Coast effects on 3-D inversion of magnetotelluric data for geothermal exploration in East Flores, Indonesia

Nowadays geothermal exploration in Indonesia is beginning to reach small islands, most of which have a prospect in the coastal area. This has influences on the MT data modelling due to the distortion of the electric field component caused by the extreme contrast of resistivity between land and sea. In these conditions, it is necessary to apply the correction of the coast effects. The seawater resistivity (0.3 Ωm) must be included in the 3-D MT modelling. A simulation was conducted to observe coast effects on 3-D MT modelling. Forward 3-D MT modelling is done to obtain synthetic data to compare homogeneous model and coast effects model. The simulation results show that the presence of seawater affects all MT data frequencies, but the most significant distortion occurs in the low frequency. The affected frequency range correlates with the distance between the MT station and seawater. If the distance of MT station to the sea is getting closer, then the disturbed frequency range is greater, and vice versa. The results of 3-D inversion of MT real data with the coast effects model are used to construct a conceptual model for geothermal systems in East Flores. The interpretation shows that the geothermal prospect area in the field is around Mount Anging. This research is expected to be a consideration for drilling recommendations and further development.