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Tectonic research of the Tibetan Plateau has long focused on its deformation style and mechanisms. The 2008 Mw7.9 Wenchuan earthquake ruptured the Longmen Shan fault located at the eastern rim of the plateau and excited a viscoelastic response of the lithosphere. We infer a three‐dimensional (3D) rheological structure of eastern Tibet from modeling nine years of postseismic displacements observed by GPS. Our solution provides tight constraints on the lower‐crustal and upper‐mantle steady‐state viscosities of the Songpan‐Ganzi Terrane as (5.0 ± 0.7) × 1018 and (1.3 ± 0.3) × 1019 Pa s, respectively, consistent with a "jelly sandwich" model of Tibet, but not with some crustal channel flow models featuring much lower viscosities. The inferred lower‐crustal and upper‐mantle transient viscosities are (5.0 ± 1.3) × 1017 and (5.0 ± 1.5) × 1018 Pa s, respectively, suggesting nonlinear deformation mechanisms. The adjacent West Qinling and Sichuan blocks feature an order‐of‐magnitude higher rheological strength, which is consistent with the changes in the crustal material properties and interseismic deformation style across the East Kunlun‐Tazang and Longmen Shan faults. Our results enable us to propose a conceptual 3D tectonic deformation model, in which the eastward extrusion of Tibet is absorbed in the Songpan‐Ganzi crust mainly by E‐W shortening and N‐S extension, accommodated through faulting of conjugate strike‐slip faults in the upper crust and distributed shear in the lower crust. Plain Language Summary: One of the fundamental questions in Earth science is the deformation mechanism of the continents, which controls the topography of the land we live on, the distribution of the resources extracted to support our living, and the origins of natural hazards such as landslides and earthquakes. The Tibetan Plateau, arguably, is the best natural laboratory to study the deformation mechanism of the continents. In this study, we address two critically important and much debated problems in Tibetan Plateau dynamics; that is, the rheologic structure of the Tibetan lithosphere and how it deforms under tectonic loading. We use nine years of mostly unpublished three‐dimensional (3D) deformation data collected in the aftermath of the 2008 Mw7.9 Wenchuan earthquake to infer the rheological structure of the eastern Tibet lithosphere. Our results are consistent with a "jelly sandwich" model, with a relatively weak lower crust underlain by a stronger upper mantle. However, they do not support the very low viscosities envisioned by some of the channel flow models of lower crustal deformation in eastern Tibet. We also propose a conceptual 3D tectonic deformation model, in which the eastward extrusion of Tibet is absorbed in the Songpan‐Ganzi crust by E‐W shortening and N‐S extension, accommodated through conjugate faults in the upper crust and distributed shear in the lower crust. Key Points: A comprehensive GPS data set is provided to cover nine years of three‐dimensional (3D) postseismic displacements after the 2008 Wenchuan earthquakeGPS constrained eastern Tibet Lithospheric rheological structure agrees with a "jelly sandwich" model, not models of much lower viscositiesA conceptual 3D tectonic deformation model in eastern Tibet is proposed to characterize its dynamic deformation style and mechanisms [ABSTRACT FROM AUTHOR]

The ecosystems of the Qinghai-Tibetan Plateau are regarded as being primarily regulated by climate because of the harsh environment of the region and the resulting sparse human population. Recent studies have revealed that Neolithic farmers and nomads extensively settled in the northeastern Qinghai-Tibetan Plateau from 5.2 ka (ka = cal ka BP); however, it is unclear how and to what extent human activity has affected its vegetation. Here we combine the results of the pollen analysis of a sediment core from Genggahai Lake, ashallow lake in Gonghe Basin on the northeastern Qinghai-Tibetan Plateau, with archaeological evidence and use them to assess the extent and nature of human impacts on the regional vegetation during the middle and late Holocene. The pollen record indicates that Stellera, an indicator of the extent of grazing-induced grassland degradation, first appeared at 4.7 ka, expanded during 3.6-3.0 ka, and finally increased significantly after 1.6 ka. In support of this finding, archaeological data indicate that the agro-pastoral Majiayao people arrived at ~5 ka and groups of Kayue people, who practiced pastoralism, intensively colonized the Gonghe Basin and nearby Qinghai Lake basin during 3.6-3.0 ka. After~ 1.6 ka, from the Tang Dynasty onwards, human settlement and grazing activity intensified on the northeastern Qinghai-Tibetan Plateau, and this is in accord with the observed high percentages of Stellera in the pollen record. Based on comparison with other records, we conclude that the sediments of Genggahai Lake provide a record of anthropogenic impacts on vegetation, and that human activity may have contributed to regional forest decline during the middle Holocene, and to grassland degradation in the late Holocene. Grassland degradation caused by human activity may be an indicator of the start of the Anthropocene and potentially may have contributed to global climate change via increased dust emission to the atmosphere. [ABSTRACT FROM AUTHOR]

Information on changes in land-surface features on the Tibetan Plateau (TP) during the Holocene may help our understanding of the forcing of monsoonal circulation. We analyse vegetation changes during the last 9000 years from pollen records of four lakes (Hurleg Lake in the Qaidam Basin; Qinghai Lake on the northeastern TP; Zigetang Lake on the central TP and Koucha Lake on the eastern TP) which represent different regions and vegetation types on the Plateau today. A set of modern pollen assemblages from 111 lake sediment samples originating from different vegetation types is used for the interpretation of the Holocene pollen records. Four types of numerical analyses are used to infer different aspects of pollen-stratigraphical and inferred vegetation changes: biome reconstruction; ordination (to infer palynological compositional turnover); rate-ofassemblage- change analysis, and a pollen-LAI (leaf area index) transfer function. Our results show strong regional differences in inferred vegetation change in terms of timing, strength and the nature of change. The greatest changes in compositional turnover and LAI are found in the Qinghai Lake record, indicating that forests were replaced by steppe vegetation in a step-wise fashion since the mid Holocene. Alpine steppe vegetation on the central and eastern TP was relatively stable throughout the Holocene, only showing a gradual replacement of temperate steppe by high-alpine meadows. The Qaidam Basin was dominated by temperate desert throughout the Holocene. The documented palynological and inferred vegetation changes can be most parsimoniously explained by climate change, although human impacts cannot be excluded as a contributing factor. Comparison of our findings with sensitivity analyses of numerical climate simulations suggests that longterm vegetation change may have had only a weak influence on regional climate change on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The article discusses the research on the complex vegetation response of the Tibetan Plateau on the climate change.