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The Minshan Uplift Zone (MUZ) is located at the eastern margin of the Tibetan Plateau, which is the junction of three tectonic terranes. The observed discrepancy between a high uplifting and low shortening rate over the MUZ is attributed to the intrusion of a viscous lower crust. In the last 50 years, several significant earthquakes occurred at the boundaries of the MUZ, that is, the Huya and Mingjiang faults. On 8 August 2017, the Jiuzhaigou earthquake (Mw 6.5) occurred on the northern extension of the Huya fault. We adopt a joint inversion of the interferometric synthetic aperture radar and teleseismic body wave data to investigate the rupture process of this event. The obtained slip model is dominated by left‐lateral strike slips on a subvertical fault presenting significant shallow slip deficit. The rupture initiation is composed of both thrust and strike‐slip mechanisms producing a non‐double‐couple solution. We also resolve a secondary fault branch forming an obtuse angle with the main fault plane at its northern end. These phenomena indicate that the northern Huya fault is a young (less mature) fault system. Focal mechanisms of the regional earthquakes demonstrate that the northern and southern Huya faults present different combinations of strike‐slip and reversed motion. We attribute such discrepancy to the lateral extension of the viscous lower crust, which appears to extrude to the east beyond the northern Huya fault, in comparison with that confined under the MUZ near the southern Huya fault. This conceptual model is also supported by geomorphological and magnetotelluric observations.

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The Altyn Tagh fault (ATF) is a major intracontinental strike‐slip fault system that defines the northern margin of the Tibetan Plateau. The fault system loses its obvious surface expression north of the Qilian Shan fold‐and‐thrust belt, but may link eastward with multiple faults in the northern Hexi Corridor and southern Alxa block. To better understand the potential connectivity and displacement transfer between the ATF and the northern Hexi Corridor fault array, we carried out a multidisciplinary field and remote sensing‐based investigation of the actively deforming Heishan and Jinta'Nanshan region north of Jiayuguan City. We document Quaternary sinistral strike‐slip motion on the Heishan fault (HF) system and active sinistral transpression within a 70‐km‐long, E‐W deforming belt east of the Heishan, which is characterized by multiple left‐stepping, en‐échelon Quaternary folds and linking faults. Cosmogenic 10Be dating of displaced terrace surfaces yields a vertical slip rate of ∼0.2 mm/a for the northern Heishan thrust and a sinistral strike‐slip rate of 0.6 ± 0.2 mm/a for the HF. Within the uplifted core of the Heishan massif, the HF contains ductilely deformed Paleozoic basement lithologies with dextral‐sense shear fabrics that indicate that the modern HF has reactivated and inverted an older shear zone. A previously published magnetotelluric profile across the HF system suggests that it roots into a steep, deeply penetrating fault that is unlinked to the Qilian Shan thrust wedge. Instead, we suggest that the active sinistral deformation belt of the Heishan‐Jinta'Nanshan represents the eastward‐evolving, upper crustal expression of the modern ATF system.

We present a three‐dimensional electrical resistivity model of the crust and upper mantle beneath the easternmost Kunlun fault (EKLf), obtained by three‐dimensional inversion of magnetotelluric (MT) data. The crust of the Songpan‐Ganzi block is characterized by high resistivity from the surface to a depth of around 20 km, and by low resistivity in the mid‐lower crust in the depth range 20–40 km. The eastern edge of the high conductivity layer is coincident with the EKLf and the Huya fault. The electrical resistivity structure provides new insights into both (1) the generation of recent M > 6 earthquakes and (2) strain partitioning on this segment of the EKLf. Our model reveals that the Huya fault is the main branch of the EKLf in the region. Together with the EKLf, the Huya fault defines the boundary between the Songpan‐Ganzi and Bikou blocks. The mid‐lower crust of the Songpan‐Ganzi block in this region has a low resistivity that likely represents a mechanically weak layer. The 2017 Jiuzhaigou Ms7.0 earthquake and other recent M > 6 earthquakes may have been controlled by the change in viscosity in the mid‐lower crust that occurs across this boundary. The high conductivity may be acting as either (1) a channel of lower crustal flow, or (2) as a weak layer that decouples the upper and lower crust. The fact that the high conductivity layer does not extend along the north side of the Sichuan Basin questions the idea that crustal flow occurs in this area.

The basement gas reservoir in the Dongping field in the Qaidam Basin is a large reservoir that is different from other basement reservoirs around the world. The basement reservoir does not contain thick mudstone with abundant organic matter that acts as both a source rock and a caprock. The natural gas came from lateral Jurassic source rocks. The basement lithologies in wellblocks Dp3, Dp1, and Dp17 are granite, granitic gneiss, and limestone with slate, respectively, but they all provide effective reservoir space for gas accumulation. The average porosities are 3.3%, 5.2%, and 3.6%, respectively, and the average permeabilities are 0.66 mD, 0.60 mD, and 0.57 mD, respectively. Tectonic fractures are the main factor for improving the physical properties of the reservoir, and secondary solution space is the key factor for the high and stable gas production in the study area. The E 1 þ 2 Formation, which contains abundant anhydrite, unconformably overlies the basement rock. Some of the anhydrite was deposited as cement and filled the fractures and pores, which led to decreased porosity and to the formation of a tight caprock with a high breaking pressure for hydrocarbon accumulation. The caprock becomes thinner from the lowland to the uplift, and it is missing in wellblock Dp3, which led to the heterogeneous distribution of gas. Anhydrite-bearing caprock is the dominant factor that controls the gas accumulation in the basement rock reservoir in the Dongping field. Studying the spatial distribution of the anhydrite-bearing caprock is important to the exploration and development of basement gas

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We present evidence for the Late Quaternary activity of the Beihewan Fault (BHWF), along the southeastern margin of the Beishan block, western China. Field observations and analysis of UAV‐derived DEMs and Google Earth images reveal an ~10‐km‐long active fault trace in a region previously considered tectonically inactive. Offset landforms and trench exposures reveal that the fault is dominantly strike‐slip, with local thrust or normal displacements. Average rates of left‐lateral motion and thrusting since the Holocene are estimated to be ~2.69 and ~0.35 mm/a, respectively. The most recent surface‐rupturing event generated ~2.5 m of strike‐slip offset since 6.2–8.6 ka; with estimated M = 6.3–6.9. Modeling and two‐dimensional inversion of new magnetotelluric data indicate that the BHWF is a subvertical low‐resistivity zone that penetrates into the lower crust. Existing geological and geophysical evidence do not support subsurface linkage between the BHWF and Altyn Tagh–Jinta‐Nanshan Fault system further south in the Hexi Corridor. Close examination of high‐resolution satellite imagery west and east of the BHWF reveals other Quaternary surface fault scarps, pressure ridges, offset drainages, and truncated lithological strike belts. Collectively, these features constitute a previously unrecognized 150‐km‐long sinistral deforming belt along the southeastern Beishan and northern Hexi Corridor boundary that we call the Southeast Beishan Wrench Belt. Recognition of Quaternary activity along the BHWF within the larger Southeast Beishan Wrench Belt challenges long‐held assumptions that the Beishan region is a relatively stable and tectonically inactive block within the Late Cenozoic Indo‐Eurasian deformation field north of Tibet.