multiple bends of the Haiyuan fault on the activities of its adjacent faults has not been clearly studied. Therefore, we investigated in detail the terraces of five rivers that were offset by the MDF, and determined the spatial variation of the MDF activity rates based on the vertical separations and abandonment ages of the terraces. We also established two finite element models showing the deformation distribution between the Haiyuan Fault and MDF on the upper crustal and crustal scales, respectively. We have found that the Menyuan Bend of the Haiyuan Fault absorbs a significant amount of shortening deformation under the regional northeastward stress field and probably causes the very low activity rate of the MDF at the Xida River site in the northeast of the bend, in contrast to the obvious higher activity rates on both sides of the site, indicating that the activity of the MDF is segmented at the Xida River. The relationship and seismic risk between the two faults are worthy of continuous attention. Key Points: The slip rates of the Minle‐Damaying Thrust Fault (MDF) show its segmentation at stepover near the Xida River with trapezoidal variation trends on both segmentsThe strain rate is lower at the Xida River site but higher at the Menyuan Bend on the Haiyuan FaultStrain accumulation at the Menyuan Bend has reduced the activity of the MDF at the Xida River site [ABSTRACT FROM AUTHOR]
- Published
- 2024
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