Three-dimensional resistivity modelling of grounded electrical-source airborne transient electromagnetic (GREATEM) survey data from the Nojima Fault, Awaji Island, south-east Japan
Three-dimensional resistivity modelling of grounded electrical-source airborne transient electromagnetic (GREATEM) survey data from the Nojima Fault, Awaji Island, south-east Japan
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DOI：
10.1071/eg12086
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发表时间：
2014-03
影响因子：
0.9
通讯作者：
S. A. Allah;T. Mogi;Hisatoshi Ito;Akira Jymori;Y. Yuuki;E. Fomenko;K. Kiho;H. Kaieda;Koichi Su
中科院分区：
文献类型：
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作者：
S. A. Allah;T. Mogi;Hisatoshi Ito;Akira Jymori;Y. Yuuki;E. Fomenko;K. Kiho;H. Kaieda;Koichi Su
在日本东南部淡路岛的野岛断层上进行了一次使用接地电源航空瞬变电磁（GREATEM）系统的航空电磁（AEM）调查，以评估GREATEM调查在研究具有复杂地形特征的沿海地区的适用性。为了获得具有最佳信噪比的高质量数据，使用了一系列数据处理技术来从现场测量数据中获取最终的瞬态响应曲线。一维反演结果是可行的，水平电阻率对比度与真实对比度相差不大，但水平电阻率值变化较大，不合理。为了避免这个问题，我们进行了数值正演模拟，使用有限差分交错网格法（Fomenko和Mogi，2002年）添加一个有限长度的电偶极子源程序，以生成一个三维（3D）电阻率结构模型从GREATEM测量数据的野岛断层区。3D模型基于由两个相邻的不同导电性的陆上和海上层组成的初始模型，使得高度导电的深度（10-40 m）的海被放置在均匀的半空间的顶部，假设内陆侧存在地形特征。我们研究了现场数据和三维正演模型计算数据之间的磁瞬变响应的拟合，后者与相应数据集的测量系统响应进行卷积。反演的三维电阻率结构表明，GREATEM系统有能力绘制陆上和海上500米深的地下电阻率结构。GREATEM调查描绘了海水如何侵入断层的陆侧，并表明断层是海水入侵的屏障。
An airborne electromagnetic (AEM) survey using the grounded electrical-source airborne transient electromagnetic (GREATEM) system was conducted over the Nojima Fault on Awaji Island, south-east Japan, to assess GREATEM survey applicability for studying coastal areas with complex topographic features. To obtain high-quality data with an optimised signal-to-noise ratio, a series of data processing techniques was used to acquire the final transient response curves from the field survey data. The 1D inversion results were feasible in that the horizontal resistivity contrast was not much higher than the true contrast, but they were not reasonable in that the horizontal resistivity values were greatly changed. To circumvent this problem, we performed numerical forward modelling using a finite-difference staggered-grid method (Fomenko and Mogi, 2002) adding a finite-length electrical dipole source routine to generate a three-dimensional (3D) resistivity structure model from GREATEM survey data of the Nojima Fault area. The 3D model was based on an initial model consisting of two adjacent onshore and offshore layers of different conductivity such that, a highly conductive sea of depth (10–40 m) is placed on top of a uniform half-space, assuming the presence of topographic features on the inland side. We examined the fit of the magnetic transient responses between field data and 3D forward-model computed data, the latter were convolved with the measured system response of the corresponding dataset. The inverted 3D resistivity structures showed that the GREATEM system has the capability to map underground resistivity structures as deep as 500 m onshore and offshore. The GREATEM survey delineated how seawater intrudes on the landside of the fault and indicated that the fault is a barrier to seawater invasion.