洱源-江川宽角地震剖面的地壳反射特征   总被引：6，自引：0，他引：6       下载免费PDF全文

张智  徐春明  孟补在  刘财  滕吉文 《地球物理学报》2007,50(4):1082-1088

通过对洱源-江川宽角反射地震资料的叠前偏移处理成像，得到了一个类似于近垂直入射多道地震数据的记录剖面.反射剖面图像与地壳速度结构共同揭示出地壳厚度由剖面西北端(约45 km)向东南端(约40 km)减薄.在洱源-楚雄西北附近深度约10 km处存在一组向东南倾斜的强反射震相，其东南约50 km处存在向西北倾斜的强射震相.易门断裂两侧地壳反射属性具有明显的差异，易门断裂之西北方向深度25～40 km处，中下地壳内存在两组强振幅，向东南方向上倾的地震反射同相轴，并被楚雄-建水断裂后期所错断，易门断裂之东南方向上，地壳内反射较为均一，未见特别明显的强间断面反射信息，这个反射结构被解释为印度板块东向俯冲与藏东缘地壳物质东向逃逸综合作用导致下地壳增厚和厚地壳变形的结果.  相似文献   

P-P波及P-SV波叠前深度偏移速度模型建立方法   总被引：11，自引：1，他引：10       下载免费PDF全文

李录明  罗省贤 《地球物理学报》1998,41(Z1):305-318

针对多波叠前深度偏移速度模型的建立问题,提出在CDP道集上利用互换原理组成伪地集作为叠前偏移速度分析的数据道集,先用叠前时间偏移方法求取层间互不影响的等效偏移速度模型,再用餐前深度偏移方法逐层求取层速度模型．对各层的速度质量、整个速度模型层位结构及速度横向变化,采用人机交互方式进行监控,并在速度叠代中引入全局寻优的遗传算法,使整个速度模型建立过程具有稳定、可靠和可视化的优点．经理论和实际资料处理结果证明,本方法是行之有效的．  相似文献   

Stochastic evaluation of fluvial to marginal marine sealing facies     

S.A. Barboza  R. Alway  T. Akpulat  W.L. Esch  P.J. Hicks Jr.  M.L. Gerdes 《Marine and Petroleum Geology》2009

Hydrocarbon top seal analyses are particularly difficult in fluvial and marginal marine settings. Although these settings often contain beds comprised of a low-permeability, clay-rich lithology associated with high quality seals, their presence does not guarantee an effective seal because individual beds within the stratal unit may be laterally discontinuous. Lateral facies changes, truncation of fine-grained beds, or the presence of crevasse splays may provide cross-stratal migration pathways, reducing the effective sealing capacity to a magnitude less than the closure height.  相似文献   

Mud volcanism and fluid geochemistry in the Cheleken peninsula,western Turkmenistan     

《Marine and Petroleum Geology》2014

A geological and geochemical study has been carried out to investigate the relationships between major mud volcano structures and deep fluid migration in the Cheleken peninsula, in the South Caspian Basin. The fluid geochemistry allowed the origin and migration of the saline waters and the hydrocarbons to be deduced along with the regional source and reservoir rocks. The emitted waters formed by the mixing of deep highly saline water from the main source rocks of the Maykop Fm with the Caspian-like pore water contained in the Pliocene reservoirs. The water composition is very similar to that emitted by the mud volcanoes in Azerbaijan, allowing comparisons to be done between the reservoirs in the western and eastern sides of the South Caspian Basin. The associated oil is derived from a mixed type II/III kerogen deposited in a sub-oxic marine environment and generated during the early oil window. The oil biomarkers indicate that the source rock is the Maykop Fm., as previously determined for the other areas of the South Caspian Basin.The spontaneous emissions, showing different morphologies, are mainly aligned along normal and transtensive fault systems, which provide effective pathways for rapid fluid ascent from deep reservoirs to the surface.  相似文献   

Escape to victory: Development,youth entrepreneurship and the migration of Ghanaian footballers     

《Geoforum》2015

This article contributes to contemporary debates over the resourcefulness and entrepreneurialism of young people in the Global South by exploring the relationship between development and the migration of male youth within the football industry. Drawing on fieldwork in Accra, the paper reveals how young Ghanaians attempt to enact development as freedom through spatial mobility. Significantly, this is coupled with an awareness that their desired spatial mobility is difficult to attain, thereby inducing a sense of involuntary immobility. For some male youth, the solution to this predicament is to invest in their sporting bodily capital and become Foucauldian ‘entrepreneurs of self’ in the form of a professional footballer. Meanwhile for others, the solution to prevailing economic pressures is to embrace financial risk by becoming entrepreneurs in the form of football club owners, and attempting to profit from the movement of players. The interests of these two sets of entrepreneurs coalesce around the fact that the mobility of footballers is crucial to generating a return on their respective investments. It is argued that the construction of young Ghanaians as responsible for their future life chances, and the growing dissonance between aspirations and the ability to migrate, is a key reason why youth are trying to migrate through football. Problematically, this can foster conditions favourable for irregular migration.  相似文献   

Weather-related influences on rural-to-urban migration: A spectrum of attribution in Beira,Mozambique     

《Global Environmental Change》2020

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Temporary labour migration and sustainable post-conflict return in Sierra Leone     

Roy Maconachie  Tony Binns  Paul Tengbe  Reynold Johnson 《GeoJournal》2006,67(3):223-240

Economic and social development indicators suggest that the small West African state of Sierra Leone is among the poorest countries in the world. Sierra Leone’s economy and quality of life deteriorated rapidly during a decade of political instability and civil war in the 1990s, when many people fled their homes and abandoned their livelihoods due to the rebel insurgency. This paper examines the post-war reconstruction scenario in Sierra Leone and presents recent evidence from two rural communities in the Eastern Province that were badly affected by the conflict. The paper considers the links between the farming and diamond mining sectors, which, despite severe dislocation during the conflict period, have proved to be remarkably resilient. It is argued that seasonal labour mobility associated with this dual economy has not only continued to be a key ingredient in sustaining livelihood portfolios, but is actually an essential pre-condition for the creation of an enabling environment for sustainable post-conflict return.

Tony BinnsEmail:

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Livelihood diversification: continuity and change in the Sahel     

Bodil Elmqvist  Lennart Olsson 《GeoJournal》2006,67(3):167-180

Livelihood diversification can be crucial for poor rural households in the African Sahel. Migration is a common diversification strategy during the dry season, but there are also areas with significant strategies on the farm, such as incomes from gum and resins. Sudan is a country where the income from gum arabic, the gum from the Acacia senegal tree, has played a large economic role for smallholders for generations, but there are signs of a declining production which is detrimental if people have no alternative incomes. The results showed that in parts of the country, the 1984 drought caused an event-driven change resulting in a discontinuation of production. However, in other parts of the country, the agricultural system providing gum arabic proved to be more resilient to the drought and the incomes from gum arabic still play a large role. The results illustrated a complexity of driving forces, regional differences and a large variability in incomes between households. Some causes were indirect such as prices, drought, precipitation and locust, whereas the others were direct and hence more controllable by households. This study underlined the direct causes, such as how labour input is prioritised between livelihood activities, which have not been given as much attention in previous literature. Secondly, the need for a holistic view of livelihoods is underlined in order to understand the future of gum arabic production. Empirical data were collected from extensive fieldwork.

Bodil ElmqvistEmail:

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Burning for zebu: The complexity of deforestation issues in western Madagascar     

《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(3):219-229

This study takes a human-geographical approach to examine the crucial problem of deforestation in Madagascar. Current land-use practices on the west coast threaten the survival of the dry primary forest, which exists in a delicate ecological balance under a climate bordering on aridity. A shifting-agriculture system, encouraged by government policy aimed at expanding crop cultivation, is the major factor contributing to the reduction of forested land. The forest is set on fire and the burns used to cultivate maize. After three years, yields drop dramatically, and people search for new areas of forest to clear. The practice is likely to lead to the complete disappearance of the western forests if nothing is done to change the current situation. The main practitioners are migrant Tandroy from the south of Madagascar. They migrate for reasons related to widespread local poverty and cultural practices linked to their reverence for cattle. They destroy the forests less for immediate survival than in order to gain possession of as many zebu as possible, which for them is the only way to acquire social status. Because Androy, their home region, is too poor to permit such acquisitions, migration to and deforestation of the western forest becomes an attractive alternative. The sale of maize to private exporters at a high price provides profits that can be used to buy cattle. This cultivation contributes little to food production in Madagascar, and the Tandroy , motivated by cultural considerations, stand at the base of a chain of exploitation that ends overseas. Agricultural and conservation policies in Madagascar currently do not address cultural and economic complexities such as these.  相似文献   

Rural household demographics, livelihoods and the environment   总被引：8，自引：0，他引：8  

Alex de Sherbinin  Leah K. VanWey  Kendra McSweeney  Rimjhim Aggarwal  Alisson Barbieri  Sabine Henry  Lori M. Hunter  Wayne Twine  Robert Walker 《Global Environmental Change》2008,18(1):38-53

This paper reviews and synthesizes findings from scholarly work on linkages among rural household demographics, livelihoods and the environment. Using the livelihood approach as an organizing framework, we examine evidence on the multiple pathways linking environmental variables and the following demographic variables: fertility, migration, morbidity and mortality, and lifecycles. Although the review draws on studies from the entire developing world, we find the majority of microlevel studies have been conducted in either marginal (mountainous or arid) or frontier environments, especially Amazonia. Though the linkages are mediated by many complex and often context-specific factors, there is strong evidence that dependence on natural resources intensifies when households lose human and social capital through adult morbidity and mortality, and qualified evidence for the influence of environmental factors on household decision-making regarding fertility and migration. Two decades of research on lifecycles and land cover change at the farm level have yielded a number of insights about how households make use of different land-use and natural resource management strategies at different stages. A thread running throughout the review is the importance of managing risk through livelihood diversification, ensuring future income security, and culture-specific norms regarding appropriate and desirable activities and demographic responses. Recommendations for future research are provided.  相似文献