Southeastern Tibetan Research Articles

A Generalized Strategy From S‐Wave Receiver Functions Reveals Distinct Lateral Variations of Lithospheric Thickness in Southeastern Tibet

AbstractThe selected rotation angle and deconvolution time window during S‐wave receiver function (SRF) calculations, and the final SRF quality control may introduce artificial interference. Here we overcome these problems by proposing a new strategy named GC_SRF for obtaining the lithospheric thickness from S‐wave receiver functions, which employs grid search and correlation analysis to obtain reliable SRFs. Extensive tests using synthetic and real data suggest that the GC_SRF strategy is a robust and reproducible approach for estimating lithospheric thickness. Specifically, this GC_SRF strategy can restore the weak Sp phases from full wavefield synthetic seismograms. Clear and distinct discontinuity patterns that do not involve artificial interference compared with those obtained in previous studies of southeastern Tibet are produced here. The post‐stack migrated SRFs reveal distinct lateral variations of lithospheric thickness in southeastern Tibet: (a) Tengchong volcano has a thin crust and thin lithosphere–asthenosphere boundary (LAB) (∼90 km); (b) the Chuandian region has a thicker crust and either a poorly defined or unclear LAB. The absence of a continuous LAB in the Chuandian region may suggest lithospheric regrowth due to the recovery processes of the mantle plume; (c) a thinner crust and clear LAB of ∼160 km depth is presented beneath the Sichuan Basin.

High-resolution mapping and driving factors of soil erodibility in southeastern Tibet

Quantifying the spatial distribution of soil erodibility (K factor) in the Qinghai-Tibet Plateau is essential for global soil erosion management. However, many K factor maps have a coarse spatial resolution at the regional scale, and high-resolution mapping is still a challenge. Quantitative analysis of the influence of environmental factors such as soil, topography, climate, and vegetation, and human activities on the K factor is also lacking. Therefore, we mapped the high-resolution (90 m) spatial distribution of the K factor values in southeastern Tibet using a random forest model with multiple environmental variables, based on remote sensing, ground observations (114 sampling points), and gridded datasets. The K factor estimates based on soil particle size composition and organic carbon content ranged from 0.09 to 0.35, showing moderate variation. The random forest model yielded a coefficient of determination > 0.9 and provided detailed information on the spatial distribution of K factor values, especially in large unsampled areas. The predicted K factor values tended to be high in the eastern area and low in the western area. Partial least squares path modeling showed that soil physical properties such as fractal dimension and mean weight diameter of aggregates had the largest influence on the K factor (path coefficient 0.695). Climate and topography also had a considerable influence on the K factor (path coefficient −0.489 and −0.469, respectively), while the influence of vegetation and human activities was minimal. Accordingly, the random forest model is an effective tool for high-resolution spatial distribution mapping of the K factor with limited sampling data.

Present-day fault kinematic around the eastern Himalayan Syntaxis and probable viscoelastic relaxation perturbation following the 1950 Mw 8.7 Assam earthquake

Strike-slip and tensile/dip-slip rates around the EHS region from the elastic block model. • An elastic block model was constructed to analyze the fault slip rates and regional kinematic around the Eastern Himalayan Syntaxis (EHS). • The postseismic viscoelastic relaxation effects caused by the 1950 Assam Mw 8.7 earthquake is still significant even after 65 years. • The interseismic slip rate across the eastern Himalaya derived from pure elastic solution may be overestimated if ignoring the viscoelastic relaxation effects. The Eastern Himalayan Syntaxis (EHS) played important role in accommodating the intracontinental deformation and material flow in southeastern Tibet. Quantifying the regional kinematics around the EHS is critical for understanding the deformation mechanism of the Tibetan Plateau. In this study, we compiled all available GPS measurements and constructed an elastic block model to analyze the fault kinematics around the EHS. The results suggest that the deformation characteristics around the EHS can be well explained by a linear spherical block model that considers the intra-block homogeneous strain. The fault slip rates from the block model agree well with the late Quaternary slip rates, suggesting that the GPS-derived slip rates can generally represent the long-term slip rates. However, some relatively large residuals, especially in the frontal EHS region, are still detectable, suggesting that various other factors, such as the postseismic viscoelastic relaxation, may also influence the deformation. We simulated the postseismic viscoelastic relaxation deformation caused by the 1950 Mw 8.7 Assam earthquake endured as the largest intracontinental earthquake ever recorded. The results indicate significant postseismic viscoelastic deformation due to the Assam earthquake even after 65 years. The interseismic convergence rates across the Mishmi thrust and the Arunachal Himalaya derived from pure elastic solution may be overestimated if ignoring the viscoelastic relaxation effects. The spatial variations of convergence rates across the central and eastern Himalayas could be partly related to the transient deformation following great Himalayan earthquakes.

