High resolution velocity analysis of ocean bottom seismometer data by theτ-p method

A method of high resolution seismic velocity analysis for ocean bottom seismometer (OBS) records is applied to the study of the shallow oceanic crust, especially sedimentary and basement layers. This method is based on the direct-p mapping and the-sum inversion. We use data obtained from a 1989 airgun-OBS experiment in the northern Yamato Basin, Japan Sea and derive P- and S-wave velocity functions that can be compared with the seismic reflection profiles. Using split-spread profile records, we obtain interface dips and true interval velocities from the OBS data. These results show good agreement with the reflection profile records, the acoustic velocities of core samples, and sonic log profiles. We also present a method for estimating errors in the derived velocity functions by calculating covariance of the derived layers' thicknesses. The estimated depth errors are about 150 m at shallow depths, which is close to the seismic wavelength used. The high resolution of this method relies on accurate determination of shot positions by GPS, spatially dense seismic observations, and the use of unsaturated reflected waves arriving after the direct water wave that are observed on low-gain component records.     

High-Order Models of Nonlinear and Dispersive Wave in Water of Varying Depth with Arbitrary Sloping Bottom

High-order models with a dissipative term for nonlinear and dispersive wave in water of va-rying depth with an arbitrary sloping bottom are presented in this article.First,the formal derivations toany high order of μ(=h/λ,depth to deep-water wave length ratio)and ε(=α/h,wave amplitude todepth ratio)for velocity potential,particle velocity vector,pressure and the Boussinesq-type equations forsurface elevation η and horizontal velocity vector U at any given level in water are given.Then,the exactexplicit expressions to the fourth order of μ are derived.Finally,the linear solutions of η,U,C(phase ce-lerity)and C_g(group velocity)for a constant water depth are obtained.Compared with the Airy theory,excellent results can be found even for a water depth as large as the wave legnth.The present high-ordermodels are applicable to nonlinear regular and irregular waves in water of any varying depth(from shal-low to deep)and bottom slope(from mild to steep).     

黄海海底地貌分区及地貌类型

本文通过多年来大量的实际调查资料,将黄海划分成北黄海海湾潮流脊与岛礁、山东半岛沿岸水下堆积岸坡及水下阶地、南黄海西部弱堆积侵蚀平原、旧黄河-古长江三角洲堆积平原、海峡等七个地貌区,它们都各具特有的地貌类型。北黄海和南黄海原为两个大型的山间盆地,尔后由于海侵、被大量沉积物充填,成为今日连成一体的黄海浅海平原。     

黄海冷水团的环流结构

运用定性分析和数值模拟，对黄海冷水团的环流结构进行了探讨，结果表明黄海冷水团的垂向环流结构为双环结构：跃层以上区为中心上升，边缘下降的弱环流;跃层以下区为中心下降，边缘上升的强环流；在冷水团的中心区域，流动很弱，且无穿越温跃层的垂向流动。同时也对以往有关黄海冷水团垂向环流结构的工作进行了讨论。     

New evidence for a glacioeustatic influence on deep water circulation, bottom water ventilation and primary productivity in the South China Sea

We provide new evidence for the development of a stable estuarine circulation characterized by stagnating water bodies, nutrient recycling and increased primary productivity in the South China Sea (SCS) during glacial intervals. This circulation was caused by the closure of the shallow and narrow straits connecting the SCS in the south and west. Our main evidence is derived from newly measured Mn concentrations and Mn/Al ratios in two sediment cores from the northern and southeastern SCS covering the last 500 ky. Concentrations and Mn/Al ratios of the redox sensitive element Mn show clear glacial–interglacial cycles with maxima during interglacial periods and minima during glacial periods. These cycles indicate ventilation cycles of the bottom water, and are connected to the glacial–interglacial changes in sea level. In contrast, total organic carbon (TOC) concentrations display an opposite pattern with pronounced maxima during glacial times, especially in the southern part of the basin. The variations in TOC can be ascribed to two factors. Firstly, variations in primary productivity are controlled by variations in the intensity of the winter monsoon. Secondly to the degree of preservation of TOC controlled by variations in ventilation, which in turn is ultimately controlled by sea level. Consequently, variations in TOC represent a superimposition of primarily sea level influenced preservation control and winter monsoon driven variations in primary productivity intensity. The decrease in Mn correspond to times when sea level dropped 40–60 m below the present level. The larger amplitude of the variations in TOC and Mn in the southern part of the basin compared to the northern site suggest that oxygen depletion and nutrient recycling was stronger in the parts of the basin situated the furthest away from the only remaining opening to the open Pacific, the Luzon Strait.     

