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[en] The EW-trending Kunlun Fault System (KFS) is one of the major left-lateral strike-slip faults on the Tibetan Plateau. It forms the northern boundary of the Bayan Har block. Heretofore, no evidence has been provided for the most recent event (MRE) of the ~70-km-long eastern section of the KFS. The studied area is located in the north of the Zoige Basin (northwest Sichuan province) and was recognized by field mapping. Several trenches were excavated and revealed evidence of repeated events in late Holocene. The fault zone is characterized by a distinct 30–60-cm-thick clay fault gouge layer juxtaposing the hanging wall bedrock over unconsolidated late Holocene footwall colluvium and alluvium. The fault zone, hanging wall, and footwall were conformably overlain by undeformed post-MRE deposits. Samples of charred organic material were obtained from the top of the faulted sediments and the base of the unfaulted sediments. Modeling of the age of samples, earthquake yielded a calibrated 2σ radiocarbon age of A.D. 1489 ± 82. Combined with the historical earthquake record, the MRE is dated at A.D. 1488. Based on the over ~50 km-long surface rupture, the magnitude of this event is nearly Mw ~7.0. Our data suggests that a ~200-km-long seismic gap could be further divided into the Luocha and Maqu sections. For the last ~1000 years, the Maqu section has been inactive, and hence, it is likely that the end of its seismic cycle is approaching, and that there is a potentially significant seismic hazard in eastern Tibet.
[en] Aeolian desertification is one of the primary factors that impede sustainable socio-economic development in China’s Tibet Autonomous Region. To develop a set of science-based preventive measures, it is first necessary to understand the temporal and spatial distribution of aeolian desertified land (ADL) and the driving factors responsible for its creation. In this study, we used Landsat MSS, TM, and ETM data from the 1970s, 1990s, 2000s, and 2010s to classify ADL into different types, and distribution of ADL in the Tibet Autonomous Region was described. The results showed that by 2010, ADL covered an area of 203,476 km2 and was primarily (91.5 %) the gravel surface (gobi) type. The area of ADL and desertification severity increased from the south-east to the north-west. During the study period, aeolian desertification experienced three development stages: initial rapid development, subsequent slower development, and a final period of slow reversal. The area of ADL increased by a total of 3134 km2 from 1977 to 2010, but the temporal trends differed among the three main sub-regions of Tibet. Increasing drought and irrational human activities have caused an expansion of desertification in some areas, whereas ecological restoration projects contributed to the reversal of desertification in others.
[en] Complete text of publication follows. Paleomagnetic study in southern Tibet and the Higher Himalayan Crystalline (HHC) was twofold: (1) the recognition of vertical and horizontal block rotations and (2) the examination of the high grade metamorphic rocks (gneisses) from the HHC for their suitability for paleomagnetic investigations. Toward the separation of local and regional tectonic effects, the results from southern Tibet reflect a regional trend in agreement with oroclinal bending and rotational under-thrusting. On the other hand, measured 'anomalous inclinations' are interpreted as a consequence of extensional tectonic, and the circular distribution of magnetic remanences is attributed to long wavelength folding within the study area as well as doming in the crust. The examination of the high grade metamorphic rocks was successful: The high quota of isolated stable and well grouping secondary magnetic remanences, demonstrate their suitability for paleomagnetic investigations. A high potential source is therefore established which enable considerable contributions within the thermo-tectonic evolution of an orogen. Data suggest no significant vertical rotation on a regional scale versus India. A regional trend comparable to that obtained for south Tibet, and expressed as a dispersion of remanence vector directions on a small circle is observed. The new findings are in disagreement with the hypothesis of a uniform clockwise rotation increasing to the east of the Himalayan arc. A major effect, inferred from paleomagnetic data, attributed to long wavelength folding, doming and associated low/high normal faults/thrust system became more evident. In summary, paleomagnetism is a potential applied method in deciphering deformation processes on local-, meso- and regional scale.
[en] The characteristics of spatio-temporal seismicity evolution before the Wenchuan earthquake are studied. The results mainly involve in the trend abnormal features and its relation to the Wenchuan earthquake. The western Chinese mainland and its adjacent area has been in the seismically active period since 2001, while the seismic activity shows the obvious quiescence of M≥7.0, M≥6.0 and M≥5.0 earthquakes in Chinese mainland. A quiescence area with M≥7.0 has been formed in the middle of the North-South seismic zone since 1988, and the Wenchuan earthquake occurred just within this area. There are a background seismicity gap of M≥5.0 earthquakes and a seismogenic gap of ML≥4.0 earthquakes in the area of Longmenshan fault zone and its vicinity prior to the Wenchuan earthquake. The seismic activity obviously strengthened and a doughnut-shape pattern of M≥4.6 earthquakes is formed in the middle and southern part of the North-South seismic zone after the 2003 Dayao, Yunnan, earthquake. Sichuan and its vicinity in the middle of the doughnut-shape pattern show abnormal quiescence. At the same time, the seismicity of earthquake swarms is significant and shows heterogeneity in the temporal and spatial process. A swarm gap appears in the M4.6 seismically quiet area, and the Wenchuan earthquake occurred just on the margin of the gap. In addition, in the short term before the Wenchuan earthquake, the quiescence of earthquake with ML≥4.0 appears in Qinghai-Tibet block and a seismic belt of ML≥3.0 earthquakes, with NW striking and oblique with Longmenshan fault zone, is formed.
