## 4 Results
### HVSR Inversion Results  
Tables 7 and 8 show the parameters of the subsurface soil model for the St3 and Typ2 sites correspondingly, which, along with the HVSR curves, were used as initial data for inversion. It is known that the shelf area where the OBSs were deployed is characterized by silty surface soils [42]. In addition, based on the characteristics of the region, we assume that the sub-bottom reflecting boundary was most likely the upper surface of the permafrost. In accordance with this, the values of the P- and S-waves velocity, as well as the density of the soil, were selected from reference materials [43]. The thickness of the surface layer (18 m) for the St3 site was estimated using Formula (2). Since it can be seen from Figure 8 that at the Typ2 site there is no resonant peak related to the contrast sub-bottom boundary, we assumed that its depth was beyond the values corresponding to representative seismic sensor frequency band, i.e., lower than 1 Hz. Therefore, according to Formula (2), we determined that for the Typ2 site, the depth of the reflecting boundary should be more than 53 m, so the value of 70 m was taken. Figure 8: HVSR plots for 6–8 h-long OBS records obtained at the St3 and Typ2 sites on 25 October, 25 November and 25 December 2019. Thick lines—average curves, thin lines—maximum and minimum curves. Semi-transparent colored numbered rectangles indicate the specific frequency ranges, described in the text. Figure 9 shows the schematic view of the OBSs deployed in the Laptev Sea with indication of sea depths and representation of the resonance effect and its relation to soil amplification curves. Figure 10 shows, in turn, the assumed initial velocity profiles for the St3 and Typ2 sites. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \(\mathbf{V_{p}}\) (P-Waves Velocity [m/s] & \(\mathbf{V_{s}}\) (S-Waves Velocity) [m/s] & **Rho (Density) [g/cm\({}^{3}\)]** & **d (Thickness) [m]** & \(\mathbf{Q_{p}}\) (P-Waves Damping) [\%]** & \(\mathbf{Q_{s}}\) (S-Waves Damping) [\%] \\ \hline
430 & 210 & 1.8 & 18 & 15 & 5 \\ \hline
2600 & 1100 & 1.8 & half-space & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The initial subsurface model for HVSR inversion for the St3 site. Figure 9: Schematic view of the OBSs deployed in the Laptev Sea, with indication of sea depths and representation of resonance effect, and its relation to soil amplification curves. Figure 11 shows the results of the HVSR inversion. In general, a correspondence was obtained between the simulated curves and the curves obtained from the observational data, i.e., the amplitude and position of the resonance peak for the St3 site, as well as the position and shape of the curves for the Typ2 site. Tables 9 and 10 show the optimized subsurface models obtained by HVSR inversion for the St3 and Typ2 sites, while Figure 12 shows the optimized velocity profiles. Figure 11: The best fit between the HVSR curves obtained for the initial (red lines) and optimized (blue lines) subsurface models for **(a)** the St3 site; **(b)** the Typ2 site. Figure 10: The initial velocity profiles (**a**) at the St3 site; **(b)** at the Typ2 site. Figure 12: The optimized velocity profiles (**a**) at the St3 site; (**b**) at the Typ2 site. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\mathbf{V_{p}}\) (P-Waves Velocity) [m/s] & \(\mathbf{V_{s}}\) (S-Waves Velocity) [m/s] & **Rho (Density)** & **d (Thickness) [m]** & \(\mathbf{Q_{p}}\) (P-Waves Damping) [\%] & \(\mathbf{Q_{s}}\) (S-Waves Damping) [\%] \\ \hline
1833 & 611 & 1.8 & 329 & 15 & 5 \\ \hline
2600 & 1100 & 1.8 & & half-space & \\ \hline \hline \end{tabular}
\end{table} 
Table 10: The optimized subsurface model obtained by HVSR inversion for the Typ2 site.