## 2 Materials and Methods
### Modeling the Response of Soft Clay Layer at the Black Sea Offshore Site  
The algorithm described above was used for modeling the response of a soft clay layer at the Black Sea offshore site. The input data were derived from the results of geotechnical engineering and seismological studies conducted in the northeast shelf zone of the Black Sea near the Anapa city in 2011 for seabed pipeline projecting. We used seismic records of the 2011 Kithaya earthquake, which occurred on 2011-05-19 20:15:25.09 UTC and had magnitude \(M_{s}=5.8\)[43]. The seismic signals of this event were recorded by three ocean-bottom seismometers (OBS) temporarily deployed on the Black Sea shelf for local microseismicity monitoring. One OBS was located on the hard flysch outcrop (\(V_{s}=1200\) m/s, \(\rho=2.6\) g/cm\({}^{3}\)), while other OBS was located on the surface of the soft clay layer of 5.5 m and 14 m thickness, respectively underlain by the flysch bedrock (Figure 4). The main parameters of the soil layers and flysch bedrock, such as thicknesses, velocities and porous medium parameters, were derived from the results of seismic surveys and core sampling. Geotechnical parameters of the clay are presented in Table 1.  
The Kutahya earthquake S-waves records of these OBS were chosen for modeling because the epicentral distance of this event (920 km) highly exceeds the maximum spacing between OBS (14 km). In this case, the effect of intermediate wave paths differs negligibly, and the records obtained on the flysch outcrop can be used as input motions at the flysch bedrock covered by the soft clay layer. The records acquired on the surface of the clay layer were used for comparison with modeling results. Figure 5 shows the time histories of the S-waves derived from the OBS records and used as input signals at bedrock and verification signals on the surface of the layers. Figure 4: Ocean-bottom seismometers (OBS) deployments at the Black Sea shelf sites: **1—**on the surface of the soft clay layer of 14 m; **2—**on the surface of the soft clay layer of 5.5 m; **3—**on the hard flysch outcrop. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Moisture Coefficient,** & **Plasticity** & **Density of Solid Grains,** & **Density of Solid Matrix,** & **Mean Density, \(\rho\)** & **Void Ratio, \(e\)** & **Saturation Factor, \(S_{r}\)** & **S-wave Velocity, \(V_{s}\)** \\
**W** & **Index, PI** & \(\rho_{S}\) (g/cm\({}^{3}\)) & \(\rho_{m}\) (g/cm\({}^{3}\)) & (g/cm\({}^{3}\)) & & **Factor, \(S_{r}\)** & **(m/s)** \\ \hline
0.75 & 21.4 & 2.71 & 0.88 & 1.54 & 2.08 & 1 & 80 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Geotechnical parameters of the soft clay at the sites on the shelf near the Anapa city. Figure 5: Input signal at bedrock (**a**) and verification signals on the surface of the soft clay layers with the thickness of 5.5 m (**b**) and 14 m (**c**), derived from the OBS records. Modeling of the Response of Synthetic Soil Deposits With Porous Medium Parameters Specific for Low Moisture Onshore and High Moisture Offshore Sites  
This section is dedicated to numerical simulation and comparison of the responses of porous water-saturated layers of cohesive and non-cohesive soils with parameters specific for low moisture onshore and high moisture offshore sites. For this purpose, synthetic soil layers were constructed (Figure 6) using some values of thickness and geotechnical parameters derived from different marine engineering studies. The parameters of the offshore soils presented in Table 2, Table 3, Table 4 were derived from the results of seismic surveys and core sampling, while the values for their onshore analogs were calculated using Equations (6), (10), (11), (13)-(15) with assumed moisture \(W\) and saturation factor \(Sr\). Here it is assumed that clay and clayey silt are cohesive soil and sand is non-cohesive soil. Flysch half-space (\(V_{s}\) = 1200 m/s, \(\rho\) = 2.6 g/cm\({}^{3}\)) is used as underlain bedrock for all synthetic profiles.