We assembled approximately 328 seismic records. The data set was from 4 digitally recording long-period and broadband stations of CDSN. We carried out the inversion based on the partitioned waveform inversion (PWI). I...We assembled approximately 328 seismic records. The data set was from 4 digitally recording long-period and broadband stations of CDSN. We carried out the inversion based on the partitioned waveform inversion (PWI). It partitions the large-scale optimization problem into a number of independent small-scale problems. We adopted surface waveform inversion with an equal block (2((2() discretization in order to acquire the images of shear velocity structure at different depths (from surface to 430 km) in the crust and upper-mantle. The resolution of all these anomalies has been established with (check-board( resolution tests. These results show significant difference in velocity, lithosphere and asthenosphere structure between South China Sea and its adjacent regions.展开更多
We assume that the density anomalies, which are transformed from seismic tomography data, are corresponding to temperature distribution in a convective mantle. We take density anomalies as the driving force for mantle...We assume that the density anomalies, which are transformed from seismic tomography data, are corresponding to temperature distribution in a convective mantle. We take density anomalies as the driving force for mantle convection and solve the basic equation with given boundary conditions in a wave-number domain by using the FFT arithmetic. Using the physical model of upper mantle convection and the seismic tomography data supplied by XU et al, we calculated upper mantle convection beneath northwestern China and adjacent region. The flow patterns in the upper mantle show that there are upward and divergent flows in the basin regions, such as Tarim, Qaidam, Junggar and Kazakhstan, where the lithosphere is thin. There are downward and convergent flows in the mountain regions, such as Tianshan, Kunlun and Qilian, where the lithosphere is thick. In addition, because of the divergent flow under the Tarim Basin the upper mantle material in this region is driven southward to the north part of Tibetan Plateau and northward to Tianshan Mountain. Maybe, it is one of the reasons for the recent uplift of the Tianshaa Mountain.展开更多
Pn velocity lateral variation and anisotropy images were reconstructed by adding about 50 000 travel times from the regional seismic networks to the datum set of near 40 000 travel times from National Seismic Network ...Pn velocity lateral variation and anisotropy images were reconstructed by adding about 50 000 travel times from the regional seismic networks to the datum set of near 40 000 travel times from National Seismic Network of China used by WANG, et al. We discussed the relation of Pn velocity variation to Moho depth, Earths heat flow, distribution of Cenozoic volcanic rock and the result of rock experiment under high pressure and high temperature. The result of quantitative analysis indicates that Pn velocity is positively correlated with the crust thickness and negatively correlated with the Earths heat flow. Two linear regression equations, one between Pn velocity and crust thickness, and the other between Pn velocity and heat flow, were obtained. The rate of variation of Pn veloc-ity vP with pressure P, Pv/p, estimated from the velocity variation with crust thickness Hv/p, is close to the result obtained from the rock experiment under high pressure and high temperature. If the effect of crust thick-ness on Pn velocity is deducted from the velocity variation, then the low Pn velocity beneath Qinghai-Xizang pla-teau is more notable. The low Pn velocity regions well agree with the Cenozoic volcanic rock. In the several re-gions with significant anisotropy, the direction of fast Pn velocity is consistent with the orientation of maximum principal crustal compressive stress, and also with the direction of present-day crustal movement. It indicates that the fast Pn velocity direction may be related to the deformation or flow of top mantle material along the direction of maximum pressure.展开更多
In the arid region of northwestern China(ARNC),water resources are the most critical factor restricting socioeconomic development and influencing the stability of the area’s ecological systems.The region’s complex w...In the arid region of northwestern China(ARNC),water resources are the most critical factor restricting socioeconomic development and influencing the stability of the area’s ecological systems.The region’s complex water system and unique hydrological cycle show distinctive characteristics.Moreover,the intensified hydrological cycle and extreme climatic and hydrological events resulting from global warming have led to increased uncertainty around water resources as well as heightened conflict between water supply and water demand.All of these factors are exerting growing pressures on the socioeconomic development and vulnerable ecological environment in the region.This research evaluates the impacts of climate change on water resources,hydrological processes,agricultural system,and desert ecosystems in the ARNC,and addresses some associated risks and challenges specific to this area.The temperature is rising at a rate of 0.31C per decade during 1961–2017 and hydrological processes are being significantly influenced by changes in glaciers,snow cover,and precipitation form,especially in the rivers recharged primarily by melt water.Ecosystems are also largely influenced by climate change,with the Normalized Difference Vegetation Index(NDVI)of natural vegetation exhibited an increasing trend prior to 1998,and then reversed in Xinjiang while the Hexi Corridor of Gansu showed the opposite trends.Furthermore,the desert-oasis transition zone showed a reduction in area due to the warming trend and the recent rapid expansion of irrigated area.Both the warming and intensified drought are threatening agriculture security.The present study could shed light on sustainable development in this region under climate change and provides scientific basis to the construction of the“Silk Road Economic Belt”.展开更多
