Present-Day Strike-Slip Faulting and Thrusting of the Kepingtage Fold-and-Thrust Belt in Southern Tianshan: Constraints From GPS Observations

Abstract

Across inherited complex fold-and-thrust belts (FTBs), shortening may be accommodated at different rates depending on structural style variations; such cases have rarely been documented We present the example of the Kepingtage FTB in southern Tianshan, which is bisected by the NNW-trending left-lateral strike-slip Piqiang Fault (PQF) into eastern and western segments. The 1.45 ± 0.31–2.10 ± 0.42 mm/a shortening rate of the eastern segment is accommodated in a diffuse-deformation pattern within the five-row thrust-anticlinal zone and the 2.36 ± 0.23–3.70 ± 0.59 mm/a shortening rate of the western segment is accommodated within the two-row thrust-anticlinal zone at the FTB front. To accommodate the latitudinal variability, the PQF exhibits a 2.30 ± 0.20–4.10 ± 0.40 mm/a segmentation strike-slip rate. The 2.35 ± 0.33–4.20 ± 0.45 mm/a shortening rate of the Kepingtage FTB and southern Tianshan Fault is one-third of the total convergence rate between the Tarim Basin and Kazakh Platform at 77°–79°E; hence, the complex Tianshan deformation occurred mainly at the FTB.

Key Points

• GPS data from 73 stations in the Kepingtage fold-and-thrust belt (FTB) and adjacent areas reveal the current Kepingtage Block crustal-movement velocity field

• Shortening rate of Kepingtage FTB and adjacent areas is ∼1/3 of the total convergence rate between the Tarim Basin and Kazakh Platform

• Shortening rates and deformation patterns vary due to the inherited evolution of the Kepingtage imbricate and pre-existing structures

Plain Language Summary

The Kepingtage fold-and-thrust belt (FTB) in southern Tianshan is a typical imbricated thrust structure divided into eastern and western segments by a NNW-trending left-lateral strike-slip fault (Piqiang Fault; PQF), which regulates inhomogeneous thrusting and shortening rates. The interaction between Kepingtage FTB shortening, PQF shear deformation, and rate accommodation within various thrust-anticlinal zones remain unclear. Investigating fault kinematics and strain distribution is essential for describing regional deformation images and understanding deformation patterns. Herein, we utilized latest GPS data from 73 stations in Kepingtage FTB and adjacent areas to obtain the current crustal-movement velocity field in the Kepingtage Block within the Eurasia reference framework. Deformation of the western segment occurs in front of Kepingtage FTB, and the shortening rate is accommodated in these structures. However, deformation and shortening rates of the east segment are diffused in the five-row thrust-anticlinal zone. The longitudinal variability can be attributed to inherited structures, wherein shortening is accommodated at different rates based on structure patterns. Our results confirm the deformation rate of active structures and effects of different faults on regional tectonic deformation. Moreover, deformation of the tectonically active foreland of Tianshan can be used as an analog for understanding the tectonic deformation of tectonically active mountain belts.

1 Introduction

Convergent orogenic belts occur through complex temporal and spatial deformation within the Earth's crust. Tectonic deformation is mainly manifested as crustal thickening, extension of mountain-range and development of foreland basins. The growth of orogenic belts influences the deformation rates in foreland basins, as the uplift and folding migrates from orogenic belts to the foreland (Butler et al., 2006; Lujan et al., 2003; Turner et al., 2010). Owing to the complex tectonic history and various tectonic styles of foreland basins, they are primarily manifested as folds, faults, or a combination of both (Allen et al., 1999; Heermance et al., 2008; Lü et al., 2021; McKnight, 1993; Yin et al., 1998). If the amount of shortening varies along strike, transition zones may be developed to accommodate this change in the form of strike-slip or tear faults (Turner et al., 2010). Additionally, structural-style variations may result from inherited tectonics (Iaffa et al., 2011). Depending on the structure style, shortening can be accommodated at different rates. However, some styles may be accommodated at a faster rate than others.

