## 5 Results  
### Results of the Passive Seismic Methods  
According to the results of the passive seismic interferometry, the dispersion curve was obtained. The dispersion was used for the calculation of the 1D averaged velocity model of the studied pipe and enclosing environment (Figure 5). The calculated model consists of seven layers, bordering depths of 10 m, 30 m, 35 m, 70 m, 250 m, 350 m, and 1200 m.  
The most probable correspondence of the obtained depths and geological formations is obtained according to the previous data [1,32,33] and is presented in Table 1. According to Table 1, more contrast formations are in the different layers of Vendian deposits. \begin{table}
\begin{tabular}{c c c} \hline
**Depth, m** & **S-Wave Velocity, m/s** & **Geological Formations** \\ \hline
0–7 & 216 & Q \\
7–28 & 660 & C2 ol \\
28–32 & 785 & C2 Vr \\
32–70 & 840 & C2 Ur \\
70–245 & 870 & Vzl (Vpd) \\
245–530 & 1850 & Vmz \\
530–1200 & 2500 & Vup \\
1200–1500 & 2700 & R \\
1500 and above & - & AR \\ \hline \end{tabular}
\end{table} 
Table 1: S-wave velocity model with corresponding geological formations. Figure 5: Results of passive seismic interferometry. Dispersion curve of the fundamental mode of Rayleigh waves (**a**) and S-wave velocity model (**b**,**c**). According to the results of the MSM, a low-velocity tubular body of a conical shape with its apex facing down was identified. The central part of the low-velocity body is in alignment with the anticipated pipe boundaries; however, the low-velocity body is more substantial in size (see Figure 6). Based on the outcomes of profiles 2 and 4, the pipe is comprised of two distinct blocks: those with low contrast and elevated intensity. The blocks with low contrast exhibit an intensity range of 1-4 dB, while those with elevated intensity display a range of 4-7 dB. The southern pipe has been identified with more certainty. Thus, the body of the pipe has been imaged at depths from 50 to 300 m.  
Both pipes have roots-oriented eastward at depths between 250 and 120 m. This depth range correlates with the lower part of the Padunskaya suite of the Vendian deposits. The pipe above 120 m is only indicated on profile 2 and exhibits a vertical eastern border and an inclined western border towards the west. Furthermore, in the western section, the southern pipe has been observed to extend into the carbon deposits. Profile 4 indicates that the northern Volchya pipe does not penetrate the Vendian deposits and exhibits a complex bend at depths between 150 and 200 m. The pipe is predominantly characterized by a low-contrast body. The upper part of the pipe at depths between 120 and 150 m is predominantly located to the west of the proposed borders. No significant anomalies were identified between the northern and southern pipes. However, it is notable that the western section of the profile displays a layered structure, while the eastern part exhibits a vertical zone of low velocities, particularly in the Padunskaya and Mezenskaya suites of the Vendian deposits. Figure 6: Results of passive seismic methods. Geophysical cross-sections according to the microseismic sounding method with profile numbers above the sections. Cross-section intersection lines marked by vertical dashed lines (**a–f**h). S-wave velocity model (**g**,**i**) calculated according to passive seismic interferometry. Horizontal dashed lines—geological formation: Q—Quaternary sediments; C—carbonate sediments; Vpd, Vmz, Vup—Padunuan, Mezen and Ust-Pinega suites of Vendian deposit; R—Riphean sediments; Ar—Archean sediments. Red horizontal dashed lines—a proposed boundary in the Padunian suite. The sub-meridional profile 7 crossed the pipe in only a few points (see Figure 4). The southern Volchya pipe is identified in points 7-4 to 7-6. The northern Volchya pipe is identified in points 7-12 and 7-15. The southern boundary is in good agreement with the data from the previous model of the pipe. Nevertheless, a minor subvertical low-velocity zone was discerned in points 7-2 and 7-3.