Characterizing groundwater/surface-water interactions in the interior of Jianghan Plain,central China

Hydrogeology Journal - Quantifying groundwater/surface-water interactions is essential for managing water resources and revealing contaminant fate. There has been little concern on the exchange...     

Landslides triggered by the 2016 Mj 7.3 Kumamoto,Japan, earthquake

The aim of this study is to establish a detailed and complete inventory of the landslides triggered by the Mj 7.3 (Mw 7.0) Kumamoto, Japan, earthquake sequence of 15 April 2016 (16 April in JST). Based on high-resolution (0.5–2 m) optical satellite images, we delineated 3,467 individual landslides triggered by the earthquake, occupying an area of about 6.9 km². Then they were validated by aerial photographs with very high-resolution (better than 0.5 m) and oblique field photos. Of them, 3,460 landslides are distributed in an elliptical area about 6000 km², with a NE-SW directed 120-km-long long axis and a 60-km-long NW-SE trending short axis. Most of the landslides are shallow, disrupted falls and slides, with a few flow-type slides and rock and soil avalanches. The analysis of correlation between the landslides and several control factors shows the areas of elevation 1000–1200 m, stratum of Q₃-Hvf, seismic intensity VIII and VIII+, and peak ground acceleration (PGA) 0.4–0.6 g register the highest landslide abundance. This study also discussed the relationship between the spatial pattern of the landslides and the seismotectonic structure featured by a strike-slip fault with a normal component and the volcanism in the study area.     

Study on the deformation and failure modes of filling slope in loess filling engineering: a case study at a loess mountain airport

Lvliang airport is a typical loess filling engineering located in 20.5 km north of Lvliang City in Shanxi Province, China. By the end of March 2012, 14 fissures extending more than 7.5 m were observed in a loess-filled slope, of which the longest fissure is up to 82 m. Field monitoring and laboratory tests have been performed to investigate the slope failure modes. The test program includes wetting tests on unsaturated compacted samples and stress path tests on saturated samples. Field monitoring and observations show that differential settlement caused by non-homogeneity in compacted loess density might lead to the formation of fissures in the loess-filled slope. It was founded that the wetting deformation contributed to the development of differential settlement. Fissures are the essential factor for the loess-filled slope failure. Four deformation stages exhibit in the loess-filled slope prior final failure including development of the fissures, softening of the compacted loess, creeping of the slope leading edge and fissuring of the trailing edge and formation of the through-sliding surface. Development of the sliding surface mainly includes upward and downward expansion of the fissures. Upward expansion is a wetting failure process in loading condition, while downward expansion is a load-off wetting process. In addition, development of the sliding surface is accelerated by softening of the compacted soils as a result of water infiltration. Therefore, the key for taking countermeasures against filling landslides is to monitor and control the development of differential settlement and fissures in the slope shoulders. Digging out and extra-filling the fissures are an effective way for preventing these landslides.     

Comparison of single- and dual-permeability models in simulating the unsaturated hydro-mechanical behavior in a rainfall-triggered landslide

Landslide-prone slopes in earthquake-affected areas commonly feature heterogeneity and high permeability due to the presence of cracks and fissures that were caused by ground shaking. Landslide reactivation in heterogeneous slope may be affected by preferential flow that was commonly occurred under heavy rainfall. Current hydro-mechanical models that are based on a single-permeability model consider soil as a homogeneous continuum, which, however, cannot explicitly represent the hydraulic properties of heterogeneous soil. The present study adopted a dual-permeability model, using two Darcy-Richards equations to simulate the infiltration processes in both matrix and preferential flow domains. The hydrological results were integrated with an infinite slope stability approach, attempting to investigate the hydro-mechanical behavior. A coarse-textured unstable slope in an earthquake-affected area was chosen for conducting artificial rainfall experiment, and in the experiment slope, failure was triggered several times under heavy rainfall. The simulated hydro-mechanical results of both single- and dual-permeability model were compared with the measurements, including soil moisture content, pore water pressure, and slope stability conditions. Under high-intensity rainfall, the measured soil moisture and pore water pressure at 1-m depth showed faster hydrological response than its simulations, which can be regarded as a typical evidence of preferential flow. We found the dual-permeability model substantially improved the quantification of hydro-mechanical processes. Such improvement could assist in obtaining more reliable landslide-triggering predication. In the light of the implementation of a dual-permeability model for slope stability analysis, a more flexible and robust early warning system for shallow landslides hazard in coarse-textured slopes could be provided.     

