## 2 Materials and Methods
### Methods
An example of experimental and theoretically fitted curves within a one-dimensional horizontal layered model was generated (Figure 6a). If the curve was complicated by fast-decaying induced polarization (IP), the solution of the inverse problem was carried out taking into account the IP (Figure 6b). Some transient responses were poorly fitted to the theoretical curve, even taking IP into account. Such cases were noted at points close to the coastline. There were inclined or vertical boundaries of thawed, and frozen rocks were located close to the points here. Therefore, the influence of a steeply dipping interface between media with different resistivity was expressed as a distortion of the right ascending branch of the curve, which increased at a very steep angle. Figure 6c shows an example of an apparent resistivity (ek) curve complicated by a three-dimensional inhomogeneity of the medium. On the experimental curve, the right ascending branch increased so rapidly with time that such a curve cannot be described by a theoretical curve in the framework of a one-dimensional horizontally layered model. The theoretical curve closest to it with standard deviation corresponded to the five-layer model. Figure 5: Scheme of measurements by the TEM method along the profile. 1—generator loop, 2— induction sensors with meters, 3—current switch and laptop, 4—profile, 5—direction of movement along the profile, dotted line—profile line. Figure 6: Examples of the curve for a one-dimensional horizontally layered medium at point 330 (**a**), RMS 4.6 %; the curve complicated by the effect of IP in the form of a signal transition to a negative area at point 340 (**b**) RMS 9.3 %; apparent resistivity curve complicated by the three-dimensional inhomogeneity of the medium at the picket 334 (**c**), RMS 12%. (1 is the experimental curve; 2 is the theoretical curve; 3 is the positive signal; 4 is the negative signal. Model: \(\varrho\) is the resistivity of the layer (Ohm\(\cdot\)m); H is the layer thickness (m), \(\eta\) is the chargeability (\(0\leq\eta\leq 1\)), \(\tau\) is the relaxation time (ms), \(c\) is the exponent (\(0<c\leq 1\)). The primary task of geophysical research was to identify in plan and trace to depth the fault zones through which water leaked from the reservoir. After receiving this information, drilling was carried out to clarify the boundaries of fault zones, types of their fracturing, and filtration characteristics. Taking into account these data, it is possible to plan certain impervious measures. According to the resistivity measured at direct current, two stratigraphic-genetic complexes were distinguished (Table 1). As a rule, the resistivity of rocks, determined by the TEM method, was somewhat lower than the resistivity measured at quasi-direct current. In addition, the TEM method was weakly sensitive to changes in resistivity in high-resistance media, where \(\rho\) exceeds 500 Ohm\(\cdot\)m.  
According to the experience of our studies using the TEM method, 40 km east of the Aikhal settlement [20], frozen carbonates had resistivity from 500-800 to 1100-1200 Ohm\(\cdot\)m. In areas of permafrost degradation, their resistance dropped to 37-95 Ohm\(\cdot\)m. Below the permafrost base, the resistivity of rocks decreased to 0.5-18 Ohm\(\cdot\)m, and in the brine horizons--to 0.5-0.8 Ohm\(\cdot\)m.  
The results of soundings by the other researchers TEM method [15] on the left bank junction showed that frozen carbonates had a resistivity of 300-1000 and more Ohm\(\cdot\)m. At a depth of about 180 m, below the permafrost base, the resistivity of rocks varied within 5-25 Ohm\(\cdot\)m.  
Thus, within the study area, frozen and thawed rocks differed well in resistivity. For the TEM method, the electrical resistivity of frozen bedrock will lie in the range of 300-1500 Ohm\(\cdot\)m, depending on the lithological composition, temperature, and salinity. The resistivity of thawed carbonates will vary from 35-100 to 250 Ohm\(\cdot\)m, depending on the fracturing and water cut.