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Based on observations, reanalysis data, and numerical experiments, the present study investigates the link between the interannual variation in precipitation over South China (SC) and the eastern Tibetan Plateau (ETP) in July during 1979–2019 and the underlying mechanisms. Results show that during May–September the variation in precipitation exhibits a dipole pattern between the two regions in July and August only, with more significance in July. The correlation coefficients of precipitation between the two regions in July and August are − 0.60 and − 0.34, statistically significant at the 99% and 95% confidence levels, respectively. The role of developing ENSO in the formation of the precipitation dipole in July is further investigated. During El Niño's development in July, precipitation increases over the tropical central–eastern Pacific, and decreases from India to the Maritime Continent and tropical Atlantic. These conditions cause anomalous cyclones over SC and the northern Bay of Bengal, and an anomalous anticyclone over Lake Balkhash to Northwest China in the middle and lower troposphere via the tropical atmospheric bridge and upper-tropospheric wave trains over Eurasia. This favors the July precipitation dipole with increased (decreased) precipitation over SC (the ETP). In La Niña's developing phase in July, the opposite is true. Moreover, numerical experiments with the ECHAM5 model can reproduce the above physical processes. [ABSTRACT FROM AUTHOR]

The Western Tibetan Vortex (WTV) is a large-scale circulation pattern identified from year-to-year circulation variability, which was used to understand the causal mechanisms for slowdown of the glacier melting over the western Tibetan Plateau (TP). A recent argument has suggested the WTV is the set of wind field anomalies resulting from variability in near-surface air temperatures over the western TP (above 1500 m), which, in turn, is likely driven by the surface net radiation. This study thereby evaluates the above putative thermal-direct mechanism. By conducting numerical sensitivity experiments using a global atmospheric circulation model, SAMIL, we find a WTV-like structure cannot be generated from a surface thermal forcing imposed on the western TP. A thermally-direct circulation generated by the surface or near surface heating is expect to cause upward motions and a baroclinic structure above it. In contrast, downward motions and a quasi-barotropic are observed in the vertical structure of the WTV. Besides, we find variability of the surface net radiation (sum of the surface shortwave and longwave net radiation) over the western TP can be traced back to the WTV variability based on ERA5 data. The anticyclonic (cyclonic) WTV reduces (increases) the cloudiness through the anomalous downward (upward) motions, causes more (less) input shortwave net radiation and thereby more (less) surface net radiations, resulting in the warmer (cooler) surface and near-surface air temperature over the western TP. The argument is constructive in encouraging examination of the radiative balance processes that complements previous studies. [ABSTRACT FROM AUTHOR]

The characteristics of crustal deformation and its dynamical mechanisms in the Sichuan-Yunnan region are of interest to many researchers because they can help explain the deformation pattern of the eastern Tibetan Plateau. In this paper, we employ a precise three-dimensional viscoelastic finite element model to simulate the crustal deformation in the Sichuan-Yunnan region, southeastern Tibetan Plateau. We investigate the influence of lower crustal flow and rheological variations by comparing the modeled results with GPS observations. The results demonstrate that lower crustal flow plays an important role in crustal deformation in the Sichuan-Yunnan region. The best fitting is achieved when the flow velocity of the lower crust is approximately 10–11 mm/a faster than that of the upper crust. Additionally, crustal rheological properties affect regional crustal deformation. When the viscosity of the middle and lower crust in the South China block reaches 10 22 and 10 23 Pa·s, respectively, the modeled results match observations well, especially for the magnitude of crustal motion within the South China block. Finally, our dynamic model shows that the maximum principal stress field of the Sichuan-Yunnan region exhibits clear zoning, gradually shifting from an approximately east-west orientation in the northern Bayan Har block to southeast in the South China block, southwest in the western Yunnan block, and a radially divergent distribution in the Middle Yunnan and Southern Yunnan blocks. [ABSTRACT FROM AUTHOR]

