Assessing pre- and post-deformation in the southern Arava Valley segment of the Dead Sea Transform, Israel by differential interferometry

Differential radar interferometry, using archived ERS data over the region of the Dead Sea Transform, allows to detect ground movement (subsidence or uplift) in playas within the southern Arava Valley segment of the Dead Sea Rift. These measurements are consistent with a mean displacement rate of about 0.4 cm/month, in the direction of the radar beam, during the 8-month period preceding the Nuweiba earthquake of 22 November 1995. In the 3 years following the earthquake, the measured rate was smaller by a factor of 10. These movements are not related to salt diapirs or water pumping activities in the area. The exact location, along faults, suggests a possible correlation with pre-seismic and post-seismic fault deformation.A simple fault model consistent with the observed phenomena associates the observed subsidence/uplift to right and left stepping en-echelon fault patterns related to inter-seismic tensional accumulation along the faults. Further observations are necessary on this site and similar fault areas to corroborate the correlation between seismic activity and the observed phenomena. Monitoring of these sites should continue with differential Global positioning system (GPS) measurements and radar interferometric analysis using Envisat and Radarsat as well as archived data (including J-ERS).     

Intra-seasonal NDVI change projections in semi-arid Africa

Early warning systems (EWS) tend to focus on the identification of slow onset disasters such famine and epidemic disease. Since hazardous environmental conditions often precede disastrous outcomes by many months, effective monitoring via satellite and in situ observations can successfully guide mitigation activities. Accurate short term forecasts of NDVI could increase lead times, making early warning earlier. This paper presents a simple empirical model for making 1 to 4 month NDVI projections. These statistical projections are based on parameterized satellite rainfall estimates (RFE) and relative humidity demand (RHD). A quasi-global, 1 month ahead, 1° study demonstrates reasonable accuracies in many semi-arid regions. In Africa, a 0.1° cross-validated skill assessment quantifies the technique's applicability at 1 to 4 month forecast intervals. These results suggest that useful projections can be made over many semi-arid, food insecure regions of Africa, with plausible extensions to drought prone areas of Asia, Australia and South America.     

东非大裂谷埃塞俄比亚段地质特征及地热资源分布特征研究

东非大裂谷代表岩石圈层位的一个大型减薄带,是陆地上最大的断裂带。东非大裂谷埃塞俄比亚段贯穿整个埃塞俄比亚岩石系列单元,是埃塞俄比亚板块(努比亚板块)和索马里板块的离散边界,延伸超过1000 km。本文通过系统总结该区域多年来的地质学、地球物理等研究成果,结合部分地质调查结果,得出埃塞俄比亚裂谷系统的北部为阿法尔洼地,是一个规模巨大的三角形构造拗陷地带;南部为埃塞俄比亚主裂谷,其内部形成较为对称的地堑系统,进而发育了数量众多的断陷湖。由于埃塞俄比亚板块和索马里板块持续性裂谷作用,裂谷系统内形成了丰富的地热资源。其中,阿法尔洼地的Danakil地区及主裂谷的阿巴塔湖(Lake Abiata)和莎拉湖(Lake Shala)的地热资源具有较好的资源勘查潜力,值得当地企业进一步关注。     

Review of the natural conditions and anthropogenic threats to the Ethiopian Rift Valley rivers and lakes

This review article considers the lakes found within the Ethiopian Rift Valley system and the rivers draining from the highlands towards them. The Ethiopian Rift Valley system extends in a north‐east–south‐west direction, bisecting the Ethiopian highlands. They differ in sizes and hydrological and hydrogeological settings. The lakes support a variety of flora and fauna, mainly fishes, reptiles, birds and mammals. The lakes and their feeder rivers, however, are currently being subjected to more human use pressure than previously experienced, attributable mainly to water abstractions for irrigation, household water supply and industrial activities in the catchments. Soil erosion, primarily attributable to the lack of soil conservation practices on farm lands, overgrazing and deforestation, along with unregulated irrigation practices, are generating large quantities of silt reaching the lakes. Improper utilization of water and land resources in the catchments, along with population growth and climate change impacts, is escalating the threats to the health of the lake and river ecosystems. As a result, some of the lakes exhibited reduced water levels and increased salinity. This article reviews the major environmental changes happening to these lakes and their feeder rivers. Visits were made to the area to update previous information while also consolidating the trends of change in the aquatic systems and the watersheds attributed to intense development practices.     

