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Application of 2-D inversion with genetic algorithms to magnetotelluric data from geothermal areas

Abstract

We apply a modified genetic algorithm, the “recombinant genetic analogue” (RGA) to the inversion of magnetotelluric (MT) data from two different geothermal areas, one in El Salvador and another in Japan. An accurate 2-D forward modelling algorithm suitable for very heterogeneous models forms the core of the inverse solver. The forward solution makes use of a gridding algorithm that depends on both model structure and frequency. The RGA represents model parameters as parallel sets of bit strings, and differs from conventional genetic algorithms in the ways in which the bit strings are manipulated in order to increase the probability of convergence to a global minimum objective function model. A synthetic data set was generated from a chessboard model, and the RGA was shown capable of reconstructing the model to an acceptable tolerance. The algorithm was applied to MT data from Ahuachapán geothermal area in El Salvador and compared with other interpretations. Data from the geothermal area of Minamikayabe in Japan served as a second test case. The RGA is highly adaptable and well suited to non-linear hypothesis testing as well as to inverse modelling.

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Correspondence to Marco A. Pérez-Flores.

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Keywords

  • Apparent Resistivity
  • Geothermal Area
  • Magnetotelluric Data
  • Forward Solution
  • Nonlinear Inversion