中国东部海域断裂构造格架与地震活动研究

渤海、黄海和东海等中国东部海域在地质构造上是大陆向海的自然延伸，海域内的构造方向与大陆一致，均为NNE-NE向，但属于不同的二级大地构造单元，渤海和北黄海属于华北地块，南黄海属于扬子地块，东海属于华南地块。由于各地块与现今活动板块边界位置不同，构造与地震活动性差异较大，渤海和北黄海地区地震活动主要受印度板块与欧亚板块碰撞形成的东喜马拉雅构造节远场效应影响，地震活动强烈；南黄海地区以中强地震活动为主；东海地区地震活动主要受菲律宾海板块与欧亚板块碰撞形成的琉球俯冲带影响。冲绳海槽是正在形成的（活动的）边缘海盆地，不仅有浅源地震，且有中源地震活动。东海陆架盆地由于受冲绳海槽扩张的影响，停止发育，构造与地震活动相对较弱。     

东海及邻域的两条剖面地球物理反演与综合解释

根据东海及邻域的布格重力异常资料,在东海海域选择了中国大陆东部—东海陆架—冲绳海槽—琉球岛弧—琉球海沟的两条剖面。利用广义逆方法对两条剖面进行重力和磁力反演,结合其它地震等地球物理及地质资料,对剖面的地壳结构进行了综合研究,给出了相应的地质解释．在此基础上,对东海陆架盆地、冲绳海槽盆地的成因与性质,以及应力作用情况进行了探讨,认为冲绳海槽地壳的纵向结构是一种“二元结构”;沟—弧—盆受的主应力方向为NW向;该区平面上地质地球物理现象的分块分带与纵向上的二元构成根本原因与菲律宾海板块和欧亚板块聚敛俯冲方向有关,还与两板块接触部位形状有关．     

东海重磁地震综合探测剖面研究

依据东海南部一条自东海陆架直至菲律宾海盆的重磁地震综合探测剖面,采用地壳结构重磁地震综合反演解释系统开展岩石圈结构的综合研究,制作了岩石圈结构地学断面图. 结果表明基隆凹陷为一中新生代沉积凹陷,沉积厚度达到14km;冲绳海槽盆地为弧后扩张地堑型盆地,地壳厚度仅为14.5km;菲律宾板块沿北西西方向向欧亚板块俯冲,莫霍面急剧下插,导致冲绳海槽的形成与发展;岩石圈厚度约为80km,但在370km处仅为53km,在450km至540km处岩石圈厚度大于100km.     

中国东部大陆与东海海域地质构造的相关性分析

分析了中国大陆东部地区和东海海域地球物理场、大地构造、地球动力学特征．根据分析得出;东海海域的重磁场特征与中国大陆重磁场特征密切相关．分布趋势与走向均与大陆边缘重磁场相同,是大陆地球物理场向海域的延伸．东海陆架盆地地区具有大陆地球物理场特征．东海东部边缘、海槽具有大陆边缘地球物理场特征．根据研究区的重磁资料计算了该区莫霍、居里界面深度与分布．地壳结构特征表明：莫霍界面在中国东部的主要走向为NE—NNE向,与东海莫霍界面的走向基本一致,说明是大陆地壳向海域的延伸．在冲绳海槽以东海域,地壳厚度由十几公里迅速减薄到几公里,表明地壳由过渡壳向洋壳的转变．因此;中绳海槽应该是大陆地壳的自然终结．中国大陆东部居里界面的差异,反映了地壳结构的不同。陆区及陆架区的磁场特征主要反映了上地壳的磁性结构,相应的也形成了不同的磁场特征与居里界面特征．地球动力学特征表明：东海海域地球动力学特征与中国东部大陆地球动力学特征关系密切,这一地区是欧亚板块与菲律宾海板块的结合地带．构造活动十分强烈．是研究中国大陆及其邻域构造运动,进行地球动力学特征分析的极为有利、重要的地区．     

东海地区现代构造应力场及其成因探讨

分析了东海东南部地区5口3 000余米深、井径测井段千余米至两千米长的钻孔孔壁崩落特征,结合以前分析过的另外11口深钻孔的孔壁崩落特征,推断出东海地区的最大水平主压应力方向为NE-SW向,水平差应力不强．分析了冲绳海槽和琉球岛弧地区1977～1998年中心地震矩张量解的P,T轴方位分布．结果表明,冲绳海槽地区的P轴方向多为NE-SW向,与海槽延伸方向一致．海槽地区地震震源机制解的T轴方向为NE-SW向,与海槽延伸方向垂直．这些特征说明,菲律宾海板块对东海地区的水平作用并不是挤压,而是拉张．利用二维弹性有限元模拟法研究了东海地区现代应力场的成因．结果表明,东海地区应力场和台湾地区的强烈北西向挤压与琉球岛弧的弧后扩张有关．东海地区水平差应力不强可能是该地区强地震少的动力原因．      