As a reactivated orogenic belt in the late Cenozoic, Tianshan is divided between basins and mountains by large-scale thrusts and fold-and-thrust belts (FTBs) to the north and south, and it accommodates the N–S convergence of crustal shortening and thickening (Figure 1; Avouac et al., 1993; Hendrix et al., 1994; Deng et al., 2000). The Kepingtage FTB in southern Tianshan is a typical imbricated thrust structure. The hanging wall of the thrust fault is composed of the Cambrian-Quaternary strata of thickness of 6–10 km and form significant topographic reliefs on the hanging walls (C. Jia et al., 2004; Zhang et al., 2019). The Kepingtage FTB has a total shortening rate of 4.0 ± 1.5 mm/a (Wang & Shen, 2020; Wu et al., 2019), as measured using GPS. Although the Kepingtage FTB is thrusting southward, the Piqiang Fault (PQF), a NNW-trending left-lateral strike-slip fault divides it into eastern and western segments. Asymmetric five- and three-row anticlinal belts exist in the eastern and western PQF sections, respectively (Allen et al., 1999; Li et al., 2013, 2020). Therefore, the PQF adjusted the deformation difference between the eastern and western segments. However, there is no effective quantitative constraint on how the thrusting of the Kepingtage FTB and the left-lateral strike-slip faulting of the PQF were coupled and how the rates were distributed.

Figure 1

(a) Topography, active structures, and earthquakes (M ≥ 5.0 during 1800–2020) in the Tianshan region. (b) GPS velocity field relative to Eurasia and major Cenozoic structures (after Tunner et al. (2010), Yao et al. (2021), and Lü et al. (2021), and our interpretations) in the Jiashi-Kepingtage and adjacent areas (location shown in Figure 1a). The P1–P11 blue dotted lines represent the GPS profile locations (see Supporting Information S1). BKFS: Bachu-Kepingtage fault system; KPT: Keping Thrust Fault; AZT: Aozigertawu Thrust Fault; KFT: Kekebuke Front Thrust Fault; PQF: Piqiang Fault; TAT: Tataiertagh Thrust Fault; YMT: Yimugantawu Thrust Fault; AYT: Aoyibulake Thrust Fault; PFT: Piqiangshan Front Thrust Fault; SLF: Selibuya Fault; BCF: Bachu Fault; SCF: Sanchakou Fault; DBF: Dabantagh Fault; YJF: Yijianfang Fault.

The crustal deformation velocity field is essential for depicting regional deformation patterns (Wang & Shen, 2020; A. Zubovich et al., 2016). In this study, we utilized the latest GPS data to determine the geodetic deformation rates and evaluate the fault kinematics, deformation patterns, and strain distribution in the Kepingtage FTB and adjacent areas. Our results confirm the distribution of active deformation and clarify how thrusting and strike-slip faulting accommodate the strain at the Kepingtage FTB.

2 Regionally Active Tectonic Framework

Tianshan in Central Asia is one of the youngest intracontinental orogenic belts worldwide, extending for >2,000 km from east to west. Since the Cenozoic, Tianshan has experienced significant crustal shortening of 100–200 km and thickening of 10–20 km as a result of the collision between the Indian and Eurasian plates (Avouac et al., 1993). From the late Cenozoic to the present, Tianshan has been dominated by N–S compressional tectonic deformation and a series of E–W-oriented thrust-fold belts in the foreland basins (Bullen et al., 2001; Deng et al., 2000; Tapponnier & Molnar, 1979). The Kepingtage FTB, located at the southwestern front of Tianshan, exhibits significant seismic moment release (Figure 1a). There were a series of strong earthquake events with Ms > 6.0 in 1997–2020 (i.e., 1997–1998 Jiashi earthquake swarm, 2003 Jiashi Mw 6.3, 2020 Jiashi Mw 6.0; Gao et al., 1997; Sloan et al., 2011; Yao et al., 2021).

The Kepingtage FTB formed as a result of the foreland-ward encroachment of Tianshan, has 5–7 E- to NE-trending thrust structures exposed at the surface (Figure 1b). The north and south boundary faults of Kepingtage FTB are the South Tianshan Fault (STF) and Keping Thrust Fault (KPT), respectively (Figure 1b); STF is the root fault between southern Tianshan and the Tarim Basin. The Kepingtage FTB is bisected by the PQF. The PQF is an NNW-trending 70-km long surface-exposed fault. Based on seismic reflection profile data combined with displacement or buckling deformation at the bottom of the sedimentary sequence, PQF is a steeply dipping basement fault (Tuner et al., 2011). Geological results indicate that there are different shortening rates in the western and eastern segments (2.5–2.7 and ∼0.3 mm/a, respectively, Li et al., 2013, 2020). The decrease in shortening rates is not gradual, but rather a sharp decrease from west to east at the PQF. Seismic-profile and surface-geology studies have shown that the faults in the Kepingtage FTB are listric, and are nearly EW-trending and stepdown-gentle; they merge with the basement detachment of the Cambrian at a depth of 6–10 km (Allen et al., 1999; Yao et al., 2021; Yin et al., 1998).