Pn velocity lateral variation and anisotropy images were reconstructed by adding about 50 000 travel times from the regional seismic networks to the datum set of near 40 000 travel times from National Seismic Network ...Pn velocity lateral variation and anisotropy images were reconstructed by adding about 50 000 travel times from the regional seismic networks to the datum set of near 40 000 travel times from National Seismic Network of China used by WANG, et al. We discussed the relation of Pn velocity variation to Moho depth, Earths heat flow, distribution of Cenozoic volcanic rock and the result of rock experiment under high pressure and high temperature. The result of quantitative analysis indicates that Pn velocity is positively correlated with the crust thickness and negatively correlated with the Earths heat flow. Two linear regression equations, one between Pn velocity and crust thickness, and the other between Pn velocity and heat flow, were obtained. The rate of variation of Pn veloc-ity vP with pressure P, Pv/p, estimated from the velocity variation with crust thickness Hv/p, is close to the result obtained from the rock experiment under high pressure and high temperature. If the effect of crust thick-ness on Pn velocity is deducted from the velocity variation, then the low Pn velocity beneath Qinghai-Xizang pla-teau is more notable. The low Pn velocity regions well agree with the Cenozoic volcanic rock. In the several re-gions with significant anisotropy, the direction of fast Pn velocity is consistent with the orientation of maximum principal crustal compressive stress, and also with the direction of present-day crustal movement. It indicates that the fast Pn velocity direction may be related to the deformation or flow of top mantle material along the direction of maximum pressure.展开更多
Using the monthly NCEP-NCAR reanalysis dataset, the monthly temperature and precipitation at surface stations of China, and the MM5 model, we examine impacts of vegetation cover changes in western China on the interde...Using the monthly NCEP-NCAR reanalysis dataset, the monthly temperature and precipitation at surface stations of China, and the MM5 model, we examine impacts of vegetation cover changes in western China on the interdecadal variability of the summer climate over northwestern China during the past 30 years. It is found that the summer atmospheric circulation, surface air temperature, and rainfall in the 1990s were different from those in the 1970s over northwestern China, with generally more rainfall and higher temperatures in the 1990s. Associated with these changes, an anomalous wave train appears in the lower troposphere at the midlatitudes of East Asia and the low-pressure system to the north of the Tibetan Plateau is weaker. Meanwhile, the South Asian high in the upper troposphere is also located more eastward. Numerical experiments show that change of vegetation cover in western China generally forces anomalous circulations and temperatures and rainfall over these regions. This consistency between the observations and simulations implies that the interdecadal variability of the summer climate over northwestern China between the 1990s and 1970s may result from a change of vegetation cover over western China.展开更多
Water demand increases continuously with an increasing population and economic development. As a result, the difference between water supply and demand becomes a sig- nificant issue, especially in arid regions. To fig...Water demand increases continuously with an increasing population and economic development. As a result, the difference between water supply and demand becomes a sig- nificant issue, especially in arid regions. To figure out the utilization of water resources in the arid region of northwestern China （ARNWC）, and also to provide methodologies to predict the water use in future, three models were established in this study to calculate agricultural irri- gation, industrial and domestic water use in the ARNWC from the late 1980s to 2010. Based on river discharges in the region, the supply and demand of water resources at the river basin level were analyzed. The results indicated that agricultural irrigation demand occupies more than 90% of the total water use in the ARNWC. Total water demand increased from 31.97 km3 in the late 1980s to 48.19 km3 in 2010. Most river basins in this arid region were under me- dium and high water stress. Severe-risk river basins, such as the Shiyang river basin and the eastern part of the northern piedmont of the Tianshan Mountains, were found in this region. It was revealed that the water supply became critical from April to May, which was the season of the lowest water supply as determined by comparing monthly water consumption.展开更多
基金State Natural Scientific Foundation (49734150) and National High Performance Computation Foundation.