松辽盆地晚中生代裂谷作用与伸展构造样式

松辽盆地中西部的裂谷作用自下白垩统沙河子组沉积期持续到营城组沉积期,东部从下白垩统沙河子组沉积期持续到登娄库组沉积期.在不同构造层次形成了变形特征有别的构造,中浅层伸展构造的基本要素是断陷盆地边界主断裂,基本结构单元是半地堑和半地垒,横向上呈多米诺型垒-堑构造.主断裂中东倾者倾角缓但向东有增大的趋势;西倾者数量有限但倾角较陡.断陷包括水平拉张量大而裂谷期沉降量小的半地堑和水平拉张量小但裂谷期最大沉降的半地堑.这些断陷盆地在北北东方向呈串珠状,自西而东成带.在中-下地壳发生韧性变形,形成一向东倾拆离带,深度范围15～30km. 裂谷的扩展有3种方式,即边界断裂的斜向后退扩展,断陷带的走向式扩展,断陷群的横向扩展.     

海—塔盆地中部断陷带南二段油藏主控因素及模式

通过油藏解剖和油藏与成藏条件之间空间匹配关系研究,认为:海—塔盆地中部断陷带南二段油藏主要为分布在断阶带、断鼻和洼中隆上的断层油藏;南二段油藏分布受南一段源岩分布范围、断陷中断阶带和洼中隆的位置、扇三角洲前缘亚相砂体分布、早期伸展断裂沟通生油岩与储层程度等4个主要因素控制;油气成藏模式为洼槽中南一段源岩生成的油气在浮力作用下,通过早期伸展断裂错断与南二段储层侧接,向断阶带或洼中隆上的断块和断层—岩性圈闭中运移聚集成藏的模式.     

南苏丹Melut裂谷盆地扇体的发现及油气意义

Melut盆地为中非剪切带走滑背景下形成的裂谷盆地,具有早期白垩世被动裂谷盆地和晚期古近纪—新近纪主动裂谷盆地相叠合的特征,长期以来一直围绕辫状河、三角洲等领域进行勘探。通过地质—地球物理综合研究,在盆地北部凹陷识别出一系列扇体沉积,包括凹陷东部Abyat扇三角洲、西部Ruman近岸水下扇等。这些扇体主要形成于盆地初始被动裂谷期,发育于下白垩统Al Renk组烃源岩及烃源岩附近的白垩系Galhak组和Al Gayger组内,具有良好的生、储、盖配置条件。扇体的发现证实了Melut等中非裂谷盆地的初始被动裂谷期同样发育类似于主动裂谷盆地的扇三角洲、水下扇等各种扇体沉积,且具有良好的成藏条件和勘探潜力,这一发现和认识拓展了中非裂谷盆地的勘探潜力和空间。     

黄骅拗陷构造运动程式探讨

黄骅拗陷是勃中三叉裂谷系中的一支裂谷，具有地幔隆起，高热流和火山活动频繁等特征．拗陷中发育着四套构造地层组合，对应着三个构造层次。裂谷盆地的演化经历了三个阶段不同方向的构造运动程式：（１）前裂谷阶段经受印支运动近南北向的挤压作用、燕山早期运动北西—南东向的挤压作用及燕山晚期运动北西西—南东东向的挤压作用等；（２）裂谷阶段经受两期裂陷作用，为北西—南东向和近南北向的引张作用；（３）压裂谷阶段裂谷萎缩引起的垂向下陷运动。     

方正断陷的形成及其动力学机制

本通过对方正地区所发现的负花状构造及其有关构造运动形迹分析的基础上，进一步提出方正断陷是走滑－拉分形成的断陷盆地。并从动力学、构造学等方面对其形成机制进行了分析探讨。     

Geophysical exploration of the Boku geothermal area, Central Ethiopian Rift

The Boku central volcano is located within the axial zone of the Central Ethiopian Rift near the town of Nazareth, Ethiopia. An integrated geophysical survey involving thermal, magnetic, electrical and gravimetric methods has been carried out over the Boku geothermal area in order to understand the circulation of fluids in the subsurface, and to localize the “hot spot” providing heat to the downward migrating groundwaters before they return to the surface. The aim of the investigations was to reconstruct the geometry of the aquifers and the fluid flow paths in the Boku geothermal system, the country's least studied. Geological studies show that it taps heat from the shallow acidic Quaternary volcanic rocks of the Rift floor. The aquifer system is hosted in Quaternary Rift floor ignimbrites that are intensively fractured and receive regional meteoric water recharge from the adjacent escarpment and locally from precipitation and the Awash River. Geophysical surveys have mapped Quaternary faults that are the major geologic structures that allow the ascent of the hotter fluids towards the surface, as well as the cold-water recharge of the geothermal system. The shallow aquifers are mapped, preferred borehole sites for the extraction of thermal fluids are delineated and the depths to deeper thermal aquifers are estimated.