Restricted lithospheric extrusion in the SE Tibetan Plateau: Evidence from anisotropic Rayleigh-wave tomography

Constraining variations of lithospheric structure and deformation across southeastern Tibet and the surrounding region are crucial for understanding the lateral growth of the plateau. Using data from two dense seismic arrays in the SE Tibetan Plateau, we obtained fine-scale Rayleigh-wave phase velocity maps by Eikonal tomography, and further inverted for 3-D shear wave velocity and azimuthal anisotropy of the crust and upper mantle. High velocities and weak lithospheric anisotropy are revealed under Dianzhong Block (DZB), where is covered by the relics of the Emeishan Large Igneous Province, while strong anisotropy is imaged around. We propose that the DZB strengthened by the paleo igneous activity plays an essential role in the evolution along the southeastern plateau margin. On the one hand, the DZB obstructs the migration of plateau material to the southeast. On the other hand, strong deformation is localized along the DZB margins, while the stress due to the plate expansion is transferred further to the Xiaojiang fault, which induced significant deformation within the Yangtze Craton. Furthermore, the lithosphere of DZB deflects the mantle flow driven by the eastward Indian subduction under the northern Indochina block.

Diversity Patterns of Wetland Angiosperms in the Qinghai-Tibet Plateau, China

The Qinghai-Tibet Plateau, has a special geological history, diverse habitats, a complex climate, and a large number of wetlands, which harbor a huge of wetland plants. In this study, we sorted out the monographs, literatures and online databases, as well as our own collection from field surveys, and comprehensively combed the checklist and county-level diversity of wetland angiosperms and endangered species in the Qinghai-Tibet Plateau for the first time. The distribution pattern of species richness was analyzed through three groups of environmental variables: energy, water, and habitat. The wetland angiosperms have high richness, with a total of 2329 species, belonging to 91 families and 438 genera, mainly hygrophytes (94.98%). The spatial distribution is uneven, and gradually decreases from the southeast to the northwest of the plateau. Species richness decreased with elevation and latitude and increased with longitude. Annual precipitation (AP) and annual mean temperature (AMT) are the most important variables affecting species diversity. Habitat environmental variables had less influence on species richness distribution and wetland area was not associated with richness distribution. The setting of endangered wetland angiosperm reserves needs to focus on the Hengduan Mountains and southeastern Tibet. Our study provided basic data for the research and protection of wetland plant diversity in the Qinghai-Tibet Plateau.

