西太平洋暖池两柱样沉积物的磁性地层学研究

根据西太平洋暖池WP92-5,WP92-3柱样沉积物的磁性地层学研究结果,发现WP92-5柱样沉积物的磁性记录了3个地球磁场漂移(地球磁场极性反转),即Gothenburg,MonoLake(或Rubjerg)和Mungo(或Maelifell),其界限年龄分别为12.5kaB.P.,24.0(23)kaB.P.和31.0(28—31)kaB.P.;WP92-3柱样沉积物的磁性也记录了前两个地球磁场漂移。这一结果表明,西太平洋暖池区对35kaB.P.以来地球磁场极性发生的3次短暂的漂移有明显的响应。由于两柱样都采集于赤道附近南半球暖池区,其磁倾角的变化有一定的特殊性。     

澳门路环地区地磁场的环境及近期变化

2002年5月,对澳门路环岛地区及相邻珠海横琴岛的地磁流动观测网的25个测点进行了地磁场总强度(F)的观测。同时还进行了地磁环境噪音的测量及十字剖面测量。2003年1月,对此流动观测网进行了复测。尽管该地区四周邻海,存在相当数量的干扰因素。但两次观测结果经通化处理后表明大多数测点的地磁场总强度的变化不大,变化量在1～2nT左右。两次观测结果的总体均方差为2．8nT。     

太阳活动周磁暴与亚洲M_S 7.0以上地震活动关系

将1996—2015年太阳黑子数、强磁暴和M_S≥7.0亚洲浅源地震,按Dst指数大小对磁暴进行分类和统计,按震级大小对地震进行分类统计,结果发现,在1996—2015年太阳活动周下降年易发生大磁暴,且M_S≥7.0地震年发生率明显高于太阳活动周上升年、极大年和极小年。     

地磁绝对子夜均值年变化量空间分布特征

选用中国21个地磁基准台站2011年的绝对子夜均值数据,分析D、H、Z分量年变化量空间分布特征。结果显示,各分量年变化量等值线分布比较均匀,其中:D分量年变化量等值线大致沿南北向分布,零经线附近台站年变化量较小;H分量年变化量等值线大致呈U型分布,且中心点位于甘肃省;Z分量年变化量等值线沿纬线方向,随纬度减小而增大。     

成灌高铁运行对成都地磁台观测数据干扰测试

成都地磁台距成灌高铁运行线路垂直距离约1.5 km,使用数字化磁通门磁力仪GM4,在轨道沿线不同距离处进行野外测试。测试结果表明,轨道交通的运行对周围地磁观测环境产生干扰,干扰距离约6 km,干扰主要来自轨道泄露电流及输电线路产生的磁场。     

滦县地磁场井下观测系统抗干扰效果

近距离铁磁性物质干扰(农田耕作、基建等)、直流供电干扰(高压直流输电、地电阻率观测等)是地磁场地面观测的主要干扰方式。在滦县地震台布设地磁场井下观测系统,检验井下观测的抗干扰效果,结果发现,地磁场井下观测可抑制近距离铁磁性物质干扰,但无法抑制直流供电干扰(可通过避让一定距离解决),该分析结果为未来地震监测手段的选取提供技术参考指标和依据。     

拉萨地磁台地磁相对记录室磁场梯度对比分析

测量拉萨地磁台观测区内自然地磁场梯度和建成地磁记录室后的地磁场梯度,并测量新建记录室内不同高度磁场梯度,对比分析新建地磁记录室内的磁场稳定性,进而找出潜在干扰源,并采取有效措施予以去除,为产出连续可靠的地磁相对记录数据提供环境条件.     

Structuring factors of the spatio-temporal variability of macrozoobenthos assemblages in a southern Mediterranean lagoon: How useful for bioindication is a multi-biotic indices approach?

The authors investigated the impact of the extension of the El Kantra Channel on the composition and structure of macrobenthic assemblages in Boughrara Lagoon (Gulf of Gabes, Tunisia along with the use of 4 biotic indices (AMBI, BENTIX, M-AMBI and TUBI). Thirteen stations were sampled seasonally in 2012–2013. Forty-one species were found in 2012–2013 not recorded in 2009–2010, including 20 species of polychaetes belonging to the trophic groups of deposit-feeders and carnivores which are expected to increase in areas disturbed by organic pollution. During the survey, we recorded a high fish mortality, essentially caused by the development of harmful algal blooms (HAB) which increased organic matter deposition, thus inducing polychaete development. This seems to weaken the bio-indicating power of biotic indices used here which, paradoxically, classified all sampled stations at a high ecological status. A review of these indices and their applicability to all marine environments is recommended.     