[en] Meteorological observations in Tibet are poor in quality with a severe amount of missing data; this is mostly caused by extreme climatological conditions and higher maintenance costs. This paper focuses on the imputation of missing data and the reconstruction of the regional temperature field. Due to insufficient observation stations and complicated topography, we employ the weather research and forecasting (WRF) model to produce the proper orthogonal decomposition (POD) basis for the study region. We then develop the gappy POD method for the imputation of missing data. Both methods are compared and tested for various missing data cases, and the results show that the gappy POD method dramatically outperforms the regularized EM algorithm when the amount of missing spatial data is not severe. Furthermore, between the two methods, only the gappy POD method is capable of reconstructing the temperature field at locations where the data are absent. The gappy POD method can also be generalized for data assimilation with the assumption that the data across all model grids have missing values.
[en] In order to better understand the ecosystems of the Qinghai-Tibet Plateau, we studied the characteristics of the vegetation and soil on Mount Sejila in Tibet, at altitudes ranging from 3700m to 4700m was studied. Eleven sampling areas were examined, and the vegetation composition, species diversity, plant biomass and soil properties were measured in each one. Representatives of 99 different plant species from 26 families were identified, and the plant communities exhibited a clear degree of altitude dependence: some species were found in all samples while others were only present in a single sampling area. Plant aboveground biomass correlated negatively with altitude, but the species diversity (based on the Shannon-Wiener and Simpson diversity indices as well as evenness and species richness measurements) were not altitude dependent. Community similarity decreased as the difference in altitude between sites increased. The measured soil properties had significant effects on plant characteristics, especially the soil nitrogen, soil moisture and temperature. The results presented herein provide a solid foundation for a more comprehensive study of the Qinghai-Tibet Plateau's ecosystems and will be useful in drawing up biodiversity and ecosystem preservation schemes. (author)
[en] Accurate measurements of wet mercury (Hg) deposition are critically important for the assessment of ecological responses to pollutant loading. The Hg in wet deposition was measured over a 3-year period in the southeastern Tibetan Plateau. The volume-weighted mean (VWM) total Hg (Hg_T) concentration was somewhat lower than those reported in other regions of the Tibetan Plateau, but the VWM methyl-Hg concentration and deposition flux were among the highest globally reported values. The VWM Hg_T concentration was higher in non-monsoon season than in monsoon season, and wet Hg_T deposition was dominated by the precipitation amount rather than the scavenging of atmospheric Hg by precipitation. The dominant Hg species in precipitation was mainly in the form of dissolved Hg, which indicates the pivotal role of reactive gaseous Hg within-cloud scavenging to wet Hg deposition. Moreover, an increasing trend in precipitation Hg concentrations was synchronous with the recent economic development in South Asia. - Highlights: • The lowest Hg_T concentration in precipitation was found at Southeast Tibet Station. • MeHg concentration and wet deposition flux were among the highest at our study site. • Hg_D dominated the concentration and flux of Hg_T in wet Hg deposition. • A long-term increasing trend in the Hg_T concentration was found at our study site. - An increasing trend in the precipitation Hg concentrations was synchronous with the recent economic development in South Asia.
[en] The contemporary tectonic stress field in China is obtained on the basis of Chinese stress field database and Harvard CMT catalogue. Result of the inverted tectonic stresses shows that the maximum principal stress axis strikes nearly north-south direction in the west part of Tibet plateau, ENE direction in North China. In Central China, its strikes show a radiated pattern, i.e., NNE in north part and NNW in south part. The detailed stress field parameters of nearly whole China are given and can be used in geodynamic stress field simulation and earthquake prediction.
[en] The Tibetan Plateau (TP) has experienced significant climate changes in recent decades. Wind stilling is one of the most evident changes based on observations. This study assesses near-surface wind speed simulations from three WRF dynamical downscalings over the TP. The assessment is conducted by comparing with observations at 83 stations over the TP and ERA-Interim in 1980–2005. Results show that the three dynamical downscalings and ERA-Interim all overestimated the annual and seasonal wind speeds over the TP, especially in winter. Overestimation of the U component is the main contributor to the overestimation of near-surface wind speeds. The difference between grid and station elevations partly contributes to the larger overestimation, particularly in 3000–4000 m. Impacts of the land surface scheme on the simulations of wind speed are also noticed. Observations show significant decreasing wind speed trend and the variability is larger at higher elevations above 4000 m, which are not represented in the ERA-Interim. Affected by forcing, the dynamical downscalings do not capture the observed significantly decreasing trend, but they outperform the forcing in winter. The better performance in winter but summer is mainly because the dynamical downscalings are unable to reproduce the observed direction of the U component in summer. The ability of dynamical downscalings to simulate the near-surface wind speed may be improved by choosing forcing with better linear trends, enhancing the momentum transports in the planetary boundary parameterization scheme, and considering the unresolved topographic features sufficiently.
[en] We use interferometric synthetic aperture radar (InSAR) and broadband seismic waveform data to estimate a source model of the 11th July, 2004 MW6.2 Zhongba earthquake, Tibet of China. This event occurred within the seismically active zone of southwestern Tibetan Plateau where the east-west extension of the upper crust is observed. Because of limitations in one pair of InSAR data available, there are trade-offs among centroid depth, rupture area and amount of slip. Available seismic data tightly constrain the focal mechanism and centroid depth of the earthquake but not the horizontal location. Together, two complementary data sets can be used to identify the actual fault plane, better constrain the slip model and event location. We first use regional seismic waveform to estimate point source mechanism, then InSAR data is used to obtain better location. Finally, a joint inversion of teleseismic P-waves and InSAR data is performed to obtain a distributed model. Our preferred point source mechanism indicates a seismic moment of ∼2.2×1018 N·m (MW6.2), a fault plane solution of 171° (342°)/42°(48°)/−83°(−97°), corresponding to strike/dip/rake, and a depth of 11 km. The fault plane with strike of 171° and dip of 42° is identified as the ruptured fault with the aid of InSAR data. The preferred source model features compact area of slips between depth of 5–11 km and 10 km along strike with maximum slip amplitude of about 1.5 m.