Investigations of the bottom current sculpted margin of Hatton Bank, NE Atlantic

The northwest Hatton Bank margin is an ideal locality to demonstrate the interaction between bottom currents and slope configuration in controlling the distribution and morphology of bottom current deposits. The slope area investigated is isolated from any major terrigenous sediment supply and at present is influenced by the Deep Northern Boundary Current (DNBC). Swath bathymetry and high resolution acoustic data allow us to evaluate both local and regional controls on slope sedimentation and the possible mechanisms for bottom-current velocity variability across a slope setting within the NW European continental margin. The slope exhibits sculpting by bottom currents that flow in a predominantly southwest to northeast direction, and is only locally modified by slope failures. Positive relief features such as the Endymion Spur play an important role in constraining and accelerating bottom-current flow and, consequently, in redistributing sediment along the margin. We demonstrate that the size, morphology and distribution of bottom-current deposits along the slope vary as a function of the interaction between bottom currents, regional slope orientation and local seafloor topography.     

波生沿岸流数值模拟

为了更好地研究近岸海域波生沿岸流,建立了基于高阶Boussinesq水波方程的波生沿岸流时域数值模型。控制方程在中等水深范围内具有较好的色散性和变浅作用性能,同时具有二阶完全非线性特征,适合描述近岸区域波浪强非线性运动。通过采用松弛造波方法实现了非线性波浪的无反射入射,采用周期性侧边界条件模拟开敞边界。通过数值试验,讨论了模型中主要参数对数值结果的影响。利用率定后的参数模拟了均匀坡度海岸上产生的沿岸流,通过和实验数据的对比验证了模型的准确性和适用性。利用模型数值模拟了不同波浪入射条件(包括周期、波高和波浪入射角度)对波生沿岸流的影响。     

重力异常分离的相关法

本文研究重力异常分离的相关法,它由测点坐标的多项式方程构建区域异常,由观测异常减去区域异常计算剩余异常,根据最大化已知测点的目标密度分界面深度与剩余异常的互相关原则来分离重力异常.互相关的最大化目标可写为最小二乘方程,并利用线性或非线性优化算法迭代求解出构建区域异常的多项式系数,进而可计算出全区的区域异常和目标密度分界面的剩余异常,实现重力异常分离.理论重力异常试验结果表明,相关法直接有效地利用了已知测点的目标密度分界面深度信息,分离效果良好、反映实际地质情况.     

EVOLUTION OF LIQUID WATER CONTENT IN A SEA FOG CONTROLLED BY A HIGH-PRESSURE PATTERN

On March 16–17, 2008, a sea fog occurred in Dianbai in the west of Guangdong Province and was accompanied by a high-pressure synoptic system. Using comprehensive observation datasets, this study analyzes the evolution of liquid water content during this sea fog and investigates the relationships between liquid water content and the average diameters and count densities of fog droplets, air temperature, wind speed and turbulence exchanges. The main results are presented as follows. (1) The sea fog showed a quasi-periodic oscillation characteristic, i.e., it developed, disappeared and then developed again. (2) During the sea fog, the number of fog droplets changed significantly while the changes in average diameter of the fog droplets were relatively small. The development and disappearance of the sea fog correlated significantly with the fog droplet numbers. (3) The air-cooling mechanism played a significant role in sea fog formation and development. However, the influences of this mechanism were not evident during fog persistence. (4) During sea fog formation, weak turbulence exchanges were helpful for fog formation. During sea fog development and persistence, liquid water content increased when turbulence exchanges weakened, and vice versa. The changes in turbulence exchanges were closely related to the quasi-periodic oscillations observed in sea fog presence.     

