Comparative analysis of predictive methods for drought durations: a case of monthly and annual streamflow droughts in Atlantic Canada

Methods based on the recursive probability, the extreme number theorem, and Markov chain (MC) concepts were applied to predict drought lengths (duration) on the standardized (termed as standardized hydrological index, SHI) sequences of monthly and annual river flows from Atlantic Canada. Results of the study indicated that the MC-based method is the most efficient, reliable and versatile method for predicting drought durations followed by the extreme-number-based method. The recursive-probability-based method was found to be computationally intensive and less efficient, although it provided a powerful means for calibrating the empirical plotting position formula needed in the MC-based method. The Weibull plotting position formula turned out to be a suitable measure of the exceedance probability in MC methodology for predicting drought lengths in Atlantic Canada. Based on results, it can be inferred that the MC-based method can be extended to MC2 and higher-order chains for predicting drought lengths on SHI sequences. The predictive capability of the extreme-number-theorem-based method is limited only to independent or weakly first-order persistent SHI sequences.

EDITOR D. Koutsoyiannis

ASSOCIATE EDITOR Q. Zhang     

A model of submarine channel-levee evolution based on channel trajectories: Implications for stratigraphic architecture

Channel-levee systems are frequently interpreted as having a long history of cut-and-fill by channel-shaped features of different scales. Results from a simple geometric model based on a centerline migration algorithm combined with a vertical channel trajectory show that an incising-to-aggrading trajectory of a single channel can produce realistic morphologies similar to systems observed on the seafloor and subsurface, including features such as a basal erosional surface, coeval inner and outer levees, internal erosional boundaries, and terraces draped by inner levee deposits. Channel migration results in composite erosional surfaces that are distinct from topographic surfaces, and their formation does not require larger than usual erosional flows. Many submarine channels interpreted as underfit were probably carved by flows similar to the ones that eroded and deposited the entire channel system. We suggest that the features of most submarine channel-levee systems do not require large temporal variations in flow magnitude but can be explained by a simpler model whereby incision, migration and aggradation of a single channel form over time results in an apparently complex system.     

极摩尔圆法计算二维平均运动学涡度

通过有限应变椭圆长短轴比(Rs)和长轴与剪切面夹角(α)构建极摩尔圆,本文计算得出二维平面应变平均运动学涡度(Wm)计算公式为Wm=cos ,并以此绘制了Wm关于Rs和α的等值线投影图。公式计算和有限应变数值投影都是计算平均运动学涡度的简捷有效的方法。极摩尔圆计算提供了判定剪切类型(简单剪切,纯剪切,减薄一般剪切,增厚一般剪切)的两种方法:α值判定瞬时应变剪切类型; Rs×tan2α值判定有限应变剪切类型。     

MR-tree空间索引的Voronoi图改进及其并行空间查询方法

对MR-tree进行邻近关系信息的存储扩充,引入Voronoi图构建VoMR-tree索引。同时,提出了一种基于VoMR-tree的空间查询算法,讨论了分布式环境下的数据处理和算法并行化问题。实验结果表明,所提出的算法在执行时间和占用存储空间上都优于常用的空间索引方法。     

Regional-typological study and mapping of geosystems: analysis of the implementation

We give an outline of the scientific-methodological principles of using the regional-typological approach in geographical research. Based on analyzing cartographic products, we demonstrate the differences in understanding and implementing the approach. The structurallogical schematic diagram for the regional-typological approach has been developed, which opens up possibilities for its implementation in the study and mapping of geosystems and can provide an integral, systemic idea of this approach.     

含油气系统概念与研究方法

“含油气系统”概念是石油天然气地质学与系统科学相结合的产物。建议采用“广义的”含油气系统概念，并将其作为石油地质学家从系统科学角度所看到的一种全新的地质实体、研究对象与系统模型的复合体。其内涵是与油气生、排、运、聚、散有关且与周围环境密切联系着的若干相互作用、相互依赖的地质要素和过程（作用）及其描述参数和联系方式的集合体。其外延应包容油气区（或者还有超油气区）、盆地（包括叠合盆地）、凹陷（或在规模     

GIS支持下山区县域农村居民点分布特征研究——以栖霞市为例

运用GIS空间分析技术、景观指数法和Voronoi图Cv值相结合的分析方法,研究了胶东山区栖霞市农村居民点的空间均匀性特征,并探讨了农村居民点在地形梯度上的分布特征。结果表明:全市农村居民点分布的Cv值为58.84%,空间分布表现为随机分布;唐家泊镇、松山镇、臧家庄镇和翠屏街道4个乡镇的农村居民点呈集群分布,其他乡镇为随机分布;农村居民点分布的优势区间在1~3地形位,随着地形位的增大农村居民点的优势度降低;农村居民点的面积、斑块数目和平均斑块面积随地形位的增大而减少,平均斑块形状指数和平均斑块分维数随地形位的增大而增大;同时,公路是影响山区农村居民点空间布局的重要因素。研究反映了栖霞市农村居民居住习惯的差异,为农村居民点的整治和规划提供了依据。     

Subcompositional Patterns in Cenozoic Volcanic Rocks of Hungary

Data selected from an extensive major element database of Cenozoic volcanic rocks (including calc-alkaline andesites, dacites, rhyolites, and alkali basalts) of Hungary are used to illustrate the detection and modeling of subcompositional patterns using a statistical analysis based on the assumption that relative differences between the observed values are more meaningful than absolute ones. In particular, two roughly linear compositional patterns (associated one to the alkaline basalts, the other to the calc-alkaline series) are revealed and evaluated, and it is shown how principal component analysis can be used to obtain the estimated subcomposition of their incidental intersection point.     

一种基于Voronoi多边形的海底底质表示方法

海底底质对舰船航行、锚泊、登陆、铺设海底管线等海上活动具有重要的影响。文中提出了一种基于同质Voronoi多边形的海底底质分布可视化方法。通过构建Delaunay三角网,求取Voronoi多边形顶点,并依次排序顶点,从而生成构成Voronoi图。在Voronoi图的基础上,提出了同底质Voronoi多边形合并的具体算法,并处理与岸线相交的区域。实验表明,文中所提方法对于海底底质分布的可视化表达,比传统方法更为形象、直观。