THE RESPONSE OF FLUVIAL GEOMORPHOLOGIC CHARACTERISTICS OF THE FUJIANG DRAINGE BASIN TO ACTIVITY OF THE HUYA FAULT ZONE

The Huya Fault, located in the steep topographic boundary of the Minshan Mountains in the eastern margin of the Tibetan plateau, has documented many major earthquakes such as the 1630(M=6 3/4), 1973 Huanglong(M_S=6.5) and the 1976 Songpan-Pingwu earthquake swarm(M_S=7.2, 6.7, 7.2). While its activity remains unclear because of lacking Quaternary sediments. In the past few decades, there have been significant advances in understanding the relationship between bedrock channel landscapes and active tectonics, indicating that the bedrock fluvial features can well record the tectonic activity. Many studies reveal that tectonism is the primary factor of landscape evolution in tectonically active regions, and the erosional landscapes can be used to reveal tectonic signals on timescales of 10³~10⁶ years. The Huya Fault crosses the Fujiang drainage basin, making it suitable for the study of bedrock rivers and tectonic uplift in the eastern margin of Minshan. In this study, we calculate the geomorphologic indeices(hillslope, local relief, normalized steepness indices and hypsometric integral) on the basis of the digital elevation model(DEM) SRTM-1. For better understanding the tectonic activity along this fault, we derive some small catchments on the two sides of the Huya fault to analyze the differences of average steepness indices and hypsometric integral. Combining with field observations, lithology, precipitation and modern erosion rates, this study suggests that tectonic activity is the controlling factor of geomorphology in the eastern margin of the Minshan Mountains. We use focal mechanism solutions, GPS data and geomorphic evidence to explore the relationship between the geomorphologic indices of the Fujiang drainage and activity characteristics of the Huya fault. Our results suggest that:(1) The Fujiang drainage basin is in a steady state. The characteristics of the knickpoints indicate that they are mainly controlled by the locally resistant substrate. (2) The suggested value of the geomorphologic index on the west side of the Huya fault is generally larger than on the east side, showing differential tectonic uplift rates across the fault. (3) The difference of the geomorphologic index of the small catchments on both sides of the Huya fault is gradually increasing from north to south along this fault, in accordance with that the north and south segments of the Huya fault are dominated by strike-and reverse-slip, respectively.     

C-RESPONSE OF GEOMAGNETIC DEPTH SOUNDING ON A 1D THIN SHELL MODEL

This paper tries to formulate the C-response of geomagnetic depth sounding(GDS)on an Earth model with finite electrical conductivity. The computation is performed in a spherical coordinate system. The Earth is divided into a series of thin spherical shells. The source is approximated by a single spherical harmonic P₁⁰ due to the spatial structure of electrical currents in the magnetosphere. The whole solution space is separated into inner and external parts by the Earth surface. Omitting displacement current, the magnetic field in the external space obeys Laplacian equation, while in the inner part, due to the finite conductivity, the electromagnetic fields obey Helmholtz equation. To connect the magnetic fields in the inner and external space, the continuity condition of magnetic fields is used on the Earth surface. The external magnetic fields are expressed by the inner and external source coefficients, from which a new parameter called C-response is computed from the inner coefficient divided by the external coefficient, thus normalizing the actual source strength. The inner magnetic fields in each layer can be recursively derived by the continuity boundary condition of both normal and tangential components of the magnetic field from the initial boundary condition at core-mantle-boundary. The consistency of our C-responses with that from a typical 1-D global model validates the accuracy of the proposed algorithm. Numerical results also show that the C-response estimated from the geomagnetic transfer function method will deviate exceeding 5%from the actual response at longer periods than about 10⁶s, which means that ignoring the curvature of the Earth at extreme long periods will make inversion result unreliable. Therefore, an accurate C-response should be computed in order to lay a solid foundation for reliable inversion.