Late Pleistocene‐Holocene Slip Rate Along the Hasi Shan Restraining Bend of the Haiyuan Fault: Implication for Faulting Dynamics of a Complex Fault System

Abstract

The Haiyuan fault is a major left-lateral strike-slip fault at the boundary between northeast Tibet and the Gobi platform. Combining measurements of offset alluvial terraces with 10 Be-26 Al cosmogenic radionuclides dating, we bracket the late Quaternary slip rate along the Hasi Shan fault section (37°00′N, 104°25′E) of the Haiyuan fault. At our reference site, terrace-riser offsets for five successive terraces range from~5 to~200 m, and associated cosmogenic radionuclide ages range from 9 ± 3 to 44 ± 7 kyr. These measurements yield a geological slip rate between 2.7 and 3.0 mm/year. Extending the offset measurements to the entire Hasi Shan front, it yields a slip rate of 3.2 ± 0.2 mm/year over the last 50 kyr. Our rate is consistent with the lower estimates of other long-term rates of 4 to 5 mm/year, as well as with geodetic rates of 3 to 5 mm/year, determined in the same area. About 150 km farther west, however, Holocene terraces and moraines offsets have suggested higher slip rate values, between 6 and 15 mm/year. We interpret such discrepancy between rates determined along the western section of the Haiyuan fault and rates determined in the Hasi Shan section as being related to the complex geometry of the Haiyuan fault system along its eastern part, with several active strands moving at the same time and resulting in distributed slip among several sections of the fault system. Key Points: • Slip rate along the Hasi Shan section of the Haiyuan fault is determined from numerous offsets and cosmogenic exposure dates over a period of 50,000 years • The Hasi Shan fault strand horizontal slip rate is about 3.2 mm/year; this rate is stable over 50,000 years; the uplift rate is about 0.5 mm/year • Combining slip rate for the Hasi Shan strand and all subparallel stands yields a slip rate of 5 to 7 mm/year for the Haiyuan fault system Supporting Information: • Supporting Information S1

Post‐20 ka Earthquake Scarps Along NE‐Tibet's Qilian Shan Frontal Thrust: Multi‐Millennial Return, ∼Characteristic Co‐Seismic Slip, and Geological Rupture Control

“…To the east, westward changes in dextral rates southeast of the Qilian pushup remain uncertain. This is because the Gulang fault branches off the Lenglongling and Haiyuan Faults (e.g., Lasserre et al, 1999Lasserre et al, , 2002, while the latter includes parallel segments (e.g., Deng et al, 1986;Gaudemer et al, 1995;Li et al, 2017;Liu-Zeng et al, 2015;Matrau et al, 2019), and active strands of the former west of Menyuan are still poorly documented. Nevertheless, the fact that the large, parallel thrusts that underlie the Qilian Shan, Daxue Shan, Shulenan Shan, Danghenan Shan, and Tergun Daba Shan, contribute to transfer strike-slip rates from the Altyn Tagh to the Haiyuan Faults is beyond doubt (e.g., Daout et al, 2016;Gaudemer et al, 1995;Hetzel et al, 2004;Liu et al, 2021;Métivier et al, 1998;Meyer et al, 1998;Tapponnier et al, 1990;Xiong et al, 2017;Xu et al, 2010;Xu et al, 2021;Zheng, Zhang, He, et al, 2013) (Figure 22).…”

Late Pleistocene slip rate of the central Haiyuan fault constrained from optically stimulated luminescence, 14C, and cosmogenic isotope dating and high-resolution topography

“…Combining 10 Be CRN ages from surface and subsurface depth profiles in a set of terraces, Matrau et al (2019) constrained a minimum slip rate of 3.2 ± 0.2 mm/yr along one of the fault strands crossing the Hasi Shan restraining bend, within the western section of the 1920 Haiyuan earthquake rupture.…”

“…However, higher slip rates have been documented (Zhang et al, 1988a;Gaudemer et al, 1995;Lasserre et al, 1999Lasserre et al, , 2002, as well as lower ones (Yuan et al, 1998;Li et al, 2009;He et al, 2010;Jiang et al, 2017;Matrau et al, 2019). Because it has been suggested that the fault slip rate might vary over time, thus, it is valuable to find multiple slip-rate constraints at a single site to constrain possible temporal slip-rate variation (e.g., Sieh and Jahns, 1984;Van der Woerd et al, 1998.…”

Geomorphic expression of the Lenglong Ling area, eastern Qilian Shan, and its coupling relationship with the deep structures

“…According to the combined results, the Lenglong Ling Fault (F9), one of the most important parts of the Qilian-Haiyuan Fault, plays an important role in not only shaping regional topography, but also accommodating the tectonic deformation of the Tibetan Plateau relative to the Gobi-Ala Shan (Guo et al, 2017;Guo, Han, Mao, et al, 2019;Jiang et al, 2017). The renewed relative slow strike-slip rate (6.6 ± 0.3 mm/a) of the Lenglong Ling Fault (F9) (Guo et al, 2017), even the Qilian-Haiyuan Fault (Matrau et al, 2019;Yao et al, 2019), is much smaller than the slip rates of the Altyn Tagh Fault ( 10 mm/a) (Zhang, Molnar, & Xu, 2007) and the east Kunlun Fault ( 10 mm/a) (Kirby et al, 2007). Therefore, tectonic deformation transferred from the Altyn Tagh Fault and the east Kunlun Fault cannot be completely accommodated by the sinistral Lenglong Ling Fault (F9) (Duvall & Clark, 2010;Loveless & Meade, 2011).…”