The M_S 6.9 Menyuan earthquake on January 8, 2022 occurred in the Qilian Mountain fault block in the northeastern margin of the Tibetan Plateau. The instrumental epicenter is located in the Lenglongling fault zone in the west section of the Haiyuan active fault system. It is another strong earthquake with M>6.5 that occurred in the fault system after the Haiyuan M 8.5 earthquake in 1920. The preliminary conclusion of the investigation results shows that the Menyuan earthquake generated two main fracture zones in the south and north separately, which are distributed in left-step oblique arrangement with a total length of nearly 23 km, and there is a surface rupture cavity with a length of about 3.2 km and a width of nearly 2 km between them. The south branch rupture (F₁) appears in the east section of the Tuolaishan fault, striking 91°, with a length of about 2.4 km. It is mainly characterized by southward thrust and sinistral strike slip, with a maximum horizontal displacement of nearly 0.4 m. The north branch main rupture (F₂) appears in the west section of the Lenglongling fault, with a total length of nearly 20 km. It is mainly sinistral strike-slip deformation, and presents an overall slightly convex arc distribution to the northeast, including the west, middle and east sections of 102°, 109° and 118°, respectively. The maximum strike-slip displacement occurs in the middle section, which is 3.0±0.2 m. In addition, a new north branch secondary fault (F₃) with a cumulative length of about 7.6 km, dominated by normal-dextral fault, is discovered on the north side of the middle to east section of the main fault of the north branch, with a cumulative maximum horizontal displacement of about 0.8 m and a maximum normal vertical displacement of about 1.5 m. Comprehensively, the whole coseismic rupture is mainly sinistral strike-slip and has the characteristics of bilateral rupture, whereas the macroscopic epicenter is located in the north branch of midway through the main fracture zone, thus the strike-slip displacement of the surface may be associated with the shallow rupture of the source. The normal-dextral rupture is likely to be caused by the differential movement of the north block dragged by the active south plate. The south Qilian block was extruded eastward along the Haiyuan sinistral strike-slip fault system due to the strong collision and compression between the Indian and Eurasian plates, which led to the simultaneous rupture of the Tuolaishan fault and the Lenglongling fault. This is the main dynamic mechanism leading to the strong earthquake. Under the background of continental dynamics, further attention should be paid to the future strong earthquake risk of the Qilian Mountain fault block and its surrounding area with the Haiyuan sinistral strike-slip fault system as the main boundary.

The thrust directions in foreland thrust belts have not been explained on theory. Based on Coulomb fracture criterion and deformation asymmetry in foreland thrust belt, the origins of fore-thrust and back-thrust faults are analyzed in this paper. Two potential conjugate fractures would occur in initial deformation stage, and the fracture requiring less applied forces might develop into thrust fault under the quasi-static equilibrium caused by deformation asymmetry in foreland thrust belts. The applied forces needed to create fault movements include the frictions along both the detachment surface and the fault surface. The fore-thrust faults will occur in most deformations in foreland thrust belts. However, where either the principal stress axes tilt toward foreland or the intersections point of the two conjugate fractures are on the detachment surface, the back-thrust faults will be preferable to occur. The applied force, the frictions along the detachment surface and the geometries of the slipping terranes will determine the principal stress axes. The findings will help to explain the selectivity of the fault dips in both contractional and extensional deformation areas.