南黄海和东海地区现代构造应力场特征的研究

分析研究了南黄海和东海地区18口石油勘探钻井的井孔崩落特征，结合对琉球岛弧和冲绳海槽地区浅源地震震源机制解的分析，确认了南黄海地区与我国华北地区有类似的现代构造应力场特征；并得出东海地区的最大水平压应力方向为NEE-SWW，最小水平压应力方向为NNW-SSE，它们分别与冲绳海槽地区的最大和最小主压应力方向接近;东海地区地壳上层的水平差应力可能不强，这与该地区没什么地震活动的特点是一致的．根据应力场特征推断，我国东部地区并未受到菲律宾海板块俯冲的推挤作用，而是可能受到垂直于冲绳海槽走向的拉伸作用的影响．     

东海的来历

东海是中国东部的大型边缘海,具有复杂的陆架盆地、特殊的沉积构成,以及西太平洋陆缘典型的沟-弧-盆构造体系,记录了大量大陆边缘演化、盆地形成和环境气候演变的信息.研究表明,在晚白垩世之前,华南大陆以东并无东海,而是古太平洋相伴.晚白垩世之后原始的东海开始形成,其后漫长的地质历史时期先后经历了晚白垩世至早始新世的被动陆缘阶段,以及中始新世以来的太平洋板块和菲律宾海板块两期俯冲和弧后扩张,奠定了现今东海西部为水深小的宽陆架,东部为水深较大的冲绳海槽的构造格局.现代的东海是在末次冰期(1 5 k a B P)之后形成的,海平面的变迁塑造了现代东海的海底地貌.     

琉球海沟的构造和运动特征

琉球海沟是欧亚板块与菲律宾海板块之间的边界，海沟西坡是大陆性质的琉球岛弧，东坡是大洋性质的菲律宾海地壳．海底地震反射探测和地震震源定位表明，菲律宾海板块沿海沟向琉球岛弧下俯冲，俯冲角度与深度沿海沟走向变化．有证据显示，由于俯冲板前缘的横向移动，海沟和岛弧正朝大洋方向后退，弧后盆地-冲绳海槽发生拉张变形．最近一次的海沟后退与冲绳海槽扩张可能是从上新世末(2Ma前)开始的，岛弧的后退移动和弧后拉张在南部与海沟走向垂直，在中部和北部与海沟走向斜交，总体上向南的运动分量占优势、与海沟后退相关的弧后拉张集中在冲绳海槽，没有证据表明对其西侧的中国东海陆架盆地产生影响、海沟后退的原因可能与俯冲板的动力不平衡以及它与周围地幔的相互作用有关．     

台湾岛以东海域加瓜“楔形”带对冲绳海槽南段的构造控制

基于实际调查资料与历史基础资料的综合分析与解释, 对台湾岛以东海域加瓜“楔形”构造带的地球物理场特征、构造属性和冲绳海槽南段弧后扩张的构造主应力方向及其变化规律进行了研究; 提出加瓜“楔形”构造带在构造上与加瓜海脊及其东、西两侧断陷盆地相对应; 并对西菲律宾海板块的运动方向和运移量进行了调整, 使构造带以东的西菲律宾海盆的北西向运动转为西侧的向北俯冲, 从而导致冲绳海槽构造主应力方向由NW-SE方向逐渐转成近南北向, 为冲绳海槽进入第二次拉张-扩张阶段提供了应力来源.     

中国东部海域及邻区岩石层地幔的P波速度结构与构造分析

利用中国大陆东部及台湾地区、日本和琉球群岛的地震观测数据，通过体波地震层析技术反演了中国东部海域及其邻近地区的P波速度结构.以此为依据分析了不同地区的岩石层性质和深部动力学条件，探讨了中朝与扬子块体、扬子与华夏块体在海区的深部边界及其构造属性，揭示出菲律宾海板块与欧亚大陆的碰撞以及板片俯冲下沉、弧后扩张作用对中国东部海域岩石层结构的影响.结果表明，中国东部海域的岩石层地幔存在明显的横向非均匀性，它们与区域构造的形成演化有一定的联系.中国大陆东部的五莲－青岛断裂与朝鲜半岛西缘断裂、济州岛南缘断裂共同构成中朝和扬子块体的边界，江绍断裂向东延伸至朝鲜半岛南端成为分隔扬子和华夏块体的边界；东海陆架与冲绳海槽的岩石层结构差异明显，东海陆架具有中国东部地区的岩石层特征，属于欧亚大陆向海域的延伸；冲绳海槽的岩石层强烈减薄，为大陆向大洋过渡的区域；沿着日本－琉球－台湾俯冲带，菲律宾海板块俯冲下沉引起的地幔扰动对中国东部海域产生了较大的影响，欧亚大陆与菲律宾海板块之间的相互碰撞导致台湾地区岩石层明显增厚.     

SCIENCE CHINA Earth Sciences SUBJECT INDEX TO VOLUME 57(2014)

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A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Distribution of throughfall and stemflow in multi‐strata agroforestry,perennial monoculture,fallow and primary forest in central Amazonia,Brazil

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd.     

Anthropogenic Eutrophication and Red Tide Outbreak in Lacustrine Systems of the Kashmir Himalaya

Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate.