DC, EM & NMR technologies

[DE-03] A development of an efficient technique for solving inversion problems using the modified Gram-Schmidt process for three-dimensional magnetotelluric joint inversion with a galvanic distortion tensor

*Tateyuki Negi¹, Munemaru Kishimoto¹ (1. Nittetsu Mining Consultants Co. Ltd (Japan))

We have developed a practical code for 3-D magnetotelluric (MT) inversion that considers galvanic distortion using QR decomposition based on the modified Gram-Schmidt process. While the modified Gram-Schmidt process is generally considered to be more accurate in deriving solutions than the method using normal equations, it does so at a slower computation speed. Without an effective strategy to improve the computation time, the practical use of the inversion code would be limited. Since the modified Gram-Schmidt process is unsuitable for parallel computation, we attempted to speed up the calculation by (1) reducing the numbers of loop statement preparations and iterative decisions, and (2) selectively computing only non-zero elements. We found, as a result, that our modified Gram-Schmidt code was approximately three times faster than the ordinary code in the first calculation, and 100 times faster in the second and later calculations with slight parameter changes.