G. Roerich’s contribution to history of Russian expeditions in Central Asia

The study of G. Roerichs scientific heritage is at its beginning. An important basis of Roerichs many-sided scientific activities were his investigations during the expeditions in Asia. The longest, most dangerous and laborious among them was the Central Asiatic expedition of his father - N.K. Roerich. The goal of this article is to examine G.N. Roerichs activities on every stage of the Central Asiatic expedition, as well as G.N. Roerichs works, publishing the results of the expedition research. G.N. Roerich presented the basic results in his monograph Trails to Inmost Asia: Five years of exploration with the Roerich Central Asian Expedition published in English in USA in 1931. Roerichs description of North and Central Tibet is unique because the theocratic state in Tibet and nomad tribes, which Roerich had observed, are no more existing. Roerichs field investigations continued the historical tradition of Russian expeditions in Central Asia. It extended our scientific knowledge about the insufficiently known regions in Asia.

Hydrochemical Characteristics of Groundwater at the Epicenter of the 2021 Biru M6.1 Earthquake in Central Tibet

Groundwater is undoubtedly important for water security and eco-environmental protection, especially in areas that experience earthquakes. Analyzing the characteristics and variation of groundwater after an earthquake is significant to obtain a better understanding of the seismic risk and rational management of groundwater resources. This study investigated the hydrogeochemical characteristics of groundwater at the epicenter of the 2021 Biru M6.1 earthquake in central Tibet, southwest China, using 23 water samples. The results showed that: (1) the hydrochemical type, hydrogen and oxygen isotope ratios, and SiO2 concentrations of three hot spring water samples in the study area were significantly different from those of samples taken elsewhere, indicating that the hot spring water originates from deeper geothermal reservoirs and has undergone more distant migration and longer fractionation processes; (2) the geochemical characteristics of groundwater from some sampling sites in the epicentral area were apparently distinct from those of other shallow groundwater or surface water samples, suggesting that the groundwater environment in the epicentral area has been affected by the earthquake. Along with the macroscopic groundwater responses in the epicentral area after the earthquake, we investigated the influencing mechanisms of the earthquake on the regional groundwater environment. We conclude that a shorter distance from the epicenter to the seismogenic fault leads to a greater possibility of the generation of new fractures, which then induce macroscopic responses and chemical characteristic variations for groundwater.

The July 2020 Mw 6.3 Nima Earthquake, Central Tibet: A Shallow Normal-Faulting Event Rupturing in a Stepover Zone

On 22 July 2020, an Mw 6.3 earthquake with a predominantly normal-faulting mechanism struck the Yibug Caka fault zone, central Tibet, where the overall tectonic environment is characterized by left-lateral strike-slip motion. This event offers a chance to gain insight into the tectonic deformation and the cause of shallow normal-faulting earthquakes in this little studied region. Here, we use Sentinel-1A/B Interferometric Synthetic Aperture Radar data to investigate the coseismic and postseismic deformation related to this earthquake. The earthquake ruptured a previously mapped West Yibug Caka fault and is dominated by normal slip with a peak value of 1.9 m at depth of 6.9 km. Postseismic deformation analysis indicates that the observed subsidence signals of up to ∼4.7 cm are a consequence of afterslip. Most of the afterslip is confined at depths between 0.8 and 8.4 km, peaking at 0.27 m at depth of 6.1 km. The significant coseismic slip and afterslip involved in the earthquake highlights a complex interaction between the major normal fault and the secondary synthetic fault. By an integrated analysis of the inversions, regional geology geomorphology, fault kinematics, and seismicity background, we propose a tectonic model that attributes the occurrence of this normal-faulting event to the release of extensional stress in a stepover zone controlled by the northeast-striking sinistral strike-slip Riganpei Co fault and Bu Zang Ai fault. Compared with that the structural stepover often acts as a barrier to affect the propagation of earthquake rupture, our study demonstrates that the failure of a stepover may potentially induce the occurrence of earthquake along the bounding strike-slip faults.

The oldest-known Lestidae (Odonata) from the late Eocene of Tibet: palaeoclimatic implications

Terrestrial fossils from the Palaeogene of Tibet could help us to better understand the past climate and environment in this area. We herein report a new late Eocene non-marine fossil site from southern Nima Basin, central Tibet, SW China, including abundant insects and fishes. These fossils are similar to those from the late Eocene (∼39.5–37 Ma) Lunpola–Nima sediment depo-centres in sharing the dominating aquatic bug Aquarius lunpolaensis and cyprinid fishes. Chalcolestes tibetensis sp. nov., the oldest representative of the modern family Lestidae, is described. Lestidae were previously only recorded in Western Europe, and the oldest records were from the uppermost Eocene of France and the UK. The present discovery demonstrates that Lestidae already had a broad distribution during the Eocene and probably originated much earlier. The recent representatives of Chalcolestes occur in the low-altitude ponds or lakes of Western Palaearctic. Together with the other freshwater fossils in this site, this new discovery indicates a humid climate and low altitude for the Nima Basin and nearby basins in the middle part of the Bangong Nujiang suture zone.

Comparative Analysis on Seismicity and Stress Triggering of Strong Earthquakes Sequence in Central Tibet

The Central Tibet constitutes part of the central part of Qinghai-Tibetan Plateau, which is one of the highest seismic activity areas in China. This paper discussed the regularity of seismic activity in this area. Based on a stratified viscoelastic earth model, we calculated the Coulomb stress changes imparted from the 4 strong earthquakes (M≥6.3) the Bengco - southeastern piedmont of Nyainqentanglha mountain fault zone in this region. The result shows that the study area may enter a new active period from 2020. There was a trigger between strong earthquakes (M≥6.3) on the Bengco fault - southeastern piedmont of Nyainqentanglha mountain fault zone. The post-seismic viscous relaxation effect of a strong earthquake had a significant impact on subsequent earthquakes(M≥6.3). In future 100 years, the Coulomb stress loading is more than 1.0 MPa in northwest section of Bengco fault and central of Nimu segment of southeastern piedmont of Nyainqentanglha mountain fault, thence strong earthquakes may occur in this two fault segments. The maximum magnitude of the earthquake will be M6.7 in the future 100 years.