上层海洋浮游生物地理分布

确定海洋浮游生物的分布区域是海洋浮游生态学研究的首要任务之一,本文总结了上层海洋(0—200m)浮游生物地理分布的研究历史、已有的认知及全球变化的影响。对浮游生物地理分布的研究可以分为19世纪末期至20世纪70年代、20世纪80年代至2000年,以及2000年以后三个时期。根据分布区资料的时间长短,浮游生物分布区分为瞬时分布区和时段分布区。大洋浮游生物地理分布呈按纬度平行分布的九带式格局:赤道条带、2个中心区条带、2个亚极区条带、位于中心区和亚极区之间的2个过渡区条带及位于南北极海区的2个极区条带。洋流和水团是除过渡区条带之外的生物分布格局决定因素,而过渡区条带的可能调控机制为中尺度涡。在核心区内生物的构成相对稳定,但在不同位置生物的丰度比例可能不同,在环流中心可能有演替顶极。在分布区的外围,洋流和中尺度涡使得生物远离核心区,繁殖能力下降不足以维持种群,从而处于流放状态。相同分布格局的生物扩散能力不同,扩散能力最差的生物是核心种,最强的为先锋种。相邻水团中核心种和先锋种的交汇可以有不同的情形,交汇的位置也会经常发生周期性的变化。由于纬度的不同和陆地的阻隔,南北半球和不同大洋的相同条带之间有不同的种类。人类活动使得有些近岸种类发生了生物入侵,而全球变暖使得大洋浮游生物分布区向极区移动。随着分子生物学技术的普及发展,微食物网生物的生物地理分布研究也逐渐开展。我国的海洋生态学研究正在走向大洋深海,对全球尺度的海洋浮游生物地理分布的关注逐渐增加,也必将有所贡献。     

地震前兆台网观测数据质量分析——中国地震背景场探测项目实施

地震前兆台网的运行直接影响产出的观测数据质量。观测数据平均连续率和平均数据完整率可以反映地震前兆台网的运行质量。对中国地震背景场探测项目试行期间(2014年)及正式启动后2015年度的观测数据质量,从以上2个指标进行分析,并对比原有仪器运行质量,可知背景场项目试运行期间,各学科台网投入仪器运行稳定,观测数据符合相关要求,总体质量良好,观测仪器可以投入正式运行。     

钟祥地震台面波震级测定

整理钟祥地震台2012年至2016年6月全球M_S≥6地震目录,与中国地震台网中心发布的面波震级进行对比分析,统计发现,该地震台面波震级误差主要集中在-1.0—+0.5,为此分析误差存在的原因,并根据实际情况给出解决办法。     

2016年3月21日金塔县M_S 4.7地震强震动记录分析

2016年3月21日11时29分甘肃省酒泉市金塔县发生M_S 4.7地震,甘肃省强震动台网中心收集到5组三分向加速度记录,常规处理后得到15条零基线校正后的三分向峰值加速度(PGA),选取土层台基类型的62XID台站加速度记录(PGA数值最大)进行分析,绘制校正后的加速度、速度和位移时程曲线及加速度反应谱,为中国西部工程震害调查提供参考资料。     

联合钻孔资料及地形数据估算宝鸡地区vS30

将地形数据经过坡度计算,利用坡度与v_S30相关关系,计算宝鸡地区场地近似v_S30。为了得到接近实际的波速分布,借助宝鸡地区钻孔资料,研究选定区域内v_S30近似值与实测结果的差异,并对差异的空间变化趋势进行分析,在此基础上,对模型估算的v_S30进行修正,进而得到接近实际的v_S30分布,并给出基于NEHRP的宝鸡地区场地分类。     

城市浅层地震勘探过障碍变观设计

在城市浅层地震勘探数据采集中,地震测线经常会遇到河流、桥、交叉路口等地表障碍。为了尽量减小地表障碍造成的影响,需要对观测系统作变观设计。作者分析总结了城市浅层地震勘探中常见障碍以及过障碍变观模式,并开发了浅层地震过障碍变观设计软件,利用此软件可在采集现场快捷地进行过障碍变观。将这种方法应用于实际工作中,有效减小了资料缺失造成的影响,提高了资料的信噪比。该软件能够根据实际工作环境和设备条件在野外现场对观测系统进行灵活变观,设计出合理的过障碍观测系统,有效地提高了变观设计的效率。     