Crustal deformation and dynamics of the south-eastern tibetan plateau from stress fields and geodesy

South-eastern Tibet rotates clockwise around the eastern Himalayan syntaxis due to the eastward extrusion of the eastern Tibetan lithosphere and it attracts much attention as a window for studying the dynamics of continental collision between India and Eurasia. Competing geodynamic models to describe the deformation of the eastern Tibet have been the debating subject and the dynamic processes responsible for plateau evolution remain poorly understood, partly because the mechanical state at depth and its relationship with surficial deformation are unclear. In this context, a continuous east-west oriented tensional zone was identified at the south-eastern edge of the Tibetan Plateau based on seismogenic stress field and global positioning system data. The profiles of surficial velocity field reveal a relatively speedy motion belt parallel to the Xianshuihe fault extending from north to south in the rotating region east of the tensional zone. Segmented features of the profiles around the extensional zone indicate its close relation with flow channels delineated from magnetotelluric images. Therefore, the deformation at the south-eastern edge of the Tibetan Plateau is mechanically coupled within the crustal depth. We propose a complex regional kinematics with a localised speedy belt and a continuously extensional zone, where material coupling and deformation compatibility were revealed within the crustal depth.

Paleoearthquakes of the Yangda-Yaxu fault across the Nujiang suture and Lancang river suture zone, southeastern Tibetan Plateau

The WNW-trending Yangda-Yaxu fault (YYF) is located in the interior of the Qiangtang block (QTB). The YYF cuts through the Nujiang suture and Lancang river suture zone and divides Nujiang fault (NF) and Lancangjiang fault (LCJF) into two sections with significantly different activity levels, suggesting that the YYF may function as a specific structure in this region. In addition, a recent work argues that the YYF plays an important role in strain partitioning in southeastern Tibet and poses a high surface-faulting risk to the Sichuan-Tibet railway. However, no M ≥ 5.0 earthquakes have been recorded, and no palaeoseismic research has been conducted along the fault, leading to limited knowledge regarding its rupture behavior, which is essential for understanding regional tectonic deformation and assessing the regional seismic potential. In this study, we constrained the timings and recurrence intervals of late Quaternary paleoseismic events along the YYF for the first time. Through trench excavations and exposure cleaning combined with radiocarbon dating, five faulting events were identified, namely, E1 through E5 from youngest to oldest (831–1,220, 3,307–6,703, 9,361–10,286, 12,729–14,651, and before 14,651 yr BP). The recurrence interval of major earthquakes along the YYF follows a quasi-periodic pattern with an interval of ∼4,000 yr. Combining the clear linear geomorphic features along the fault and the paleoearthquake results in this paper, we believe that YYF is a newly-generated active fault, and has a significant control effect on the late Quaternary evolution of the NF and the LCJF. Further analysis revealed that the YYF also plays an important role in accommodating crustal deformation.

Contemporary kinematics along the Xianshuihe-Xiaojiang fault system: Insights from numerical simulation

The slip rates on the Xianshuihe-Xiaojiang fault system (XXFS) are crucial for understanding the strain partitioning and evaluating its seismic risk. Here, we establish a 3D viscoelastic FEM model incorporating the faults as contact discontinuities to gain a numerical image of the XXFS's continuous slip rate. The viscosity of Southeastern Tibet and the locking depth of the XXFS were investigated and constrained by interseismic GPS observations. We estimated that the viscosities of the lower crust and the mantle lithosphere of southeastern Tibet were 1 × 1018 and 5 × 1019 Pa s, respectively. The interaction between the Daliangshan fault and the Anninghe-Zemuhe fault governs slip partitioning around the middle part of the XXFS. The XXFS’ overall mechanical efficiency is improved by the initiation and development of the Daliangshan fault. The interseismic strain buildup rate appears to be spatially heterogeneous, depending on the changes in slip rate along the strike of the XXFS. The accumulated strain energy in the Shimian-Miannning and Mianning-Xichang seismic gaps has enhanced the seismic hazard, which should be closely monitored.

