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VLF wave impedance measurements have been successfully used to detect air-filled drainage galleries near the town of Alcala, Spain. The galleries are detectable by H-polarization electric field measurements due to the electric field anomalies associated with the galleries and overlying gravel deposits. The forced deviation of the primary current flowlines around the 2D void results in a higher-than-normal apparent resistivity and a relative phase low above the gallery. The findings support earlier theoretical predictions that at very low frequencies (VLFs), galvanic current effects may dominate over vortex currents in moderately conductive terrains. Theoretical modelling confirmed that for a resistive target no detectable E-polarization response can be expected from either magnetic or electric field measurements since current line deviations and vortex effects are negligible under such circumstances. The results demonstrate the importance of using at least two orthogonal VLF transmitters in order that anomalies arising from both galvanic and inductive effects may be identified, irrespective of orientation. 相似文献
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使用高灵敏度的G856,DTZ-2型核子旋进式磁力仪,对乌鲁木齐地磁台199个测点的磁场梯度进行了复测,经过严格的数据校正处理,重新作出了ΔF等磁力线图,并分析讨论了台站院内环境磁场的变化特征,测量结果表明;乌鲁木齐地磁台仍处于磁场正常区,工作环境符合《地磁台站观测规范》要求。 相似文献
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本文用不同经度的7对中低纬台站水平磁场分量H,求得1965年随世界时(UT)变化的Sq指数(一种描述Sq电离层发电机电流强度的地磁指数).结果表明,Sq发电机电流不仅有显著的逐日变化,而且有很大的UT变化.UT变化主要表现在电流总强度的强弱和电流涡焦点纬度移动两方面,这意味着决定发电机过程的太阳潮汐风场和电离层电导率随UT而变.用求得的Sq指数重新构造出的Sq变化与观测值符合得较好,它不仅显示出Sq幅度逐日变化的特点,而且还能复现出Sq形态的某些逐日变异性. 相似文献
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A. APPARAO T. GANGADHARA RAO R. SIVARAMA SASTRY V. SUBRAHMANYA SARMA 《Geophysical Prospecting》1992,40(7):749-760
Depth of detection of a target can be defined as that depth below which the target cannot be detected with a given electrode array assuming that the minimum detectable anomaly is 10%. Following this definition, physical modelling was carried out to determine depths of detection of conductive targets of limited lateral extent such as a vertical sheet, a horizontal cylinder and a sphere (infinitely conducting). It is seen that the two-electrode array has the greatest depth of detection followed by the three-electrode array, while a Wenner array has the smallest depth of detection, when the array spread is in-line (i.e. perpendicular to the strike direction). On the other hand, the depth of detection with a Wenner array improves considerably and is almost equal to that of the two-electrode array when the array spread is broadside (i.e. along the strike direction). With an increase in the depth extent of the vertical sheet from 10 to 20 times its thickness, there is an increase in the depth of detection with all arrays except for the three-electrode array when the array spread is in-line, and with the Wenner array when the array spread is broadside. 相似文献
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M. K. SEGUIN 《Geophysical Prospecting》1975,23(3):471-491