The Bachu–Kepintage fault system (BKFS) includes the Bachu fault system (SSE-trending transformations or strike-slip tear faults) in the Tarim Basin and a NNW- trending strike-slip fault or tear fault in the Kepintage FTB, which is perpendicular or oblique to the Kepintage FTB (Figure 1b, Tunner et al., 2010; Lü et al., 2021).

3 GPS Velocity Field and Deformation Pattern

3.1 GPS Velocity Field and Data Processing

Our GPS data set for the Kepingtage FTB includes data from 1998 to 2020, acquired from a variety of GPS instrument types. Our GPS network consisted of 73 GPS stations across the entire Kepingtage FTB (Table S1). We have described the data processing method of GPS data set in Supporting Information S1. The GPS velocity field shows a tendency to move northward, which essentially depicts a constant motion with respect to Eurasia (Figure 1b). Owing to the lack of active faults and strong earthquakes, the Tarim Basin can be considered a tectonically stable craton. GPS stations in the basin move northward at 17–18 mm/a (Figures 1b and 2). However, northward across the Kepingtage FTB, the GPS rates decrease to 12–13 mm/a (Figure 2a; Wang & Shen, 2020; Yang et al., 2008; A. V. Zubovich et al., 2010). To quantify the deformation rate and strain distribution of the Kepingtage FTB, we constructed 11 GPS velocity profiles, six perpendicular (NEE-trending) and five parallel (NNW-trending) to the PQF orientation (Figure 1b). All GPS velocities of each profile were projected onto the NW17° component parallel to the PQF (Figures 2 and 3). The GPS velocity profiles were spaced at 20–30 km (for the locations and widths see Supporting Information S1). The weighted least squares method was used to estimate the differential slip rate across faults for all GPS velocity profiles.

Figure 2

NEE-trending velocity profiles perpendicular to the Piqiang Fault (PQF). All GPS velocity data in the profile are projected to the NE17° component parallel to PQF. GPS velocities are indicated by violet dots with one-sigma formal error bars. Dark blue lines are the best fit lines of the velocity data. Light blue strips denote acceptable ranges of average velocity components. Topographic profiles (topographic data from the 30-m shuttle radar topography mission (SRTM) DEM, downloaded from the geospatial data cloud) are in the same location and width as the GPS velocity profiles.

Figure 3

NNW-trending velocity profiles parallel to the Piqiang Fault (PQF). All GPS velocity data in the profile are projected to the NE17° component parallel to PQF. GPS velocities are indicated by violet diamonds. Dark blue line is the best fit line of velocity data. Light blue strips denote acceptable ranges of average velocity components. Topographic profiles (topographic data from the 30-m shuttle radar topography mission (SRTM) DEM, downloaded from the geospatial data cloud) are in the same location and width as the GPS velocity profiles. The geometry of the fault is according to Allen et al. (1999) and Lü et al. (2021).

3.2 NEE Velocity Profiles Perpendicular to the PQF

NEE-trending profiles (P1–P6) were used to detect differential motion along the PQF. We constructed velocity profiles from the Kashi FTB to the eastern margin of the Kepingtage FTB (Figures 1b and 2). The GPS measurements of the b–e profiles reveal a significant velocity gap between the eastern and western PQF segments, with the velocity at the western segment being generally less than that at the eastern segment. Longitudinally, the rate of the PQF gradually decreases from 4.10 ± 0.40 to 2.30 ± 0.20 mm/a from north to south, reaching 0.57 ± 0.22 mm/a in the basin (Figure 2). We noted that the velocity decline is stepwise and not uniform; this may be because the PQF is a left-lateral strike-slip fault that regulates the shortening of differential thrusting in the Kepingtage FTB. The off-fault deformation of the PQF is shown in Figure 2 (Dolan & Haravitch, 2014; Gold et al., 2021; Milliner et al., 2015). The distribution of deformation was asymmetrical along the fault, with 10–20 and 30–50 km widths on the east and west sides of the fault, respectively (Figures 2b–2d). This indicates that the 2.30 ± 0.20–4.10 ± 0.40 mm/a left-lateral strike-slip rate is not entirely accommodated by the PQF but is diffused within 40–70 km width.