Crustal thickness and paleo-elevation in SE Tibet during the Eocene-Oligocene: Insights from whole-rock La/Yb ratios

The topographic evolution of SE Tibet is essential for understanding the growth of this orogenic plateau margin and the mechanism of continental deformation in general. Stable isotopes have been used to construct the paleo-elevation of SE Tibet during the Cenozoic. However, this methodology's reliability for the region is controversial; the results require validation through other independent constraints. The Eocene-Oligocene adakite-like rocks exposed along the Jinshajiang Suture are mostly the production of melts from the lower crust, and thus their geochemical features are used to track ancient crustal thickness and plateau elevation of SE Tibet. The whole-rock [La/Yb]N ratios indicate a thickened SE Tibet. Meanwhile, the paleo-elevation based on the calculated crustal thickness shows that central and southeastern Tibet had reached modern heights by the early Oligocene, corroborating results by stable isotope paleoaltimetry. Synthesizing previous studies and our results, we suppose that the deformation caused by the India-Aisa collision had propagated to and thickened central and southeastern Tibet before the Eocene-Oligocene. The uplifted and low-gradient plateau margin of SE Tibet had already been formed by this time. The lateral extrusion has mainly accommodated the deformation with minor shortening since the late Eocene.

Uncertainties of Global Historical Land Use Datasets in Pasture Reconstruction for the Tibetan Plateau

Global historical land use datasets have been widely used in global or regional environmental change studies. Historical pasture data are essential components of these spatially explicit global datasets, and their uncertainties have not been well evaluated. Using the livestock-based historical pasture dataset for the Tibetan Plateau (TP), we evaluated the uncertainties of these representative global historical land use datasets in pasture reconstruction for the TP over the past 300 years in terms of pasture area estimation and spatial pattern mapping. We found that only the Sustainability and the Global Environment (SAGE) dataset can roughly reflect the temporal and spatial characteristics of historical pasture changes on the TP. The History Database of the Global Environment (HYDE) version 3.2 and the Pongratz Julia (PJ) datasets overestimated pasture area for the TP dramatically, with a maximum area ratio of about 221% and 291%, respectively, and the Kaplan and Krumhardt 2010 (KK10) dataset underestimated pasture area for the TP dramatically, with a minimum area ratio of only 9%. As for the spatial pattern, all these global datasets overestimated the spatial scope of grazing activities obviously. The KK10 dataset unreasonably allocated pasture to forest areas in southeastern Tibet because only climate and soil factors were considered in assessing land suitability for grazing. Using population to estimate pasture area and only using natural factors to allocate pasture area into grids is unsuitable for the TP historical pasture reconstruction. In the future, more information directly related to grazing activities, e.g., the number of livestock and its spatial distribution, and social-cultural factors, including technology and diet, should be used for area estimation and spatial pattern mapping to improve the accuracy of pasture data in these global datasets.

March–May Snow Cover Extent Reconstruction for the Past Four Centuries Based on the Tree-Ring Early-Wood on the Southeastern Tibetan Plateau

The snow cover extent (SCE) on the southeastern Tibet Plateau (SETP) has an important impact on the dynamics of the East Asian winter monsoon and the runoff changes of the first and third largest rivers in Asia, namely, the Yangtze River and the Yarlung Zangbo River. Unfortunately, the shortness of instrumental SCE data of a few decades limits our ability to understand its long-term variability before the industrial era. Here, we developed Abies faxoniana tree-ring total ring width (TRW), early-wood width (EWW), and late-wood width (LWW) chronologies for the past four centuries at Little Qamdo Village (XQDV), Markam County, on the SETP. The most significant positive correlation (r = 0.62, p < 0.01) was found between the EWW chronology and SCE from March to May (SCE3–5). The SCE would affect the onset of the growing season through soil moisture, restricting the early-wood growth of trees. Thus, we presented a reconstruction of SCE3–5via EWW chronology since AD 1660 for SETP. We observed two abrupt changes from low to high around the years 1685 and 1998 for our reconstructed SCE3–5. In addition, we found that the positive anomalies of the reconstructed SCE3–5 after 1988 cohered with the distinct increase of the East Asian winter monsoon.

