Geotechnical properties of submarine sediments in the Seto Inland Sea     

Shigeyasu Okusa  Takaaki Nakamura  Naoki Dohi 《Marine Georesources & Geotechnology》2013,31(2):131-152

Abstract

Sampling of submarine sediments by an improved piston corer and a bucket dredger has been carried out since 1973. The length of the core samples ranged from 0.9 m to 5.4 m. The recovery ratio ranged from 39.1 percent to 98.9 percent. The physical and engineering properties of 16 sediment cores and the physical properties of 125 dredged samples were determined, and variation of these properties was analyzed.

Clayey silts and silty clays cover the floor of relatively wide bays and sea areas. Sands and sandy silts blanket the floor of channels that have swift currents, and are also found in the vicinity of estuaries.

The piston core samples showed considerable sample disturbance, which should be estimated quantitatively in the future.  相似文献   

Evaluating and comparing methods of sinkhole susceptibility mapping in the Ebro Valley evaporite karst (NE Spain)     

J.P. Galve  F. Gutirrez  J. Remondo  J. Bonachea  P. Lucha  A. Cendrero 《Geomorphology》2009,111(3-4):160-172

Multiple sinkhole susceptibility models have been generated in three study areas of the Ebro Valley evaporite karst (NE Spain) applying different methods (nearest neighbour distance, sinkhole density, heuristic scoring system and probabilistic analysis) for each sinkhole type separately (cover collapse sinkholes, cover and bedrock collapse sinkholes and cover and bedrock sagging sinkholes). The quantitative and independent evaluation of the predictive capability of the models reveals that: (1) The most reliable susceptibility models are those derived from the nearest neighbour distance and sinkhole density. These models can be generated in a simple and rapid way from detailed geomorphological maps. (2) The reliability of the nearest neighbour distance and density models is conditioned by the degree of clustering of the sinkholes. Consequently, the karst areas in which sinkholes show a higher clustering are a priori more favourable for predicting new occurrences. (3) The predictive capability of the best models obtained in this research is significantly higher (12.5–82.5%) than that of the heuristic sinkhole susceptibility model incorporated into the General Urban Plan for the municipality of Zaragoza. Although the probabilistic approach provides lower quality results than the methods based on sinkhole proximity and density, it helps to identify the most significant factors and select the most effective mitigation strategies and may be applied to model susceptibility in different future scenarios.  相似文献   

Remote sensing and fish-habitat relationships in coral reef ecosystems: Review and pathways for multi-scale hierarchical research   总被引：1，自引：0，他引：1  

Camille Mellin  Serge Andréfouët  Mayeul Dalleau 《Marine pollution bulletin》2009,58(1):11-19

  相似文献   

A case study of spatial heterogeneity of soil moisture in the Loess Plateau, western China： A geostatistical approach   总被引：9，自引：2，他引：7  

BI Huaxing    LI Xiaoyin  LIU Xin  GUO Mengxia    LI Jun Prof.  College of Soil  Water Conservation  Beijing Forestry University  Beijing  China  Key Laboratory of Soil  Water Conservation  Desertification Combating  Ministry of Education  China Researcher  Ji-xian National Ecological Station of China  China Graduate student 《国际泥沙研究》2009,24(1):63-73

