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.

During unexpected earthquake catastrophes, timely identification of damaged areas is critical for disaster management. On the 24 March 2021, Baicheng county was afflicted by a Mw 5.3 earthquake. The disaster resulted in three deaths and many human injuries. As an active remote sensing technology independent of light and weather, the increasingly accessible Synthetic Aperture Radar (SAR) is an attractive data for assessing building damage. This paper aims to use Sentinel-1A radar images to rapidly assess seismic damage in the early phases after the disaster. A simple and robust method is used to complete the task of surface displacement analysis and building disaster monitoring. In order to obtain the coseismic deformation field, differential interferometry, filtering and phase unwrapping are performed on images before and after the earthquake. In order to detect the damage area of buildings, the Interferometric Synthetic Aperture Radar (InSAR) and Polarimetric Synthetic Aperture Radar (PolSAR) techniques are used. A simple and fast method combining coherent change detection and polarimetric decomposition is proposed, and the complete workflow is introduced in detail. In our experiment, we compare the detection results with the ground survey data using an unmanned aerial vehicle (UAV) after the earthquake to verify the performance of the proposed method. The results indicate that the experiment can accurately obtain the coseismic deformation field and identify the damaged and undamaged areas of the buildings. The correct identification accuracy of collapsed and severely damaged areas is 86%, and that of slightly damaged and undamaged areas is 84%. Therefore, the proposed method is extremely effective in monitoring seismic-affected areas and immediately assessing post-earthquake building damage. It provides a considerable prospect for the application of SAR technology.

Low-porosity tight rocks are widely used as building and engineering materials. The freeze–thaw cycle is a common weathering effect that damages building materials in cold climates. Tight rocks are generally supposed to be highly frost-resistant; thus, studies on frost damage in tight sandstone are rare. In this study, we investigated the deterioration in mechanical properties and changes in P-wave velocity with freeze–thaw cycles in a tight sandstone. We also studied changes to its pore structure using nuclear magnetic resonance (NMR) technology. The results demonstrate that, with increasing freeze–thaw cycles, (1) the mechanical strength (uniaxial compressive, tensile, shear strengths) exhibits a similar decreasing trend, while (2) the P-wave velocity and total pore volume do not obviously increase or decrease. (3) Nanopores account for >70% of the pores in tight sandstone but do not change greatly with freeze–thaw cycles; however, the micropore volume has a continuously increasing trend that corresponds to the decay in mechanical properties. We calculated the pressure-dependent freezing points in pores of different diameters, finding that water in nanopores (diameter 5.9 nm control the evolution of frost damage in tight sandstone. We suggest that pore ice grows from larger pores into smaller ones, generating excess pressure that causes frost damage in micropores and then nanopores, which is manifested in the decrease in mechanical properties.

On 24 March 2021, an Mw 5.3 earthquake struck northwest Baicheng, located in the Kuqa fold‐and‐thrust belt (FTB), northwest China. In the current study, interferometric synthetic aperture radar (InSAR) data were used to investigate the associated fault rupture solution (dip, dip direction, and slip sense), to determine the geometry of the seismogenic structure; the high‐resolution images of the surface rupture were obtained using an unmanned aerial vehicle (UAV). This geometric model, along with the co‐seismic slip distribution from the InSAR data, and deformation characteristics of co‐seismic surface rupture revealed that: (a) it was a shallow event, the focal depth was 0.5–2 km, and the co‐seismic slip was distributed in the 0–7 km range with high dip angles (66°, 70°). (b) A 4‐km long surface rupture with obvious left‐lateral strike‐slip was distributed on the surface, and the maximum strike‐slip displacement and width were 0.79 and 0.7 m, respectively. This left‐lateral strike‐slip event indicates that the relative motion between the Tianshan and Tarim blocks is a continuous and diffuse deformation process. The study shows that, when evaluating the earthquake risk of the Kuqa FTB, we should consider both the front position of the fault outburst and the internal compressional salt‐related structures, which can also produce moderate to strong earthquakes.

The 2020 Jiashi Mw 6.0 earthquake occurred at the Kepingtage fold-and-thrust belt in the South Tianshan front, Northwestern China. The ground shaking caused extensive co-seismic deformation of the Xiker dam in the meizoseismal area. We obtained strata distribution characteristics of the dam foundation through drilling. Using laboratory andin situtests, the particle size distribution, standard penetration, and shear wave velocity of each layer were obtained. Along with peak ground acceleration, we evaluated the potential of sand liquefaction in various layers and proposed a relationship between dam fissures and sand liquefaction. Our results suggest that sand liquefaction occurred in the silty sand layer 0–3 m beneath the dam foundation. Sand liquefaction occurs behind the dam, resulting in uneven settlement of the dam foundation, making the horizontal deformation of the backslope of the dam significantly larger than the foreslope of the dam. Using numerical simulations, we found that sand liquefaction behind the dam can cause different horizontal deformation vectors (maximum deformation is ∼7.45 cm) in the dam foreslope and backslope, which cause the dam to rotate in the downstream direction. Large fissures also formed on the dam crest.