京津冀地区地壳应力场特征

基于标量断层类型值,对京津冀地区及邻区2 187个中小地震震源机制解进行分类,统计结果显示研究区震源机制类型以走滑断层和正断层为主,P轴优势方位为NEE—EW和SWW—EW向;采用MSATSI软件包反演该区1°×1°网格的精细地壳应力场,结果表明:最大主压应力轴最优解的优势方向为NEE—EW向,与P轴优势方位一致;所有网格的相对应力大小R值均小于0.5,表明京津冀地区应力状态偏拉张性质,而且最小主压应力轴的不确定度变化范围相对稳定,表明现今京津冀地区地壳应力场处于一个相对统一的NNW—SSE向的拉张作用控制下。39°N以北地区最大主压应力轴方位最优解显示一定角度的偏转,同时最大、中等、最小主压应力轴最优解推断的应力状态由西向东存在一个正断层—走滑断层—正断层的转换过程;而39°N以南地区的现今构造应力场保持稳定,最优主压应力轴呈NEE—SWW向,大部分网格应力状态显示走滑型。构造应力场的反演结果与活动构造、GPS主应变方向和剪切波分裂的快波偏振方向等相关研究结果基本一致。     

小江断裂中段及邻区构造应力场分布特征

本文利用小江断裂及邻区1998年1月～2007年9月发生的613个ML≥2.5地震的垂直向直达SV波和P波地动位移振幅比计算得出了这些地震的震源机制解;并根据区域构造对小江断裂中段及邻区现代构造应力场进行了分区。以小江断裂为界,将小江断裂中段及其邻区分为A、B(包含小江断裂带)两个区,为了研究断裂带上的应力特征,又将小江断裂带区域划分出来进行独立分析;同时采用网格1°×1°,以及0.5°空间滑动分区的办法进行研究。分析了该区震源机制解特征,并在此基础上利用应力张量反演方法,对研究区域的应力场进行反演。结果表明:①小江断裂中段及邻区的断层错动方式主要以走滑为主,A区、B区和断裂带区域走滑断层分别占81.28%、69.63%、72.97%。②A区的最大主应力σ1方位大致为NNW向,B区和断裂带区的最大主应力σ1方位大致为NWW向;从应力结构来看,应力以水平作用为主,走滑特征明显。③在整个滇中块体,应力场的主体方位由NNW向变为NWW向。但在元谋断裂以东,普渡河断裂以西的区域,主压应力方位表现出明显的南北向滑移,而在小江断裂区域主压应力则主要为NW向。从小江断裂继续往东的滇东块体上,应力场主压应力方位为NW-NNW向。     

小浪底水库区震源机制解特征

利用小浪底水库台网8个台站的地震波形数据,采用垂直向P波、S波最大振幅比和初动方法测定2009年1月—2012年12月水库区域45次小地震的震源机制。结果表明:该区域45次震源机制中正断层13次、逆断层15次,走滑断层17次;主压应力轴(P轴)总体为NEE方向(220°～230°),与华北地区近水平构造应力场不完全一致,显示了小浪底水库区域受华北构造应力场的控制作用较弱,应该与水库区域地下介质构造复杂和水库蓄水有关。     

利用小震震源机制解反演濮阳地区应力场

利用双差定位法测得河南濮阳地区的地震的平均深度为8.4km,由于油田地震的深度一般在6km以内,推测该区的地震多为构造地震,油田地震只占这里地震的一小部分。利用GEPHART的方法对该区域的42个震源机制进行应力张量反演,反演出的结果显示有走滑断层的特征,最大压应力轴σ1为32°、倾伏角为3°;中等压应力轴σ2为292°、倾伏角为71°;最小压应力轴σ3为124°、倾伏角为19°;应力比R为0.6,取σ1的方向为该区的应力场方向。     

岫岩-海城Ms5.4地震序列震源机制解

应用 P波初动符号资料 ,求解得到了岫岩 -海城 5.4级地震前、主、余震 2 0个 ML ≥ 4.0的震源机制解。分析表明 ,该地区的主压应力轴 (P)大多为 NEE- SWW向 ,主张应力轴 (T)大多为 NNW- SSE向 ,P、T轴仰角基本上小于 30°,表明力轴以水平者最多。N轴大多较陡。A、B节面的走向分别为 NWW向和 NNE向。岫岩 -海城地震主要为走滑断层类型。余震震源机制解绝大多数与主震相近 ,结果比较稳定 ,表明余震的应力场主要受主震震源应力场的控制     

河北及邻区震源机制与构造应力场

采用CAP方法反演2008年1月至2013年11月河北及邻区M_L3.5以上地震的震源机制,结果显示:震源错动类型以走滑断层类型为主,兼有一定数量的正断层;构造应力场最大主压应力轴方向NEE,与之前的研究结果一致,但呈现出暂时的正断层兼走滑的应力状态,具有继承性和差异性特征,推测可能与中等地震易受局部构造活动影响以及巨大地震改变了区域构造应力作用方式有关。     

云南地震类型分区特征研究

对云南地震序列和强震震源机制的分析与研究表明,云南地区具有较明显的地震类型分区特征.总体上云南全区地震断层以走向滑动为主，地震序列以主余震型为主.考虑到非走滑地震断层和非主余震型地震序列所占的比例，可以将云南地区划分为4个具有不同特点的分区: 滇中(A1)走滑-主余震型区、 滇西北(A2)斜滑-震群型区、滇西(B1)走滑-双震型区和滇西南(B2)准走滑-主余震型区.      

华北地区的震源机制

本文作出了1980年以来华北中、强地震震源机制;分析整理出1937年以来华北地区85个地震的震源机制资料。结果表明,半个多世纪以来,该区地震主要为走滑断层类型,震源机制两组节面的走向分别为北北东向和北西西向;主压应力P轴大都为北东东—南西西,主张应力T轴大都为北北西—南南东向。通过对不同时段进行研究推测,华北地震的震源机制不仅具有空间上的一致性,而且在时间上具有稳定性。     

用F-K方法确定腾冲火山区震源机制*

介绍了计算理论地震图的 F- K方法在不同深度 ,不同震中距 ,不同震源类型的情况 ,表明这种方法在高频区和多层水平层状模型计算效果较好 ,适用于研究中小地震的震源机制。采用 F- K方法得到了发生在腾冲火山区的 3个地震的震源机制 ,结果表明地震 1和地震 2是走滑断裂 ,地震 3是逆断层。 3个地震的主压应力轴基本呈北西向 ,与云南地区主压应力轴方向基本吻合 ,因此 ,推断这 3个地震是构造地震。     

由M_L≥4.0地震震源机制解推断四川理县-黑水断裂构造特征

基于四川台网宽频带数字地震波形资料和CAP波形反演方法,提取了四川理县-黑水地区2008年1月至2014年12月10个M_L≥4.0中等强度地震的震源机制解。结果显示:10个中等强度地震震源机制解节面分布主要集中在北西-南东和北东-南西两个优势分布方向。据众多学者研究结果推断,北西-南东向展布的节面为发震断层面;理县-黑水断裂大致沿北47°西(近北西向)展布,属高倾角陡峭断裂,主倾向南西;压应力(P轴)呈近东西水平挤压特征,与断层面斜交,以左旋走滑运动为主;张应力(T轴)呈近南北水平撕裂特征;中等强度地震的震源主压应力方向与青藏地块东部地区主压应变率方向比较一致,说明理县-黑水断裂主要是受区域应力场控制的一个区域性构造左旋走滑断裂。     

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.