Soil moisture distribution shows highly variation both spatially and temporally. This study assesses the spatial heterogeneity of soil moisture on a hill-slope scale in the Loess Plateau in West China by using a geostatistical approach. Soil moisture was measured by time-domain reflectometry （TDR） in 313 samples. Two kinds of sampling scales were used （2 × 2 m and 20 ×20 m） at two soil layers （0-30 cm and 30-60 cm）. The general characteristics of soil moisture were analyzed by a classical statistics method, and the spatial heterogeneity of soil moisture was analyzed using a geostatistical approach. The results showed that the spherical model is the best-fit model to simulate soil moisture on the experimental hill-slope. The parameters of this model indicated that the spatial dependence of soil moisture in the selected hill-slope was moderate. Even the 2 × 2 m sampling scale was too coarse to show the detailed spatial variances of soil moisture in this area. The dependent distance increased from 27.4 m to 494.16 m as the sampling scale became coarse （from 2× 2 m to 20 ×20 m）. A map of soil moisture was generated by using original soil moisture data and interpolated values determined by the Kriging method. The average soil moisture （area weighted） in the different layers of soil was calculated on the basis of this map （10.94% for the 0-30 cm soil layer, 11.88% for the 30-60 cm soil layer）. This average soil moisture is lower than the corresponding average effective soil moisture, which suggests that the soil moisture is not sufficient to support vegetation in this area.  相似文献   

Assessment of grazing effect on sheep fescue (Festuca valesiaca) dominated steppe rangelands, in the semi-arid Central Anatolian region of Turkey     

H.K. F&#x;r&#x;nc&#x;olu  S.S. Seefeldt  B. ahin  M. Vural 《Journal of Arid Environments》2009,73(12):1149-1157

In the semi-arid steppe rangelands of Central Turkey, Festuca valesiaca and Thymus sipyleus ssp rosulans have become the dominant species on degraded pastures. We hypothesized that decreases in species richness and abundance are correlated with increasing prevalence of these two species. Therefore, our objectives were to determine whether there are patterns in examined vegetation; how dominant species contribute to these patterns; and how patterns differ between grazed and ungrazed vegetation. We determined that protection from grazing increased species richness. Grazing significantly changed composition through decreasing total plant, forb, grass and F. valesiaca covers, while substantially increasing T. sipyleus cover. Topography, soil and grazing appear to impact the dominance of plant communities where F. valesiaca and T. sipyleus prevail. These two dominant species had a significant effect in shaping vegetation patterns. Based on regression analysis, alterations in species richness with changes in cover of forbs and shrubs were evident, and spatial heterogeneity of F. valesiaca and T. sipyleus indicated unstable vegetative patterns in heavily grazed pastures and successional changes in protected pastures. Our study results identify F. valesiaca and T. sipyleus as indicator species of vegetation suppression in condition assessments of degraded steppe rangelands.  相似文献   

重庆市县域综合发展水平差异的时空特征分析     

彭丽  秦趣  苏维词 《世界地理研究》2009,18(3):61-67

选择重庆市40个县域2001年和2006年的相关统计数据,采用因子分析法建立县域综合发展水平测度模型．运用统计学软件SPSS15．0．对重庆市县域综合发展水平差异进行评价和类型区划．并利用ARCGIS9．2软件分别绘制出2001和2006年40个县域的综合发展水平空间分异图。结果表明．县域综合发展水平的差距依然比较显著．在因子上由2001年的社会发展规模因素转化为2006年的工业化发展因素．空间上呈现出距离区域增长极空间位置的远近和交通可达的难易而逐层递减的圈层分异特点。  相似文献   

中国及邻近地区CHAMP卫星磁异常的分布特征   总被引：2，自引：4，他引：2       下载免费PDF全文

康国发  高国明  白春华  王军  邵丹 《地球物理学报》2010,53(4):895-903

本文利用CHAMP卫星磁测资料建立的新一代高阶地磁场模型POMME-4.2S,计算中国及邻区400 km高度的卫星磁异常及其垂直梯度,给出7个磁场分量的分布图,比较了截断水平对磁异常分布的影响,初步分析了磁异常与岩石圈构造的关系.主要结果表明,在四川盆地、塔里木盆地和松辽盆地等主要磁异常区,ΔZ异常中心的南北两边出现ΔX的异常中心,东西两边出现ΔY的异常中心.在球谐模型为90阶时,磁异常分布的基本形态已经确定,更高的模型阶数对磁异常只有微小调整.在磁异常较强的地区,磁异常及其垂直梯度同步变化.卫星磁异常与地形变化、断裂带分布、莫霍面深度和岩石圈厚度没有直接的对应关系,而与居里等温面深度、磁性层厚度有明显的相关性.居里等温面深、磁性层较厚的地区显示正磁异常,居里等温面浅、磁性层较薄的地区显示负磁异常.  相似文献   