The NEE-trending profiles also reveal a velocity gradient between the Kepingtage and Kashi FTBs (Figure 2). At their contact position (77°E), the velocity gradient is 1.80 ± 0.23–3.30 ± 0.34 mm/a (Figures 2b–2e); however, the velocity gradient decreases to ∼0.48 mm/a in the Tarim Basin, which is within the error range of the GPS measurements (Figure 2f), indicating that there may be no measurable velocity gradient between the Kepingtage and Kashi FTBs in the basin. This can be explained by considering the Tarim Basin as a tectonically stable craton with a constant northward movement rate, and the Kepingtage and Kashi FTBs as two separate tectonic systems being independently pushed southward. Furthermore, the internal geometries and kinematic characteristics of the two FTBs are different, resulting in different velocity gradients at different latitudes (Figure 2).

3.3 NNW Velocity Profiles Parallel to the PQF

We constructed five velocity profiles (P7–P11) to investigate deformations across the Kepingtage FTB and southern Tianshan. The movement and shortening rates of the Tarim Basin, Kepingtage FTB, and STF are evident in the profiles (Figure 3). The GPS velocity vectors in the Tarim Basin were 15–18 mm/a and moved in the N3–10°E direction. The faults in the Tarim Basin are considered as locked or inactive, whereas the northward displacement is accommodated by the FTB and active structures in front of and inside Tianshan (Avouac et al., 1993; Deng et al., 2000; Tapponnier & Molnar, 1979; Yin et al., 1998). However, P7 reveals that the left-lateral strike-slip rates of the DBF and YJF are 1.10 ± 0.30 and 0.90 ± 0.26 mm/a, respectively (Figure 3a). These faults are considered to have been inactive since the Late Pleistocene and belong to the Quaternary (C. Z. Jia, 1997; Lü et al., 2021; Qu et al., 2003; Xiao et al., 2002).

The GPS velocity was bound by the PQF in the Kepingtage FTB, whereas the two segments exhibited different motion characteristics. In the eastern segment, the KPT is the most active forward-thrust fault-anticline zone, thereby accommodating most of the shortening rate. The maximum shortening rate is 2.10 ± 0.42 mm/a (P8), whereas it is reduced at the sides to 1.45 ± 0.31 and 1.62 ± 0.32 mm/a (P7 and P9, respectively; Figures 3a–3c). The segmented activity of the KPT can be explained by the fault being divided into multiple segments under the influence of a BKFS tear fault. Although the KPT as a whole pushes southward, these NS-trending strike-slip faults modulate the KPT shortening rate with different left-lateral strike-slip rates, thereby resulting in a segmented shortening rate along the fault (Figure 3a). However, there is no significant velocity gradient with the four anticline rows north of the KPT, which indicate that these anticlines are currently inactive or active at a lower rate (Figures 3a–3c). In the western segment of the Kepingtage FTB, the 2.10 ± 0.26, 1.1 ± 0.46, and 0.5 ± 0.26 mm/a shortening rates of the KPT, AZT, and KFT, respectively, can be identified in P10 (Figure 3d). The shortening rates of the KPT and AZT in P11 were 1.76 ± 0.13 and 0.60 ± 0.19 mm/a, respectively (Figure 3e). Although all three anticline rows push southward, the KPT and AZT at the foreland are more active and accommodate most of the shortening rate. The shortening rates of these anticlines gradually decrease westward; this is consistent with the geometry of the Kepingtage FTB westward dipping (Figure 1b). We note that although the KPT, being the main thrust-fault anticline, accommodates most of the shortening rate, the remaining shortening rate is diffused in the other four thrust-anticline rows of width 70 km in the eastern segment. In contrast, the western segment, with the KPT and AZT as the main active structures, accommodates almost the entire shortening rate. Overall, the shortening rates of the eastern and western segments of the Kepingtage FTB are 1.45–2.10 and 2.36–3.70 mm/a, respectively. This is consistent with the findings of a previous study (Li et al., 2020), which showed that the geological shortening rate of the western segment is higher than that of the eastern segment.

The STF is a Holocene active fault and the boundary fault between southern Tianshan and the Tarim Basin (Figure 1a; Wu et al., 2019). The GPS velocity profile shows that the STF also accommodates a part of the southward pushing shortening rate of Tianshan. Wu et al. (2019) concluded that the Late Quaternary geological shortening rate of the STF (i.e., Maidan Fault) was 1.19 ± 0.25 mm/a; the geodetic shortening rate in this region was 1.15 ± 0.12–2.10 ± 0.15 mm/a, and therefore highly consistent. The geodetic shortening rate of the STF gradually decreased westward to 0.20 ± 0.14–0.30 ± 0.11 mm/a (Figures 3d and 3e), and the fault was characterized by westward dipping (Figure 1b).

