Practical incorporation of local and regional topography in three-dimensional inversion of deep ocean magnetotelluric data
Practical incorporation of local and regional topography in three-dimensional inversion of deep ocean magnetotelluric data
复制标题
深海大地电磁数据三维反演中局部和区域地形的实际结合
DOI：
10.1093/gji/ggt115
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
Kiyoshi Baba
中科院分区：
文献类型：
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作者：
Dawson;J. R.;Kiyoshi Baba
本文提出了一种深海大地电磁（MT）数据的三维反演方法，该方法能够同时考虑局部小尺度地形效应和区域大尺度地形效应，其长度尺度与反演所要解决的地幔结构的长度尺度相当。我们假定大地电磁阻抗张量Z近似等于总结构的大地电磁响应Z ts，它由局部地形畸变项Dlt和对区域结构的响应Z rs的乘积表示，区域结构由地幔电导率结构Z上的区域地形组成，Z <$Zts= Dlt Zr rs。我们还假定Dlt可以看作是一个不依赖于反演中所要求解的电导率结构的场地校正项，Dlt是在反演迭代之前通过对地幔结构的良好初始猜测，通过Zt和Zrs的正演模拟计算出来的。然而，初始Zts是由另一个正演模拟程序，这是更有效的计算成本方面单独建模。反演的模型空间仅包括区域结构，因此模拟响应为Zrs。因此，在反演中，根据Zr和在每次迭代时建模的Dlt; Zr计算Zts，但Dlt在整个反演过程中是固定的。在Dlt为常数的情况下，计算了Zts对电导率的灵敏度。该方案只需要在反演过程中对区域尺度结构进行建模，节省了计算资源和时间，这在三维情况下至关重要。使用合成模型和数据的测试表明，将局部地形的影响，在这个计划是成功的，并产生了一个精确的重建给定的地幔结构。
We propose a three-dimensional (3-D) inversion scheme for deep ocean magnetotelluric (MT) data that enables us to incorporate both the local small-scale topography effect and regional large-scale topography effect, whose length scale is comparable with that of the mantle structure to be resolved by the inversion. We assume that the MT impedance tensorZis approximately equal to the MT response of the total structureZts, expressed by the product of the local topographic distortion termDltand the response to the regional structureZrsthat consists of the regional topography over the mantle electrical conductivity structureZ≈Zts=DltZrs. We also assume thatDltmay be treated as a site correction term, which is not dependent on the conductivity structure to be solved in the inversion.Dltis calculated before the inversion iteration is carried out through the forward modelling ofZtsandZrsusing a good initial guess for the mantle structure. However, the initialZtsis separately modelled by another forward modelling program, which is more efficient in terms of computation cost. The model space of the inversion includes only the regional structure so that the modelled response isZrs. Thus, in the inversion,Ztsis calculated fromZrsandDlt;Zrsis modelled at every iteration butDltis fixed throughout the inversion. The sensitivity ofZtsto the conductivity is calculated consideringDltas a constant. This scheme requires modelling only of the regional scale structure in the inversion process, saving computational resources and time, which is critical in the 3-D case. Tests using a synthetic model and data demonstrate that incorporating the local topography effect in this scheme was successful and produced an accurate reconstruction of the given mantle structure.