突变理论在断层活动机理分析中的应用     

施泽进  罗蛰潭  彭大钧  贺振华 《地球科学与环境学报》1996,(1)

本文扼要阐明了突变理论的基本思想，介绍了突变理论的Ａ３尖点突变模型。建立了断层运动过程中的势函数，在此基础上，通过对平衡曲面方程的Ｔａｙｌｏｒ级数展开，求取了其标准形式，结合Ｔｈｏｍ的Ａ３类尖点突变，讨论了在不同情况下断层的活动方式。  相似文献   

A critical review of the glaciomarine model for Irish sea deglaciation: evidence from southern Britain,the Celtic shelf and adjacent continental slope     

J. D. Scourse  M. F. A. Furze 《第四纪科学杂志》2001,16(5):419-434

In support of their ‘glaciomarine’ model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach‐face gravels and sands around the shores of the Celtic Sea. Glacial and sea‐level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south‐central Celtic Sea. Relative sea‐levels were lower, and therefore glacio‐isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice‐rafting at a time of high relative sea‐levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Energetic Electrons as a Field Line Topology Tracer in the High Latitude Boundary/CUSP Region: Cluster Rapid Observations     

Q. G. Zong  T. A. Fritz  A. Korth  P. W. Daly  M. Dunlop  A. Balogh  J. F. Fennell  J. D. Sullivan  R. W. H. Friedel  H. Reme 《Surveys in Geophysics》2005,26(1-3):215-240

Energetic electrons (e.g., 50 keV) travel along field lines with a high speed of around 20 R_Es⁻¹. These swift electrons trace out field lines in the magnetosphere in a rather short time, and therefore can provide nearly instantaneous information about the changes in the field configuration in regions of geospace. The energetic electrons in the high latitude boundary regions (including the cusp) have been examined in detail by using Cluster/RAPID data for four consecutive high latitude/cusp crossings between 16 March and 19 March 2001. Energetic electrons with high and stable fluxes were observed in the time interval when the IMF had a predominately positive B_z component. These electrons appeared to be associated with a lower plasma density exhibiting no obvious tailward plasma flow (<20 keV). On the other hand, no electrons or only spike-like electron events have been observed in the cusp region during southward IMF. At that time, the plasma density was as high as that in the magnetosheath and was associated with a clear tailward flow. The fact that no stable energetic electron fluxes were observed during southward IMF indicates that the cusp has an open field line geometry. The observations indicate that both the South and North high latitude magnetospheric boundary regions (including both North and South cusp) can be energetic particle trapping regions. The energetic electron observations provide new ways to investigate the dynamic cusp processes. Finally, trajectory tracing of test particles has been performed using the Tsyganenko 96 model; this demonstrates that energetic particles (both ions and electrons) may be indeed trapped in the high latitude magnetosphere.  相似文献   

盘锦市红海滩碱蓬空间特征研究     

李建国  杨德明  胡克  介冬梅  李亚繁 《吉林大学学报(地球科学版)》2006,(Z1)

基于1987年和2000年遥感数据,提取了红海滩碱蓬空间分布特征信息,以景观破碎度、斑块分形维数等作为评价指标,结合区域GIS数据,对比研究了区域内碱蓬景观的空间变化特征,分析了其消长机制。分析结果表明:(1)研究期内碱蓬退化严重,总面积从356.74hm2退化到103.51hm2,退化了253.23hm2,退化速率为19.48hm2/a;(2)碱蓬的消长主要受控于人类活动的影响,而人类活动主要通过水量、水质控制与直接占地两种途径作用于碱蓬;(3)三角洲水库以南地区生成的翅碱蓬应首先得到保护。  相似文献   

烟台第一海水浴场沙源匮乏型海滩地貌和表层沉积物粒度特征     

解燕  ;王张华  ;金秉福 《山东地质》2008,(5):37-40

在烟台第一海水浴场,利用经纬仪进行2条海滩横剖面形态测量,并在不同地貌单元采集沉积物样品进行粒度分析。测量显示,该海滩仅有小规模沙坝和沟槽体系。后滨上有风成沉积,但滩肩和海岸沙丘发育均不明显。粒度分析结果表明,海滩沉积物以中砂、粗砂为主,杂以砾或细砂,比山东半岛其他海滩沉积物明显要粗。由陆向海沉积物呈带状分布,平均高潮线附近和沙坝迎水坡侵蚀作用均显著。因此认为缺乏沙源供应的基岩岬湾式海岸是导致沙滩地貌发育不典型、海滩侵蚀作用显著的主要原因。  相似文献   