A model study of spin-down and circulation in a cold water dome

A three-dimensional prognostic hydrodynamic model in cross sectional form is used to examine the influence of bottom friction, mixing and topography upon the spin-down and steady-state circulation in a cold water bottom-dome. Parameters characteristic of the Irish Sea or Yellow Sea cold water domes are used. In all calculations, motion is induced by specifying an initial temperature distribution characteristic of the dome, and an associated along frontal flow. The spin-down of the dome is found to be influenced by the coefficient of bottom friction, with a typical time scale of order 10 days, and in general to be independent of the chosen initial vertical profile of along frontal flow. However, in the case in which the along frontal flow is such that the near bed velocity is zero, then bottom stress is also zero, and there is no appreciable spin-down. Calculations showed that the formulation of viscosity and diffusivity had a greater effect upon the steady-state circulation than topography, suggesting that background mixing of tidal origin is important. The lack of topographic influence was due mainly to the formulation of the initial conditions which were taken to be independent of topography. The steady-state circulation was characterized by a cyclonic flow in the surface region, with an anti-cyclonic current near the bed, where frictional effects produced a bottom Ekman layer and an across frontal flow. This gave rise to vertical circulation cells in the frontal region of the dome with prevailing downwelling motion inside the dome. A detailed analysis of the dynamic balance of the various terms in the hydrodynamic equations yielded insight into the processes controlling the steady-state circulation in cold water domes. Responsible Editor: Phil Dyke     

准噶尔盆地腹部白垩系底部不整合特征

准噶尔盆地经历了海西、印支、燕山、喜马拉雅等多期构造运动,形成了多个不整合,这些不整合对于准噶尔盆地的油气运聚具有重要的控制作用.白垩系底部不整合在盆地腹部地区广泛分布,通过对该不整合面上下岩石组合、物质成分以及电性特征的研究,该不整合具有明显的3层结构特征,可以划分为不整合面之上的底块砂岩、不整合面之下的风化粘土层和半风化淋滤带.底块砂岩是一套好的储层;风化粘土层由于遭受了长期的风化作用,富Al3 、Fe3 ,贫Si4 、Ca2 ,是一套局部有效的盖层;半风化淋滤带由于长期遭受地表水的下渗淋滤溶蚀,储层物性得到了很好的改善,是一套好的储层.沿白垩系底部不整合形成了上下两套优质储盖组合,形成了大量隐蔽性的非构造圈闭组合,是盆地腹部最主要的勘探领域之一,通过该项研究为盆地腹部地区的油气勘探提供有益资料.     

An assessment of soil contamination due to heavy metals around a coal-fired thermal power plant in India

Combustion of coals in thermal power plants is one of the major sources of environmental pollution due to generation of huge amounts of ashes, which are disposed off in large ponds in the vicinity of the thermal power plants. This problem is of particular significance in India, which utilizes coals of very high ash content (∼55 wt%). Since the thermal power plants and the ash ponds are located in densely populated areas, there is potential chance for contamination of soil and groundwater of the surrounding areas from the toxic trace elements in the ash. An attempt has been made to study the extent of soil contamination around one of the largest thermal power plants of India located at Kolaghat, West Bengal India. Chemical analysis of the top soils and the soils collected from the different depth profiles surrounding the ash ponds, show that the top soils are enriched in the trace elements Mo, As, Cr, Mn, Cu, Ni, Co, Pb, Be, V, Zn, which show maximum enrichment (2–5) in the top soils collected from all the soil profiles. These elements are also enriched in the pond ash. Since there are no other sources of industrial effluents, it can be said that the enrichment of the trace elements (Mn, Co, Mo, Cr, Cu, Pb, Zn, As, Ni, Be, V) is attributed to their input from ash from the disposal pond. The study has been further strengthened by log-normal distribution pattern of the elements.     

南海东北部海陆联测与海底地震仪探测

利用三分量海底地震仪、陆上便携式地震仪和海上气枪震源在南海东北部首次进行了海陆联合的深地震探测,测线呈北北西-南南东方向,垂直于区域构造走向,总长达500km,所获得的数据质量好,深部信息丰富,可分辨出Pg、Pn、PmP等地震相,为南海东北部深部地壳结构及油气盆地形成演化的研究提供了重要的基础数据。     

重力梯度仪的发展及其应用

随着欧空局GOCE项目的进一步深入及相关技术报告的公布,人们对该卫星及其有效载荷有了更多的了解,尤其是倍受关注的核心器件重力梯度仪有了更多认识的机会,本文在跟踪当前欧空局研制中的星载重力梯度仪的测量原理、仪器设计的基础上进行了综合、分析和总结,以期对该领域的研究有更清晰、深入的了解,同时为国内进行该领域研究的机构提供可能的参考.