唐山断裂现代活动性研究

利用1984～2008年唐山台跨断层基线和水准数据,分时段研究断层的运动特征,计算出唐山断裂水平形变、垂直形变特征及断层活动速率。求解断层及周边地区的的应变特征和主应变方向,研究唐山断裂的活动特征。探讨唐山断裂活动与地震活动的关系。     

1976年唐山MS7.8地震同震及现今形变特征

基于1976年唐山M_S7.8地震的同震位移和现今GPS速度结果, 本文分析了该地震的同震破裂参数、 同震应变释放分布及其现今应变积累特征． 对唐山同震位移二维位错解析公式的拟合结果显示, 唐山地震前的断层闭锁深度约为18—23 km, 断层倾角可能介于74°—90°之间, 同震位错量约为3.1—3.4 m． 在同震过程中沿发震断层表现出显著的右旋错动特征, 在发震断层两侧沿NE向表现出左旋应变释放特征． 在本文现有的GPS测站密度和精度情况下, 尚无法识别出现今阶段沿唐山断裂的明显蠕滑特征． 唐山同震应变释放和现今GPS应变率积累结果均显示, 唐山断裂SE侧的剪切形变(速率)量值大于其NW侧, 同震与现今阶段的形变量值相差约1000倍．      

唐山地震前地壳的异常隆起及无震蠕动

根据唐山地区震前11期水准复测资料,对本区的地壳形变的时空变化特征进行了分析.结果表明:唐山地震前1968年-1969年震中区发生了幅度为50毫米、持续时间2年的异常隆起,并在唐山及宝坻附近的唐山断层和蓟运河断层显示出应变积累与无震蠕动叠加的作用.采用了均匀应变积累及弹性位错理论分别计算了唐山、宝坻附近测点由于各处断层蠕动引起的垂直位移理论值,按残差均方根最小的原则确定历年应变积累及蠕动断层参数的最佳值.1969年-1975年唐山地下发生蠕动的断层走向为北东47、倾角87、倾向南东的右旋正断层,断层长度为8公里、宽度6公里、断层上界深度为2公里、走滑与倾滑错距分别为104厘米及8厘米,平均应变积累速度为0.910-7/年.同时得到断层走向、倾向蠕动速度分别为18.6厘米/年及1.4厘米/年.另外由蓟运河断层结果得到.宝坻附近蠕动断层的规模比唐山小,但蠕动速度比唐山大.本文分析了上述异常隆起及蠕动断层与唐山地震的关系,认为地壳的异常隆起是孕震的早期显示,而无震蠕动可能是浅源地震的又一前兆特征.唐山地震经历了长期应变积累-体积膨胀-蠕动-形变反向(或蠕动速度减慢)-发震的过程.      

京津冀地区地震重新定位及其与活动断裂的关系

地震重新定位为地震活动和活动构造等研究提供了相对精确的地震参数。本文采用双差地震定位法对京津冀及周边地区2007年12月~2016年3月底的地震进行重新定位,并结合区内的活动断裂资料,探讨重定位后地震的空间分布特征、震源深度分布特征及其与已知活动断裂的关系,并根据重定位后地震空间线性条带的走向揭示隐伏断裂。研究结果表明,重定位后,地震主要集中在唐山、邢台、张渤带西段和文安地区,震中在空间上的分布比由常规地震确定的初始震中更为集中,沿断裂走向更加收敛;震源深度分布更加合理,主要集中在1~20km的中上地壳层;定位结果显示唐山断裂、卢龙断裂为北西倾高角断层,新河断裂为北西向低倾角断层,张北震区、延矾盆地和怀涿盆地断裂、黄庄—高丽营断裂、夏垫断裂等地区的地震活动剖面呈近直立分布;另外,根据重定位后地震的线性分布还刻划出唐山断裂北段的南侧、文安北部两条近NNE方向的隐伏断裂。本文的研究结果对京津冀地区的地震活动、断层构造以及地震孕育发生环境具有重要意义。     

利用唐山地震台资料研究唐山断裂活动特征

本文研究了唐山地震台内的唐山断裂形变、断层活动协调比、断层土壤气CO₂的变化特征。结果显示,唐山地震台内的唐山断裂近35年来整体上在水平方向呈微弱的右旋张性活动,垂直方向呈正断活动,但不同时段的运动状态有所不同;综合分析认为,唐山地震台形变和流体前兆观测对附近及华北因区域地壳应力场调整引起的中小地震有一定的显示,说明该台具有一定的前兆异常显示能力;随着观测资料和经验的持续积累,在该区域发生更大地震前,有望捕捉到更显著的前兆异常。     