The finding that the shortening rate of the western segment is higher than that of the eastern segment in the Kepingtage FTB does not account for the shortening rate accommodated by the southward thrusting of the STF. Overall, the shortening rates are accommodated by the Kepingtage FTB and STF, and the total shortening rates from east to west are 2.60 ± 0.33, 4.20 ± 0.44, 2.35 ± 0.33, 3.90 ± 0.6, and 2.66 ± 0.26 mm/a (Figure 3; P7–P11). Evidently, the total shortening rate of the eastern segment is greater; therefore, when the total shortening rate is longitudinally constant, the trade-off between the shortening rates of the Kepingtage FTB and STF along the strike reflects the latitudinal tectonic transformation.

3.4 Velocity Field of the Kepingtage FTB and Adjacent Areas

The 11 velocity profiles revealed the current geodetic rates of the Kepingtage FTB, STF, and adjacent areas; however, no further details were obtained from the EW- and NS-trending profiles. Therefore, we constructed a velocity-field contour map of the Kepingtage FTB and adjacent areas (Figure 4a; for the method, see Supporting Information S1).

Figure 4

(a) Velocity-field contour map of the Kepingtage fold-and-thrust belt (FTB) and adjacent regions. Red regions represent higher rates (i.e., Tarim Basin); blue regions represent lower rates (i.e., southern Tianshan). The direction of the GPS velocity data is normalized to NNW17° (i.e., parallel to the Piqiang Fault [PQF]). We identify the deformation rate (i.e., strike-slip and shortening) of the PQF, Keping Thrust Fault (KPT), and South Tianshan Fault (STF) along the strike by comparing the rate difference between the two walls of the fault. The violet dots, and orange and blue diamonds represent the geodetic rates of the PQF, STF, and KPT, respectively (data from profiles P1–P11). (b) Tectonic evolution model of the Kepingtage FTB and Bachu–Kepintage fault system (BKFS) revealing the inherited evolution of the Kepingtage FTB and pre-existing structures.

Under the force of collision between the Indian and Eurasian plates, the movement rates of the GPS stations in the Tarim Basin are 16–18 mm/a. The KPT, being the boundary between the Kepingtage FTB and Tarim Basin, accommodates most of the shortening rate (1.45 ± 0.31–3.70 ± 0.59 mm/a). The Kepingtage FTB exhibits segmental activity under the force of the BKFS strike-slip tear faults; among them, the most significant is the PQF, dividing the Kepingtage FTB into two segments, whereas the shortening rate of the western segment is considerably higher than that of the eastern segment. We found that the KPT and AZT in the western segment accommodate most of the shortening rate, with a distinct velocity gradient (from 16–18 to 12–13 mm/a) in the hinterland. In the eastern segment, the situation is completely different: There is a uniform velocity decrease instead of a velocity gradient among the four thrust-anticline rows north of the KPT. This indicates that the formations of these five thrust-anticline rows is closely related and interactive, and is also reflected in the out-of-sequence time series. Additionally, the STF is not only the boundary fault between southern Tianshan and Tarim Basins, but also a velocity step across the Kepingtage FTB and southern Tianshan (Figure 4a).

4 Discussion and Conclusion

The Indo-Eurasian collision since Cenozoic has resulted in continental crust compression and strong crustal shortening (Molnar & Tapponnier, 1975; Tapponnier et al., 1982). Currently, the Tarim Basin is being pushed northward at a rate of 20 ± 2 mm/a; however, across Tianshan, this rate of the Kazakh Platform is only 1–2 mm/a, indicating that a rate of nearly 20 mm/a is accommodated in the range front and interior structures of Tianshan (Wang & Shen, 2020; Yang et al., 2008; A. V. Zubovich et al., 2010). Nevertheless, it is not clear how these structures accommodate this rate. GPS measurements (from 73 stations) of the Kepingtage FTB and adjacent areas reveal that the shortening rates of the Kepingtage FTB and STF are 1.45–3.70 and 0.20–2.10 mm/a, respectively, which is nearly one-third of the total convergence rate between the Tarim Basin and Kazakh Platform at 77°–79°E. This also suggests that Kepingtage and other FTBs developed in front of southern Tianshan are the main structural systems that absorb the convergence rate.