文摘We assembled approximately 328 seismic records. The data set was from 4 digitally recording long-period and broadband stations of CDSN. We carried out the inversion based on the partitioned waveform inversion (PWI). It partitions the large-scale optimization problem into a number of independent small-scale problems. We adopted surface waveform inversion with an equal block (2((2() discretization in order to acquire the images of shear velocity structure at different depths (from surface to 430 km) in the crust and upper-mantle. The resolution of all these anomalies has been established with (check-board( resolution tests. These results show significant difference in velocity, lithosphere and asthenosphere structure between South China Sea and its adjacent regions.
基金The Project of Knowledge Innovation Program of Chinese Academy of Sciences (KZCX3-SW-131) and National Natural Science Foundation of China (40274033)
文摘We assume that the density anomalies, which are transformed from seismic tomography data, are corresponding to temperature distribution in a convective mantle. We take density anomalies as the driving force for mantle convection and solve the basic equation with given boundary conditions in a wave-number domain by using the FFT arithmetic. Using the physical model of upper mantle convection and the seismic tomography data supplied by XU et al, we calculated upper mantle convection beneath northwestern China and adjacent region. The flow patterns in the upper mantle show that there are upward and divergent flows in the basin regions, such as Tarim, Qaidam, Junggar and Kazakhstan, where the lithosphere is thin. There are downward and convergent flows in the mountain regions, such as Tianshan, Kunlun and Qilian, where the lithosphere is thick. In addition, because of the divergent flow under the Tarim Basin the upper mantle material in this region is driven southward to the north part of Tibetan Plateau and northward to Tianshan Mountain. Maybe, it is one of the reasons for the recent uplift of the Tianshaa Mountain.
基金State Key Basic Research Project of Development and Programming Mechanism and Prediction of Continental Strong Earthquakes (G1998040700).
文摘Pn velocity lateral variation and anisotropy images were reconstructed by adding about 50 000 travel times from the regional seismic networks to the datum set of near 40 000 travel times from National Seismic Network of China used by WANG, et al. We discussed the relation of Pn velocity variation to Moho depth, Earths heat flow, distribution of Cenozoic volcanic rock and the result of rock experiment under high pressure and high temperature. The result of quantitative analysis indicates that Pn velocity is positively correlated with the crust thickness and negatively correlated with the Earths heat flow. Two linear regression equations, one between Pn velocity and crust thickness, and the other between Pn velocity and heat flow, were obtained. The rate of variation of Pn veloc-ity vP with pressure P, Pv/p, estimated from the velocity variation with crust thickness Hv/p, is close to the result obtained from the rock experiment under high pressure and high temperature. If the effect of crust thick-ness on Pn velocity is deducted from the velocity variation, then the low Pn velocity beneath Qinghai-Xizang pla-teau is more notable. The low Pn velocity regions well agree with the Cenozoic volcanic rock. In the several re-gions with significant anisotropy, the direction of fast Pn velocity is consistent with the orientation of maximum principal crustal compressive stress, and also with the direction of present-day crustal movement. It indicates that the fast Pn velocity direction may be related to the deformation or flow of top mantle material along the direction of maximum pressure.
基金supported by the National Key Research and Development Program(2019YFA0606902)the National Natural Science Foundation of China(U1903208)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2019431).
文摘In the arid region of northwestern China(ARNC),water resources are the most critical factor restricting socioeconomic development and influencing the stability of the area’s ecological systems.The region’s complex water system and unique hydrological cycle show distinctive characteristics.Moreover,the intensified hydrological cycle and extreme climatic and hydrological events resulting from global warming have led to increased uncertainty around water resources as well as heightened conflict between water supply and water demand.All of these factors are exerting growing pressures on the socioeconomic development and vulnerable ecological environment in the region.This research evaluates the impacts of climate change on water resources,hydrological processes,agricultural system,and desert ecosystems in the ARNC,and addresses some associated risks and challenges specific to this area.The temperature is rising at a rate of 0.31C per decade during 1961–2017 and hydrological processes are being significantly influenced by changes in glaciers,snow cover,and precipitation form,especially in the rivers recharged primarily by melt water.Ecosystems are also largely influenced by climate change,with the Normalized Difference Vegetation Index(NDVI)of natural vegetation exhibited an increasing trend prior to 1998,and then reversed in Xinjiang while the Hexi Corridor of Gansu showed the opposite trends.Furthermore,the desert-oasis transition zone showed a reduction in area due to the warming trend and the recent rapid expansion of irrigated area.Both the warming and intensified drought are threatening agriculture security.The present study could shed light on sustainable development in this region under climate change and provides scientific basis to the construction of the“Silk Road Economic Belt”.
