**2.3 Horizontal gradient of the geomagnetic field**

The total horizontal poleward gradient was calculated by analyzing the lateral variability of the geomagnetic field (**Figure 2A**). The Shakhpakhty tectonic step exhibits intermediate values of the gradient of this transformant (from 0 to 0.002 nT/m), which increase to the north up to 0.010 nT/m, in the direction of the Central Ustyurt system of dislocations. Conversely, in the south direction, toward the Assakeaudan depression, the gradient decreases to 0 to 0.006 nT/m (**Table 1**). These findings directly confirm the presence of lateral inhomogeneities of magnetically disturbing masses in the study region.
