地中电偶极源极低频电磁场的分布与传播特征

利用层状大地中偶极源响应的正演算法, 计算地中电偶极源激发的极低频地震电磁场并分析其在地球环境下的传播特征.设计了多个水平层状地球模型, 分别模拟和展示了深埋地中的电偶极源的响应和空间分布特征.重点分析了含地壳波导+LAI波导模型的高阻大地中, 倾斜电偶极源激励响应随观测点的偏移距和垂直位置、激励源深度、地壳波导结构和参数变化时各场量响应的幅频特征.研究表明, 用倾斜电偶极源模拟和分析高阻大地中孕震电磁辐射的响应及在大地电磁系统中的传播特性是可行的; 模拟的高阻大地中的电磁辐射在地壳波导和LAI波导中均表现有慢衰减或幅值增强特性, 但两个波导效应具有不同的频率选择性; 高阻大地中的电磁辐射在波导的高阻介质中具有幅值强、衰减慢的特点.建议在高阻地层出露的地表、井中或海底的高阻岩层中以及大气层中布设测站.

     

城市边缘带识别研究进展与展望

城市边缘带作为城市与乡村相交接的特殊地带,是城市化进程中最为敏感的区域;城市边缘带的定量识别是研究边缘带社会结构、景观格局和发展梯度的基础工作,也是城市化生态环境效应定量分析的前提条件。但边缘带识别的理论与方法未受到足够重视,缺乏系统梳理。本文在对比分析城市边缘带及相关概念的基础上,明确了城市边缘带识别的实质与内涵;提出了基于指示要素—空间单元—判别模型的城市边缘带识别概念框架,并从上述三方面系统回顾了国内外城市边缘带识别研究进展;对未来研究进行了展望,认为城乡作用机理探析、多要素综合识别、非参数化模型融合、多尺度转换以及长时间序列动态监测等将是下一步重点研究方向。     

2-D or 3-D interpretation of conductivity anomalies: example of the Rhine-Graben conductivity anomaly

Summary. Evidence of a conductivity anomaly in the Rhine-Graben was first given about 15 years ago and consequently led to the definition of various models of induction in the region for periods ranging from a few minutes to a few hours. These models reflect two antagonistic ways of explaining the observed anomalous variations of the magnetic field: direct induction in a two-dimensional (2-D) structure or static distortion of telluric currents by the resistive crystalline Vosges (France) and Schwarzwalde (Germany) massifs. We discuss the two approaches using a simple formalism. In particular, we show that the self-induction related to the anomalous currents flowing in the Rhine-Graben is negligible for periods larger than 1000 s, and that, even though the static distortion of telluric currents does account for the observed anomaly, 2-D models can explain some of its features. We also show how the channelled currents are induced in the large sedimentary basins surrounding the area under study.
An experimental verification of this result is given.     

南疆尼雅地区4000a来的地化元素分布特征与古气候环境演化的初步研究

通过应用因子分析法对尼雅剖面中的多种地化元素和氧化物的分析,在R、Q型因子分析的基础上,提取出古气候信息。初步的研究表明:近4000a来,尼雅地区气候环境仍以干旱化为主,但此期间出现过多次不同程度的干湿变化,大致可分为5个气候期:4.0~3.0kaB P.相对暖干期;3.0~2.2kaB.P.相对冷湿期;2.2~1.6kaB.P.相对暖干期;1.6~1.0kaB.P.相对冷湿期;1.0kaB.P.左右之后的相对暖干期。     

Incorporating Spatial Dependence in Predictive Vegetation Models: Residual Interpolation Methods*

Predictive vegetation modeling can be used statistically to relate the distribution of vegetation across a landscape as a function of important environmental variables. Often these models are developed without considering the spatial pattern that is inherent in biogeographical data, resulting from either biotic processes or missing or misspecified environmental variables. Including spatial dependence explicitly in a predictive model can be an efficient way to improve model accuracy with the available data. In this study, model residuals were interpolated and added to model predictions, and the resulting prediction accuracies were assessed. Adding kriged residuals improved model accuracy more often than adding simulated residuals, although some alliances showed no improvement or worse accuracy when residuals were added. In general, the prediction accuracies that were not increased by adding kriged residuals were either rare in the sample or had high nonspatial model accuracy. Regression interpolation methods can be an important addition to current tools used in predictive vegetation models as they allow observations that are predicted well by environmental variables to be left alone, while adjusting over‐ and underpredicted observations based on local factors.     

Finite element analysis of the effect of corrosion on the behavior of reinforced earth walls

A simple model for the corrosion‐induced loss of stiffness and strength of the steel strips of earth‐reinforced walls was introduced in a finite element simulation of the long‐term behavior of the wall, in which the backfill‐strips interactions are taken into account by means of a generalized homogenization procedure (called a multiphase model). The results show an initial phase of slow displacements induced by the loss of stiffness, followed after a few decades by a steep acceleration of the displacements, leading to wall failure. The influences of the parameter controlling corrosion, the backfill cohesion and the heterogeneity of the corrosion process are discussed. Results are used to discuss a strategy for reinforced earth wall surveillance. Copyright © 2011 John Wiley & Sons, Ltd.     

内蒙古贺根山蛇纹岩化流体来源的H-O-B同位素地球化学制约

对内蒙古贺根山蛇绿岩带内3个采样点的蛇纹岩样品开展了主量、微量元素和H-O-B同位素分析,以揭示其构造属性、蛇纹石化温度和流体来源。贺根山蛇纹岩具有低Al_2O_3含量(0.2%~1.3%)、高Mg~#(89~92)特征,为难熔地幔残余。蛇纹岩的U型稀土元素配分模式、相对富集LILE和亏损HFSE的微量元素地球化学特点,反映其原岩为化学成分高度亏损的俯冲带型(SSZ)超基性岩。样品的dD值相对均一(dD=-120‰~-133‰);理论计算显示,这些蛇纹岩的H同位素组成可能是蛇绿岩剥露地表后与区域大气降水发生再平衡作用的结果。贺根山蛇纹岩的d~(18)O变化在4.3‰~9.8‰之间,反映不同地点蛇纹石化的温度存在差别:其中贺根山东样品具有相对较高的d~(18)O值(d~(18)O=7.7‰~9.8‰),蛇纹石化温度为90~130℃,同时部分样品中出现碳酸盐矿物,表明蛇纹石化作用发生在近海底环境;小坝梁样品具有最低的d~(18)O值(d~(18)O=4.3‰~5.0‰),其蛇纹石化温度在205~235℃之间;贺根山南样品的d~(18)O值变化范围较大(d~(18)O=6.0‰~9.7‰),其蛇纹石化温度在90~170℃之间。3个采样点蛇纹岩的d~(11)B值也显示出一定的变化(d~(11)B=9.1‰~14.7‰),指示蛇纹石化流体来源于脱水的蚀变洋壳和海底沉积物;理论模拟和计算结果显示,这些板片流体的d~(11)B值变化在15‰~25‰之间。     

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