## 7 Conclusions  
The Gorontalo graben zone is a weak zone with open fractures and high permeability. Water can easily penetrate rock owing to its high permeability, causing it to become a water catchment (discharge) area. Furthermore, the Gorontalo graben zone controls and confines subsurface fluid circulation, ensuring a continuous supply of meteoric water into the geothermal system and thus supporting the Pentadio geothermal energy conservation system. The appearance of hot springs in the graben zone shows that the geological structure controls the geothermal system and serves as a conduit for geothermal fluids to reach the surface. Meteoric water infiltration is circulated by convective currents and reappears on the graben zone surface. These features agree with the results of [62; 63] when considering the relationship between the presence of a conductive zone and a fault system, as well as geothermal fluids.  
The 3D resistivity model of the Limboto Lake--Pentadio area was obtained by inverting MT data from 26 stations. The model confirmed the presence of fault and graben systems as the controlling factors of the regional geothermal system. The graben system is filled with conductive bodies (\(\sim\)1-15 \(\Omega\)m) corresponding to alluvium deposits, which are flanked by resistive bodies (\(\sim\)100-1000 \(\Omega\)m) representing andesitic and granitic lavas. The emergence of a hot spring complex confirms the existence of a fault system in the Limboto Lake--Pentadio area as a conduit for geothermal fluids to reach the surface. The fault and graben systems were confirmed from the present geological study and the 2D density model.  
Figure 12: A conceptual model of Limboto Lake—Pentadio derived from the 3D MT resistivity model, 2D gravity forward modeling, and geological studies.  
**Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app13010644/s1](https://www.mdpi.com/article/10.3390/app13010644/s1)]([https://www.mdpi.com/article/10.3390/app13010644/s1](https://www.mdpi.com/article/10.3390/app13010644/s1)), Supplementary Material 1: The curves of apparent resistivity and phase of impedance for all the measuring stations. Supplementary Material 2: Apparent resistivity and phase fitting between observed and calculated data generated from 3D inversion for MT data from all MT stations. The blue solid line depicts observed field data, the green circles depict resampled data at the ten frequencies chosen, and the red solid line depicts calculated data. Supplementary Material 3: The comparison between the observed and the calculated data in terms of apparent resistivity and phase of impedance maps, as well as their RMS values for all periods.  
**Author Contributions:** [PERSON] and [PERSON] supervised the direction of this study. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] designed and conducted geological and geophysical field surveys. Numerical interpretation of the data was conducted by [PERSON], [PERSON] and [PERSON]; [PERSON] and [PERSON] wrote the final manuscript. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was partially funded by Domestic Postgraduate Education Scholarships (BPPDN) provided by the Ministry of Education and Culture of Republic of Indonesia (grant No. 2903.3/D3/PG/2017), awarded to the first author.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors would like to thank the Laboratory of Modeling and Inversion, Physics of Earth and Complex Systems, ITB for the permission to use its facilities in support of this study.  
**Conflicts of Interest:** [PERSON] is employed by Tri Ariesta Dinamika Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.