3-D magnetotelluric inversion for resource exploration
3-D magnetotelluric inversion for resource exploration
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DOI：
10.1190/1.1816392
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
Randall L. Mackie;W. Rodi;M. Donald Watts
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文献类型：
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作者：
Randall L. Mackie;W. Rodi;M. Donald Watts
解决非线性地球物理反演问题的标准方法是通过迭代、线性化反演，当运行完成时，该方法使模型空间上的目标函数最小化。然而，这种方法需要计算雅可比（灵敏度）矩阵，并在每次反演迭代时求解模型空间上的非稀疏线性系统。这些计算任务，虽然易于处理的一维（1-D）和二维（2-D）的反问题，是禁止更大和更复杂的三维（3-D）的问题。对于大地电磁三维反演，我们采用非线性共轭梯度法（NLCG）直接求目标函数的最小值。由于MT问题的结构，NLCG方法取代了计算的Jacobian矩阵和解决方案的一个大型线性系统的计算相当于只有三个正演问题，每次反演迭代，大大提高了收敛速度。该算法已被测试的合成和真实的数据。在这两种情况下，结果与实际模型或已知地质情况吻合良好。计算时间适中，在400 MHz台式计算机上使用20次NLCG迭代来反演5个频率的100个站大约需要10-12小时。
Summary The standard approach to solving nonlinear geophysical inverse problems is by iterative, linearized inversion, which when run to completion minimizes an objective function over the space of models. This method, however, requires computing a Jacobian (sensitivity) matrix and solving a nonsparse, linear system on the model space at each inversion iteration. These computational tasks, while tractable for one-dimensional (1-D) and two-dimensional (2-D) inverse problems, are prohibitive for larger and more complicated three-dimensional (3-D) problems. For 3-D magnetotelluric (MT) inversion, we use the method of nonlinear conjugate gradients (NLCG) applied directly to the minimization of the objective function. Given the structure of the MT problem, the NLCG method replaces computation of the Jacobian matrixand solution of a large linear system with computations equivalent to only three forward problems per inversion iteration, dramatically increasing the speed to convergence. The algorithm has been tested on both synthetic and real data. In both cases, the results are in good agreement with either the actual model or with known geology. The computation times are modest, taking approximately 10–12 hours on a 400 MHz desktop computer to invert 100 stations at 5 frequencies using 20 NLCG iterations.