地磁Z分量日变形态畸变与周边低点位移异常关系初探

通过对2010年1月1日至2011年12月31日期间中国大陆地磁低点位移异常数据及蒙城地震台地磁垂直分量日变形态畸变统计,按低点位移分界线到蒙城地震台的距离,分段探讨该台地磁垂直分量日变形态畸变与其周边低点位移异常的关系.     

Sensitivity analysis of the probability distribution of groundwater level series based on information entropy

Information entropy is an effective method to analyze uncertainty in various processes. The principle of maximum entropy (POME) provides a guide line for the parameter estimation of probability density function (PDF). Mutual entropy analysis is well qualified for delineating the nonlinear and complex multivariable relationship. The probability distribution of model output is the element of model uncertainty analysis. In this paper, a synthetic groundwater flow field is build to produce groundwater level series (GLS). The probability distribution of GLS is obtained by the frequency analysis method based on POME and Chi-Squared test. The important uncertainty factors that affect the parameters of PDF of GLS are assessed by the sensitivity analysis methods, which include stepwise regression analysis and mutual entropy analysis. Results of this analysis indicate that most of the GLS follow normal distribution (or log-normal distribution), while a few obey others. The mean and variance of normal GLS are affected differently by the input variables of groundwater model. Mutual entropy analysis is more competitive and appropriate for delineating the nonlinear and nonmonotonic multivariable relationship than stepwise regression analysis.     

Tomographic velocity inversion for ADCIGs in areas with a rugged surface

Pre-stack depth migration velocity analysis is one of the key techniques influencing image quality. As for areas with a rugged surface and complex subsurface, conventional prestack depth migration velocity analysis corrects the rugged surface to a known datum or designed surface velocity model on which to perform migration and update the velocity. We propose a rugged surface tomographic velocity inversion method based on angle-domain common image gathers by which the velocity field can be updated directly from the rugged surface without static correction for pre-stack data and improve inversion precision and efficiency. First, we introduce a method to acquire angle-domain common image gathers (ADCIGs) in rugged surface areas and then perform rugged surface tomographic velocity inversion. Tests with model and field data prove the method to be correct and effective.     

GPS动态变形分析中的傅里叶级数恒星日滤波

针对恒星日滤波中计算GPS卫星轨道运行周期提前时间的问题,提出一种基于傅里叶级数曲线拟合的提前时间估计方法。根据跨度达8 526 d的广播星历计算每天中所有可用卫星运行周期相对于前1 d的平均提前时间,将此平均提前时间作为采样点,以8阶三角函数形式展开的傅里叶级数进行曲线拟合,将卫星运行周期的提前时间拟合成关于时间的单一变量函数,免去了繁琐的计算步骤。实验结果表明,傅里叶级数恒星日滤波法缩小了监测点N、E、U三个方向坐标残差序列的均方根值,有效消除了GPS动态变形监测分析中的多路径影响,提高了复杂工程环境下动态变形监测中变形信息提取的能力。     

峨眉山大火成岩省烂纸厂铁矿床地质特征、成因及其找矿勘查启示

烂纸厂铁矿床是峨眉山大火成岩省玄武岩建造中查明的首例中型规模铁矿床。矿床的形成与玄武岩建造具有密切的时空及成因联系,矿体主要赋存于峨眉山玄武岩下段致密块状玄武岩与玄武质角砾岩接触带附近,产出特征受矿山梁子破火山口构造控制,多层位产出,矿石发育草莓状结构、韵律结构和纹层状构造、条带状构造、致密块状构造、绳状构造、角砾状构造等矿石组构,发育铁质结核和铁碧玉,同生沉积层控成矿特征明显。岩(矿)石主、微量元素分析结果表明,研究区岩浆演化遵循Fenner分异趋势,成矿作用与热水沉积作用有关。地质和地球化学特征表明,矿床成因类型为火山喷发(溢)沉积型陆相火山岩型铁矿床。烂纸厂铁矿床是我国在铁矿找矿勘探类型上的新突破和在峨眉山大火成岩省找矿实践取得的新进展,它的发现打破了在玄武岩建造中不具备寻找成型矿床的固有勘查模式的思想束缚,为相似地质环境寻找铁矿给予了诸多启迪和经验借鉴。     

