Approximate treatment of seafloor topographic effects in three-dimensional marine magnetotelluric inversion
Approximate treatment of seafloor topographic effects in three-dimensional marine magnetotelluric inversion
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DOI：
10.5047/eps.2012.04.005
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发表时间：
2012-11
期刊：
影响因子：
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通讯作者：
N. Tada;K. Baba;W. Siripunvaraporn;M. Uyeshima;H. Utada
中科院分区：
文献类型：
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作者：
N. Tada;K. Baba;W. Siripunvaraporn;M. Uyeshima;H. Utada
使用海底电磁计的海底大地电磁观测提供了有关大洋地幔电导结构的信息。三维(3-D)分析对于海洋大地电磁数据特别重要，因为海底观测到的电场和磁场受到崎岖的海底地形以及陆地和海洋分布的扭曲。在3D模型中加入地形对于准确估计大洋地幔的传导性结构至关重要。在这里，我们提出了一种近似的海底地形处理方法，在不显著增加计算负担的情况下，准确地考虑了地形的影响。首先，通过体积平均将地形(水深的横向变化)转换为有效电导率的横向变化。其次，由交错网格上的电场分量计算用于计算任意点大地电磁响应的电场分量和磁场分量，使用改进的内插和外推方法。为了验证这种海底地形近似处理方法在三维反演中的性能，我们使用合成海底数据集以及三维正演和反演对该方法进行了测试。综合反演的结果表明，经过多次迭代，可以以足够的精度恢复给定的大洋上地幔电导率异常。
Seafloor magnetotelluric (MT) observations using ocean bottom electromagnetometers (OBEMs) provide information on the electrical conductivity structure of the oceanic mantle. A three-dimensional (3-D) analysis is particularly important for marine MT data because the electric and magnetic fields observed on the seafloor are distorted by the rugged seafloor topography and the distribution of land and ocean. Incorporating topography into 3-D models is crucial to making accurate estimates of the oceanic mantle’s conductivity structure. Here we propose an approximate treatment of seafloor topography to accurately incorporate the effect of topography without significantly increasing the computational burden. First, the topography (lateral variation in water depth) is converted to lateral variation in effective conductivity by volumetric averaging. Second, we compute the electric and magnetic field components used to calculate the MT responses at arbitrary points from the electric field components on staggered grids, using a modified interpolation and extrapolation scheme. To verify the performance of this approximate treatment of seafloor topography in 3-D inversions, we tested the method using synthetic seafloor datasets and both 3-D forward modeling and inversion. The results of the synthetic inversions show that a given conductivity anomaly in the oceanic upper mantle can be recovered with sufficient accuracy after several iterations.