Oblique Right‐Lateral Faulting Along the Northern Margin of the Ili Basin in the Northern Tian Shan, Northwest China

Abstract

The quantification of the geometry and kinematics of the boundary faults of an active orogenic belt is key to exploring its deformation pattern. The Kashihe fault (KSHF), which bounds the northern margin of the Ili Basin and is more than 400 km long, is a WNW-striking fault in the northern Tian Shan. Although the KSHF displays active faulting and is the seismogenic fault of the 1812 Ms 8 Nilka earthquake, the quantitative slip rate and its role in regional strain accommodation have not been reported. Here, we quantify the late Quaternary activity of the KSHF based on high-resolution remote sensing image interpretations and detailed field investigations. Six field observation sites along a~270 km active fault in the Chinese Tian Shan indicate that the KSHF is characterized by dextral strike-slip faulting and N-S thrusting. Based on the surveying of offset geomorphic surfaces with an unmanned drone and the dating of late Quaternary sediments using optically stimulated luminescence (OSL) and radiocarbon methods, we estimated a late Quaternary right-lateral strike-slip rate across the fault of 2.39 ± 0.55 mm/yr and a shortening rate of 0.62 ± 0.30 mm/yr. Analysis of field investigations and fault section exposing indicated that a young paleoearthquake event occurred on the western segment of the KSHF. Active tectonics around the Ili Basin imply that the rigid Ili block extrudes westward along its boundary strike-slip faults and rotates counterclockwise. We propose that this block rotation driven by dextral faulting accommodates regional N-S convergence and sinistral shearing.

Opposite Sense of Strike‐Slip Faulting and Crustal Rotation Accommodating Left‐Lateral Shear Between the Tianshan Mountains and Kazakh Platform

“…The KSHF and DAF have right-lateral slip rates of 0.7 ± 0.2 mm/yr and 1.0 ± 0.3 mm/yr, respectively (Figure 3), which are obviously less than the total slip rate of ∼4.0 mm/yr inferred from geological studies (Campbell et al, 2013;Wu et al, 2020). An explanation for this difference may be the counterclockwise rotation (Platt & Becker, 2013) of the Ili Basin and Koguqin Range.…”

“…GPS velocity components parallel to profiles B and C depict a continuous velocity gradient (Figure 3), suggesting westward extrusion of the Koguqin Range and rigid Ili block at a rate of ∼1 – 2 mm/yr and obvious E‐W extension deformation in the block interior (Zubovich et al., 2010). The westward extrusion caused by right‐lateral faulting of the DAF and KSHF seems to transform into crustal shortening and range uplift in the Alatau region (Wu et al., 2020). The decrease in the right‐lateral slip rate on the DAF across the ENE‐trending Alatua Range (Shen et al., 2003) attests to this possible slip transfer.…”

“…The decrease in the right‐lateral slip rate on the DAF across the ENE‐trending Alatua Range (Shen et al., 2003) attests to this possible slip transfer. In addition, coseismic surface ruptures generated by the 1,812 Ms 8 Nilka earthquake and 1,944 Ms 7.3 Wusu earthquake on the NW‐striking structures were mainly dominated by right‐lateral slip faulting (Shen et al., 2003; Wu et al., 2020). In contrast, focal mechanisms of several instrumental earthquakes with moderate magnitude in the Alatau region display thrust/reverse faulting (Grützner et al., 2019), which further verifies this deformation pattern.…”

East Tacheng (Qoqek) Fault Zone: Late Quaternary Tectonics and Slip Rate of a Left‐Lateral Strike‐Slip Fault Zone North of the Tian Shan

“…Another two active faults oriented NW northwest of the Tacheng Basin were mapped as right‐lateral strike‐slip faults (Campbell et al., 2015), which are poorly studied. South of the Junggar fault, a fault along the northern margin of the Ili Basin (NIF) strikes WNW‐ESE and has an apparently right‐lateral strike‐slip component (Figure S12) (Wu et al., 2020). Further south and west, long NW‐SE trending right‐lateral strike‐slip faults also stand out on the satellite imagery, such as the Talas‐Ferghana (TF) and Dzhalair‐Naiman (DNF) faults (Tapponnier & Molnar, 1979) (Figure 1a).…”

A Shallow and Left‐Lateral Rupture Event of the 2021 Mw 5.3 Baicheng Earthquake: Implications for the Diffuse Deformation of Southern Tianshan

“…However, since 1947, the mountain has been relatively free from the effects of strong earthquakes, and only one M ≥ 7.0 event (1992 Mw 7.2 Suusamyr event) was recorded. Among these earthquakes, apart from the 1812 Nileke (M 8.0), 1885 Belovodskoe (M 6.9), 1889 Chilik, and 1911 Chon Kemin events that produced spectacular surface ruptures (Abdrakhmatov et al., 2016; Arrowsmith et al., 2016; Wu et al., 2020), all other earthquakes produced only limited or no surface ruptures.…”