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.

Strain Accommodation and Seismic Hazards of the Kalpin Fold‐And‐Thrust Belt, Southwestern Tian Shan Foreland, China: Insights From the 2020 Mw 6.0 Kalpin Earthquake

“…Although these two tracks have different viewing geometry, we believe this is mainly because the short time span (∼8 months) of descending stack had loosely constrained the interseismic deformation estimation. As the interseismic deformation is at the level of 2–4 mm/yr (J. Li et al., 2022), we considered the short time baseline results in an unstable estimates of $$\alpha {V}_{0}$$.…”

“…The Kalpin fold extends along the southernmost KFTB, has hosted three large earthquakes in the instrumental era: the 1977 M w 5.8, 2011 M w 5.6, and 2020 M w 6.0 Kalpin earthquakes (Figure 1b). The underlying fault, the Kalpin thrust fault, has created a series of topographic scarps that reveal a late Quaternary geological slip rate of 2–3 mm/yr (A. Li et al., 2020) and a geodetic slip rate of 1.8–2.1 mm/yr (J. Li et al., 2022). The Kalpin thrust fault has an approximately listric geometry in seismic reflection profiles, but some variation in dip occurs before flattening to the basal décollement horizon at ∼6–10 km depth (Allen et al., 1999; Yin et al., 1998; Figure 1c).…”

“…Recent GNSS measurements show that the shortening of the KFTB is primarily concentrated at the frontal structures (J. Li et al, 2022), implying: (a) an evolutionary process with deformation progressively migrating toward the Tarim Basin, and (b) inactive or strongly locked faults in the hinterland.…”

“…Li et al, 2020) and a geodetic slip rate of 1.8-2.1 mm/yr (J. Li et al, 2022). The Kalpin thrust fault has an approximately listric geometry in seismic reflection profiles, but some variation in dip occurs before flattening to the basal décollement horizon at ∼6-10 km depth (Allen et al, 1999;Yin et al, 1998; Figure 1c).…”

“…In this study, we investigated strain accommodation and seismic hazards of the Kalpin fold‐and‐thrust belt (KFTB) in the southwestern Tian Shan foreland. The KFTB, which accommodates almost one‐third of the total geodetic convergence rate between the Tarim Basin and Kazakh Platform at this longitude (J. Li et al., 2022), consists of three rows of splay faults rising from a weak décollement (Figure 1), underlain by faults widely distributed within the crystallized Tarim Basin basement (e.g., Allen et al., 1999; Lü et al., 2021; Turner et al., 2010). Since the 1902 M w 7.8 Artux earthquake (e.g., Kulikova & Krüger, 2017), which ruptured the fold‐thrust‐belt to the west of the KFTB, there has been a question as to whether the KFTB is capable of rupturing the weak décollement all the way to the surface through the splay faults along its southernmost margin, generating large earthquakes (Hubbard et al., 2015).…”