The Xunhua, Guide and Tongren intermontane basin system in the NE Tibetan Plateau, situated near the Xining basin to the N and the Linxia basin to the E, is bounded by thrust fault-controlled ranges. These include to the N, the Riyue Shan, Laji Shan and Jishi Shan ranges, and to the S the northern West Qinling Shan ( NWQ). An integrated study of the structural geology, sedimentology and provenance of the Cenozoic Xunhua and Guide basins provides a detailed record of the growth of the NE Tibetan Plateau since the early Eocene. The Xining Group ( ca. 52-21 Ma) is interpreted as consisting of unified foreland basin deposits which were controlled by the bounding thrust belt of the NWQ. The Xunhua, Guide and Xining subbasins were interconnected prior to later uplift and damming by the Laji Shan and Jishi Shan ranges. Their sediment source, the NWQ, is constrained by strong unidirectional paleocurrent trends towards the N, a northward fining lithology, distinct and recognizable clast types and detrital zircon ages. Collectively, formation of this mountain-basin system indicates that the Tibetan Plateau expanded into the NWQ at a time roughly coinciding with Eocene to earliest Miocene continental collision between India and Eurasia. The Guide Group ( ca. 21-1.8 Ma) is inferred to have been deposited in the separate Xunhua, Guide and Tongren broken foreland basins. Each basin was filled by locally sourced alluvial fans, braided streams and deltaic-lacustrine systems. Structural, paleogeographic, paleocurrent and provenance data indicate that thrust faulting in the NWQ stepped northward to the Laji Shan from ca. 21 to 16 Ma. This northward shift was accompanied by E-W shortening related to nearly N-S-striking thrust faulting in Jishi Shan after 11-13 Ma. A lower Pleistocene conglomerate (1.8-1.7 Ma) was deposited by a through-flowing river system in the overfilled and connected Guide and Xunhua basins following the termination of thrust activity. All of the basin-mountain zones developed along the Tibetan Plateau's NE margin since Indian- Tibetan continental collision may have been driven by collision-induced basal drag of old slab remnants in the manner of N-dipping and flat-slab subduction, and their subsequent sinking into the deep mantle. [ABSTRACT FROM AUTHOR]

A three-dimensional viscoelastic finite element model of the Qinghai–Tibet Plateau and its adjacent regions was used to explore the relationship between the Mw7.2 Yutian earthquake in 2008 and the 2014 Mw6.9 Yutian earthquake. We further analyzed the Coulomb failure stress change caused by the Yutian Mw6.9 earthquake on faults surrounding the Bayan Har block and discussed the relationship between the Coulomb stress change and aftershock distribution. The preliminary results showed that: (1) The Coulomb failure stress change caused by the Mw7.2 Yutian earthquake in 2008, which was projected on the slip direction of the 2014 Yutian Mw6.9 earthquake, exceeded the earthquake triggering threshold of 0.01 MPa, implying an apparent triggering effect. Specifically, the coseismic Coulomb failure stress changes were 0.0167 MPa and 0.0170 MPa when assuming apparent friction coefficients of 0.4 and 0.6, respectively. The Coulomb failure stress changes, including viscoelastic relaxation effects, were 0.0187 MPa and 0.0194 MPa respectively. Combined with the tectonic stressing rate, the Mw6.9 Yutian earthquake in 2014 was advanced 21.4–24.9 years by the 2008 Mw7.2 Yutian earthquake; (2) The stress changes derived from the viscoelastic relaxation effect were much less than that from the coseismic effect, which was possibly interpreted as the shorter elapsed time between the two earthquakes relative to the characteristic time; (3) The Coulomb failure stresses increased on the mid-northern segment of the Altyn Tagh fault, the middle segment of the Mani-Yushu fault and the western segment of the eastern Kunlun fault, which demonstrated increasing seismic potential. In particular, the Coulomb failure stress on the middle segment of the Altyn Tagh fault increased by 2.8 × 10 3 Pa, the most significant increase. In contrast, the Coulomb failure stress decreased on the western segment of the Mani-Yushu and Minjiang faults, with the western segment of the Mani-Yushu fault dropping by 3.6 × 10 3 Pa. The Coulomb stress changes on most faults surrounding the Bayan Har block were calculated to have increased, while the Minjiang fault on the eastern boundary was inhabited due to the enhancement of coseismic compressive stresses; (4) Combining the relocation of the aftershock sequence with the coseismic failure stress change, we concluded that the Mw6.9 Yutian main-shock triggered the aftershock sequences. [ABSTRACT FROM AUTHOR]