Petrophysical characterisation of tight sandstone gas reservoirs using nuclear magnetic resonance: a case study of the upper Paleozoic strata in the Kangning area,eastern margin of the Ordos Basin,China

Residual and movable porosity are significant parameters for characterising petrophysical properties, especially in tight reservoirs. Eight tight sandstone samples from the upper Paleozoic gas-bearing strata in the Kangning area, from the eastern margin of the Ordos Basin, were analysed using nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), petrography, and porosity and permeability tests. The lithology and pore types were identified and classified using petrography and SEM. The residual and movable porosity were obtained with NMR. In addition, NMR was used to visualise pore structure and pore size distribution. The results suggest that the upper Paleozoic sandstones in the study area mainly comprise feldspathic litharenite and litharenite. The sandstone porosity and permeability are low, with means of 5.9% and 0.549 mD, respectively. Four pore types exist in the tight sandstones: residual primary pores, grain dissolution pores, micropores (clay-dominated) and microfractures. The T₂ spectra under water-saturated conditions correlate with pore size and can be used to distinguish small and large pores based on the transverse relaxation time cutoff value of 10 ms, which corresponds to a pore diameter of 0.232 μm. Small pores account for 72% of the pores in the tight sandstones. The continuous bimodal T₂ spectra suggest good connectivity between small and large pores, despite the low porosity and permeability. In this study, the movable porosity of the major tight sandstone gas reservoirs is higher than the residual porosity, which confirms the effective evaluation of movable porosity to tight sandstone reservoirs, based on NMR experiments.     

Geochemical Characteristics and Tectonic Significance of Aoyougou Group Basalts in Western North Qilian

The North Qilian orogenic belt is a typical plate suture zone, which is studded with numerous different sizes of fragments of micro-continental crust consisting of pre-Sinian metamorphic rocks and the North Qilian orogenic belt provides important study carrier for studying the pre-orogenic tectonic process of the North Qilian. The relatively complete volcanic-clastic-carbonate rocks formation of Zhulongguan Group, Changchengian System, Mesoproterozoic are distributed in the Kawa-Qiqing area, Western North Qilian orogenic belt. Geochemical characteristics of the Aoyougou Group basalts in the North Qilian indicated that the contents of major element were relatively stable, high K₂O contents(4.27%~6.07%), TFe₂O₃(10.49%~13.01%),TiO₂(1.96%~2.90%)and middle MgO(5.37%~6.71%,Mg^# 48~51), CaO(2.57%~5.51%)content. Thus, the Aoyougou Group basalts belong to potassium alkaline basalt. The contents of Cr and Ni of the basalts decreased with the decreasing of Mg^#, and there was a positive correlation between CaO and CaO/Al₂O₃, Furthermore, the Eu anomaly of samples was slightly negative, high contents of high field strength elements (HFSE, Nb, Ta, Ti), and the ratios of Gd/Yb(2.5~3.0), Zr/Y(8.6~10.2), Ta/Yb(0.96~1.23), Ti/Yb(5 074~6 021), Zr/Yb(81~97), Ce/Nb(1.87), Zr/Nb(6.41)indicated that the Aoyougou Group basalts had obvious OIB-type magmatic affinity. In combination with the regional geological background, the study results showed that Aoyougou Group alkaline basalt generated from deep enrichment mantle similar to the source of OIB, with fractional crystallization of olivine and monoclinic pyroxene and a certain degree of contamination of continental crust in the process of magmatism, formed in the background of continental rift, might response to the Proterozoic Columbia supercontinent rifting, which further provides important petrological evidences for the relationship between North China Craton rifting events and Columbia supercontinent rifting during Proterozoic.     