蔚广盆地南缘断裂带唐山口段山前断层活动性研究

蔚广盆地是山西地堑系北端京西北盆岭构造区内的一个半地堑盆地,蔚广盆地南缘断裂带为控制该盆地形成的边界断裂。该断裂带位于唐山口段的山前断裂在冲洪积扇体上形成了线性特征显著的断层陡坎。横跨断层陡坎开挖的探槽表明该条山前断裂属于全新世活动断裂,探槽揭示了2条活动断层以及相应的3次古地震事件。在距今约9ka时其中一条断层首次活动,之后在距今约7.3ka时该条断层再次活动并引发了另一条断层的形成与同步活动。最后它们又发生了第三次活动,而最新一次活动的时间由于相应地表沉积的缺失而无法获得。这3次古地震事件的累积垂直位错约为8.1m。估算出整条山前断裂的平均复发周期约为1.7ka、平均滑动速率约为1.6mm/a。此外还依据经验公式估算出了各次古地震的参考震级。     

The effect of seafloor topography in the Southern Ocean on tabular iceberg drifting and grounding

Antarctic tabular icebergs are important active components in the ice sheet-ice shelf-ocean system. Seafloor topography is the key factor that affects the drifting and grounding of icebergs, but it has not been fully investigated. This study analyzes the impact of seafloor topography on the drifting and grounding of Antarctic tabular icebergs using Bedmap-2 datasets and iceberg route tracking data from Brigham Young University. The results highlight the following points. (1) The quantitative distributions of iceberg grounding events and the tracking points of grounded icebergs are mainly affected by iceberg draft and reach their peak values in sea water with depths between 200 m and 300 m. The peak tracking point number and linear velocity of free-drifting icebergs are found in the Antarctic Slope Front (water depth of approximately 500 m). (2) The area of possible grounding regions of small-scale icebergs calved from ice shelf fronts accounts for 28% of the sea area at water depths less than 2000 m outside the Antarctic coastline periphery (3.62 million km²). Their spatial distribution is mainly around East Antarctica and the Antarctic Peninsula. The area of possible grounding regions of large tabular icebergs with long axes larger than 18.5 km (in water depths of less than 800 m) accounts for 74% of the sea area. (3) The iceberg drifting velocity is positively correlated with ocean depth in areas where the depth is less than 2000 m (R=0.85, P<0.01). This result confirms the effect of water depth variations induced by seafloor topography fluctuations on iceberg drifting velocity.     

Processes of initial collision and suturing between India and Asia

The initial collision between Indian and Asian continents marked the starting point for transformation of land-sea thermal contrast, uplift of the Tibet-Himalaya orogen, and climate change in Asia. In this paper, we review the published literatures from the past 30 years in order to draw consensus on the processes of initial collision and suturing that took place between the Indian and Asian plates. Following a comparison of the different methods that have been used to constrain the initial timing of collision, we propose that the tectono-sedimentary response in the peripheral foreland basin provides the most sensitive index of this event, and that paleomagnetism presents independent evidence as an alternative, reliable, and quantitative research method. In contrast to previous studies that have suggested collision between India and Asia started in Pakistan between ca. 55 Ma and 50 Ma and progressively closed eastwards, more recent researches have indicated that this major event first occurred in the center of the Yarlung Tsangpo suture zone (YTSZ) between ca. 65 Ma and 63 Ma and then spreading both eastwards and westwards. While continental collision is a complicated process, including the processes of deformation, sedimentation, metamorphism, and magmatism, different researchers have tended to define the nature of this event based on their own understanding, an intuitive bias that has meant that its initial timing has remained controversial for decades. Here, we recommend the use of reconstructions of each geological event within the orogenic evolution sequence as this will allow interpretation of collision timing on the basis of multidisciplinary methods.     

宾川地区的地壳厚度和泊松比分布特征研究

This paper presents the changes of crust thickness and Poissons ratios distribution in the Binchuan region,where the first air-gun transmitting station and its a small dense array were deployed.From September 2011 to January 2014,more than 239 teleseismic events of M≥6.0 were recorded in 16 stations in the Binchuan region.Their P-wave receiver functions were analyzed respectively.The high spatial resolution result shows that the average crust thickness of Binchuan region is 45.3km,it follows the rule of"deeper in the north and east part,shallower in the south and west part."The deepest region is in Xiaoyindian Station;the crust thickness is 47.9km;the shallowest region is in Paiying Station,it has the thickness of 42.1km.It shows that the deeper Moho surface nearby the Chenghai fault and shallower nearby the Honghe fault;the isoline distribution of thickness changes greatly nearby the Chenghai fault and slowly nearby the Honghe fault.From the distribution of Poissons ratios,it is unevenly in the study area with a great difference from the north part to the south part,which shows a characteristic of"lower in the north,higher in the south".The Poissons ratio nearby the Honghe fault is medium too high(0.26≤σ≤0.29);lower nearby the Chenghai fault(σ≤0.26).This paper concludes the possible reason of different characteristic between Poissons ratio and crust thickness is thicker in the upper crust in the Binchuan region.