| Abstract |
Dependency of three-dimensional (3-D) inversion of magnetotelluric (MT) data on the observation error and the station interval was examined. The 3-D inversion technique, which was used in this work, utilizes the finite difference method for the forward modeling and the least-squares method for the inversion part. The inversion incorporates the observation error as the weight in the Jacobian matrix. Experiments with the MT data obtained in the Northern Negros geothermal field, central Philippines, with different weight settings indicated that an accurate estimate of the observation error in the field measurement and an appropriate setting of the weights for the Jacobian matrix in the inversion are important to obtain reliable 3-D models. The interval of MT stations is a difficult decision in the field design. The effect of the station interval on 3-D inverted models was examined using a large volume MT dataset obtained in the Ogiri geothermal area, Japan. The average station interval of the Ogiri MT survey was approximately 250 m. 3-D inversions were conducted using several subsets of the data. When the station interval is around 1 km, the resultant 3-D model is lacking a resolution for delineating the reservoir structure. This suggests that the station interval should be less than several hundreds meters, when we seek for detailed imaging of geothermal reservoirs at a depth range of 500 รป 2000 m. |