Influence of ancient thrust faults on the hydrogeology of the Blue Ridge Province

The Blue Ridge Province contains ubiquitous northeast-southwest-trending thrust faults or smaller thrust "slivers" that greatly impact the nature and character of ground water flow in this region. Detailed investigations at a field site in Floyd County, Virginia, indicate that high-permeability zones occur in the brittle crystalline rocks above these thrust faults. Surface and borehole geophysics, aquifer tests, and chlorofluorocarbon and geochemical data reveal that the shallow saprolite aquifer is separated from the deeper fault-zone aquifer by a low-fracture permeability bedrock confining unit, the hydraulic conductivity of which has been estimated to be six orders of magnitude less than the conductivity of the fault zones at the test site. Within the Blue Ridge Province, these fault zones can occur at depths of 300 m or more, can contain a significant amount of storage, and yield significant quantities of water to wells. Furthermore, it is expected that these faults may compartmentalize the deep aquifer system. Recharge to and discharge from the deep aquifer occurs by slow leakage through the confining unit or through localized breach zones that occur where quartz accumulated in high concentrations during metamorphism and later became extensively fractured during episodes of deformation. The results of this investigation stress the importance of thrust faults in this region and suggest that hydrogeologic models for the Blue Ridge Province include these ancient structural features. Faults in crystalline-rock environments may not only influence the hydrology, they may dominate the flow characteristics of a region.     

Spatial variability of in situ microbial activity: biotracer tests

Biotracer tests have been proposed as a means by which to characterize the in situ biodegradation potential for field-scale systems. In this study, field experiments were conducted at two sites to evaluate the utility of the biotracer method for characterizing the spatial variability of microbial activity. The first site is a mixed waste-contaminated surficial aquifer in Utah, and the second site is a chlorinated solvent-contaminated regional aquifer in Tucson, Arizona. Mass recovery of the biotracer decreased approximately linearly with increasing residence time for the Tucson site. Similar behavior was observed at the Utah site, except in the region adjacent to the injection zone, where percent recoveries were much lower than those predicted using a correlation determined using data collected downgradient of the injection zone. First-order biodegradation rate coefficients obtained from model calibration of the tracer data varied between 0.2 and 0.5/day for the Tucson site. For the Utah site, the values varied between 0.1 and 0.6/day downgradient of the injection wells, and between 0.7 and 2.6/day near the injection wells. Considering the large range over which biodegradation rate coefficients can vary, the rate coefficient exhibited relatively minimal spatial variability (factor of 2.5) for the Tucson site. Conversely, the spatial variability of the rate coefficient was an order of magnitude greater for the Utah site. These differences in variability are consistent with conditions associated with the respective sites. For example, the greater microbial activity observed in the vicinity of the injection wells for the Utah site is consistent with the biomass distribution determined from analysis of core samples, which shows larger bacterial cell densities for the region near the injection wells. These results illustrate the utility of biotracer tests for in situ characterization of microbial activity (e.g., biodegradation potential), including evaluation of potential spatial variability.     

钻地炸弹爆炸诱发了地震？

提供4次钻地炸弹爆炸前、 后各一年内在离爆点分别为500 km和1 000 km范围内发生的Mge;5地震的活动情况. 4次爆炸分别为1999年南斯拉夫科索沃的爆炸、 1991年伊拉克巴格达的爆炸、 2001年阿富汗托拉波拉的爆炸和2003年伊拉克基尔库克的爆炸. 地震活动资料表明钻地炸弹爆炸可能触发了一些远处的地震. 在地震活动区应该禁止进行钻地炸弹爆炸.      

2003至2008财年及未来NOAA科研战略规划 认识从海底到太阳表面的环境

在新的2003至2008财年NOAA战略规划中，面向科技前沿的研究已被列为重要的跨部问题，规划同时还强调TDH强科学研究对于提高服务能力的重要性。NOAA研究院及其伙伴致力于通过进行广泛的基础和应用研究来支持NOAA总体任务的完成，并在此过程中认识和描绘全球环境，从而提高当前服务水平并达到优化效果。NOAA战略规划及此NOAA研究院补充规划展示了一幅充满进取精神的实现这些目标的蓝图。     

第10代国际地磁参考场

国际地磁与超高层大气物理学协会（IAGA）于2004年12月12日发表了第10代国际地磁参考场（IGRF）。这是对地球主磁场标准数学描述的最新版本，在对地球深部、地壳、电离层及磁层的研究中有广泛应用。国际地磁参考场系数由国际地磁与超高层大气物理学协会的一个特别工作组最终确定下来。国际地磁参考场是地磁场模型工作者和全世界从事卫星及台站地磁观测数据收集和发布的单位共同努力的结果。     

地震学史

引言 目前，地震学是指关于震源（主要为天然地震）、地震波及其传播所在介质属性的研究。在此定义下，地震学仅仅只有100年的历史，但是人类试图了解地震却可追溯到科学发展的初期。地震学这门学科，比之其他的学科更受到其研究对象的影响。从1755年葡萄牙的里斯本地震到1995年日本神户地震的发生，破坏性地震不断激发科学界的兴趣，     

苏门答腊地震后阿拉斯加兰格尔火山周期性触发的地震活动性

当2004年12月26日苏门答腊地震的面波掠过阿拉斯加时，它们在远至11000km的兰格尔火山附近触发了历时11min的包括14个近震的震群。这些地震是在20～30s的间隔期间发生的，并在瑞利波掠过期间产生了最大的垂直正位移。由于异常长的面波和近震附近的地震台站相结合，使得我们能够观测到这种相关性。瑞利波运动的相位主要由25kPa的水平张应力控制。这些观测结果意味着，近震是由正断层上简单的剪切破裂触发的。