Crustal anisotropy beneath southeastern Tibet inferred from directional dependence of receiver functions

The present study reveals depth-dependent crustal anisotropic signatures beneath southeastern Tibet. It is used to characterize the rheology of major faults and shear zones, which is important for understanding crustal deformation and geodynamic processes beneath the study area. The depth-dependent anisotropic orientations have been investigated based on the directional dependence of radial and tangential receiver functions (RFs). To achieve our objective, we first computed 3683 good-quality P-RFs from 174 teleseismic earthquakes (M ≥ 5.5) recorded within epicentral distance range of 30∘ to 90∘ at 70 seismic stations of the Eastern Syntaxis experiment (XE Network). After that, we employed the harmonic decomposition technique at each seismic station to retrieve the first (k = 0), second (k = 1) and third (k = 2) degree harmonics from the RF dataset. Our study characterizes the type (horizontal or plunging) of the symmetry axis. The anisotropic axes of the upper crust (0–20 km) appear to vary from approximately N-S to NE-SW. They are usually orthogonal to orientations of major faults and suture zones in the region, implying the effect of structure-induced anisotropy. It can be explained by regularly oriented cracks or macroscopic structure alignment along the major faults. The anisotropic orientations of the middle crust (20–40 km) are NE-SW to E-W direction, reflecting a different pattern than those estimated in the upper crust. The lower crustal (40–70 km) anisotropic pattern (E-W or ESE-WNW direction) exhibits distinct orientations than the upper and middle crust. The crystal preferred orientations (CPO) of the mica and amphibole minerals are likely to cause anisotropy observed at mid-to-lower crustal depth ranges, emphasizing the role of ductile deformation due to material movement towards the east underneath southeastern Tibet. Our results, along with S(K)KS and direct S-waves splitting signatures, suggest mid-to-lower crust and lithospheric mantle material movement towards the east, while the discrepancies in anisotropic symmetric axes directions may be indicative for the partial coupling between the crust and upper mantle beneath the region.

Giant river-blocking landslide dams with multiple failure sources in the Nu River and the impact on transient landscape evolution in southeastern Tibet

Giant landslides have frequently occurred in deeply-incised valleys during the topographic development of the Tibetan Plateau, and these landslides commonly blocked rivers and in turn affected fluvial processes. The giant Qianjincun landslide, with a volume of ~110 × 106 m3, created the highest natural dam among all the completely river-blocking landslides identified along the trunk of the Nu River in the southeastern Tibetan Plateau. This giant landslide, which developed on a granite hillslope and dammed the river with a height of ~175 m, was dominated by long-term fluvial incision responding to uplift in one of the deepest valleys in the world. The dammed lake was breached around the end of the Dali glaciation (~10 ka), and the deposits remaining in the valley indicated an earlier landslide from the opposite failure source beside the Qianjincun landslide. The Geduicun landslide on the right bank evolved from gravitational deformation of toppling controlled by schist foliations, while the Qianjincun failure on the left hillslope was governed by the seismically-triggered detachment of granite cut by rock joints. The kinematic process of the Qianjincun landslide was numerically investigated under seismic loading, indicating high-velocity sliding from a thousand-meter-high source. In comparison to the soft rock failure preceded by the long-term gravitational effect, the mass movement on the granite slope was catastrophically induced by dynamics with high initial kinetic energy, and the subsequent overwhelming river blockage transiently caused stronger landscape evolution than any other landslides in the catchment. The inventory of river-damming landslides compiled along the trunk of the Nu River suggested a prominent tendency that all the dammings occurred in the region where the relief is greater than 2000 m. The analysis provided the power-law correlations of the geomorphic parameters of dams that can help predict the disastrous effects of future river blockages. The insight into landscape feedbacks between giant landslides and fluvial processes could contribute to effective risk assessments of disaster chains in high-relief reaches.

