P-wave traveltime and polarization tomography of VSP data

The presence of anisotropy requires that tomographic methods be generalized to account for anisotropy. This generalization allows geological structure to be correctly imaged and allows the anisotropic parameters to be estimated. Use of isotropic inversion for imaging anisotropic structures gives systematic trends in the traveltime and polarization residuals. However, due to the limited directional coverage, the traveltimes along may not be sufficient to study the anisotropic properties of the structure. Polarizations can provide independent information on the structure. Traveltime and polarization inversion are applied to synthetic examples simulating VSP experiments. Transverse isotropy and 1-D structure are assumed. Plots of traveltime and polarization residuals are an important tool to detect the anomalies due to the presence of anisotropy. For receivers located in anisotropic layers, polarization residuals display consistent anomalies of several degrees. The synthetic examples show that even the simple 1-D problem is difficult, when using direct arrivals only. Large a posteriori errors in anisotropic parameters are obtained by traveltime inversion in layers where available incidence angles are less than 45°. Resolution of the tomographic image of VSP data is greatly improved by a combination of traveltime and polarization information. In order to obtain accurate inversion results, the measurement error of polarization data should be kept to within a few degrees.     

The Lake Nyos disaster: model calculations for the flow of carbon dioxide

In order to explain the origin of the Lake Nyos Disaster, a three-dimensional model for carbon dioxide flow has been calculated. The boundary conditions were based on the field observations. Calculations show that CO₂ tends to flow down slope by gravity and velocity tends to increase on steep slopes. The results of calculation are in good agreements with the effects observed in the field. The initial velocity of the gas jet should have been 28 m/s, the volume of pure CO₂ 0.6 km³ and the gas release should occur in a very short time (a few minutes). The gas was released as a jet half way from the center on the south-south west side of the lake.     

国外对地缘视野下边境地区的研究进展及其启示

边境地区是国家重要的国土安全屏障和对外开放门户。在全球化、信息化的背景下,边境地区成为地理学、政治学和政治经济学的研究热点。科学认识和总结国际边境研究是推进学科发展的前提。本文以科学引文索引(Web of Science)中边境研究的学术论文为依据,借助于Citespace科学计量工具,系统回顾了国外1990-2015年边境研究的发展脉络、研究领域重点和研究趋势。从文献计量统计分析来看,1990年以来刊文量最大的期刊包括《政治地理学》(Political Geography)、《地缘政治学》(Geopolitics)等。国外边境研究的领域集中于政治地理、环境生态、商业经济、公共管治、人文艺术等方面。地缘政治视角下的领土、国家权力始终是边境研究的重要内容。新世纪以来,边境研究在汲取了批判性地缘政治学、人本主义地缘政治的精髓后,逐渐增强了对边境环境、社会治理等方面的反思。在文献计量分析的基础上,重点阐述了边境的地理涵义和政治属性、经济商贸交流、边境一体化、边境冲突与安全、文化与社会建构、跨境合作制度等领域的研究趋势。最后提出,未来中国边境研究应增强边境地区的综合性发展战略研究,搭建适应于中国特色发展的跨境合作平台与机制,融入国际政治学、民族学、自然地理学等多学科视角。     

矿床三维地质建模及储量估算——以丰村铅锌矿径口矿段为例

钦杭成矿带是我国最重要的成矿带之一,丰村铅锌矿位于钦杭成矿带南段庞西垌地区,是区内典型的沉积热液改造型矿床。依据现代成矿预测理论,结合已有的地形地质图、勘探线剖面图、钻孔数据等资料,运用三维地质建模技术建立了丰村铅锌矿径口矿段的地表模型、断裂模型、地层实体模型、矿体模型。在此基础上分别应用地质块段法和块体模型统计法进行了矿体的资源储量估算,并将两种估算结果进行了对比分析。结果表明,块体模型统计法比地质块段法应用范围更广,效果更精准,可以清晰表达矿体品位值变化特征,进而加深对矿体、矿床的空间分布规律的认识。同时,利用多元信息进行三维地质建模,可靠性高,可视化效果好。将传统的二维地质拓展到三维空间进行定位与定量化,有助于分析矿区地质构造特点与矿床成因,是现代寻找矿床的一种有效手段。     

Groundwater flow dynamics of weathered hard-rock aquifers under climate-change conditions: an illustrative example of numerical modeling through the equivalent porous media approach in the north-western Pyrenees (France)