从地震折射和反射剖面结果讨论唐山地震成因

通过唐山震中的地震测深以及深反射剖面,揭示了唐山震源区的浅部及深部构造图象,它与以往的推测很不相同。 唐山东面的开平向斜属中生代构造,探测的结果表明,向斜轴是一近于直立的地壳断裂。唐山地震时的水平地形变主要是由开平地壳断裂的位移引起的,它是北北东-南南西向右旋走滑断裂。开平地壳断裂西面的陡河断层是一自地表向南东方向下插的正断层,断层倾角为26°,延伸至5km深处。陡河正断层刚好插到唐山市震中区的正下方。唐山地震时的垂直地形变主要是由陡河正断层的滑动引起的。 野鸡坨-丰台断层通过震源区的西部边缘,断层以西的第四纪沉积层,在过去一百万年间曾经沿北北东方向水平滑移15km,表明它也是一个右旋的走滑断层。但是它在近代数百年间并无地震活动,唐山地震时该断层的滑动亦不明显。 开平地壳断裂和陡河正断层在唐山地震时同时滑动,说明地震的作用力除区域水平构造力外,地壳上方还存在一个附加的引张力。在开平断裂处,上部地壳的反射面倾角杂乱,而且在它的正下方,莫霍界面明显错断,因此,地幔顶部的热物质可能自开平地壳断裂中上升。热物质产生的热应力在地壳上方可表现为张应力,而在地壳下方却表现为压应力,这与反射地震剖面图的现象相符合。开平地壳断裂中热物质的上升对地震的产生有     

唐山强震前后北京、天津周围地区应力的变化过程

本文根据近二十年来400多次地震的连续资料,分析了北京、天津周围地区在1976年唐山强震发生前的应力变化。其特征是以水平应力作用为主,表现为东西受挤压,南北受引张.与唐山主震震源机制解结果和野外宏观考察结果基本一致.变化持续时间达四年半之久,并于强震发生后又恢复到原有状态.通过对此地区应力变化过程与震前3级以上地震空间活动及其震源机制的分析,进一步探讨了唐山强震前后应力集中和断层活动的关系.发现震前应变能集中于沧东断裂北端,其释放是近几十年来的第一次.反映了唐山强震的发生背景.      

2013年甘肃岷县漳县M_s6.6地震前地壳形变特征研究

基于2013年岷县漳县M6.6地震震源区及其邻区1999年以来的GPS观测资料,通过应变率动态特征分析、多期次GPS剖面分析和基线变形速率的分析讨论了地震的震前变形特征.GPS速度场和块体应变率表明,汶川地震的发生导致了柴达木地块运动与变形状态发生明显调整,但由于西秦岭北缘等深大断裂的存在,岷-秦地块对其响应不明显;GPS连续应变率显示,在汶川地震引起的区域地壳变形调整过程中岷县漳县地震震源区附近的应变积累速率有减缓的迹象;GPS剖面显示,平行于岷县漳县主破裂带的运动分量对汶川地震响应显著,汶川震后表现为剪切变形速率的增强,而垂直于主破裂带的运动分量则对汶川地震响应不明显;震中周边GPS基线变形速率表明,基线伸缩变化率总体呈现NW向拉张、NE向压缩状态,且拉张量明显小于压缩量.上述地壳变形动态特征表明西秦岭北缘断裂及其附近地区的应变积累水平和断层闭锁程度可能处于较高水平,在岷县漳县地震前该区表现出局部“硬化”迹象.     

唐山大震及其前后的地震活动

1976年7月28日北京时间03时42分56秒河北省唐山市区(东经118°11′;北纬39°38′)发生7.8级地震,震中烈度达十一度。当日18时45分37秒于附近的滦县商家林(东经118°39′;北纬39°50′)又发生7.1级地震,震中烈度达九度。本文简述唐山地震参数的测定及其发震的地质背景,并对大震前本区较大范围内地震活动的某些异常特征,如围空区、密集—平静、b值下降及条带状的空间分布等进行了一些讨论。根据大震时的地面断裂走向、P波初动图解、大震前后的垂直形变以及余震位置分布等资料推测,7.8级地震可能是北东走向的断层以走滑为主的右旋滑动结果。7.1级地震可能是近南北走向的滦河断层受北东向断层牵动发生的水平左旋运动。文中还从唐山余震时空分布特点出发,讨论了震源的破裂过程及其对余震发展的影响。并指出唐山大震的发生时间可能与当天的天文条件有关     

华北地区震前断层水平异常活动特征

分析了首都圈及邻近地区跨断层基线测量资料, 研究了唐山、大同及张北地震前后断层水平异常活动特征。结果表明, 震前在震中外围存在显著的断层水平异常活动, 监测断层水平活动是地震预测的有效手段; 同一测点震前断层水平异常活动具有相似性特征; 唐山地震前在震中附近一定范围内出现的断层水平异常活动, 具有断层预位移性质。     

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

正~~     

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.