青海高原东部河湟谷地生态风险评价——以海东市为例

以位于青海高原东部河湟谷地的海东市为研究区,在土地利用变化分析的基础上构建生态指数,利用移动窗口法获得区域空间连续的生态风险指数,再结合GIS空间分析获得与土地利用空间尺度相一致的生态风险评价结果。结果表明：1999-2009年,青海高原东部农业区土地利用变化明显,有林地、灌木林地、建设用地面积迅速增加,耕地、水浇地、草地面积持续大幅减少,土地利用变化区域占总面积的42.04%;生态高风险区面积增加显著,增长率达27.11%,主要位于未利用地和建设用地区域;生态中风险地区面积减少,主要位于旱地、水浇地、草地分布区域;生态微、低风险区域主要位于林地、灌木林地区域。     

对塔里木盆地南缘绿洲可持续发展的思考与建议

基于策勒国家野外站长期监测与研究成果,以塔里木盆地南缘绿洲可持续发展为主题,总结分析指出,当前绿洲可持续发展的核心还是以水资源为主线的绿洲适宜规模开发。在认识论层面,需要对绿洲化进行再认识,强调荒漠化与绿洲化的本质统一,即在极端干旱背景下,荒漠化或风沙危害加剧的深层原因还是绿洲"入侵"的不合理性。在方法论层面,需要重视绿洲规模不确定性的本质特征,并在充分考虑自然与社会各模块基础上,提出绿洲适宜规模不确定性的概念模型。最后,强调多学科交叉、长期监测网络在绿洲研究中的重要性。总之,解决新疆极端干旱背景下风沙危害治理、实现绿洲生态稳定与可持续发展的核心问题是探寻绿洲与荒漠共存的平衡点(阈),进而对绿洲持续利用与保护提供理论依据和决策支持     

南岭东段岩前钨矿床地质特征及成岩成矿时代

岩前钨矿位于南岭东西向构造与滨太平洋北北东向构造带的交汇复合部位,南岭成矿带东段北部。主要矿床类型有矽卡岩型白钨矿和石英脉型黑钨矿,矿体产于燕山早期花岗岩内外接触带内。在区域地质和矿床地质研究的基础上,采用LA-ICP-MS 锆石U-Pb 法和辉钼矿Re-Os等时线方法,对与成矿关系密切的岩前花岗岩和含矿石英脉中辉钼矿进行精确定年,获得花岗岩的单颗粒锆石U-Pb谐和年龄加权平均值为(160.6±0.72) Ma,黑钨矿化石英脉中的辉钼矿为(159.2 ±2.3) Ma。这一成果揭示,花岗岩的就位年龄与含矿石英脉的形成几乎在相同热过程完成。结合前人研究,进一步得出南岭地区160~150 Ma成岩成矿作用主要分布于南岭中东段,成岩成矿作用与华南地区东部岩石圈大规模伸展的构造运动力学背景有关。岩前钨矿与区内盘古山、画眉坳、柿竹园等著名矿床具有相同的成矿时代、成矿背景和相似的成矿条件,属同一个成矿亚系列,预测岩前钨矿具有较大的找矿潜力,重点突破对象为内接触带石英脉型和接触交代矽卡岩型钨多金属矿体。     

Influence of human pressure on forest resources and productivity at stand and tree scales: The case study of Yunnan pine in SW China

This paper examines human impact on stands and individual trees of Pinus yunnanensis growing near the small mountain villages of Pianshui and Yangjuan in southwestern Sichuan Province,China.In an effort to assess whether use of these forests was sustainable,we examined the effects of human use in two ways.First,we directly measured the effect of cutting branches,for fuel and fodder,on tree growth.We hypothesized that branch cutting would negatively impact tree growth.We established 12 plots on four hills and compared 14 pairs of trees,one tree in each pair with an apparently full crown and the other with a considerable portion of the crown removed.Second,we assessed stand and tree properties over a 500 m elevation gradient above the villages where we hypothesized that as elevation increases,stand and tree properties should show fewer human impacts.Although extensive branch cutting reduced the live crown,tree height and diameter,compensatory processes likely enabled trees to recover and to add basal area increments(BAIs) similar to those added by trees with full crowns.Trees and stands close to villages showed less growth and lower basal areas,respectively,than stands and trees at intermediate or distant elevations from villages.Areas relatively close to the villages showed considerable effects of human-related disturbances such as branch cutting,grazing,tree and shrub removal,losses of litter,and human and animal trails.Such areas had increased soil erosion and often loss of the ‘A’ horizon.Stands close to villages had younger trees,lower stand basal areas,smaller basal area increments,and more stumps.Our results suggest an increasingly vulnerable interface between occupants of these two villages and their surrounding forests.