A consideration of sea effects on MT data obtained in an east Indonesian island: Lembata Island

Geothermal energy is renewable and emits only minute amounts of carbon dioxide gas. It can be the most effective energy source not only economically but also environmentally when considering power generation for remote and relatively small islands like those in Eastern Indonesia. For the development of geothermal energy in the islands, magnetotelluric (MT) surveys have been conducted, but failed to properly image the electrical conductivity structure of the subsurface due to the impact of the existence of the surrounding sea, known as the 'sea effect'. MT data are severely distorted by the electrical conductivity of seawater and thus should be corrected before inversion or directly inverted to take into account the sea effects. However, both strategies can be effective only when the sea effects at a target area are properly simulated. This study investigated sea effects at Atadei geothermal field in Lembata Island to build a resistivity model that can accurately describe sea effects. In the process of determining the proper sea model, we constructed several sea models of Lembata Island, and compared simulated MT responses for each model in order to analyze the sea effects. The process can serve as a good strategy in dealing with MT data obtained in islands located in complex sea environments. Our future work will interpret the MT data using the properly constructed sea model.