Classification and sediment estimation for debris flow-prone catchments in the Parlung Zangbo Basin on the southeastern Tibet

Glaciers in alpine mountains create special landforms that store large amounts of sediment, providing loose materials for debris flows. Various types of catchments have diverse storage modes for such materials, resulting in differences in the location and volume of sediment. However, little is known about this phenomenon due to the lack of data. Hence, taking the Parlung Zangbo basin as an example, we identify the main sediment according to the catchment type and propose sediment calculation methods for different types. The results show that tributary catchments can be divided into five types: deep U-shaped catchments, shallow U-shaped catchments, glacial hanging catchments, fluvial catchments after glaciation, and fluvial catchments. The sediments include glacial deposits, landslides, talus slopes, fans, etc. Non-glacial sediments can be calculated by the morphological method, while the thickness of glacial deposits can be calculated effectively by the proposed curve-fitting method. The volumes of glacial deposits are obtained and compared with those of other sediments. Glacial deposits are one or two orders of magnitude larger than other deposits. Glacial deposits in the first three types are concentrated on gentle downstream slopes, while in the fourth type was in steep location.

New Insights into Ice Avalanche-Induced Debris Flows in Southeastern Tibet Using SAR Technology

Drastic climate change has led to glacier retreat in southeastern Tibet, and the increased frequency and magnitude of heavy rainfall and intense snow melting have intensified the risk of ice avalanche-induced debris flows in this region. To prevent and mitigate such hazards, it is important to derive the pre-disaster evolutionary characteristics of glacial debris flows and understand their triggering mechanisms. However, ice avalanche-induced debris flows mostly occur in remote alpine mountainous areas that are hard for humans to reach, which makes it extremely difficult to conduct continuous ground surveys and optical remote sensing monitoring. To this end, synthetic aperture radar (SAR) images were used in this study to detect and analyze the pre-disaster deformation characteristics and spatial evolution in the Sedongpu Basin and to detect changes in the snowmelt in the basin in order to improve our understanding of the triggering mechanism of the ice avalanche-induced debris flows in this region. The results revealed that the maximum average deformation rate in the basin reached 57.3 mm/year during the monitoring period from January 2016 to October 2018. The deformation displacement in the gully where the ice avalanche source area was located was intimately correlated with the summer snowmelt and rainfall and was characterized by seasonal accumulation. Clear acceleration of the deformation was detected after both the most recent earthquake and the strong rainfall and snowmelt processes in the summer of 2018. This suggests that earthquakes, snowmelt, and rainfall were significant triggers of the Sedongpu ice avalanche-induced debris flows. The results of this study provide new insights into the genesis of the Sedongpu ice avalanche-induced debris flows, which could assist in disaster warning and prevention in alpine mountain regions.

Late Oligocene-early Miocene Origin of the First Bend of the Yangtze River explained by thrusting-induced river reorganization

The origin of the First Bend of the Yangtze River is key to understanding the birth of the modern Yangtze River. Despite considerable efforts, the timing and mechanism of formation of the First Bend remain highly debated. Inverse river-profile modeling of three tributaries (Chongjiang, Lima, and Gudu) of the Jinsha River, integrated with regional tectonic and geomorphic interpretations, allows the onset of incision at the First Bend to be constrained to 28–20 Ma. The spatio-temporal coincidence of initial river incision and activity of Yulong Thrust Belt in southeastern Tibet highlights thrusting to be fundamental in reshaping the pre-existing stream network at the First Bend. These results enable us to reinterpret a change in sedimentary environment from a braided river to a swamp-like lake in the Jianchuan Basin south of the First Bend, recording the destruction of the hypothesized southwards-flowing paleo-Jinsha and Shuiluo Rivers at ~36–35 Ma by magmatism. During the late Oligocene-early Miocene, the paleo-Shuiluo River was diverted to the north by focused rock uplift due to thrusting along the Yulong Thrust Belt, which also led to exhumation of the Jianchuan Basin. Diversion of the paleo-Shuiluo River can be explained by capture from a downstream river in the footwall of the Yulong Thrust Belt. Subsequent rapid headward erosion, that was caused by thrusting-induced drop of local base level, is recorded by upstream younging ages for the onset of incision and led to the formation of the First Bend. The combination of new ages for the onset of incision at 28–20 Ma at the First Bend and younger ages upstream indicates northwards expansion of the Jinsha River at a rate of 62 ± 18 mm/yr. Our results suggest that the origin of the First Bend was likely triggered by thrusting at 28–20 Ma, after which the Yangtze River formed.

