The topographies of the 410-km and 660-km discontinuities have important implications for mantle dynamics.Here we present high-resolution seismic imaging of the 410-km and 660-km discontinuities beneath the North Chin...The topographies of the 410-km and 660-km discontinuities have important implications for mantle dynamics.Here we present high-resolution seismic imaging of the 410-km and 660-km discontinuities beneath the North China Craton (NCC) employing the receiver function method.Depth anomalies (deeper or shallower than the global average depths) at both discontinuities were detected by introducing a three-dimensional regional velocity model.The depressions of the 410-km discontinuity are mostly located in the eastern NCC.A local elevation of the 660-km discontinuity appeared in the northwest of the NCC and a significant depression of the 660-km discontinuity is located in the southeast of the NCC.Two dynamic mantle regimes are speculated to explain the formation of the anomalous depth zones in the NCC.One possibility is a complex mantle upwelling linked to edge-derived convection between the stagnant slab and the thick cratonic root.The other potential dynamic regime is slab stagnating,sinking,and induced upwelling at the neighboring slab front.These regimes hint that the mantle flow was possibly dominated by dynamic interactions among the subducting slab,cratonic root,and ambient mantle beneath the NCC.展开更多
It is important to quantify the effect of the root diameter, the embedment length of the root and load speed on the soil-root interface mechanical properties for studying the root anchorage. The soilroot interface mec...It is important to quantify the effect of the root diameter, the embedment length of the root and load speed on the soil-root interface mechanical properties for studying the root anchorage. The soilroot interface mechanical properties can be obtained through the pullout force and root slippage curve(F-S curve). About 120 Pinus tabulaeformis single roots whose diameters ranged from 1 mm to 10 mm divided into 6 groups based on different root embedment length(50 mm, 100 mm and 150 mm) and different load velocity(10 mm·min^(-1), 50 mm·min^(-1), 100 mm·min^(-1) and 300 mm·min^(-1)) were investigated using the pullout method. This study aims to explore the mechanical properties of the soil-root interface in the real conditions using the pullout test method. The results showed two kinds of pullout test failure modes during the experimental process: breakage failure and pullout failure. The results showed that the roots were easier to be broken when the root diameter was smaller or the loading speed was larger. The relationship between the maximum anchorage force and root diameter was linear and the linearly dependent coefficient(R^2) was larger than 0.85. The anchorage force increased with the root embedment length. An increase of 10%^(-1)5% for the maximumanchorage force was found when load speed increased from 10 to 300 mm.min^(-1). The mean peak slippage of the root was from 13.81 to 35.79 mm when the load velocity varied from 10 to 300 mm.min^(-1). The study will be helpful for the design of slopes reinforced by vegetation and in predicting risk of uprooting of trees, and will have practical benefits for understanding the mechanism of landslide.展开更多
