An electrical resistivity survey was carried out using the pole–pole configuration around the Sayanokami spring area in the northern part of Ito Campus (Kyushu University, Fukuoka, Japan) to study the groundwater aquifer and its electrical characteristics. A Code Division Multiple Transmission (CDMT) system was used. The CDMT system transmits 24 currents simultaneously and measures 24 potential responses with monitoring of actual current waveforms. The system can inject current from multiple electrodes into the underground environment simultaneously using different individual current waveforms. The two-dimensional (2-D) inversion results of the electrical resistivity data indicate three layers from top to bottom, as follows: (a) a thin layer with a thickness of 3 m and a low resistivity (< 50 Ω m) representing topsoil; (b) a groundwater aquifer layer with an average resistivity between 50 and 170 Ω m and with a thickness ranging from 7 to 10 m, and (c) a highly resistive bedrock layer with resistivities higher than 200 Ω m and occupying depths from 15 m to the base of the model.

The Obama geothermal field is located on the western part of Kyushu Island, Japan. This area has importance due to its high geothermal content which attracts sporadic researchers for study. In 2003 and 2004, Obama was covered by gravity surveys to monitor and evaluate the geothermal field. In this paper, the surveyed gravity data will be used in order to delineate and model the subsurface structure of the study area. Gradient methods such as analytic signal and vertical derivatives were applied to the gravity data. The available borehole data and the results of the gradient interpretation techniques were used to model the Obama geothermal field. In general, the obtained results show that the gradient interpretation techniques are useful to obtain geologic information from gravity data.