Crustal anisotropy and deformation of the southeastern Tibetan Plateau revealed by seismic anisotropy of mylonitic amphibolites

The composition and deformation patterns in the deep crust of southeastern Tibet are remain controversial. In this study, we present microstructures, fabric and seismic properties of amphibolites from the Ailao Shan-Red River shear zone, western Yunnan, China. The amphibolites display a distinct mylonitic foliation, and the amphibole grains show low intracrystalline deformation, slight compositional zoning but strong crystallographic preferred orientations (CPOs). We explain these CPOs could have formed by rigid body rotation during deformation accommodated by diffusion creep and grain boundary sliding. The amphibolites show strong seismic anisotropies (AVp = 4.6–9.3% and Max. AVs = 3.2–9.0%). Rock recipe modelling results indicate the seismic anisotropies of the mylonitic amphibolites are dominated by the content of biotite and amphibole. The delay time (0.28–1.01 s, average of 0.58 s) calculated for a 40 km-thick amphibolite layer is consistent with the observed delay time (0.52 s) of Pms wave splitting in this region, which indicates a thick amphibolitic layer in the crust of the southeastern Tibetan Plateau. The observed Pms wave splitting, extensive fold deformation and low velocity zones (LVZs) in the Diancang Shan (DCS) massif indicate two anisotropic layers in the crust. The upper layer related to frozen fabrics of amphibolites, which deformed during compressional folding and strike-slip shear. The lower layer related to the alignment of amphibole and melt pocket induced by present-day channel flow. The observed Pms wave splitting in the Ailao Shan (ALS) massif is attributed to amphibolites with vertical foliation and horizontal lineation which are generated by compressional folding and strike-slip shearing.

The Variation of Functional Traits in Leaves and Current-Year Twigs of Quercus aquifolioides Along an Altitudinal Gradient in Southeastern Tibet

Clarifying the adaptation mechanism of alpine plants to climate or habitat under the alpine environmental gradient on the Qinghai–Tibet Plateau is substantially important to understand the their geography in alpine regions and their responses to future climate change. The spatial distribution characteristics of functional traits in leaves and current-year twigs of Quercus aquifolioides on five consecutive altitudinal gradients in Southeastern Tibet were analyzed. The relationship between the functional traits and habitat factors (topographic and soil factors) was explored. Key results: the functional traits of leaves and current-year twigs of Quercus aquifolioides in Southeastern Tibet showed significant linear variations along the altitudinal gradients (p < 0.001). Quercus aquifolioides at low altitudes tended to have shorter current-year twigs and less leaves with larger LA (leaf area) and higher RWC (relative water content) than those at high altitudes. Strong trade-off and coordination relationship were found between the functional traits of leaves and those of current-year twigs, respectively. SL (slope) and TN (total nitrogen) contributed the most to leaf functional traits (p < 0.05); AL (altitude) was the main determinant of functional traits in current-year twigs of Quercus aquifolioides in southeast Tibet. In conclusion, our observation demonstrate that the ecological adaptation strategy of Quercus aquifolioides was formed through the trade-off mechanism among various functional traits, the variation of hydrothermal conditions and soil environmental factors caused by altitude in the alpine region lead to differences in functional traits of Quercus aquifolioides along an altitudinal gradient in southeast Tibet.

