Late Holocene linkages between decade–century scale climate variability and productivity at Lake Tanganyika, Africa     

Andrew S. Cohen  Kiram E. Lezzar  Julia Cole  David Dettman  Geoffrey S. Ellis  Meagan Eagle Gonneea  Pierre-Denis Plisnier  Victor Langenberg  Maarten Blaauw  Derrick Zilifi 《Journal of Paleolimnology》2006,36(2):189-209

Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between ∼∼2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little terrigenous component, interpreted as windy/dry season deposits. Laminated portions of the studied cores consist of conspicuous dark and light colored bundles of laminae couplets. Light and dark bundles alternate at decadal time scales. Within dark bundles, both light and dark half couplets are significantly thinner than within light bundles, implying slower sediment accumulation rates during both seasons over those intervals.Time series analyses of laminae thickness patterns demonstrate significant periodicities at interannual–centennial time scales. Longer time scale periodicities (multidecadal to centennial scale) of light and dark half couplet thicknesses are coherent and in some cases are similar to solar cycle periods on these time scales. Although laminae thickness cycles do not strongly covary with the actual Δ¹⁴C record for this same time period, two large Δ¹⁴C anomalies are associated with substantial decreases in both light and dark laminae thickness. In contrast to the multidecadal– centennial time scale, significant annual to decadal periodicities, which are broadly consistent with ENSO/PDO forcing and their impact on East African climate, are not coherent between light and dark half couplets. The coherency of light–dark couplets at decadal–centennial time scales, but not at shorter time scales, is consistent with a model of a long-term relationship between precipitation (recorded in wet season dark laminae thickness) and productivity (light laminae thickness), which is not manifest at shorter time scales. We hypothesize that this coupling results from long-term recharging of internal nutrient loading during wet periods (higher erosion of soil P) and reduced loading during drought intervals. The relationship is not expressed on short time scales during which the dominant control on productivity is wind-driven, dry season upwelling, which is uncorrelated with wet-season precipitation. Our record greatly extends the temporal record of this quasi-periodic behavior throughout the late Holocene and provides the first evidence linking decade- to century-scale episodes of enhanced productivity to enhanced precipitation levels and nutrient recharge in a productive tropical lake.  相似文献   

Verification of the motion fields over Southeast Asia by the Florida State University (FSU) superensemble forecast     

Mastura Mahmud  Robert S. Ross 《Singapore journal of tropical geography》2006,27(2):176-190

The Florida State University (FSU) multimodel superensemble forecast is evaluated against several other operational weather models for the Southeast Asia region. The superensemble technique has demonstrated its exceptional skills in forecasting precipitation, motion and mass fields compared to either individual global operational or ensemble mean forecasts. The motion field investigation for the season of 2001 reveals that the superensemble forecasts are closer to the observed data compared to the other global member operational models through its low systematic errors at the 850 hPa level. The FSU multimodel superensemble forecasts exhibit the lowest root mean square errors (RSMEs), the highest correlation against the best observed data and the lowest systematic errors compared to the other operational model members. These forecasts have the potential to provide better daily weather predictions over the Southeast Asia region, particularly during the early northeast monsoon that often causes heavy rainfall in the equatorial part of the Southeast Asia region.  相似文献   

Initiation and development of pull-apart basins with Riedel shear mechanism: insights from scaled clay experiments     

Nassima Atmaoui  Nina Kukowski  Bernhard Stöckhert  Diethard König 《International Journal of Earth Sciences》2006,95(2):225-238

Typical pull-apart structures were created in scaled clay experiments with a pure strike-slip geometry (Riedel type experiments). A clay slab represents the sedimentary cover above a strike-slip fault in the rigid basement. At an early stage of the development of the deformation zone, synthetic shear fractures (Riedel shears) within the clay slab display dilatational behaviour. With increasing basal displacement the Riedel shears rotate and open further, developing into long, narrow and deep troughs. The shear displacement and the low angle with the prescribed principal basal fault set them apart from tension gashes. At a more evolved stage, synthetic segments (Y-shears) parallel to the basal principal fault develop and accommodate progressive strike-slip deformation. The Y-shears connect the tips of adjacent troughs developed from the earlier Riedel shears, resulting in the typical rhomb-shaped structures characteristic for pull-apart basins. The Strait of Sicily rift zone, with major strike-slip systems being active from the Miocene to the Present, comprises pull-apart basins at different length scales, for which the structural record suggests development by a mechanism similar to that observed in our experiments.  相似文献   

Potential of High-Resolution Satellite Data in the Context of Vulnerability of Buildings   总被引：1，自引：2，他引：1  

Marina Mueller  Karl Segl  Uta Heiden  Hermann Kaufmann 《Natural Hazards》2006,38(1-2):247-258

High-resolution space-borne remote sensing data are investigated for their potential to extract relevant parameters for a vulnerability analysis of buildings in European countries. For an evaluation of large earthquake scenarios, the number of parameters in models for vulnerability is reduced to a minimum of relevant information such as the type of building (age, material, number of storeys) and the geological and spatial context. Building-related parameters can be derived from remote sensing data either directly (e.g. height) or indirectly based on the recognition of the urban structure type in which the buildings are located. With the potential of a fully- or semi-automatic inventory of the buildings and their parameters, high-resolution satellite data and techniques for their processing are a useful supporting tool for the assessment of vulnerability.  相似文献   