A numerical groundwater model of the weathered crystalline aquifer of Ursuya (a major water source for the north-western Pyrenees region, south-western France) has been computed based on monitoring of hydrological, hydrodynamic and meteorological parameters over 3 years. The equivalent porous media model was used to simulate groundwater flow in the different layers of the weathered profile: from surface to depth, the weathered layer (5?·?10^?8?≤?K?≤?5?·? 10^?7 m s^?1), the transition layer (7?·?10^?8?≤?K?≤?1?·? 10^?5 m s^?1, the highest values being along major discontinuities), two fissured layers (3.5?·?10^?8?≤?K?≤?5?·?? 10^?4 m s^?1, depending on weathering profile conditions and on the existence of active fractures), and the hard-rock basement simulated with a negligible hydraulic conductivity (K = 1 10 ^?9 ). Hydrodynamic properties of these five calculation layers demonstrate both the impact of the weathering degree and of the discontinuities on the groundwater flow. The great agreement between simulated and observed hydraulic conditions allowed for validation of the methodology and its proposed use for application on analogous aquifers. With the aim of long-term management of this strategic aquifer, the model was then used to evaluate the impact of climate change on the groundwater resource. The simulations performed according to the most pessimistic climatic scenario until 2050 show a low sensitivity of the aquifer. The decreasing trend of the natural discharge is estimated at about ?360 m³ y^?1 for recharge decreasing at about ?5.6 mm y^?1 (0.8 % of annual recharge).     

Extreme <Superscript>15</Superscript>N Depletion in Seagrasses

Seagrass beds form an important part of the coastal ecosystem in many parts of the world but are very sensitive to anthropogenic nutrient increases. In the last decades, stable isotopes have been used as tracers of anthropogenic nutrient sources and to distinguish these impacts from natural environmental change, as well as in the identification of food sources in isotopic food web reconstruction. Thus, it is important to establish the extent of natural variations on the stable isotope composition of seagrass, validating their ability to act as both tracers of nutrients and food sources. Around the world, depending on the seagrass species and ecosystem, values of seagrass N normally vary from 0 to 8?‰ δ¹⁵N. In this study, highly unusual seagrass N isotope values were observed on the east coast of Qatar, with significant spatial variation over a scale of a few metres, and with δ¹⁵N values ranging from +2.95 to ?12.39?‰ within a single bay during March 2012. This pattern of variation was consistent over a period of a year although there was a seasonal effect on the seagrass δ¹⁵N values. Seagrass, water column and sediment nutrient profiles were not correlated with seagrass δ¹⁵N values and neither were longer-term indicators of nutrient limitation such as seagrass biomass and height. Sediment δ¹⁵N values were correlated with Halodule uninervis δ¹⁵N values and this, together with the small spatial scale of variation, suggest that localised sediment processes may be responsible for the extreme isotopic values. Consistent differences in sediment to plant ¹⁵N discrimination between seagrass species also suggest that species-specific nutrient uptake mechanisms contribute to the observed δ¹⁵N values. This study reports some of the most extreme, negative δ¹⁵N values ever noted for seagrass (as low as ?12.4?‰) and some of the most highly spatially variable (values varied over 15.4?‰ in a relatively small area of only 655 ha). These results are widely relevant, as they demonstrate the need for adequate spatial and temporal sampling when working with N stable isotopes to identify food sources in food web studies or as tracers of anthropogenic nutrients.     

Applicability of CPT-based methods in predicting toe bearing capacities of driven piles in sand

This paper presents a study on applicability of predicting toe bearing capacities from cone penetration test (CPT) for PHC (pretensioned spun high-strength concrete) driven piles into deep sandy deposits in the Nakdong River deltaic area west of Busan City in South Korea. Using toe bearing capacities obtained from pile driving analyzer (PDA) tests as reference values, which were reliably calibrated by on-site O-cell tests, the applicability of the CPT-based methods was evaluated using a statistical rank index (RI). A total of 82 piezocone penetration test soundings and 190 PDA test piles were used for reliability analysis in this study. Three correction steps were applied to obtain reliable PDA and CPT data sets before ranking is carried out. The RI index is combined from four criteria: (1) the best-fit line, (2) the arithmetic mean and standard deviation, (3) the cumulative probabilities, and (4) the log-normal and histogram distributions. Based on these criteria the performance of some SPT-based methods in the literature is evaluated.     

分辨率和陆面方案对长江流域短期气候预测影响

利用区域气候模式RegCM4.5,分别选取不同陆面参数化方案和空间分辨率,对5个长江流域降水异常年份进行短期气候回报试验,分析对气温和降水预测效果的影响及其最优组合。结果表明:空间分辨率的提高可以改善流域降水和气温的预测性能;而不同陆面方案引起的地表净辐射能量分布不同及其地表蒸散差异,最终导致流域内气温和降水预测效果不一致。RegCM（CLM4.5+30 km）对流域内小雨预测结果最好,而RegCM（BATS+30 km）预测流域内大雨和暴雨效果最优;RegCM（CLM3.5+30 km）对流域内气温预测能力最好。