大同阳高震区及其邻区壳幔速度结构与深部构造   总被引：2，自引：1，他引：1       下载免费PDF全文

张成科  张先康  盖玉杰  赵金仁  聂文英  任青芳 《地震地质》1998,20(4):104

利用通过本区６条宽角反射／折射剖面资料对大同阳高震区及邻区地壳上地幔速度结构与构造进行了详细的研究。结果表明,地壳上地幔速度结构与构造在纵向和横向上具有明显的不均一性。浅部基底断裂发育,而在其深部,根据波组特征、壳内界面及速度等值线起伏变化和低速异常体的边界等推测有３处地壳深断裂带。本区最明显的上地壳低速体位于大同—阳原附近,其南界存在地壳深断裂,大同阳高地震群与该低速异常体和深断裂有关。  相似文献   

天山上地幔结构及其对壳内构造运动的作用   总被引：17，自引：0，他引：17       下载免费PDF全文

胥颐  刘福田 《地震地质》1998,20(4):118-412

以深部地球物理资料为基础,介绍了天山地震带上地幔的基本结构,讨论了天山不同地区上地幔介质的动力学性质和可能的驱动机制。认为水平挤压形变是造成西天山和天山毗邻西昆仑附近区域上地幔岩石圈缩短和增厚的主要原因;而在中天山和东天山靠近准噶尔盆地南缘一带,除了板块运动造成的水平挤压力之外,上地幔热物质有可能上浮甚至侵入到地壳之中。它们与水平运动一样,对壳内脆性介质的构造活动起到非常重要的作用,特别是地壳底部莫霍面附近的低速滑脱层成为震源区深部构造的一个明显标志。此外,自从印度 亚洲大陆碰撞以来,天山部分地区固结冷却的山根有可能在多重挤压变形和小尺度热对流的共同作用下,脱离它们的原有的层位而沉入上地幔  相似文献   

大同 阳高震区及其邻区壳幔速度结构与深部构造   总被引：8，自引：1，他引：7       下载免费PDF全文

张成科  张先康 《地震地质》1998,20(4):104-398

利用通过本区６条宽角反射／折射剖面资料对大同 阳高震区及邻区地壳上地幔速度结构与构造进行了详细的研究。结果表明,地壳上地幔速度结构与构造在纵向和横向上具有明显的不均一性。浅部基底断裂发育,而在其深部,根据波组特征、壳内界面及速度等值线起伏变化和低速异常体的边界等推测有３处地壳深断裂带。本区最明显的上地壳低速体位于大同—阳原附近,其南界存在地壳深断裂,大同 阳高地震群与该低速异常体和深断裂有关  相似文献   

Tectono–Magmatic Evolution and Metallogenesis along the Northeast Jiangxi Deep Fault, China     

Ying Ye  Hidehiko Shimazaki  Masaaki Shimizu  Shouxi Hu 《Resource Geology》1998,48(1):43-50