辽宁乡镇天气预报中风和相对湿度及云量的空间插值方法   总被引：2，自引：1，他引：1       下载免费PDF全文

陆忠艳  蔡福  刘文明  袁子鹏  陈艳秋  陈明强 《气象与环境学报》2009,25(4):54-57

针对开展乡镇天气预报时对高精度逐日气象要素输入值的需要,以辽宁地区为例, 在乡镇预报前期研究成果的基础上,选用距离权重反比法作为基本方法,综合考虑海拔高度,建立风向、风速、相对湿度和云量历史资料库。结果表明：风速、相对湿度可由经度和纬度求算权重,然后采用海拔高度订正插值误差最小;风向和云量可由经度、纬度和海拔高度求算空间距离确定权重插值误差最小。  相似文献   

Space–time modelling of catchment scale drought characteristics     

Lena M. Tallaksen  Hege Hisdal  Henny A.J. Van Lanen   《Journal of Hydrology》2009,375(3-4):363-372

Drought may affect all components of the water cycle and covers commonly a large part of the catchment area. This paper examines drought propagation at the catchment scale using spatially aggregated drought characteristics and illustrates the importance of catchment processes in modifying the drought signal in both time and space. Analysis is conducted using monthly time series covering the period 1961–1997 for the Pang catchment, UK. The time series include observed rainfall and groundwater recharge, head and discharge simulated by physically-based soil water and groundwater models. Drought events derived separately for each unit area and variable are combined to yield catchment scale drought characteristics. The study reveals relatively large differences in the spatial and temporal characteristics of drought for the different variables. Meteorological droughts cover frequently the whole catchment; and they are more numerous and last for a short time (1–2 months). In comparison, droughts in recharge and hydraulic head cover typically a smaller area and last longer (4–5 months). Hydraulic head and groundwater discharge exhibit similar drought characteristics, which can be expected in a groundwater fed catchment. Deficit volume is considered a robust measure of the severity of a drought event over the catchment area for all variables; whereas, duration is less sensitive, particular for rainfall. Spatial variability in drought characteristics for groundwater recharge, head and discharge are primarily controlled by catchment properties. It is recommended not to use drought area separately as a measure of drought severity at the catchment scale, rather it should be used in combination with other drought characteristics like duration and deficit volume.  相似文献   

1980—2014年中国台风大风和台风极端大风的变化     

陆逸  朱伟军  任福民  王昕 《气候变化研究进展》2016,12(5):413-421

基于1980—2014中国670站日最大风速资料,利用改进的客观天气图分析法（OSAT）分离出中国陆地的台风大风（6级以上,≥10.8 m/s）,并定义了台风极端大风,进而研究了台风大风和台风极端大风的变化特征。分析表明：在地理分布上,台风大风年均日数和占比均自海岸线向内陆迅速减小,在海南、华南和东南沿海省份以及江苏南部,台风大风占比一般为30%～70%;台风极端大风年均日数大值主要分布在沿海省市（除河北和天津）,特别是华东和华南沿海,局部地区台风极端大风日数占比达100%。从季节变化看,在台风活跃的7—9月,中国台风极端大风频次总体上超过了季风极端大风;就全国而言,当阈值从最低值（11.5 m/s）提升至12级（32.7 m/s）时,台风极端大风频数占比则从12%急剧攀升至77%。1980—2014年,中国台风大风和台风极端大风年日数均显著减少,而台风极端大风年平均强度增强;这期间引起中国台风大风和台风极端大风的台风频数均显著减少,但引起台风极端大风的台风在生命期和影响期的平均强度均显著增强,这可能是上述显著变化特征的主要原因。  相似文献