The effect of wind on the residual current velocities in the inlets of Venice lagoon

The residual flow in the inlets of Venice lagoon subject to Bora and Sirocco winds has been studied. Current velocities have been monitored since 2001 using Acoustic Doppler Current Profilers (ADCP) installed on the beds of the inlets that connect the lagoon to the Adriatic Sea; these inlets are Lido, Malamocco and Chioggia. Wind velocity data have also been continuously measured at an oceanographic platform 14.8 km offshore from the lagoon; these data were subsequently decomposed into Principal Components, which are associated with Bora and Sirocco wind directions. Analyses show that the inflow in Lido inlet is strongly related to the Bora wind. The outflow in Chioggia inlet occurs during Bora events but shows a slightly weaker correlation with the wind speed, while Malamocco inlet shows little or no influence of Bora winds on flow patterns. A net residual inflow through Lido and Malamocco inlet was found, while outflow prevails in Chioggia inlet. During Bora events, the average residual inflow increased three-fold in Lido inlet, whereas the outflow in Chioggia inlet doubled. The current velocities in Lido and Chioggia inlets are best described by an exponential function of wind velocity with exponents of −0.1187 and −0.0924, respectively. The response to Sirocco events was evident mainly in Chioggia inlet. Specifically, there was a slow down of the outflow in linear proportion to wind speed. In excess of 10 m/s a complete current reversal was observed. Lido and Malamocco inlets showed little or no response to Sirocco winds, except during rare cases when wind speeds exceeded 15 m/s.     

高密度电阻率法在阿联酋某城C9～C11测区溶洞勘察中的应用

阿拉伯联合酋长国卡里法市B城是一座新规划城市，位于中东海湾沙漠海滩区，由于经三系，第四系地导台含有大量的石膏等萨布哈（Subkha)蒸发盐岩类，大范围发育有大量地下溶洞，其埋藏深度一般为5 m-15m，严重影响了城市建设及工业区开发，在该区采用了高密度电阻率法，克服了地表接地电阻大和溶洞与围岩电性差异小的困难，查明了地下20m深度范围内地下溶洞分布情况，经阿方技术专家验证评价，该次勘查成果可靠，达到了预期目的。     

Spatial and seasonal variations in the ecological characteristics of the free-living nematode assemblages in a large microtidal estuary

This study has determined the ways in which the density, number of species, species composition and trophic structure of free-living nematode assemblages in the subtidal waters of a large southern hemisphere microtidal estuary change spatially and seasonally, and has explored whether those four biotic characteristics are related to certain environmental factors. Based on data derived from samples collected seasonally at 12 sites throughout the estuary, the densities and number of species of nematodes decreased progressively with distance from estuary mouth, to reach a minimum at sites where salinities were most variable, and then increased slightly in the uppermost part of the estuary where salinities were least. Densities were also generally greatest in spring, due largely to increases in the abundance of epistrate-grazing species at this time and thus when the amount of primary food (microphytobenthos) peaked. The spatial distribution of the composition of the nematode assemblages was closely correlated with salinity and, to a lesser extent, grain-size composition and amount of particulate organic material (%POM) in the sediment. Although species composition changed sequentially along the estuary, the change was particularly pronounced between sites above and below the area where salinities started to decline markedly and become more variable and %POM increased markedly. This reflected, in particular, far greater abundances of Spirinia parasitifera at the six downstream sites and of Theristus sp. 1 at the six sites further upstream. Species composition underwent pronounced seasonal cyclical changes at all sites, presumably reflecting interspecific differences in the timing of peak reproduction and thus of recruitment. The trophic structure of the nematode assemblages changed both spatially and temporally in relation to the relative abundance of different food sources. Thus, for example, non-selective deposit feeders, such as Theristus sp. 1, dominated samples in the upper estuary, where %POM was by far the greatest, and was rare or absent at downstream sites. Conversely, epistrate grazers, such as species of the Chromadoridae, were most abundant at downstream sites in spring, when the density of the microphytobenthos reached its maximum.     