文摘Pn velocity lateral variation and anisotropy images were reconstructed by adding about 50 000 travel times from the regional seismic networks to the datum set of near 40 000 travel times from National Seismic Network of China used by WANG, et al. We discussed the relation of Pn velocity variation to Moho depth, Earths heat flow, distribution of Cenozoic volcanic rock and the result of rock experiment under high pressure and high temperature. The result of quantitative analysis indicates that Pn velocity is positively correlated with the crust thickness and negatively correlated with the Earths heat flow. Two linear regression equations, one between Pn velocity and crust thickness, and the other between Pn velocity and heat flow, were obtained. The rate of variation of Pn veloc-ity vP with pressure P, Pv/p, estimated from the velocity variation with crust thickness Hv/p, is close to the result obtained from the rock experiment under high pressure and high temperature. If the effect of crust thick-ness on Pn velocity is deducted from the velocity variation, then the low Pn velocity beneath Qinghai-Xizang pla-teau is more notable. The low Pn velocity regions well agree with the Cenozoic volcanic rock. In the several re-gions with significant anisotropy, the direction of fast Pn velocity is consistent with the orientation of maximum principal crustal compressive stress, and also with the direction of present-day crustal movement. It indicates that the fast Pn velocity direction may be related to the deformation or flow of top mantle material along the direction of maximum pressure.
基金sponsored by the National Basic Research Program of China (2009CB421404)the Chinese COPES project(GYHY200706005)+1 种基金the National Natural Science Foun-dation of China (40890052,40890053)the National Basic Research Program of China (2003DIB3J120)
文摘Using the monthly NCEP-NCAR reanalysis dataset, the monthly temperature and precipitation at surface stations of China, and the MM5 model, we examine impacts of vegetation cover changes in western China on the interdecadal variability of the summer climate over northwestern China during the past 30 years. It is found that the summer atmospheric circulation, surface air temperature, and rainfall in the 1990s were different from those in the 1970s over northwestern China, with generally more rainfall and higher temperatures in the 1990s. Associated with these changes, an anomalous wave train appears in the lower troposphere at the midlatitudes of East Asia and the low-pressure system to the north of the Tibetan Plateau is weaker. Meanwhile, the South Asian high in the upper troposphere is also located more eastward. Numerical experiments show that change of vegetation cover in western China generally forces anomalous circulations and temperatures and rainfall over these regions. This consistency between the observations and simulations implies that the interdecadal variability of the summer climate over northwestern China between the 1990s and 1970s may result from a change of vegetation cover over western China.
基金National Key Project on Basic Research(973),No.2010CB951003The National Science and Technology Project,No.2014BAD10B06
文摘Water demand increases continuously with an increasing population and economic development. As a result, the difference between water supply and demand becomes a sig- nificant issue, especially in arid regions. To figure out the utilization of water resources in the arid region of northwestern China （ARNWC）, and also to provide methodologies to predict the water use in future, three models were established in this study to calculate agricultural irri- gation, industrial and domestic water use in the ARNWC from the late 1980s to 2010. Based on river discharges in the region, the supply and demand of water resources at the river basin level were analyzed. The results indicated that agricultural irrigation demand occupies more than 90% of the total water use in the ARNWC. Total water demand increased from 31.97 km3 in the late 1980s to 48.19 km3 in 2010. Most river basins in this arid region were under me- dium and high water stress. Severe-risk river basins, such as the Shiyang river basin and the eastern part of the northern piedmont of the Tianshan Mountains, were found in this region. It was revealed that the water supply became critical from April to May, which was the season of the lowest water supply as determined by comparing monthly water consumption.
