海原-六盘山断裂带现今地震危险性的数值模拟分析     

蒋锋云  季灵运  赵强 《地质力学学报》2021,27(2):230-240

基于正交各向异性理论表征断层的变形行为,将平行断层面的剪切模量和周围介质剪切模量的比值作为反演参数,以海原-六盘山断裂附近现今GPS观测地壳水平运动速度场作为约束,通过构建三维有限元模型,采用遗传算法,反演了海原-六盘山断裂平行断层面的剪切模量分布。结果显示:六盘山断裂中南段平行断层面剪切模量与周围介质接近,且沿断层面地震动活动较为稀疏,反映六盘山断裂两侧近场差异变形较小,和汶川地震前龙门山断裂的情况类似,可能断裂带处于强闭锁状态。整个狭义的海原断裂带平行断层面剪切模量比周围介质要小的多,在0.4以下,且0~5 km要比深部大,可能反映了1920年海原8.5级地震之后,该断裂仍然处于震后调整状态。西段金强河断裂、毛毛山断裂、老虎山断裂浅部0~5 km剪切模量较小,而在5~20 km剪切模量相对较高,结合沿断层面地震活动分布特征,认为金强河、毛毛山断裂浅部可能存在蠕滑,而深部5~20 km存在应变能积累特征,具有强震发生的背景,而老虎山断裂由地表至深部地震活动较为密集,可能存在贯通性蠕滑,强震发生的可能性较小。   相似文献   

Engaging Diasporas for Development: a case study of Pitcairn Island     

Maria Amoamo 《The Australian geographer》2015,46(3):305-322

Diaspora engagement is a growing trend and many governments, international organisations and policy makers are increasingly focusing on the role of diaspora in development strategies for the homelands. Such policies are predominantly critical to island-dense regions such as the Caribbean and Pacific that have suffered high rates of outmigration during the postcolonial period. One such Pacific island is Pitcairn, a British Overseas Territory, and is the focus of this article. But while most of the literature focuses on the positive benefits of diaspora engagement, this paper examines the dynamics of diaspora (dis)engagement and (dis)affection. Each diaspora has a unique set of needs and capabilities based on its historical experience and the present realities of its countries of origin and destination. While much has been written celebrating the role of diasporas in development, diaspora have also shown themselves to have dual natures, with sometimes conflicting identities and allegiances. Based on analysis of a recent Pitcairn Diaspora Survey and ethnographic data, discussion in this paper reveals that the best intentions of engaging diaspora for development can be impeded by several factors including: (1) the complex nature of identity, place and politics; (2) difficult negotiations between past, present and future intentions of movers; and (3) shifting ‘roots/routes’ and boundaries of identification. Consequently, the paper aims to highlight the realities of settlement and relationships of diaspora space and subjectivity with the homeland.  相似文献   

A simple prediction model for wall deflection caused by braced excavation in clays     

《Computers and Geotechnics》2015

Deep excavations particularly in deep deposits of soft clay can cause excessive ground movements and result in damage to adjacent buildings. Extensive plane strain finite element analyses considering the small strain effect have been carried out to examine the wall deflections for excavations in soft clay deposits supported by retaining walls and bracing. The excavation geometry, soil strength and stiffness properties, and the wall stiffness were varied to study the wall deflection behavior. Based on these results, a simple Polynomial Regression (PR) model was developed for estimating the maximum wall deflection. Wall deflections computed by this method compare favorably with a number of field and published records.  相似文献   

A stabilized single-point finite element formulation for three-dimensional dynamic analysis of saturated soils     

《Computers and Geotechnics》2015

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Mobile bodies: Animal migration in North American history     

《Geoforum》2015

North Americans have had a profound affect on wildlife, especially migratory animals such as elk, bison, salmon, and many species of birds. Migration is a vital adaptation for these and other species. Yet despite this importance and the myriad ways in which people have influenced and understood migration, environmental geographers have devoted scant attention to it. This paper examines the role of animal migration in North American history. North Americans have affected and managed animal migrants in six primary ways: transforming migrant habitats; harvesting migrants; obstructing and facilitating migrants; working across borders; visualizing migrants; and accepting and resisting migrants. I examine these different aspects of animal migration history in North America and end with a discussion of how other geographers such as environmental historical geographers, political ecologists, and animal geographers can employ this framework.  相似文献   

Geochemical constraints on the contribution of Louisville seamount materials to magmagenesis in the Lau back-arc basin,SW Pacific     

Zheng-Gang Li  Yan-Hui Dong  Ji-Qiang Liu  Ling Chen 《International Geology Review》2015,57(5-8):978-997