Abstract: From the southernmost part of Jiangsu province to the northeastern part of Jiangxi province, China, the Northeast Jiangxi Deep Fault runs for about 400 km length with a width of 30 to 40 km. This fault marks the suture zone of two ter-ranes of Proterozoic age. At the both sides of the fault, Yanshanian granitic activity is recognized. That is, the Dexing-Wuyuan porphyry belt on the NW side of the fault, and the Damaoshan-Lingshan granite belt on the SE side. The former activity is characterized by the occurrence of small stocks of granodioritic composition, rich in siderophile elements but poor in LIL elements. No distinct Eu anomaly is recognized in the REE pattern, and a low initial ⁸⁷Sr/⁸⁶Sr ratio is reported. Magnetite, sphene and apatite are observed as accessory minerals. On the contrary, granitic activity on the SE side of the fault is characterized by the occurrence of composite batholiths, in general of granitic to monzogranitic composition, rich in LIL and alkali elements but poor in siderophile and alkali earth elements. A strong Eu anamaly is recognized in the REE pattern, and initial ⁸⁷Sr/⁸⁶Sr ratios are as high as 0. 716. Fluorite, zircon and REE minerals are observed as accessory minerals. These two contrasting granitic activities are refered to as syntexis– and transformation–types, respectively, following the classification commonly used in China, and have similar petrochemical characteristics to those defined for the magnetite– and ilmenite–series, and I– and S-type granitoids. Considering that the above igneous activity occurred far from the supposed subduction zone along the East Coast of China, intracontinental A-type (continent to continent) subduction is proposed to have occurred northwestwards along the NE Jiangxi Deep Fault during Yanshanian time due to a strong compressional stress from SE to NW. A-type subduction introduced the continental slab to some depth, and resulted in the production of the paired granitic activity observed on both sides of the fault. Many mineral deposits are associated with both granitic belts. In the Dexing-Wuyuan porphyry belt, the Dexing porphyry Cu and Yinshan polymetallic deposits are representative, whereas in the Damaoshan-Lingshan granite belt, several tens of rare metal deposits are known such as the Geyuan Nb–Ta–W–Sn deposits. Metal assemblages of those deposits reflect the source materials of magmas in both granitic belts.  相似文献   

The structure of the Baltic Shield region on the basis of DSS and earthquake data     

H. Korhonen  M. T. Porkka 《Pure and Applied Geophysics》1981,119(6):1093-1099

The lithospheric models obtained for the Baltic Shield by using deep seismic soundings are discussed and results from different parts of the shield are compared with models achieved by the investigation of surface waves and of P to S converted waves. The results are found to agree rather well with each other particularly with regard to the first interface (at a depth of 10–15 km) and the whole thickness of the crust (c. 40 km). The macroseismic focal depth determinations of regional earthquakes are correlated with lithospheric structure. The main maximum in the focal depth distributions of Finnish earthquakes occur at a depth of 10–12 km. The geographical distribution of the earthquake epicentres suggests several seismo-active zones in the northern Baltic Shield. One new finding in this field concerns the Lapland zone, which runs in a north-westerly direction.  相似文献   

Application of a vanishing, quasi-sigma, vertical coordinate for simulation of high-speed, deep currents over the Sigsbee Escarpment in the Gulf of Mexico   总被引：1，自引：0，他引：1  

Dmitry S. Dukhovskoy  Steven L. Morey  Paul J. Martin  James J. O&#x;Brien  Cortis Cooper 《Ocean Modelling》2009,28(4):250-265

Recent observations over the Sigsbee Escarpment in the Gulf of Mexico have revealed extremely energetic deep currents (near 1 m s⁻¹), which are trapped along the escarpment. Both scientific interest and engineering needs demand dynamical understanding of these extreme events, and can benefit from a numerical model designed to complement observational and theoretical investigations in this region of complicated topography. The primary objective of this study is to develop a modeling methodology capable of simulating these physical processes and apply the model to the Sigsbee Escarpment region. The very steep slope of the Sigsbee Escarpment (0.05–0.1) limits the application of ocean models with traditional terrain-following (sigma) vertical coordinates, which may represent the very complicated topography in the region adequately, can result in large truncation errors during calculation of the horizontal pressure gradient. A new vertical coordinate system, termed a vanishing quasi-sigma coordinate, is implemented in the Navy Coastal Ocean Model for application to the Sigsbee Escarpment region. Vertical coordinate surfaces for this grid have noticeably gentler slopes than a traditional sigma grid, while still following the terrain near the ocean bottom. The new vertical grid is tested with a suite of numerical experiments and compared to a classical sigma-layer model. The numerical error is substantially reduced in the model with the new vertical grid. A one-year, realistic, numerical simulation is performed to simulate strong, deep currents over the Escarpment using a very-high-resolution nested modeling approach. The model results are analyzed to demonstrate that the deep-ocean currents in the simulation replicate the prominent dynamical features of the observed intense currents in the region.  相似文献   

