青藏块体及其边缘的强震活动图象及动力源讨论

通过对中国西部地区强震活动特征的研究，发现该地区存在有３组取向不同，然而近似三等间距分布的６级以上强震空带，相邻空带间距约５°，宽约１°。从青藏块体边界可能作用有周期性力的角度对上述现象进行了初步的解释，认为这种现象可能是边界上３组周期力产生的应力波在块体内迭加形成的驻波所致，其波长与前人所得到的构造波波长非常符合。     

中国大陆西部及邻区地震时空分布特征及其强震趋势预测

通过分析中国大陆西部及邻区地震活动的时空韵律性特征,较详细地研究了该区域的强震等间距、强震空带等间距的空间分布格局以及时间分布上的23a太阳活动准周期,同时探讨了活动期内主体活动区的迁移规律。综合考虑认为第5活动期的结束时间大约在2005年,主体活动区在天山带,未来几年内,该区可能会有相当8级地震的能量释放。     

中等地震的时空分布和强震

基于AkioYoshida等人的研究思路 ,以大华北地区 (30°～ 4 2°N ,10 9°～ 12 5°E)为例 ,来探讨我国大陆区域强震和中等地震时空分布之间的联系。通过对大华北地区 1970年以来 12次ML≥ 6地震的空间—时间分布情况进行研究后发现 ,该区强震发生前后 15年内 ,强震周围 2 0 0km内通常都有 5级以上地震活动。根据区域构造特点等因素 ,将大华北地区近期的强震活动分成 3个区域 ,并对该区近期的地震活动作了回顾和展望。     

昆仑构造带强震活动的特点

分析了昆仑构造带的强震活动后认为，昆仑地震带强震活动在时空分布上具有轮回性、等间距性及由西向东的迁移特点；昆仑地震带强震震级西弱东强，而强震发震频次西高东低；西昆仑构造带帕米尔结点的强震活动对大陆地震活跃幕有前兆意义。     

青藏高原东北部东西向构造及其地震活动和构造力学模式研究

本文通过对重力和航磁资料解译,研究了青藏高原东北部东西向构造特征。在该区域存在6条大型东西向构造带,它们的共同特点是:(1)东西向延伸超过1000km,南北宽约60km;(2)越向深部东西向构造越明显;(3)两条相邻构造带的间距为1°20′,显示等间距分布特征;(4)在大型东西向的构造带之外还有次级东西向构造带存在。青藏高原东北部强震活动与东西向构造有密切的关系,这是由于在北东向主压应力作用下东西向构造左旋剪切运动的结果。     

青藏高原东北部东西向构造及其地震活动和构造力学模式研究

本文通过对重力和航磁资料解译,研究了青藏高原东北部东西向构造特征。在该区域存在6条大型东西向构造带,它们的共同特点是:(1)东西向延伸超过1000km,南北宽约60km;(2)越向深部东西向构造越明显;(3)两条相邻构造带的间距为1°20'',显示等间距分布特征;(4)在大型东西向的构造带之外还有次级东西向构造带存在。青藏高原东北部强震活动与东西向构造有密切的关系,这是由于在北东向主压应力作用下东西向构造左旋剪切运动的结果。     

天山地震带强震活动特征

利用周边国家天山地震目录、中国天山地震目录及USGS地震目录,对天山地震带强震活动的时、空分布特征进行了分析讨论。结果表明,在研究时段内,天山地震带的强震在空间分布上有西强东弱、西密东疏且在40°〈φN〈42°范围出现强震的空白区并存在特殊的易发震地区。强震在南、北天山之间有往复迁移的特征,并在迁移的过程中有单发-双发-群发,但未出现过单发迁移后出现群发的过程。在时间分布上有较明显的周期特征及南、北天山交替发生的特征。在强度上,7级以上地震主要沿天山构造带分布,而6级地震不但有沿天山分布的还有沿斜切天山带的次级构造分布的,且6级以上地震出现高频地区,集中在东经77°±1°的天山地区。     

苏联斋桑7.3级地震前地震活动的某些特征

1990年6月14日苏联斋桑7.3级强震发生在重力异常梯度带的拐弯处;强震前存在明显的M_s≥3.5级地震围成的空区;空区走向为北西西向,与斋桑强震发震构造走向一致,长轴约170km。1990年2月14日4.0级地震可视为信号震。最后初步讨论了阿勒泰活动区的地震趋势。     

芦山MS7.0级地震余震序列重新定位及构造意义

利用四川省地震台网的震相数据和双差定位方法对芦山M_S7.0级地震及其余震序列进行了精确定位,根据余震分布确定了发震断层的位置和断层面的几何特征,并对余震活动进行了分析.结果显示,芦山M_S7.0级地震的震中位于30.28°N、102.99°E,震源深度为16.33 km.余震沿发震断层向主震两侧延伸,主要分布在长约32 km、宽约15~20 km、深度为5~24 km的范围内.地震破裂带朝西南方向扩展范围较大,东北方向略小,余震震级随时间迅速衰减.震源深度剖面清晰地显示出发震断层的逆冲破裂特征,推测发震断层为大川—双石断裂东侧约10 km的隐伏断层.该断层走向217°、倾向北西,倾角约45°,产状与大川—双石断裂相比略缓,它们同属龙门山前山断裂带的叠瓦状逆冲断层系.受发震断裂影响,部分余震沿大川—双石断裂分布,西北方向的余震延伸至宝兴杂岩体的东南缘,与汶川地震的破裂带之间存在50 km左右的地震空区,有可能成为未来发生强震的潜在危险区.     

活动地块假说理论框架的提出、发展及未来需关注的科学问题

由中国科学家提出的"中国大陆强震受控于活动地块运动与变形"的假说,不仅可用于解释中国大陆强震的空间分布,同时基于其理论和定义可将中国大陆划分为6个Ⅰ级活动地块和22个Ⅱ级活动地块。活动地块之间的边界带往往由活动构造带组成,一般宽约几km至百余km,是强烈地震的多发区。活动地块假说指出,已发生的近100%的8级以上强震、约80%的7级以上强震震中均位于地块边界带上。近年来,中国大陆几次7级以上强震也都发生在活动地块边界带,这不仅验证了活动地块假说的理论模型,同时还预测了未来强震就发生在活动地块边界带内某些有利于应力集中的部位。活动地块假说经过近20a的发展,已建立并逐步完善了其理论框架,奠定了中国活动构造与强震预测的理论基础,正推动着强震预测由概率预测向物理预测过渡。但就活动地块的概念和理论框架而言,还存在的诸多问题需进一步回答和解释。众所周知,强震是活动地块边界带特殊构造部位应变逐渐积累、介质突发失稳和能量释放的结果,地震预测的突破性进展需要建立在充分理解其整个物理过程的基础之上。因此,以边界带断裂的活动性、现今的变形状态、深浅构造的耦合关系、强震孕育环境及震源物理模型为主要研究内容,开展针对活动地块边界带强震活动机理与预测的研究,是活动地块理论完善和研究未来关注的重要内容和重要科学问题。     

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.