## 4 Results
### Electrical Anisotropy
#### 4.2.3 Induction Vectors  
The orientation of the induction vectors can be related to and depend on the presence of electrical anisotropy or lateral variation of the resistivity and the regional geoelectric strike direction. If the latter is not parallel to the eventual inferred anisotropy direction, it can also influence the direction of the induction vectors [24; 40]. In cases where phase split and/or phase tensor ellipticity are generated by a lateral conductivity gradient that also generates induction vectors, a consistent correlation should be observed between the high magnitude induction vectors, ellipticity of the phase tensor and phase split (shown, respectively, in Figures 6-8). High magnitude induction vectors seem to be confined to the intermediate periods and appear in a discontinuous form rather than in a lateral and continuous form that could be related to a large single 2D heterogeneity. That means the high magnitude induction vectors appears as a localized and isolated conductors along 2D profile having more elongated vertical scale rather than the lateral scale particularly at center of the rift (Figure 8). This pattern can also be related to the noise or uncertainty of magnitude induction data (Appendix A). On the other hand, a continuous phase split and consistent ellipticity are evidenced for the intermediate and long periods (Figures 6 and 7) along the same 2D profile. High magnitude induction populated for the intermediate periods may explain high conductivity contrast related to the variation of geoelectric strike of short periods to the long periods, which corresponds to the two different directions of anisotropy (Figure 7). Moreover, the induction vectors may be deflected from isotropic layer to anisotropic layer or from two anisotropic medium having different anisotropy direction where anisotropy period dependent is generated by the magnitude of conductivity gradient or discontinuity between the two medium [40]. The latter affirmation may be hypothesized in the Asal rift case and that is why high  
Figure 7: Pseudo-section of phases tensor ellipses along 2D profile MT sites (Figure 1).  
magnitude induction vector exist at the intermediate periods between the first anisotropic medium corresponding for short periods and the second anisotropic medium for long periods. Additionally, a general pattern of low magnitudes induction vectors can be observed where a mean geoelectric strike is well-defined for each of both long and short periods (Figures 3, 4, 7 and 8). Consequently, with this lack of correlation and the fact that 75% of magnitude induction vectors data are less than 0.2 (which can be interpreted as low values) except those related to the increase in uncertainty (Appendix A). Thus, in this case the anisotropy signature explains this data pattern and the idea that high induction vectors are generated by lateral conductivity gradient can be excluded. However, another possible explanation of the mechanism that can induce the high magnitude induction may be associated by the presence of oriented conductive dyke that intrudes inside relative resistive anisotropic medium, which in turn generate high magnitude of conductivity gradient between the conductive dykes and relative anisotropic medium. Evidence of vertical conductive zones that could be associated with dykes will be presented in the next section of the 2D inversion models.  
Figure 8: Magnitude of the real induction vectors. Delaunay triangulation method is used.