A study of the monsoonal beach processes around Alleppey,Kerala     

N. P. Kurian  T. S. Shahul Hameed  M. Baba 《Journal of Earth System Science》1985,94(3):323-332

The responses of a sandy beach to the southwest monsoonal waves are studied based on biweekly observations. The onslaught of the first spell of monsoonal breakers causes maximum erosion in the sub-aerial section of the beach. However, further spells of high breakers do not affect this zone significantly. The erosion in the sub-aerial zone is followed by accretion in the nearshore zone and vice versa. Whereas the sub-aerial zone has a net erosion the total section of the beach including the nearshore zone shows near equilibrium condition. It is concluded that in spite of erosion or accretion of the sub-aerial zone, equilibrium conditions may be found in the total section of the beach.  相似文献   

海平面上升—夹河断流背景下烟台套子湾海滩砂粒度变化          下载免费PDF全文

刘立新  王昕  陈浩宇  李训鹏 《山东国土资源》2022,38(5):63-70

将烟台套子湾2021年与2005—2006年夹河口东西两侧海滩砂的粒度特征进行对比分析,揭示了近16年来套子湾海滩沉积物粒度特征变化对全球海平面上升—夹河入海水沙减少等过程的具体响应。研究表明,现代套子湾海滩砂样品以中砂、细砂为主,分选极好或好,标准偏差介于0.23~0.4,夹河口东侧的海滩砂平均粒径（Mz：1.39~1.64Φ）比西侧海滩砂平均粒径（Mz：1.47~1.91Φ）粗,主要组分中的粗砂和中砂含量比西侧高,表明现代夹河口东侧区域水动力较夹河口西侧强,该区海滩砂受到海洋动力的长期改造分选较好。近16年夹河口两侧海滩砂粒度明显粗化,表现在海滩砂平均粒径变粗、主要组分粒度变粗约0.5Φ、概率累积曲线的粗细截点变粗0.5~1Φ及滚动、跃移、悬移组分含量明显变化。夹河入海物质减少,海平面快速上升,导致海洋动力增强是研究区海滩砂粒度粗化、海滩侵蚀的主要原因,该研究结果可以为套子湾海滩防护提供科学指导。  相似文献   

High population connectivity and Pleistocene range expansion in the direct-developing plough shell Bullia rhodostoma along the South African coast     

T Muteveri  CA Matthee  RCK Bowie 《African Journal of Marine Science》2015,37(1):21-31

Pleistocene climatic and oceanographic changes have influenced the distribution of marine biodiversity in southern Africa. Most evidence, however, has been derived from rocky shore or demersal taxa; data on sandy shore species are limited, despite severe threats to many sandy beach ecosystems. To test the effects of past climatic changes on sandy shore species, we sampled 140 smooth plough shell Bullia rhodostoma individuals from eight localities and generated phylogeographic data derived from the mtDNA cytochrome c oxidase subunit 1 (COI) marker. Nuclear markers (ATPSα, ATPSβ, ANT, SRPS4, TBP, LTRS and ZMP) showed no sequence variation. Bullia rhodostoma exhibited shallow genetic differentiation (Φ_ST = 0.07, p < 0.05) across its range. Isolation-by-distance suggests a stepping-stone model of migration, which is expected given the species’ direct-development life-history strategy. Demographic reconstruction suggests a post-LGM (Last Glacial Maximum) range expansion, concordant with the signal of shallow genetic differentiation. Phylogeographic patterns obtained suggest that, during lower sea levels than current, B. rhodostoma could have been restricted to the South-West Coast, the central Agulhas Bioregion and probably also the East Coast. When climatic conditions changed and temperatures began to rise after the LGM, the species began a rapid westward range expansion from these refugial regions.  相似文献   

Application of Boundary Collocation Method to Two-dimensional Wave Propagation     

曹雪玲  游亚戈  盛松伟  彭雯  叶寅 《海洋工程》2015,29(4):579-587

Boundary Collocation Method (BCM) based on Eigenfunction Expansion Method (EEM), a new numerical method for solving two-dimensional wave problems, is developed. To verify the method, wave problems on a series of beaches with different geometries are solved, and the errors of the method are analyzed. The calculation firmly confirms that the results will be more precise if we choose more rational points on the beach. The application of BCM, available for the problems with irregular domains and arbitrary boundary conditions, can effectively avoid complex calculation and programming. It can be widely used in ocean engineering.  相似文献   

风暴潮、大潮对广西涠洲岛西南沙滩侵蚀的影响分析     

李明杰  吴少华  刘秋兴  董剑希 《海洋学报》2015,37(9):126-137

本文统计分析了广西涠洲岛沿海气候、潮汐和风暴潮等历史资料,利用耿贝尔方法推算了涠洲岛多年一遇年极值高潮位,并估算了其漫滩范围分布,指出近几年高潮位出现的频次和极值均越来越高是涠洲岛西南部沙滩侵蚀愈加严重的重要原因,最后结合风暴潮-海浪耦合数值模拟了研究区域内"0312"号台风风暴潮漫滩的情况,分析了风暴潮和大潮对涠洲岛西南部沙滩侵蚀的影响,对当地岸滩修复和防护具有一定的指导意义。  相似文献