滇中及邻区地球物理构造特征与地震关系的研究

<正>滇中及邻区地处云贵高原,该区地震活动频率高、强度大、周期短、震源浅、破坏性强,历史有记载的6级以上地震达46次,其中7级以上地震11次,8级以上地震1次。该区域各种地球物理特征的变化剧烈。本文在前人工作的基础上,采用二维小波变换和3D平均滑动法处理了滇中及邻区(23°~27°N,100°~105°E)重,磁数据,重点分析了重磁特征以及水系与地震的关系。将自地震记录有史以来至2014年10月中国地震台网中心所公布的大于MS5.0的地震震中位置投影至     

关于黄海深部构造的地球物理认识

利用黄海海区重磁观测数据,以最新的地震层析成像和浅层反射地震探测结果作为约束,并利用小波分解、纹理特征图像处理等手段,对研究区进行了地球物理场特征分析、岩石物性总结、断裂信息提取和磁性基底埋深反演计算,同时对南黄海海域三条剖面进行了广义逆重磁数据拟合反演和地震P波速度成像.根据地球物理数据的各种处理结果,提出在南黄海西部存在一条串珠状地球物理线性构造带,并将这条NNW向断续延伸的构造带称之为南黄海西缘断裂带.该断裂带延伸长,断裂两侧前新生代地层差异较大,有可能是造成陆区和南黄海南部盆地区前新生代油气远景差异的原因之一.文中得到南黄海磁性基底埋藏分布具有“中间浅四周深”的分布特征,与地震层析成像结果相吻合.磁性基底的局部起伏和局部构造的边界断层共同控制了前新生代残留盆地的格架和残余厚度分布,反映出“区域控制局部,深层约束浅层”的规律.     

青藏高原在岩石圈磁场模型中的巨大空白——同“青藏高原及邻区的地壳磁异常特征与区域构造”作者商榷

康国发等[1]"青藏高原及邻区的地壳磁异常特征与区域构造"一文采用高阶地磁场模型NGDC-EMM-720-V3系统研究了青藏高原及邻区(24°～40°N,76°～108°E)的磁异常特征并分析与区域构造的一些对应关系.该文利用岩石圈磁场模型研究地质构造单元具有独特优势,但在使用岩石圈磁场模型时应对模型构建的局限性予以重视.NGDC-     

南沙海域及邻区△T磁异常化极的实现

在对南沙海域及邻区(2°N～17°N,104°E～122°E)1960～2000年间地磁倾角/偏角等地磁要素特征变化及△T磁异常数据特点分析研究的基础上,通过对低纬度化极方法的综合分析及实验对比试算,提出了滤波与偏移抽样法结合的化极处理方法模式及数据分带划块的具体实施措施,实现了该超低磁纬区,亦称零磁纬区(地磁倾角变化范围:-15°～+20°;地磁偏角变化范围:-1°～+1.3°)大范围、多来源、长测量时间间隔实测△T磁异常的变倾角变偏角化极,并给出了对化极结果的评价及验证。△T磁异常化极的实现,为深入研究该区域内磁性地质体特征,提供了更为密切直接的依据。     

青藏高原冈底斯带及邻区重磁三维反演及岩浆岩特征研究

岩浆岩在青藏高原的大陆动力学研究中有着重要的作用,它既是构造演化的记录,又是重要构造-岩浆-成矿带的指示.本文主要基于冈底斯带及邻区的地面重力和航磁数据,首先进行地质-地球物理先验信息约束下的重磁2.5维交互式反演,再将2.5维反演结果作为参考模型加入到三维反演计算中,得到地下三维密度和磁化率结构.结合岩浆岩密度、磁化率统计资料和岩浆岩地球化学成果,推断研究区基性岩、I型花岗岩和S型花岗岩的三维分布图,得到如下结论:S型花岗岩主要分布在冈底斯东带和冈底斯弧背断隆带以北;北冈底斯的西部无明显的岩浆活动,而在其南侧和北侧,发现大量的隐伏基性岩和零散分布的I型花岗岩;中生代I型花岗岩在南冈底斯和冈底斯弧背断隆带广泛分布,且到新生代才出现大量的S型花岗岩.上述结果为中生代班公湖—怒江洋壳和新特提斯洋壳的双向剪刀式俯冲模式的观点提供了重要佐证,并认为班公湖—怒江洋壳在北冈底斯西部约84°E—88°E的范围内先后存在向北和向南俯冲的可能,北向羌塘地体下俯冲,南向冈底斯地体下俯冲.     

