## 2 Materials and Methods
### Electromagnetic Monitoring of Strain-Sensitive Zones in the Tien Shan  
Anisotropy is the most sensitive parameter in electromagnetic monitoring as it responds to changes in the stress-strain state (SSS) of rocks at a quantitative level. These changes are reflected in the structural and textural rearrangement of rock. In the experimental data obtained from the central Tien Shan region, a clear variation in electrical resistivity along orthogonal azimuths has been observed [33; 43; 44]. Kyrgyzstan, being a seismically active zone, is continuously studied [45]. The observation system remains consistent, and transitioning to another system is equivalent to considering gradient anisotropic media. The task is to transform the model from a micro-heterogeneous rock structure to a homogeneous anisotropic one. The measured macroscopic parameters and internal structure can be described using effective media approximation (EMA). Furthermore, the relationship between effective parameters and geodynamic processes is considered while respecting the electromagnetic reciprocity transfer (ERT) principle. As an example of studying the anisotropy parameter using field data, we can refer to the results of passive electromagnetic monitoring in a geodynamically active region. Electromagnetic monitoring using Phoenix MTU-5 equipment has been conducted in the northern Tien Shan since 2003 [34; 44]. The magnetotelluric sounding (MTS) installation is physically oriented at the observation point \(xy\) and \(yx\) (\(0^{\circ}\) and \(90^{\circ}\)) following standard procedures [46], ensuring a strict northerly orientation. The installation is placed in 0.25 m trenches on the ground surface. One of the key parameters monitored is the soil's moisture content, as this influences the electric current flow through the porous media and generates electromagnetic perturbations. Over time, variations in the soil's geotechnical and hydraulic properties occur, often influenced by lunar-solar tides. Apparent electrical resistivity (\(\rho_{k}\)) and its inverse parameter, electrical conductivity (\(\sigma\)), are well-known indicators of soil condition, exhibiting high variability in fracture zones near long-lived active faults. This method is widely used by numerous scientists to understand changes in the underground environment [28; 38]. Phoenix MTU-5 equipment is typically used to record variations in five components of the electromagnetic field (\(E_{x}\), \(E_{y}\), \(H_{x}\), \(H_{y}\), \(H_{z}\)) for horizontally layered media. To obtain effective parameters, values for apparent resistivity (\(\rho_{k}\)), impedance tensor components (\(Z_{xx}\), \(Z_{xy}\), \(Z_{yx}\), \(Z_{xx}\)), or impedance phases (\(\varphi\) = 2 arg \(\mathbf{Z}\) + \(\pi/2\)) are used. The general formula for apparent resistivity is \(\rho_{k}=\frac{|\mathbf{Z}|^{2}}{\omega\eta_{0}}\), where \(\omega\) represents the observed frequency and \(\mu_{0}\) represents vacuum magnetic permeability [46]. Rotations are performed along both the main components (\(Z_{xy}\) and \(Z_{yx}\)) and the additional components (\(Z_{xx}\) and \(Z_{yy}\)) of the impedance tensor. In this case, an example is given with the rotation of the main components to better illustrate their relationship with various geophysical parameters (although additional components may be more correlated at specific observation points). The Tien Shan region, with its complex mountainous and geological conditions, exhibits significant heterogeneity [47; 48], which can be described in terms of bianisotropic media. To establish the relationship between conductivity variations and the direction of rotational angles, the following equations (Equation (1)) proposed in [46] are used to calculate the values of the impedance tensor and the corresponding variations for arbitrary azimuths:  
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