## 4 Results
### Three-Dimensional Inversion Model of MT Data  
We present our preferred 3D model of the electrical structure of the northern Sumatran Fault zones, based on full inversion of impedances as given in Figure 12a with the RMS error given in Figure 12b. The horizontal cross-sections at several interval depths from \(\sim\)0 km to \(\sim\)5 km are given in Figure 13 to better show the continuity of the resistivity zone. The horizontal cross-sections resulting from the inversion in Figure 13 are confirmed by the DOP analysis in Figure 10 by qualitative comparison of the pseudosection, which has a depth that includes the depth of the horizontal cross-section. The pseudosection of the DOP at a frequency of 10 Hz ranging from 0.19 km to 2.97 km is given in Figure 11c, and it has been compared qualitatively to the horizontal cross-section at the depth of 1 km, as shown in Figure 13b. It can be seen that the east of the Aceh Segment is dominated by low-resistivity zones, as shown in Figure 13b, which qualitatively match the low-resistivity zones of the pseudosection in the east of the Aceh Segment at a frequency of 10 Hz, as shown in Figure 11c. Similarly, the high-resistivity zones in the west of the Aceh Segment shown in Figure 13b match with the high-resistivity zones of the pseudosection in the western of the Aceh Segment at frequency of 10 Hz, as shown in Figure 11c. Furthermore, the horizontal cross-sections at the other depths (depth of 2 km, 3 km, 4 km, and 5 km) were also analyzed using DOP analysis, in the same way as previously performed. It can therefore be assumed that the anomalies calculated by the model can be reliably interpreted. This assumption is supported by the RMS error given in Figure 12b, which has a downtrend pattern. The RMS of the last iteration of this inversion is 7.138. Figure 9: Regional conductivity strike direction of the Sumatran Fault System area based on the Groom–Bailey decomposition technique. Figure 10: Depth of penetration at frequencies of (**a**) 320 Hz, (**b**) 100 Hz, (**c**) 10 Hz, (**d**) 1 Hz, (**e**) 0.1 Hz, and (**f**) 0.05 Hz. Figure 11: Planar view the pseudosection of MT data at frequencies of (**a**) 320 Hz, (**b**) 100 Hz, (**c**) 10 Hz, (**d**) 1 Hz, (**e**) 0.1 Hz and (**f**) 0.05 Hz. To see an overview of the RMS conditions that reached 7.138 in the model, an analysis was carried out by taking several samples of the observed data and the calculated data from several stations (six stations), as shown in Figure 14. The observed and calculated data of those samples were compared to each other, including the apparent resistivity and phase curves. The apparent resistivity and phase curves between the observed and calculated data from six stations had to fit each other for both _yx_-data components and _xy_-data components, which showed the same pattern. It can be concluded that the data calculated from the inversion represent the observed data from the field measurements. For further studies of the resistivity cross-section of the 3D Earth model and to characterize the Aceh Segment and Seulimeum segment faults, the inversion result was investigated in three profiles in Figure 15: Profile 1 (P1), Profile 2 (P2), and Profile 3 (P3). Those profiles were selected to show the representative images that cut across the fault direction (P1 and P2 are perpendicular to the fault direction, while P3 forms a certain angle to the fault direction). The cross-sections of P1, P2, and P3 are given in Figure 16, Figure 17, and Figure 18, respectively. Figure 14: _Cont._  
Figure 13: The horizontal cross-section of the 3D resistivity model from (**a**) 0 km, (**b**) 1 km, (**c**) 2 km, (**d**) 3 km, (**e**) 4 km, and (**f**) 5 km beneath the Earth’s surface. Figure 14: Apparent resistivity and phase between observed and calculated data from 3D inversion of MT data from the (**a**) ACH06 (**b**) KEMA, (**c**) ACH07, (**d**) TANG, (**e**) ACH08, and (**f**) KAWA stations. Figure 15: Profile map for further studies of the resistivity cross-section (noted by the red straight line with the label).