The NNW-trending left-lateral strike-slip PQF developed in the interior of the Kepingtage FTB is different from other FTBs distributed on both sides of Tianshan. The PQF divides the Kepingtage FTB into eastern and western segments with different geometric and kinematic characteristics (Allen et al., 1999; Li et al., 2020; Lü et al., 2021; Qu et al., 2003). The evident differential movement may have been caused by the evolution of the pre-existing structure superposition in the region. The BKFS was formed in the Paleozoic, when strong thrusting occurred along the Tumuxiuk Fault (Figure 4b1; Tian, 2006). The rapid uplift of Pamir was caused by the northward extrusion of the Tarim Block during the Mesozoic. The Kepingtage-Bachu region is a frontal uplift, resulting in the absence of Mesozoic and Paleogene strata from the Kepingtage FTB (Figure 4b1). During the Paleogene, the convergence of the Indian and Eurasian plates resulted in the main tectonic deformation in this region. The SLF also formed during this period and faulted the Pre-Sinian to Paleogene-Neogene strata to form the complete BKFS (Figure 4b2). Since the Neogene, with the strong southward pushing of Tianshan, the strong imbricated thrust structure of the Kepingtage FTB was generated, and several NNW-trending pre-existing faults in the Kepingtage FTB and BKFS were reactivated. These faults were converted into tear faults with inhomogeneous thrusting, thereby regulating the displacement of the differential thrust in the foreland (Figure 4b3). The PQF is a major fault that transects Neogene strata and deformation, showing the abrupt change. Additionally, there is an ∼800 m net loss of Paleozoic sediment east of the PQF (Turner et al., 2010, 2011); hence, the PQF is a pre-existing fault that may have been reactivated before the Neogene (Del Angel, 2012). We observed that additional strike-slip faults or tear faults may be responsible for compartmentalization of the segment within the Kepingtage FTB. Although they do not form large strike-slip faults (such as the PQF) cutting through the Kepingtage FTB, they cut the KPT and regulate the shortening rate along the strike, for example, the YJF and DBF (Figure 4a).

Based on GPS measurements, the Kepingtage FTB accommodated a total shortening rate of 1.45–3.70 mm/a. This shortening rate is distributed across all structures, except the KPT at the southernmost end, which had a higher shortening rate of 1.45–2.10 mm/a. The formation thickness, pre-existing structures, and detachment depth may contribute to the variation in the residual shortening rate between the eastern and western segments of the Kepingtage FTB. The shortening rate of the eastern segment is diffused in the thrust-anticlinal zone 60 km north of the KPT (Figure 4a); the shortening rate of the western segment is accommodated by the AZT and has a significant velocity step (reduced to 11 mm/a) at its north side. Finally, the uneven latitudinal thrusting of the Kepingtage FTB is reflected longitudinally as the segmentation left-lateral strike-slip rate of the PQF (2.30 ± 0.20, 2.50 ± 0.27, 3.70 ± 0.33, and 4.10 ± 0.40 mm/a). The complex deformation style and variable shortening rate along the strike of the Kepingtage FTB are caused by the superposition of differential thrusting of imbricate and pre-existing structures. Additionally, because the structures of the western segment at the front of the Kepingtage FTB accommodate all the shortening rates, it is easier to accumulate stresses and release earthquakes there (e.g., the 1961 Mw 7.0, 1993 Mw 6.3, and 2020 Mw 6.0 earthquakes) than at the eastern segment (Figure 1a). Therefore, the seismic risk of the Kepingtage FTB should be evaluated separately for the eastern and western segments.

Acknowledgments

This study was supported by the National Natural Science Foundation of China (42102275, 41874015, 41731071), Science for Earthquake Resilience of China Earthquake Administration (XH20067), Key R&D Program of Xinjiang Uygur Autonomous Region (2020B03006-1, 2), Natural Science Foundation of Xinjiang Uygur Autonomous Region (2022D01B44), and Special Projects for Basic Research Work of the Institute of Geology, China Earthquake Administration (IGCEA1810). The authors would also like to thank Dr. T. Li for fruitful discussions. The authors acknowledge critical and thorough review of the manuscript by two anonymous reviewers and Editor L. Flesch to improve the original version.

Conflict of Interest

The authors declare no conflicts of interest relevant to this study.

Open Research

Data Availability Statement

The GPS velocities of the Kepingtage fold-and-thrust belt data are stored in Zenodo and can be accessed online (https://doi.org/10.5281/zenodo.6424658).