###### Abstract  
The Sumatran Fault runs from the southeast (SE) to the northwest (NW) of Sumatra Island, with the highest slip rates reaching about 3.0 cm per year in the northwestern part. There is a seismic gap along this fault, including the northern Aceh domain, which consists of the Aceh and Seulimeum fault segments. Previous studies have used various methods to investigate the Sumatran Fault system, including seismic, geoelectric, gravity anomaly, and magnetotellurics (MT). The MT method has proven advantageous as it can non-destructively image a wide range of depths. However, previous studies using the two-dimensional (2D) MT inversion did not represent realistic information of the subsurface conditions. Therefore, a three-dimensional (3D) MT data inversion was used in this study to obtain more realistic information about the resistivity structure of the Aceh and Seulimeum segments. The results confirmed that the Sumatran Fault is a strike-slip fault, with a relatively northwest (NW)-southeast (SE) direction of conductivity strike with an angle of S 71.61\({}^{\circ}\) E from Groom-Bailey decomposition of MT data. The 3D resistivity distribution model from 33 stations showed that the Aceh Fault Segment is 20-30 km away, while the Seulimeum Fault Segment is 55-60 km away based on the MT data. The results also indicated a creeping zone at a depth of 2 km beneath the Aceh Fault Segment. Different rock formations were identified beneath the fault system, with the western part of the Aceh Segment dominated by high-resistivity metamorphic rocks (150-1000 \(\Omega\)m) from the Triassic-Cretaceous age. The zone between the Aceh and Seulimeum fault segments exhibited low resistivity, characterized by volcanic rocks (1-15 \(\Omega\)m) from the Lam Teuba Volcanic Formation and the Indrapuri Formation. Beneath the eastern part of the Seulimeum Fault Segment was found to consist of low-resistivity quaternary volcanic rocks (1-15 \(\Omega\)m) and high-resistivity andesite rocks (4.5 \(\times\) 10\({}^{4}\)-1.7 \(\times\) 10\({}^{5}\)\(\Omega\)m). These findings correlated well with the geological map. m 2024 14 11335 1135  
to oblique subduction at a 45\({}^{\circ}\) angle at the Sunda Trench. Based on the MORVEL model, slip rates of the subduction between the Indian and the Sundaland plates are 46-48 mm per year off Sumatra Island [1]. Because of the oblique subduction, the trench-parallel strike-slip fault was formed on the southwestern coast of Sumatra Island [2]. Sumatra Fault was created due to the oblique subduction process of the Indo-Australia plate beneath the Eurasian plate [3; 4; 5; 6]. It stretches for 1900 km from 10\({}^{\circ}\) N to 7\({}^{\circ}\) S and has 19 major fault segments [7]. Apart from being a trench-parallel strike-slip fault in an oblique subduction system, the Sumatra Fault is also part of a volcanic arc [8]. A seismic creep down has been identified in the northern segment of the Sumatran Fault. It occurs at a depth of 7.3 \(\pm\) 4.8 km with a rate of 2.0 \(\pm\) 0.6 cm per year [9]. This slip rate is higher than that of the southern segment of the Sumatran Fault, which has an estimated locking depth of 14.8 \(\pm\) 3.4 km with a slip rate of 1.6 \(\pm\) 0.6 cm per year [9]. Despite the shallow creep, the estimated width of the locked zone is 9.4 \(\pm\) 6.4 km in the northwestern part of the Sumatran Fault zone. These findings indicate that the northern segment has the potential to cause earthquakes with a magnitude of 7 [9]. Geological estimates of slip rates on the Sumatran Fault increase from southeast to northwest, with the maximum rates reaching about 3.0 cm per year in the northwestern part of Sumatra Island [7; 10; 11; 12; 13]. The Sumatran Fault also has a seismic gap for earthquakes with historical earthquakes of a magnitude of M \(\geq\) 7. This gap includes the northern Aceh domain, which consists of the Aceh and Seulimeum segments in northwestern Sumatra Island. This information was reported in a historical observation of seismicity [7; 14].