Stability of an immersed tunnel in offshore conditions under deep water wave impact     

T. Kasper  J.S. Steenfelt  L.M. Pedersen  P.G. Jackson  R.W.M.G. Heijmans 《Coastal Engineering》2008

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The mid-depth circulation of the northwestern tropical Atlantic observed by floats     

Matthias Lankhorst  David Fratantoni  Michel Ollitrault  Philip Richardson  Uwe Send  Walter Zenk 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1615-1632

A comprehensive analysis of velocity data from subsurface floats in the northwestern tropical Atlantic at two depth layers is presented: one representing the Antarctic Intermediate Water (AAIW, pressure range 600–1050 dbar), the other the upper North Atlantic Deep Water (uNADW, pressure range 1200–2050 dbar). New data from three independent research programs are combined with previously available data to achieve blanket coverage in space for the AAIW layer, while coverage in the uNADW remains more intermittent. Results from the AAIW mainly confirm previous studies on the mean flow, namely the equatorial zonal and the boundary currents, but clarify details on pathways, mostly by virtue of the spatial data coverage that sets float observations apart from e.g. shipborne or mooring observations. Mean transports in each of five zonal equatorial current bands is found to be between 2.7 and 4.5 Sv. Pathways carrying AAIW northward beyond the North Brazil Undercurrent are clearly visible in the mean velocity field, in particular a northward transport of 3.7 Sv across 16°N between the Antilles islands and the Mid-Atlantic Ridge. New maps of Lagrangian eddy kinetic energy and integral time scales are presented to quantify mesoscale activity. For the uNADW, mean flow and mesoscale properties are discussed as data availability allows. Trajectories in the uNADW east of the Lesser Antilles reveal interactions between the Deep Western Boundary Current (DWBC) and the basin interior, which can explain recent hydrographic observations of changes in composition of DWBC water along its southward flow.  相似文献   

Numerical modelling of deep sea air-lift   总被引：2，自引：0，他引：2  

K. Pougatch  M. Salcudean   《Ocean Engineering》2008,35(11-12):1173-1182

Deep sea air-lifting of solid particles from depth of 1600 m is simulated with a mathematical model of the three-phase flow in an upward pipe. The computations are carried out for an axisymmetric domain in a transient way. Phase distributions, pressure and velocity profiles together with flow rates for all phases are presented and analysed. The influence of the pipe diameter on the air-lift efficiency was studied for air-lift pipes of different lengths and found to be significant. The lifting efficiency increases with the increase of the pipe diameter due to the reduction of the wall friction influence on the flow. In addition, the efficiency also increases with the increase of the solid particles volume fraction at the inlet. The presented numerical model can be utilized during various stages of the design of the air-lift pumps to help answer fundamental questions on the process, and during their operation to select optimal process parameters and to address possible problems.  相似文献   

History,effort distribution and landings in an artisanal bottom longline fishery: An empirical study from the North Atlantic Ocean     

《Marine Policy》2015

Commercial fishing data were used to reconstruct historical spatio-temporal patterns of fishing effort and landings in the bottom longline fishery of the Azores. Key events during an important 15-year period were charted, through fisher interviews together with GIS analysis. While effort distribution varied over time, the prevailing pattern was a shift in focus from eastern to western areas and from shelf/slope to offshore banks and seamounts in response to policy measures (e.g. banning bottom longline inside 3 NM, public aids for modernization of the fleet) and reduced fishing yields. Areas 12–50 NM from shore represented the most vital fishing grounds in terms of fishing effort and production. Declining landings of the major demersal species, in recent years, indicate that present catch levels are not sustainable and further measures need to be taken in order to sustain fisheries resources. Knowledge of fleet behavior and the distribution of fishing effort, particularly in patchy environments, provide valuable insights into the impacts of past management decisions and help predict the outcome of new policies both in this region and elsewhere.  相似文献