Seamounts are an integral part of element recycling in global subduction zones. The published trace element and Pb-Sr-Nd isotope data for basaltic lavas from three key segments (Central Lau Spreading Ridge (CLSR), Eastern Lau Spreading Ridge (ELSR), and Valu Fa Ridge (VFR)) of the Lau back-arc basin were compiled to evaluate the contribution of Louisville seamount materials to their magma genesis. Two geochemical transitions, separating three provinces with distinct geochemical characteristics independent of ridge segmentation, were identified based on abrupt geochemical shifts. The origin of the geochemical transitions was determined to be the result of drastic compositional changes of subduction components added into the mantle source, rather than the transition from Indian to Pacific mid-ocean ridge basalt (MORB) mantle, or due to variable mantle fertilities. The most likely explanation for the drastic shifts in subduction input is the superimposition of Louisville materials on ‘normal’ subduction components consisting predominantly of aqueous fluids liberated from the down-going altered oceanic crust and minor pelagic sediment melts. Quantitative estimation reveals that Louisville materials contributed 0–74% and 21–83% of the Th budget, respectively, to CLSR and VFR lavas, but had no definite contribution to the lavas from the ELSR, which lies farthest away from the subducted Louisville seamount chain (LSC). The spatial association of the subducted LSC with the Louisville-affected segments suggests that the Louisville signature is regionally but not locally available in the Tonga subduction zone. Besides, the preferential melting of subducted old Cretaceous LSC crust instead of the old normal Pacific oceanic crust at similar depths implies that elevated temperature across the subduction interface or seamount erosion and rupture were required to trigger melting. A wider implication of this study, thus, is that seamount subduction may promote efficiency of element recycling in subduction zones.  相似文献   

新疆东天山突出山铜铁矿床地球化学特征与地质意义          下载免费PDF全文

尚海军  张志欣  李卫东  张耀选  仇银江  刘锋  周可法  李强  王金林 《地质科学》2015,(4):1102-1119

突出山铜铁矿床是东天山雅满苏石炭纪弧前-岛弧带中代表性的铁多金属矿床, 矿体呈透镜状、脉状、似层状赋存于上石炭统底坎尔组下亚组火山岩中。矽卡岩阶段包裹体均一温度为151℃~>380℃, 盐度为1.91%~23.18% NaCl_eq, 密度为0.76~1.09 g/cm³, 热液硫化物阶段包裹体均一温度为101℃~280℃, 盐度为0.35%~23.05% NaCl_eq, 密度为0.74~1.13 g/cm³, 表明成矿流体属于中-高温、中-低盐度、中-低密度的NaCl-H₂O体系。(绿泥石)绿帘石矽卡岩、磁铁矿(镜铁矿)矿石、含磁铁矿灰岩的稀土配分模式均为轻稀土相对富集的右倾型(LREE/HREE=2.85~9.21), 以出现负铕异常(δEu=0.22~1.09)和铈异常不发育为特征, 与底坎尔组火山岩相似, 表明成矿物质来源于底坎尔组火山岩。矿区矽卡岩可能是火山热液交代碳酸盐岩形成的, 成矿条件为中-高温、较为宽广的氧化还原环境, 矿床成因属火山热液交代型。  相似文献   

探测仪器特性曲线异常分析     

敬颖  闵锦忠  刘立辉  吴恒  徐爽 《气象科技》2015,43(4):601-606

探测仪器感应曲线发生变化,造成升速异常、等压面的温度、湿度错误、雷达〖CD*2〗气压高差偏大、时间〖CD*2〗高度线曲变化异常造成的规定高度上的风误差偏大,使部分资料或整份资料失真,影响探测准确性。本文主要从仪器的感应曲线变化后对各气象要素产生的影响进行分析,得出结论：不同的元件变性对气象要素产生的影响不同,气压变化的影响侧重于高差和升速,温度变化则侧重于规定等压面的温度绝对误差和规定等压面高度的偏差。采用绝对误差计算、加密气象要素计算等方法,结合图形、数据对比,可以确定感应曲线变化时间,从而及时、有效的对探测数据做出合适的处理,进一步提高探测数据的精准度。  相似文献   

地理国情要素数据成果的一致性检查方法     

李海  周进  闫庆庆  陈春希 《测绘通报》2021,(12):115-119

本文结合全国地理国情要素数据成果过程质量控制、质量复核工作,以及地理国情要素数据成果自身、与地表覆盖分类数据成果、与外业调查核查数据、与专题资料的一致性要求,通过分析检查中发现的质量问题,提出了地理国情要素数据成果的质量控制方法。该方法为国情要素数据成果的质量控制提供了技术参考,为质检工作提供了方法依据。  相似文献   

云南马关火山角砾岩及其包体岩石岩相学和元素地球化学特征及其地质意义   总被引：1，自引：0，他引：1  

李春辉  刘显凡  赵甫峰  陶专  吴冉  楚亚婷  王艳艳  肖继雄  宋祥峰 《地质科技情报》2011,30(3):48-56

对云南马关地区的爆破火山角砾岩及其中各类包体岩石开展了系统的岩相学和元素地球化学研究.结果表明,与爆破火山角砾岩有成因联系的岩石有3类:①以爆破火山角砾岩胶结物形式产出的碧玄岩和钾玄岩.②作为寄主岩的碧玄岩和钾玄岩中包含(携带)的尖晶石相地幔橄榄岩包体,进一步划分为两类:一类是具原始地幔性质的岩石,成分较单一,地幔交代...  相似文献