Objective Analysis on Large-scale Circulation Type and Its Links to Precipitation over China

Atmospheric circulation anomaly is a direct cause of weather and climate change. In the past, most researches for the relationship between Weather Type (WT) and precipitation have mainly focused on the subjective classification and diagnosis. Compared to the subjective analysis, objective classification uses more consistent index and standard unification, thus, we can get more WTs, and it has been widely used in many areas. By using daily 12UTC Sea Level Pressure (SLP), Precipitable Water (PW), and 700 hPa wind speed (UV700) data from ECMWF’s Interim Reanalysis, the classification of WTs over China was performed with the method of obliquely rotated T-mode principle component analysis. WT and its link to precipitation over China were further analyzed. The results show that the influence of different WTs on precipitation is not uniform over China, and also show distinctly difference in different seasons. A common feature is that WTs great impact on the regions and months with large precipitation, while less impact on regions and months have with less precipitation. In addition, precipitation trends originating from WT intensity changes are much more deterministic, significant, and predictable than trends from WT frequency changes.     

Water Cycle Analysis of Social and Economic System in Tarim River Basin

Water cycle includes natural water circulation and social economic system water cycle. The concept of virtual water provides a new method and means for studying social water circulation. This paper is based on the theory of water circulation in social and economic system, using input-output analysis method quantitatively describes the Tarim River basin of social water cycle paths and analysis of water resources management in Tarim River basin sustainable development process of the key issues. The results show that the main sectors of virtual water export in the Tarim River Basin are agriculture, petroleum, natural gas and food industry. Agricultural water accounts for more than 98% of total water consumption, most of which is transferred to the food and textile industries, and the food industry export water from the agricultural sector. Shandong Province is the largest virtual water transport area in the Tarim River Basin. The main sector of virtual water input in the Tarim River Basin is the metallurgical industry. Finally, in view of the problems arising from the inter-industrial and inter-regional social water circulation in the Tarim River basin, the paper puts forward the ways and strategies of regulating agricultural and industrial water use in the Tarim River Basin.     

Performance of GPS and GPS/SINS navigation in the CE-5T1 skip re-entry mission

A CE-5T1 spacecraft completed a high-speed skip re-entry to the earth after a circumlunar flight on October 31, 2014. In addition to the strapdown inertial navigation system (SINS), a lightweight GPS receiver with rapid acquisition was developed as a navigation sensor in the re-entry capsule. The GPS receiver effectively solved the poor accuracy problem of long-term navigation using only the SINS. In contrast to ground users and low-earth-orbit spacecraft, numerous factors, including high altitude and kinetic characteristics in high-speed skip re-entry, are important for GPS positioning feasibility and were presented in accordance with the flight data. GPS solutions started at nearly 4900 km orbital altitude during the phases of re-entry process. These solutions were combined by an inertial measurement unit in a loosely coupled integrated navigation method and SINS navigation initialization. A simplified GPS/SINS navigation filter for limited resources was effectively developed and implemented on board for spacecraft application. Flight data estimation analyses, including trajectory, attitude, position distribution of GPS satellite, and navigation accuracy, were presented. The estimated accuracy of position was better than 42 m, and the accuracy of velocity was better than 0.1 m/s.     

Mapping hourly dynamics of urban population using trajectories reconstructed from mobile phone records

Understanding the spatiotemporal dynamics of urban population is crucial for addressing a wide range of urban planning and management issues. Aggregated geospatial big data have been widely used to quantitatively estimate population distribution at fine spatial scales over a given time period. However, it is still a challenge to estimate population density at a fine temporal resolution over a large geographical space, mainly due to the temporal asynchrony of population movement and the challenges to acquiring a complete individual movement record. In this article, we propose a method to estimate hourly population density by examining the time‐series individual trajectories, which were reconstructed from call detail records using BP neural networks. We first used BP neural networks to predict the positions of mobile phone users at an hourly interval and then estimated the hourly population density using log‐linear regression at the cell tower level. The estimated population density is linearly correlated with population census data at the sub‐district level. Trajectory clustering results show five distinct diurnal dynamic patterns of population movement in the study area, revealing spatially explicit characteristics of the diurnal commuting flows, though the driving forces of the flows need further investigation.