南海构造格局及其演化

依据重磁资料在南海及其邻区识别出17条深大断裂和10个重磁异常区.据此并结合其他地质资料,在南海及其邻区划分出7个地质结构不同的构造单元.早白垩世南海地区曾形成过统一的基底,新生代时统一的南海基底发生肢解,这一个肢解过程经历了两个在时空上接踵发生、交叠作用的构造事件.第一个构造事件为巽他地块与华夏古陆之间古南海的萎缩、闭合和地块碰撞;第二个构造事件为南沙地块裂离华夏古陆并向巽他地块增生,且伴随新南海的持续扩张,直至中中新世.区域构造演化控制了南海沉积盆地呈"北三南三、东西两竖"格局分布,进而控制了油气富集区的分布.     

对黄海-东海研究区深部结构的一些新认识

综合地震层析成像与重磁数据的处理结果,选择26°N～36°N,120°E～130°E的范围作为研究区,讨论了黄、东海研究区的深部结构特点及其与周边各地质单元的相互关系,完成了研究区两条剖面的密度结构反演,认为东海陆架地区地壳厚度变化与大陆地区相比并不明显,显著减薄开始于冲绳海槽地区,中地壳消失;琉球岛弧处地壳厚度明显再度增加,特别是上地壳的厚度增加最大,推断其原因应与俯冲作用及俯冲带附近板块与地幔的运动速率之差有关.地球物理场“东西分带”是黄海—东海地区壳内结构从西向东变化的反映,但随着深度的增加,研究区的岩石层结构出现以近EW向为优势的构造格局.因此推断深部近EW向的异常是三叠纪时期南北板块碰撞、挤压所致,浅部的NE向条带异常是后期构造运动在岩石层较浅部位构造效应的反映.黄海—东海地区岩石层结构存在浅部与深部优势构造方向不协调的现象.层析成像结果证实了南黄海东缘断层的存在,还勾绘出绍兴—十万大山碰撞带为以40°左右的倾角向NW方向倾斜的高速带,另一条倾向基本相同的高速带则是南、北扬子块体结合带在深部的反映.     

重磁对应分析技术在缅甸X区块的应用研究

缅甸X区块属于陆上低成熟勘探区块,地震采集覆盖面积较少.为了预测研究区构造特征及火山岩分布情况,研究分析该区重磁异常的同源性,利用位场数据处理中的重磁对应分析技术、最大梯度模等方法,对该区重磁资料进行了处理和认识.综合分析了研究区重力场、磁力场、重磁对应分析中相关系数的基本特征,结合研究区已有地质资料及地震解释,进行构造特征认识,并综合分析了断裂划分及圈定勘探远景区.     

基于OBS数据的南黄海沉积地层速度结构特征

南黄海盆地是在前古生代变质基底及中-古生代海相沉积基底之上发育起来的中-新生代陆相叠合盆地.本文基于南黄海深部地学探测的主动源地震数据(OBS2013测线),通过多尺度层析成像方法利用初至波走时反演得到测线下方沉积层的纵波速度结构,结合多道地震、重、磁等资料,综合分析南黄海盆地北部沉积地层的特征.结果表明,OBS2013测线下方的地层纵、横向上有多个速度分界面,纵向上以印支面为界,下部挤压与上部伸展地层速度分别呈现高、低速特征;横向上表现为众多断裂,断裂控制了盆地发育,个别断裂发生走滑.断裂将速度剖面划分为四个纵波低速区和五个高速区,6km深度以内纵波速度的低值区(<4.5km·s-1)是中-新生代沉积地层;而高值区(>5km·s-1)归属于不同的形成机制:北部高速区对应千里岩隆起区的变质岩,中部高速区是被挤压的海相沉积地层,南部高速区属于中部隆起,为埋藏较浅、但厚度较大的中、古生代海相地层,部分位置可能含有火成岩.北部坳陷的中、南部区域,在陆相中-新生代沉积盆地之下的海相地层中发育砂岩,该区域(埋深不超过6km)的砂岩沉积分布于约2km厚度的地层中.     

长江中下游—南黄海地震带地震活动趋势分析

对长江中下游－南黄海地震带地震活跃期,幕划分及其发展趋势进行了研究,对江苏及其邻区今后几年地地震在形势及重点危险区进行了判定,分析认为：长南带从１９７１年以来进入第二活跃期的第３幕,该幕地质活动将持续到２０１０年前后,最高活动水平为６．５级左右,今后几年江苏东部至南黄海海域发生５－６级或６级以上地震的可能性较大。     

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

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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.     

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.     

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.