Suppressing non‐Gaussian noises with scaled receiver wavefield for reverse‐time migration: comparison of different approaches     

Yi Tao  Mrinal K. Sen 《Geophysical Prospecting》2013,61(4):761-770

Numerical implementation of the gradient of the cost function in a gradient‐based full‐ waveform inversion (FWI) is essentially a migration operator used in wave equation migration. In FWI, minimizing different data residual norms results in different weighting strategies of data residuals at receiver locations prior to back‐propagation into the medium. In this paper, we propose different scaling methods to the receiver wavefield and compare their performances. Using time‐domain reverse‐time migration (RTM), we show that compared to conventional algorithms, this type of scaling is able to significantly suppress non‐Gaussian noise, i.e., outliers. Our tests also show that scaling by its absolute norm produces better results than other approaches.  相似文献   

Soil quality and human migration in Kenya and Uganda     

Clark L. Gray 《Global Environmental Change》2011,21(2):421-430

Soil degradation is widely considered to be a key factor undermining agricultural livelihoods in the developing world and contributing to rural out-migration. To date, however, few quantitative studies have examined the effects of soil characteristics on human migration or other social outcomes for potentially vulnerable households. This study takes advantage of a unique longitudinal survey dataset from Kenya and Uganda containing information on household-level soil properties to investigate the effects of soil quality on population mobility. Random effects multinomial logit models are used to test for effects of soil quality on both temporary and permanent migration while accounting for a variety of potential confounders. The analysis reveals that soil quality significantly reduces migration in Kenya, particularly for temporary labor migration, but marginally increases migration in Uganda. These findings are consistent with several previous studies in showing that adverse environmental conditions tend to increase migration but not universally, contrary to common assumptions about environmentally-induced migration.  相似文献   

Temperature affects the timing of spawning and migration of North Sea mackerel     

Teunis Jansen  Henrik Gislason 《Continental Shelf Research》2011,31(1):64-72

Climate change accentuates the need for knowing how temperature impacts the life history and productivity of economically and ecologically important species of fish. We examine the influence of temperature on the timing of the spawning and migrations of North Sea Mackerel using data from larvae CPR surveys, egg surveys and commercial landings from Danish coastal fisheries in the North Sea, Skagerrak, Kattegat and inner Danish waters. The three independent sources of data all show that there is a significant relationship between the timing of spawning and sea surface temperature. Large mackerel are shown to arrive at the feeding areas before and leave later than small mackerel and the sequential appearance of mackerel in each of the feeding areas studied supports the anecdotal evidence for an eastward post-spawning migration. Occasional commercial catches taken in winter in the Sound N, Kattegat and Skagerrak together with catches in the first quarter IBTS survey furthermore indicate some overwintering here. Significant relationships between temperature and North Sea mackerel spawning and migration have not been documented before. The results have implications for mackerel resource management and monitoring. An increase in temperature is likely to affect the timing and magnitude of the growth, recruitment and migration of North Sea mackerel with subsequent impacts on its sustainable exploitation.  相似文献   

2010年玉树MS7.1地震前的中长期加速矩释放(AMR)问题   总被引：3，自引：0，他引：3       下载免费PDF全文

蒋长胜  吴忠良 《地球物理学报》2011,54(6):1501-1510

2010年4月14日青海玉树MS7.1地震前的加速矩释放(AMR)现象的研究,对理解这次地震的孕震过程、对于时间相依的地震危险性分析(或中长期地震预测)具有重要意义.鉴于以往AMR研究中的争论,本文不刻意选取AMR分析的时空尺度,而是在已知发震时刻和震中位置情况下,对T-R-MC三维空间中矩释放指数m值的分布进行分析,...  相似文献   

正则化偏移成像的全局优化快速算法          下载免费PDF全文

李振华  王彦飞  杨长春 《地球物理学报》2011,54(3):828-834

目前,偏移后的地震剖面往往只是一个地质构造图像,还不能为后续的岩性分析和油气储层属性的提取提供更精确的信息.为了得到高分辨率真振幅的图像,建议采用正则化偏移成像方法.针对本问题数据规模大和正演算子矩阵稀疏的特点,提出采用一种新的算法--无记忆拟牛顿-模拟退火法对偏移算子方程进行求解.该方法综合了无记忆拟牛顿法优良的局部...  相似文献   

New friends in new places: Network formation during the migration process among Poles in the UK   总被引：1，自引：0，他引：1  

Nick Gill  Paula Bialski 《Geoforum》2011,42(2):241-249

This paper contributes to on-going work that seeks to understand the dynamic nature of immigrant social network formation. We explore three propositions, derived from the literature, that might be expected to characterise the ways in which migrant associational ties evolve during and immediately after arrival in their destination country. Evidence is drawn from 42 interviews conducted between January and December 2008 with predominantly Polish migrants to the UK (28) as well as domestic service providers (14). In agreement with the existing literature on immigrant social network formation we find that weak associational ties between migrants are locally dense and rapidly formed. More surprisingly, we also find that the Poles in our sample from lower socio-economic groups tended to rely heavily upon weak associational ties while higher socio-economic group Poles tended to rely on associations made through their employing institutions. This illustrates the importance of socio-economic status in framing co-ethnic migrant network formation. This is significant because we also find that weak associational ties are not unambiguously beneficial to lower socio-economic group migrants who tend to (have to be) more compromising about, and therefore more compromised by, the social ‘friendships’ that result.  相似文献   

Migrant pathways to resource access in Lampung’s political forest: Gender, citizenship and creative conjugality     

Rebecca Elmhirst 《Geoforum》2011,42(2):173-183

An important theme in studies of enclosure and resource access in Southeast Asian hinges on the concept of the ‘political forest’, a particular constellation of power constituted by ideas, practices and institutions that seek to regulate peoples’ access to resources, providing recognition and legitimacy to some, whilst excluding and criminalizing others. Whilst issues of class and ‘race’ underpin work in this vein, in Indonesia, much less attention has been directed towards the ways in which gender inheres in the regularisation of land and livelihood, and the ordering of upland spaces. Drawing on recent feminist and queer theorizing of the links between citizenship, recognition and hetero-normativity, and on analyses of the social relationships through which resource access is negotiated and realized, the paper presents a feminist political ecology of the gender dynamics inherent in the power plays of resource access as land-poor rural migrants negotiate a shifting landscape of enclosure in Lampung province. Through an analysis of three periods of resource governance and control in the province, the paper shows how the negotiation of resource access is simultaneously a process of self-regulation and subject-making that draws on particular ideas about family and conjugal partnership, inculcating gendered and hetero-normative ideologies of the “ideal citizen”. Through particular representational strategies - positionings - necessary to qualify for resource access, and through the material practices necessary to realize the benefits of resource access, conjugal partnership is reiterated and remade as an important social relationship through which resource access may be realised, for men as well as for women.  相似文献   

塔里木盆地巴麦地区寒武—奥陶纪碳酸盐岩台地演化     

白晓亮  张哨楠  谢世文 《新疆地质》2011,29(3)

通过对塔里木盆地巴麦地区寒武—奥陶系地震、沉积特征研究,运用地震、钻井岩心资料,对该区层 序特征分析,巴麦地区经历了由碳酸盐岩缓坡型台地向镶边斜坡型台地演化,主要控制因素是构造活动和海平面变化早— 中寒武世为缓坡型台地演化阶段,由于海平面频繁升降变化,台地边缘经历3次迁移;晚寒武世该区处于拉张环境形 成被动大陆边缘,海平面开始上升,发育镶边斜坡型台地,海平面相对上升速率小于沉积物供应速率,台地边缘向 盆地方向迁移;早奥陶世,海平面上升速率加快,大于沉积速率,台地以追补型叠加形式向台地方向迁移.  相似文献   

玉溪常里温泉成因探讨     

宋子德 《云南地质》2011,30(1):67-70

常里温泉处于普渡河断裂与大密罗-马官屯断裂交汇带,地质构造条件特殊,地下水循环较复杂.温泉水温高、水质好、埋藏浅、易开采、交通方便等优势,具有较高的开发价值.温泉形成机理,补、径、排循环系统的研究,有助于科学、合理指导开发利用温泉资源.  相似文献   

Migrations de charnières et vecteurs de déplacements sur des modèles analogiques de plis superposés     

Francis Odonne 《Geodinamica Acta》2013,26(2):139-146

Résumé

La modélisation analogique d’une superposition de plissements dans une série sédimentaire stratifiée, représentée ici par un multicouche de paraffine et graisse, fait apparaître le rôle déterminant de la géométrie des plis initiaux. Les plis ouverts peuvent évoluer sous l’effet de la seconde compression :

- Si les directions des axes de ces plis sont parallèles à la seconde compression, on verra apparaître des plis superposés.

- Si les directions des axes sont obliques à celle-ci, on observera la réutilisation des plis qui seront alors réorientés grâce à la migration de leur charnière. En fin de déformation la ou les familles de plis présentes dans le modèle ne sont perpendiculaires ni à la première ni à la seconde direction de compression.  相似文献