An Assessment of Glacier Inventories for the Third Pole Region

A glacier inventory contains data that are important for understanding the hydrology, water resources, and impacts of climate change in glaciated regions. Ten glacier inventories have been created for the Third Pole Region (TPR) or high-mountain Asia, but they vary largely in spatial coverage area and data quality. Therefore, it is necessary to assess the data quality to help potential users choose the right glacier inventories for their research. Using the analytical hierarchy process, this study selects eight assessment factors and quantifies the quality of eight glacier inventories of the TPR. The eight glacier inventories that we assessed are the Randolph Glacier Inventory (RGI), the Glacier Area Mapping for Discharge in Asian Mountains (GGI18), the Second Chinese Glacier Inventory (CGI-2), the Glacier Inventory of the Hindu Kush–Himalayan Region (HKHGI), the Glacier Inventory for the Western Himalayas (WHGI), the Glacier Inventory for the Karakoram and Pamir Region (KPGI), the Second Glacier Inventory of Pakistan (PGI-2) and the Glacier Inventory for the Southeastern Tibetan Plateau (SETPGI). The assessment results indicate that the overall quality of the small-scale glacier inventories of WHGI, KPGI, PGI-2, and SETPGI is higher than that of the large-scale inventories of RGI, GGI18, CGI-2, and HKHGI. For the large-scale inventories, the quality-ranking order from high to low is CGI-2, GGI18, RGI, and HKHGI. However, the comprehensive quality of CGI-2 and GGI18 is comparable over the area covered by CGI-2. The comprehensive quality of CGI-2, GGI18, and RGI exhibits clear spatial differences. Overall, the data quality is higher for the inner TPR than for the surrounding areas. By merging the products of the eight glacier inventories, a new glacier inventory product of the best comprehensive quality was derived for the entire TPR. This new product resembles the spatial distribution of the best-quality glacier inventories of the regions where the different products overlap. In terms of specific regions, the CGI-2 and GGI18 are the best products for most parts of the TPR in China, except for an area of southeastern Tibet where the highest-quality data are from the SETPGI. The other main distributions of the best products are the WHGI for the western Himalayas, the GGI18 and HKHGI for the Hindu Kush and the middle and eastern Himalayas, the PGI-2 for Pakistan, the KPGI for the Karakorum–Pamir area, and the GGI18 and CGI-2 for the Tianshan Mountains. The new data product greatly promotes the quality of a single glacier inventory for the entire TPR. This database will meet the needs of a variety of potential researchers, including those who prefer to get information for a particular parameter from a single glacier inventory (http://data.tpdc.ac.cn/en/data).

High‐Precision Vertical Movement and Three‐Dimensional Deformation Pattern of the Tibetan Plateau

AbstractThe Tibetan Plateau is characterized by high elevation and complex fault systems. High‐precision vertical movement data can provide important constraints for understanding the growth and expansion of the Tibetan Plateau. We collected approximately 116,000 km of leveling data, 21 continuous GNSS data sets, and their connecting surveying data; we jointly processed these data using a Helmert joint adjustment method to acquire the high‐precision vertical velocity field of the Tibetan Plateau and its surrounding areas. The primary results are as follows: (a) Vertical uplift is dominant on the southern, northeastern, and southeastern margins of the plateau, with uplift rate ranges of 2.0–3.0, 1.0–3.8, and 1.0–2.0 mm/yr, respectively; (b) Conspicuous subsidence is located along the southern portion of the Ganzi fault, with vertical rates ranging from −3.3 to −0.5 mm/yr; (c) Velocity profiles show that vertical deformation varies in different parts of the Tibetan Plateau, which is mostly accommodated by large strike‐slip and thrust faults, such as the Kunlun, Ganzi, and Longmenshan faults. Most of the surface uplift is accommodated by crustal shortening in the interior of the Tibetan Plateau; abrupt changes in vertical rates in eastern Tibet and the widely distributed surface subsidence of southeastern Tibet are consequences of crustal flow and gravitational collapse. Overall, the Tibetan Plateau is characterized by continuous deformation, with large spatial variations accommodated by complicated tectonic processes.