The present paper shows the practical use of a combined electromagnetic and magnetic helicopter transported system in the search for steeply dipping high-grade magnetic taconite bodies (magnetic ribbons). The principles of operation of the heliported system and the essential parts of the instrumentation are described. The quantitative interpretation of the data allows the geophysicist to calculate the tonnage of magnetite within the iron ores and to obtain an approximate idea of their grade. According to the tonnage and grade calculations obtained from the surveys, three regions in the west-central sector of the Labrador trough (Wishart Creek, Knob Lake Ridge, and Swampy Bay areas) appear to be the most interesting locations for the site of a magnetic taconite deposit (the Howells River area, which has been evaluated previously, is excluded from the discussion). The tonnages calculated by this geophysical method are not to be compared with probable or possible mineable ore reserves, but are only rough estimates in terms of mining engineering standard. The physical parameters determined with such a system are also used as a tool for indirect geological mapping of the areas flown when interpreted carefully. Practical examples related to results obtained on the magnetic iron formations of the Schefferville mining district are presented. 相似文献
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本文用不同经度的7对中低纬台站水平磁场分量H,求得1965年随世界时(UT)变化的Sq指数(一种描述Sq电离层发电机电流强度的地磁指数).结果表明,Sq发电机电流不仅有显著的逐日变化,而且有很大的UT变化.UT变化主要表现在电流总强度的强弱和电流涡焦点纬度移动两方面,这意味着决定发电机过程的太阳潮汐风场和电离层电导率随UT而变.用求得的Sq指数重新构造出的Sq变化与观测值符合得较好,它不仅显示出Sq幅度逐日变化的特点,而且还能复现出Sq形态的某些逐日变异性. 相似文献
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浅层地震勘探在沿海地区隐伏断层探测中的应用 总被引:16,自引:6,他引:16
中国沿海地区的第四系厚度变化较大,在大部分地区存在淤泥、黏土和砂层的多重互层情况,这种地层结构对地震波的传播十分不利,容易造成对高频信号能量的强烈耗散。沿海地区又具有人口密度大、工业干扰强烈的特点,地震波的激发、接收条件较差。文中给出了在粤东、天津和唐山覆盖层厚度变化较大的地区,利用浅层地震勘探开展隐伏断层探测的应用实例。较系统地介绍了野外工作、资料处理和解释方法。阐述了在强干扰环境下提高信噪比和分辨率的有效技术途径。所给实例中的反射波组能量强,隐伏断层的反应明显,经跨断点钻探验证,结果证实地震勘探确定的界面深度、断点位置和基岩错距等参数都是可靠的。所述技术方法对类似地区的城市活断层探测和工程物探工作都有较重要的参考价值 相似文献
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多年来,H 磁变仪磁系被地震震翻事件在多震区的地磁台常有发生。这不同程度地影响着磁变仪的正常工作及记录资料的连续性。如何解决这一矛盾,一直是地磁工作者关注的问题。文中主要总结并介绍了喀什台在这方面积累的经验、采取的措施以及收到的效果 相似文献
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近年来,国际上利用地震反射波勘探技术直接找油气的探索研究受到普遍重视.本文试图针对这一发展历史作一综述. 首先,介绍Knott(1899)和Zoeppritz(1919)分别导出的反射波振幅公式进行的数值计算,从而发现振幅与入射角的变化关系及其受反射面两侧岩层泊松比值的影响.然后,列举了几处油气区地震波勘探直接找油气的实例,以试验此项新原理在实践中所遇到的问题,说明直接找油气的地球物理新方法是可取的,是有前途的,但目前还不够有效,要达到实用还有一段较长的距离,因此,有进一步加强基础性实验研究的必要. 相似文献
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近年来,国际上利用地震反射波勘探技术直接找油气的探索研究受到普遍重视.本文试图针对这一发展历史作一综述. 首先,介绍Knott(1899)和Zoeppritz(1919)分别导出的反射波振幅公式进行的数值计算,从而发现振幅与入射角的变化关系及其受反射面两侧岩层泊松比值的影响.然后,列举了几处油气区地震波勘探直接找油气的实例,以试验此项新原理在实践中所遇到的问题,说明直接找油气的地球物理新方法是可取的,是有前途的,但目前还不够有效,要达到实用还有一段较长的距离,因此,有进一步加强基础性实验研究的必要. 相似文献
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本文考虑了元件预加接触压力、套芯应力解除和元件率定等手续,对采用接触预压式元件的钻孔变形法地应力测量的全过程进行力学分析,得出了孔壁折算位移的精确公式,从而揭示了初始接触压力、套芯解除半径和率定实验的试件大小等因素对折算位移的影响。文中对围压率定法优于哈斯特率定法的原因作了进一步解释;还讨论了围压法率定中围压室隔层对围压传递的影响。文末提出了恰当使用这种地应力测量法的若干建议。 相似文献
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本文考虑了元件预加接触压力、套芯应力解除和元件率定等手续,对采用接触预压式元件的钻孔变形法地应力测量的全过程进行力学分析,得出了孔壁折算位移的精确公式,从而揭示了初始接触压力、套芯解除半径和率定实验的试件大小等因素对折算位移的影响。文中对围压率定法优于哈斯特率定法的原因作了进一步解释;还讨论了围压法率定中围压室隔层对围压传递的影响。文末提出了恰当使用这种地应力测量法的若干建议。 相似文献
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在二维三分量MHD数值模拟的基础上 ,对地球磁尾不同类型磁结构的形成作磁螺度分析 .研究表明 ,对于由晨昏电场产生的磁尾驱动重联过程 ,通过系统边界输运的磁螺度通量是引起系统总磁螺度变化的直接原因 .不同的初始磁螺度密度分布和磁螺度通量输运 ,可以引起中性片区域磁螺度密度分布的不同演化 ,从而导致具有不同拓扑位形磁结构的形成 . 相似文献