Based on the 3-D Earth model, the common convert points-phase weighted stacks (CCP-PWS) migra- tion method is used to image the upper mantle discontinuities beneath Northeast China (longitude 120°―132°; lat...Based on the 3-D Earth model, the common convert points-phase weighted stacks (CCP-PWS) migra- tion method is used to image the upper mantle discontinuities beneath Northeast China (longitude 120°―132°; latitude 38°―40°) with 802 observed receiver functions. Teleseismic records are obtained from 4 stations belonging to CCDSN and 19 stations belonging to PASSCAL. A low-velocity layer has been detected at the depth of 620 km. This low-velocity layer rises to 600 km in the east of the study region close to the subducted slab. We consider that this low-velocity layer might be the accumulated oceanic crustal material delaminated from the western Pacific subducted slab. Additionally, we detect the obvious depression of 660 km discontinuity which was attributed to the interaction between the upper mantle and subducted slab. The maximum depth of 660 km discontinuity approaches 700 km, and 660 km discontinuity splits into multiple discontinuities in the northeast of the study region.展开更多
Active velocity tomography was used to determine the stress state and rock burst hazards in a deep coal mine. The deepest longwall face, number 3207 in the Xingcun colliery, was the location of the field trials. The p...Active velocity tomography was used to determine the stress state and rock burst hazards in a deep coal mine. The deepest longwall face, number 3207 in the Xingcun colliery, was the location of the field trials. The positive correlation between stress and seismic velocity was used to link the velocity data with stratum stresses. A GeoPen SE2404NT data acquisition system was used to collect seismic data from 300 g explosive charges fired by instantaneous electric detonator and located in the tail entry. The geophones were installed on the rock bolts in the head entry of LW3207. Velocity inversion shows an inhomogeneous distribution of stress in the longvvall face that could not be obtained from theory or numerical simulations. Three abnormally high P-wave velocity regions were identified that were located on the corners of the two roadways and at the face end near the rail entry side. The maximum velocity gradient is located at the open cut off near the rail entry and is the area most dangerous for rock burst. Mining-induced tremors recorded by a micro-seismic monitoring system demonstrated that the position of energy release during mining coincides with the high velocity gradient area. This technology aids technicians in the coal mine as they design measures to weaken or eliminate potential danger during subsequent mining.展开更多
大伦敦政府成立的背景
伦敦是英国首都,是英国的经济、文化和交通中心,也是英国最大海港和首要工业城市.它位于英格兰东南部,跨泰晤士河下游两岸,距河口88公里.伦敦面积约1580平方公里,其东西轴长近48公里,南北轴长42公里.伦敦范围分为...大伦敦政府成立的背景
伦敦是英国首都,是英国的经济、文化和交通中心,也是英国最大海港和首要工业城市.它位于英格兰东南部,跨泰晤士河下游两岸,距河口88公里.伦敦面积约1580平方公里,其东西轴长近48公里,南北轴长42公里.伦敦范围分为两个圈层:内层被称内伦敦,有12个自治市(borough)和伦敦城(the City of London)1,面积310平方公里;外层被称为外伦敦,有20个自治市,面积为1270平方公里.由于地方自治的传统面临城市快速发展的挑战,伦敦城市管理体制经历了若干次变迁.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 90814002)Chinese Academy of Sciences
文摘The topographies of the 410-km and 660-km discontinuities have important implications for mantle dynamics.Here we present high-resolution seismic imaging of the 410-km and 660-km discontinuities beneath the North China Craton (NCC) employing the receiver function method.Depth anomalies (deeper or shallower than the global average depths) at both discontinuities were detected by introducing a three-dimensional regional velocity model.The depressions of the 410-km discontinuity are mostly located in the eastern NCC.A local elevation of the 660-km discontinuity appeared in the northwest of the NCC and a significant depression of the 660-km discontinuity is located in the southeast of the NCC.Two dynamic mantle regimes are speculated to explain the formation of the anomalous depth zones in the NCC.One possibility is a complex mantle upwelling linked to edge-derived convection between the stagnant slab and the thick cratonic root.The other potential dynamic regime is slab stagnating,sinking,and induced upwelling at the neighboring slab front.These regimes hint that the mantle flow was possibly dominated by dynamic interactions among the subducting slab,cratonic root,and ambient mantle beneath the NCC.
