Figure 1 shows a section of seismic refraction on the most stable side of the park. Deposits of soft materials are observed at the center of the line with Vp values less than 400 m/s (typical velocities of weathered materials). The line extension allows defining a second layer with an irregular structure with poorly consolidated materials (Vp=700 m/s). Vp values greater than 1200 m/s can be associated with the substratum at depths greater than 10 m. Figure 2a shows the selection of the first arrivals of all refraction records using 24 sources and 48 receptors. Direct arrivals show that Vp in the first layer is approximately 400 m/s. Refracted arrivals (after a critical distance of 20 m) exhibit large dispersion, indicating the substratum is irregular with a Vp average of 1200 m/s. Figure 2b shows the velocities representation on the discretized model. The average depth of the substratum is 8 m. A higher velocity zone is observed in the northern part of the array, between 8 and 10 m depth (according to the refraction section shown in Figure 1), with Vp reaching up to 3000 m/s.