## 4 Results
### Group-Bailey Decomposition and the Depth of Penetration (DOP)  
In addition to using dimensional analysis, such as polar diagrams and induction arrows, the MT data were also analyzed using the Groom-Bailey decomposition technique to identify regional conductivity strikes. The Groom-Bailey decomposition technique at each MT station (Figure 9) helps verify the presence of geological strikes for fault analysis. The Groom-Bailey decomposition technique applied in the MT data is plotted in the rose diagrams of the regional conductivity strikes. Those diagrams were calculated for each station at multiple frequencies before calculating the average value of them as shown in Figure 9. The average value showed the direction of the conductivity strike in the study area, which was shown to be relatively northwest (NW)-southeast (SE) with an angle of S 71.61\({}^{\circ}\) E, which was also confirmed by geological study [7]. The result of the Groom-Bailey decomposition in Figure 9 confirms the induction arrows analysis in Figure 7.  
Data resolution analysis was performed based on the depth of penetration (DOP), which is mathematically given by Equation (21) [60]:  
\[DOP=\frac{\delta_{\text{{slitdepth}}}}{\sqrt{2}} \tag{21}\]Figure 8: Induction arrows for frequencies of (**a**) 317 Hz, (**b**) 100 Hz, (**c**) 10 Hz, (**d**) 1 Hz, (**e**) 0.1 Hz, and (**f**) 0.05 Hz in the same scale of induction arrows. The red arrows depict the real part of tipper vector \(\mathbf{T}_{Re}\) and the black diagrams depict the imaginery part of tipper vector \(\mathbf{T}_{im}\) (using Parkinson convention, red arrows point to the conducting body). The data resolution analysis using DOP compared to the model resulted from inversion, which was used qualitatively to validate the depth sensitivity of the model. The DOP plot was analyzed at several frequencies as given in Figure 10: 320 Hz, 100 Hz, 10 Hz, 1 Hz, 1 Hz, 0.1 Hz, and 0.05 Hz. The representative frequencies with specifically high frequency at 10 Hz and low frequency at 0.1 Hz have been reported below. The DOP for the high frequency (f = 320 Hz) has a range of approximately 0.02 km to 0.37 km in Figure 10a. The depth of 0.02 km corresponds to the low-resistivity zones in the eastern of the Aceh Segment, as shown in the pseudosection in Figure 11a, while the depth of 0.37 km corresponds to the high-resistivity zones in the western of the Aceh Segment, as shown in the pseudosection in Figure 11a. This is consistent with the skin depth concept, where the low-resistivity zones have shallower field penetration depth, while the high-resistivity zones have deeper field penetration depth. Next, the DOP for the low frequency (f = 0.1 Hz) ranges from approximately 2.24 km to 57.49 km, as shown in Figure 10e. The depth of 2.24 km corresponds to the low-resistivity zones in the eastern of the Aceh segment, as shown in the pseudosection in Figure 11e, while the depth of 57.49 km corresponds to the high-resistivity zones in the west of the Aceh segment, as given in Figure 11e. This is also consistent with the skin depth concept, where the low-resistivity zones have shallower field penetration depth, while the high-resistivity zones have a deeper field penetration depth. Figure 10b shows the depth of penetration at a high frequency of 100 Hz, with a range of approximately 0.04 km to 0.89 km. Figure 10c shows the depth of penetration at a high frequency of 10 Hz, with a range of approximately 0.19 km to 2.97 km. Figure 10d shows the depth of penetration at a high frequency of 1 Hz, with a range of approximately 0.44 km to 10.07 km. Figure 10e shows the depth of penetration at a high frequency of 0.1 Hz, with a range of approximately 2.24 km to 57.49 km. Figure 10f shows the depth of penetration at a high frequency of 0.05 Hz, with a range of approximately 3.32 km to 71.11 km. These values correspond to the pseudosection in Figure 11b-f, which matches the skin depth concept.