基金supported by the Fundamental Research Funds for the Central Universities(No.YX2010-20)the Open Projects Foundation of Key Laboratory of Soil and Water Conservation & Desertification Combat (Beijing ForestryUniversity), Ministry of Education of P.R. China (No.201002) the National Natural Science Foundation of China (No. 31570708, No.30901162)
文摘It is important to quantify the effect of the root diameter, the embedment length of the root and load speed on the soil-root interface mechanical properties for studying the root anchorage. The soilroot interface mechanical properties can be obtained through the pullout force and root slippage curve(F-S curve). About 120 Pinus tabulaeformis single roots whose diameters ranged from 1 mm to 10 mm divided into 6 groups based on different root embedment length(50 mm, 100 mm and 150 mm) and different load velocity(10 mm·min^(-1), 50 mm·min^(-1), 100 mm·min^(-1) and 300 mm·min^(-1)) were investigated using the pullout method. This study aims to explore the mechanical properties of the soil-root interface in the real conditions using the pullout test method. The results showed two kinds of pullout test failure modes during the experimental process: breakage failure and pullout failure. The results showed that the roots were easier to be broken when the root diameter was smaller or the loading speed was larger. The relationship between the maximum anchorage force and root diameter was linear and the linearly dependent coefficient(R^2) was larger than 0.85. The anchorage force increased with the root embedment length. An increase of 10%^(-1)5% for the maximumanchorage force was found when load speed increased from 10 to 300 mm.min^(-1). The mean peak slippage of the root was from 13.81 to 35.79 mm when the load velocity varied from 10 to 300 mm.min^(-1). The study will be helpful for the design of slopes reinforced by vegetation and in predicting risk of uprooting of trees, and will have practical benefits for understanding the mechanism of landslide.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40574024 and 40374009)
文摘Based on the 3-D Earth model, the common convert points-phase weighted stacks (CCP-PWS) migra- tion method is used to image the upper mantle discontinuities beneath Northeast China (longitude 120°―132°; latitude 38°―40°) with 802 observed receiver functions. Teleseismic records are obtained from 4 stations belonging to CCDSN and 19 stations belonging to PASSCAL. A low-velocity layer has been detected at the depth of 620 km. This low-velocity layer rises to 600 km in the east of the study region close to the subducted slab. We consider that this low-velocity layer might be the accumulated oceanic crustal material delaminated from the western Pacific subducted slab. Additionally, we detect the obvious depression of 660 km discontinuity which was attributed to the interaction between the upper mantle and subducted slab. The maximum depth of 660 km discontinuity approaches 700 km, and 660 km discontinuity splits into multiple discontinuities in the northeast of the study region.
基金support for this work was provided by the National Basic Research Program of China (No. 2010CB226805)the National Natural Science Foundation of China (Nos. 50474068 and50490273)+1 种基金the Independent Foundation of State Key Laboratory of Coal Resources and Mine Safety (No. SKLCRSM10X05)the Open Foundation of State Key Laboratory of Coal Resources and Mine Safety (No. 10KF05)
文摘Active velocity tomography was used to determine the stress state and rock burst hazards in a deep coal mine. The deepest longwall face, number 3207 in the Xingcun colliery, was the location of the field trials. The positive correlation between stress and seismic velocity was used to link the velocity data with stratum stresses. A GeoPen SE2404NT data acquisition system was used to collect seismic data from 300 g explosive charges fired by instantaneous electric detonator and located in the tail entry. The geophones were installed on the rock bolts in the head entry of LW3207. Velocity inversion shows an inhomogeneous distribution of stress in the longvvall face that could not be obtained from theory or numerical simulations. Three abnormally high P-wave velocity regions were identified that were located on the corners of the two roadways and at the face end near the rail entry side. The maximum velocity gradient is located at the open cut off near the rail entry and is the area most dangerous for rock burst. Mining-induced tremors recorded by a micro-seismic monitoring system demonstrated that the position of energy release during mining coincides with the high velocity gradient area. This technology aids technicians in the coal mine as they design measures to weaken or eliminate potential danger during subsequent mining.
文摘大伦敦政府成立的背景
伦敦是英国首都,是英国的经济、文化和交通中心,也是英国最大海港和首要工业城市.它位于英格兰东南部,跨泰晤士河下游两岸,距河口88公里.伦敦面积约1580平方公里,其东西轴长近48公里,南北轴长42公里.伦敦范围分为两个圈层:内层被称内伦敦,有12个自治市(borough)和伦敦城(the City of London)1,面积310平方公里;外层被称为外伦敦,有20个自治市,面积为1270平方公里.由于地方自治的传统面临城市快速发展的挑战,伦敦城市管理体制经历了若干次变迁.