鲜水河断裂带南东段的深部孕震环境与2014年康定M_S6.3地震

2014年11月22日16时55分在四川省甘孜藏族自治州康定县发生的6.3级地震,结束了鲜水河断裂带近30多年以来没有较大地震发生的历史,其潜在的地震危险性再次引起国内外地学工作者的关注.为了研究鲜水河断裂带南东段深部孕震环境和探求康定MS6.3地震的成因,本文先利用四川区域数字地震台网和康定地区及周边所布设的流动地震台阵在2009年1月1日至2014年12月5日期间所记录到7397次区域地震事件的99287条P波到时资料,反演得到了鲜水河断裂带南东段上地壳范围内不同深度的三维P波速度结构特征;再对康定震区及周边的重力、航磁数据进行视密度、视磁化强度反演,得到了壳内不同深度密度的横向变化信息和视磁化强度的分布特征;在此基础上综合研究鲜水河断裂带南东段的深部孕震环境.研究结果表明,雅江—九龙一带的低速区与泸定—宝兴高速区的速度结构特征表明了鲜水河断裂带南东段两侧壳内物质存在显著的横向介质差异,康定MS6.3地震发生在该高低速异常区的分界线上;结合康定MS6.3地震的1028个余震序列的精确定位结果可以看出,重新定位后的余震沿着鲜水河断裂带南东段呈条带状分布,且震源深度优势分布层位深度为8~15km,该余震序列的空间分布特征与鲜水河断裂南东段的深部介质条件密切相关.鲜水河断裂带南东段特有的视密度和视磁化强度异常分布特征反映了康定地区东西两侧块体的基底性质存在明显差异,康定—石棉及其以东地区所表现出的磁异常高和重力高的位场特征,反映该区域由强磁性、高密度物质组成,而康定MS6.3地震就发生在康定—石棉重力梯度变化带上、雅安—泸定磁性穹窿区的西边界线上.随着川青块体向南东方向滑移,受到四川盆地西缘边界刚性基底对川青块体的强烈阻挡,加剧了康定—石棉及其以东地区基底岩层的褶皱变形并产生了强烈的应力积累,所积累的应力突然释放导致了康定MS6.3地震的发生,这正是此次鲜水河断裂带南东段康定地区强震孕育和发生的深部构造环境和介质特征.根据本文对鲜水河断裂带南东段深部孕震环境的综合研究成果可知,石棉段处于重磁异常梯级带上且其北东侧表现出的高密度、强磁性和高波速等物性特征有利于区域应力的相对集中,因此,鲜水河断裂带南东段石棉地区的地震活动趋势和地震危险性背景值得进一步关注和研究.     

Fast imaging of subsurface conductors using very low‐frequency electromagnetic data

The study presents a fast imaging technique for the very low‐frequency data interpretation. First, an analytical expression was derived to compute the vertical component of the magnetic field at any point on the Earth's surface for a given current density distribution in a rectangular block on the subsurface. Current density is considered as exponentially decreasing with depth, according to the skin depth rule in a particular block. Subsequently, the vertical component of the magnetic field due to the entire subsurface was computed as the sum of the vertical component of the magnetic field due to an individual block. Since the vertical component of the magnetic field is proportional to the real part of very low‐frequency anomaly, an inversion program was developed for imaging of the subsurface conductors using the real very low‐frequency anomaly in terms of apparent current density distribution in the subsurface. Imaging results from the presented formulation were compared with other imaging techniques in terms of apparent current density and resistivity distribution using a standard numerical forward modelling and inversion technique. Efficacy of the developed approach was demonstrated for the interpretation of synthetic and field very low‐frequency data. The presented imaging technique shows improvement with respect to the filtering approaches in depicting subsurface conductors. Further, results obtained using the presented approach are closer to the results of rigorous resistivity inversion. Since the presented approach uses only the real anomaly, which is not sensitive to very small isolated near‐surface conducting features, it depicts prominent conducting features in the subsurface.     

Gaussian states in de Sitter spacetime and the evolution of semiclassical density perturbations.

The evolution of Gaussian quantum states in the de Sitter phase of the early universe is investigated. The potential is approximated by that of an inverted oscillator. We study the origin and magnitude of the density perturbations with special emphasis on the nature of the semiclassical limits