The complex terrain and marked anisotropy of regional tectonic stress field in western China make the crustal stress state an important assessment parameter. Understanding the regional crustal stress state lays the foundation for assessing the layout at the tunnel design stage and predicting rockburst, fault slip and other engineering disasters in the tunnel construction process. This study aims to explore the current in-situ stress state of the super-long highway tunnels in southern Shaanxi. We did hydraulic fracturing in-situ stress measurement of the Boreholes ZK10 and ZK11 in the Guxiandong tunnel and the Hualongshan tunnel, respectively, and thus characterized the current in-situ stress distribution of the two tunnels. The measurement results show that: The S_H values at the maximum buried depths of the Guxiandong and Hualongshan super-long deep tunnels are 13 MPa and 22 MPa, respectively. The stress relations of the Guxiandong and Hualongshan tunnels are S_H>S_h>S_v and S_H>S_v>S_h, respectively, and horizontal principal stress plays a leading role. The S_H direction is NW-NWW, which is basically consistent with the direction of the maximum principal stress in the basic database of crustal stress environment in mainland China. Three conclusions were drawn from the results of in-situ stress measurement in combination with related theories and assessment criteria. Firstly, the angle between the direction of maximum horizontal principal stress and tunnel axis is beneficial to the stability of tunnel surrounding rocks. The overall layout of the two tunnels is reasonable. Secondly, rock burst with moderate strength or above will not occur in the two tunnels according to a comprehensive study using the rock strength-stress ratio method, Tao Zhenyu criterion, Russenes criterion and rock stress-strength ratio method. Thirdly we used Mohr-Coulomb criterion and Bayer's law, let the friction coefficient μ have the value between 0.6~1.0, and then we analyzed the present stress state of the two tunnels. It is found that the stress of the fault zone near the two tunnels did not reach the critical condition of sliding instability of shallow faults in the crust, while it is in a stable stress state.

The Ounan depression is a favorable structural unit for the Carboniferous hydrocarbon migration and accumulation, which demonstrates certain exploration potential. However, the organic matter enrichment mechanism is still unclear, which results in the absence of effective guidance for predicting the distribution of high-quality source rocks and restricts the process of oil and gas exploration. Based on geochemical analysis and XRD, SEM and other tests, the main factors influencing the enrichment of organic matters in Carboniferous source rocks have been identified through a comprehensive investigation into the aspects such as mineral composition, organic matter abundance, kerogen type, thermal evolution degree, formation environment, and the relationship between TOC and primary minerals. The results reveal that shales and carbonate source rocks have been developed in the Carboniferous, a large quantity at poor-medium level and a few at good or above level. They were deposited in the environment of intercontinental shelf with saline-water, arid-hot climate and weak oxidation and reduction. The dispersed organic matters are composed of mixed marine and terrestrial origins, which are overall in a "maturity-high maturity stage". The Carboniferous clastic source rocks are mainly residual type Ⅲ kerogen, but the extracted chloroform bitumen "A" is mainly derived from type Ⅱ kerogen.TOC values increase with the growing of quartz minerals because the high-abundance source rocks are rich in siliceous biological fossils. The SiO₂ in the high-SiO₂ source rocks has been identified as biogenic, suggesting that the participation of siliceous organisms in the Carboniferous cause the enrichment of marine organic matters and greatly improve the primary productivity of the sediments. This study provide the basis for predicting the distribution of Carboniferous high-quality source rocks and the deployment of oil and gas resources in the study area.

Active geological disasters induced by earthquakes, rainfalls and human engineering activities occur frequently in the Loess Plateau. However, there is a lack of systematic understanding of the development and distribution of active geological disasters in the Loess Plateau due to the wide area, active structure, diverse landforms and great difference in loess characteristics. InSAR technology can observe surface deformation in a wide range. Based on 40 sentinal-1 SAR data from January 1, 2019 to March 31, 2020, a total of 3286 active geological disasters in the Loess Plateau of 624, 600 km² were interpreted by InSAR, including 1135 landslides, 1691 mining collapses, 368 subsidences and 92 landfills. Combined with geomorphological and optical image characteristics, four types of active geological hazards were interpreted, which reveals that they are mainly distributed in eight regions, including four landslide areas, three mining collapse areas and one subsidence area. The spatial distribution of active landslides is obviously regional and clustered, concentrating in the middle and west of China; while that of mining collapse and land subsidence densely developed in groups in the middle and west of China. There is a relationship between landslide development density and topography. The development of these geological disasters has an obvious spatio-temporal regularity. Regionally, the development intensity of geological disasters is controlled by topography and mineral resources; and in terms of scale, disasters identified by InSAR are all above medium size, which is different from traditional statistical methods. InSAR identification results objectively reflect the distribution of geological disasters in the Loess Plateau, and deepened our understanding on that as well. InSAR technique, meanwhile, can effectively detect the surface damage induced by underground coal mining, including its distribution, scope, strength, and monitor the depth and scope of opencast coal mine, and then infer the intensity of coal production activities.