## 5 Discussion
### Subsurface Conductivity Structure and Associated Interpretations  
#### 5.3.1 Hydrothermal System and Fluid Circulation  
Results from 2D inversion show the conductivity structure under the Asal rift, with a general pattern of relative conductive environment (C4 and C3) bounded at the bottom by dipping moderately resistive layers (R2 and R3) and at the top by highly conductive layers (C1 and C2). Similar structures found in hydrothermal systems and geothermal prospect zones [8; 9; 63; 64] were interpreted as shallow hot aquifer or cap rock that covers high enthalpy hydrothermal/geothermal reservoir. In the present case, the latter is likely fractured due to the extension rate of rift and the presence of approximate horizontal electrical anisotropy direction and could host significant quantities of fluids (liquid or steam) in the rift zones, where the activity of an overpressure magmatic reservoir at the center inject either a hot material into dyke or magmatic fluid. The latter is often considered as the source of vertical heat transfer that can migrate laterally toward the rift segment termination [65; 66; 67]. Surface deformation studies [3; 17; 18] and related interpretations of the presence of deep hydrothermal fluid circulation will be compared with the electrical conductivity structure model developed in this study (Figure 9). Numerical modelling results of 2D thermo-mechanical [18] yielded temperatures consistent with the measured temperatures of deep geothermal wells. However, some disagreement between the measured and modeled temperature of A5 located close to the center of the rift (Figure 1) was interpreted as local thermal effects generated by the fluid circulation [18], which corresponds to the high conductance zones of the three conductive layers C2, C3 and C4 (Figure 9). Furthermore, [3] noted that a faulting process, mainly controlled by deep hydrothermal fluid circulation coming from an over pressurized magmatic system, injects fluid into fractured zones connected to the deep part of the faults and hence triggers in a decrease in the effective normal stress on the locked section at depth of faults which in turn induces faults slip. These authors focused their study on active faults located at the center and at the north-east of the rift. Their results corroborate to the width extension of conductive layers C1, C2 and C3 between the center and the north-east part of the rift (Figure 9). In addition, as proposed by [17], 70% of the actual deformation beneath the rift is concentrated toward the northeastern part rather than the southwestern part. And the northeastern part was recently interpreted as a preferred zone of fluid filled fractures with a potential hydrothermal fluid circulation at shallow crust that can likely be a geothermal target [6]. Groundwater circulation between Asal lake and Ghoubbet Bay inferred from self-potential (SP) measurements in the study of [5] proposed a schematic representation of fluid circulation where two large zones at the shoulders of the rift have positives SP anomalies that were interpreted as slow and rewarmed fluid flow, whereas a narrow zone with negative SP at the center of rift separating the two previous zones is more related to a rapid and cold fluid flow. The latter study is in good agreement with the resistivity model, where high conductance of the superposed conductive layers (C2, C3 and C4) is clearly visible at the center whereas at the shoulders of the rift, thickness of those layers decreases (Figure 9). Thus, an alternative explanation of the general pattern of fluid circulation can be proposed. And this general pattern is related to the interaction of a deep heat source likely located in the center with a wide hydrothermal reservoir (C3 and C4) that responds to the pressure changes in fluid-filled rocks deformed. Thus, the cause of rocks deformation is likely due to the extension of the rift, which creates the development of shear zones and fractures at the crust where dyke can intrude.