## 5 Discussion
### Two Main Directions of Anisotropy Varying with Depth  
#### 5.2.1 Presence of 2D Anisotropic Structure  
A straightforward method to identify electrical anisotropy is the presence of consistent phase tensor split with low values of magnitude induction vectors [24; 39] as shown in Figures 6 and 8 for short periods. However, for the long periods, degree of consistent phase split is more important (Figure 6) and a moderate to low values of magnitude induction vectors is present for periods greater than 70 s (Figure 8) that can be interpreted again as anisotropy effect from 2D anisotropic structure or 2D heterogeneity. Furthermore, the high regional skew is influenced by induction and is related either to 3D inductive effects or to anisotropy [21; 29; 37]. Consistent correlation between high regional skew and the high magnitude induction vectors (Figures 2 and 8) may result from a common origin that could be the consequence of the 2D anisotropic or 3D structure in the study area. Indeed, consistent and slightly varying geoelectric strike for the corresponding range of periods should not expected if a 3D conductivity structure was the origin of the consistent correlation between high regional skew and the high magnitude induction vectors. Moreover, the author argue that the common origin between them could be the anisotropy signature notably 2D anisotropic, since the moderate to low value of magnitude induction vectors exclude the assumption of the presence of a 1D anisotropic structure in which the absence of tipper is expected [24; 25]. For the short periods, the consistent ellipticity of the phase tensor with the relative moderate values of geometric mean of the principal values of the phase tensor that has a well-defined geoelectric strike of N43\({}^{\circ}\)E (Figure 7) on one side, and the minor phase difference between the two polarizations (Figure 6) on the other side, can be interpreted together to linked to the presence of regular and homogenous anisotropic medium. Additionally, the assumption of absence 2D isotropic structure as in the case of this work, is evidenced by the values of phase tensor skew angle (Figure 5) greater than zero [25]. The latter author also suggested that a nonzero phase tensor skew angle can indicate structure having azimuthal anisotropy varying with depth if 3D isotropic structures can be excluded. This suggestion is what can be proposed in Asal rift because a well-defined geoelectric and anisotropy directions in both short and long periods (Figure 7) and a general low value of regional skew which is produced by 3D inductive structure can be inferred (Figure 2). For the long periods, the consistent moderate phase split, high regional skew and the high geometric mean angle of the principal value of the phase tensor (Figures 2, 6 and 7), notably for the MT stations close to the center of the rift (rift axis), can be associated with a pattern resulting from anisotropic medium which is more heterogenous, irregular and more conductive than for the MT stations located at the margins of rift (far from the rift center). A similar pattern was found by [44] in their study which argue that the middle crust conduction mechanism is governed by electronic conduction due to the graphite rather than electrolytic conduction.