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Three dimensional magnetotelluric inversion using heterogenious smoothness-constraint least-squares method

Negi, Tateyuki*; Mizunaga, Hideki*; Asamori, Koichi; Umeda, Koji

Electromagnetic surveys have been widely used for several decades in geothermal, mining and oil exploration or disaster prevention. More recently, three-dimensional surveys have been increasingly carried out. However, they require the large-scale inversion consuming significant computation time. Traditional inversion algorithms based on the linear sensitivity matrix consume time to update the sensitivity matrix in the several iterations. In the presentation, we show a rapid calculation algorithm for the electromagnetic inversion procedure that allows to bypass updating of the sensitivity matrix. In the procedure, a fixed sensitivity matrix for a homogeneous half-space is used in all iterations. Instead of the fixing sensitivity matrix, the Laplace filter coefficients in the each element are updated based on the resistivity smoothness calculated by reconstructed structure. This substitution is not only expected to reduce the computing time required for the large-scale inversion such as for the three dimensional surveys, but also expected to allow the reconstruction for sharp boundary structure. We applied the algorithm for the three dimensional magnetotelluric inversion algorithms to confirm the effectiveness. In the presentation, we show the calculation results using several synthetic data examples with different structures and conditions.

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