Fast computation of Hankel Transform using orthonormal exponential approximation of complex kernel function     

Pravin K. Gupta  Sri Niwas  Neeta Chaudhary 《Journal of Earth System Science》2006,115(3):267-276

The computation of electromagnetic (EM) fields, for 1-D layered earth model, requires evaluation of Hankel Transform (HT) of the EM kernel function. The digital filtering is the most widely used technique to evaluate HT integrals. However, it has some obvious shortcomings. We present an alternative scheme, based on an orthonormal exponential approximation of the kernel function, for evaluating HT integrals. This approximation of the kernel function was chosen because the analytical solution of HT of an exponential function is readily available in literature. This expansion reduces the integral to a simple algebraic sum. The implementation of such a scheme requires that the weights and the exponents of the exponential function be estimated. The exponents were estimated through a guided search algorithm while the weights were obtained using Marquardt matrix inversion method. The algorithm was tested on analytical HT pairs available in literature. The results are compared with those obtained using the digital filtering technique with Anderson filters. The field curves for four types (A-, K-, H-and Q-type) of 3-layer earth models are generated using the present scheme and compared with the corresponding curves obtained using the Anderson sc heme. It is concluded that the present scheme is more accurate than the Anderson scheme  相似文献   

On global forces of nature driving the Earth’s climate. Are humans involved?     

L. F. Khilyuk  G. V. Chilingar 《Environmental Geology》2006,50(6):899-910

The authors identify and describe the following global forces of nature driving the Earth’s climate: (1) solar radiation as a dominant external energy supplier to the Earth, (2) outgassing as a major supplier of gases to the World Ocean and the atmosphere, and, possibly, (3) microbial activities generating and consuming atmospheric gases at the interface of lithosphere and atmosphere. The writers provide quantitative estimates of the scope and extent of their corresponding effects on the Earth’s climate. Quantitative comparison of the scope and extent of the forces of nature and anthropogenic influences on the Earth’s climate is especially important at the time of broad-scale public debates on current global warming. The writers show that the human-induced climatic changes are negligible.  相似文献   

The geography of suicide terrorism in Israel     

Nurit Kliot  Igal Charney 《GeoJournal》2006,66(4):353-373

Palestinian suicide terrorism has been a key feature in the latest phase of the Israeli–Palestinian conflict. During the past decade, and particularly since September 2000, there has been a substantial increase in the use of this type of warfare. Recent studies suggest that, contrary to common belief, suicide terrorism is highly rational and driven by strategic considerations. This article explores the rationality of Palestinian suicide terrorism from a geographical perspective. It is argued that suicide terrorism works along two parallel paths: rationality and randomness. It complies with geographical fundamentals, and target selection is highly rational, subject to spatial considerations such as distance, agglomeration, and accessibility. As the permeability to Israel became more difficult, suicide bombers and their organizers had to adopt more flexible practices which emphasized other spatial considerations. Timing is of importance both for strategic and tactical reasoning. Obstructing negotiations and peace talks has been a salient objective, but the exact timing of suicide bombings has been influenced by tactical considerations, which aim at maximizing casualties.  相似文献   

杨庄截潜工程趾板段帷幕灌浆效果分析     

张文珍 《华南地质与矿产》2006,(1):72-76

杨庄截潜工程趾板段建基面以下为弱风化白云岩和含燧石条带白云岩,透水性较强,造成库水漏失严重.为解决建基面以下基岩渗漏问题,采用趾板段帷幕灌浆封堵基岩裂隙而形成防渗帷幕,以减少库水漏失.通过趾板段帷幕灌浆达到封堵基岩裂隙的目的,满足工程设计的防渗要求.  相似文献   

江西省宜春城区地面塌陷特征及防治建议   总被引：2，自引：0，他引：2  

刘细元  马振兴  杨永革  吕少俊  张永忠  陶木金 《中国地质灾害与防治学报》2006,17(2):89-94

宜春城区属岗阜低丘地形,分布石炭系-二叠系覆盖型及裸露型碳酸盐岩,占城区面积近70%。浅部岩溶发育,覆盖层厚度一般小于20m,土洞较多,基岩面起伏大,第四系岩性结构复杂,地下水埋藏浅。由于抽采地下水及建筑施工振动等人为因素影响,诱发地面塌陷12处,造成重大经济损失。在城市规划功能布局时应充分考虑地面塌陷的易发程度及场地建设适宜性;应限制诱发塌陷因素的强度,在易发区须严格控制地下水开采,严禁新建开采井;塌陷治理的主要方法有填堵、跨越、灌注、深基础控制抽排水强度、及其它综合治理或避让方法,同时做好灾害的监测预报工作。  相似文献   

福建平潭虎潮山滑坡成因机理分析与评价   总被引：3，自引：0，他引：3  

秦刚  姚环  林燕滨 《中国地质灾害与防治学报》2006,17(3):10-13

虎潮山滑坡位于平宏公路12k 704~12k 884段北侧山坡体上,是平潭海岛通往陆地的唯一公路通道。论文通过定性的工程地质分析和定量计算评价了虎潮山坡体稳定性的变化趋势,提出改建公路超挖深切坡脚和持续长时间强降雨导致的孔隙水压力作用是边坡发生滑动破坏的主要因素。  相似文献