Delineation of a Fault Zone Beneath a Riverbed By an Electrical Resistivity Survey Using a Floating Streamer Cable
Delineation of a Fault Zone Beneath a Riverbed By an Electrical Resistivity Survey Using a Floating Streamer Cable
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使用浮动拖缆通过电阻率测量来描绘河床下方的断层带
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
T. Uchida
中科院分区：
文献类型：
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作者：
Hyoung;Jungho Kim;Hee;Jin;Ki;C. Jung;Seungbong Lee;T. Uchida
近年来，由于大量的隧道和桥梁建设工程在河流或湖泊的网站，水下地质结构的成像已经在很大程度上的需求。在这种情况下，电阻率测量可能很有效，因为它提供了水层下方断层或薄弱区的地下图像。尽管在水覆盖区域中的常规电阻率勘测（其中电极安装在水底）确实给出了高分辨率的地下图像，但是需要大量的时间和精力来安装电极。因此，寻求一种更简单、更方便的方法来寻找主要薄弱区的走向，特别是对于普查。本文研究了拖缆电阻率测量方法的适用性，该方法利用船或船拖曳的拖缆电缆中的电极来划定断层带。我们这样做，通过数值实验与模型的水覆盖区。我们证明，断层带可以成像，不仅通过安装电极在水底，而且还通过使用浮动电极，当水的深度小于两倍的电极间距。此外，我们还比较了四种适用于流注电阻率法的电极阵列的信噪比和分辨率。在此数值研究之后，我们对位于韩国首尔汉江的计划隧道施工现场进行了常规和拖缆电阻率调查。为了获得高分辨率的电阻率图像，我们使用传统的方法，并安装电极的水底沿着的计划路线的隧道下河。应用二维反演方案的测量数据，我们发现了三个独特的低电阻率异常，我们解释为与断裂带。为了确定这三条断裂带的走向，我们在附加网格式测线上采用了快速方便的流光电阻率测量。这样，就可以很有效地圈定河床下断层的走向。
Recently, the imaging of geological structures beneath watercovered areas has been in great demand because of numerous tunnel and bridge construction projects on river or lake sites. An electrical resistivity survey can be effective in such a situation because it provides a subsurface image of faults or weak zones beneath the water layer. Even though conventional resistivity surveys in water-covered areas, in which electrodes are installed on the water bottom, do give high-resolution subsurface images, much time and effort is required to install electrodes. Therefore, an easier and more convenient method is sought to find the strike direction of the main zones of weakness, especially for reconnaissance surveys. In this paper, we investigate the applicability of the streamer resistivity survey method, which uses electrodes in a streamer cable towed by ship or boat, for delineating a fault zone. We do this through numerical experiments with models of water-covered areas. We demonstrate that the fault zone can be imaged, not only by installing electrodes on the water bottom, but also by using floating electrodes, when the depth of water is less than twice the electrode spacing. In addition, we compare the signal-to-noise ratio and resolving power of four kinds of electrode arrays that can be adapted to the streamer resistivity method. Following this numerical study, we carried out both conventional and streamer resistivity surveys for the planned tunnel construction site located at the Han River in Seoul, Korea. To obtain highresolution resistivity images we used the conventional method, and installed electrodes on the water bottom along the planned route of the tunnel beneath the river. Applying a two-dimensional inversion scheme to the measured data, we found three distinctive low-resistivity anomalies, which we interpreted as associated with fault zones. To determine the strike direction of these three fault zones, we used the quick and convenient streamer resistivity survey on additional grid-style survey lines. In this way, we could delineate the strike direction of faults beneath the riverbed very efficiently.