This paper proposes an approach to the calculation and assessment of local velocities of seismic P-waves in a volcanic zone based on the use of the grid method. The numerical algorithm is tested on the experimentally obtained arrival times of P-waves from a vibration source of the SV-10/100 type for the mount Karabetova mud volcano. Registration was carried out by 35 receivers during sounding from 5 points of the vibrator in the frequency range of 10-60 Hz. It follows from the results of numerical modeling that the selection of nonlinearity in the travel time curve of seismic P-waves in the area of a volcanic edifice is possible with the number of grid nodes from 60x60 or more, which corresponds to 31.2 m along the X-axis and 48.1 m along the Y-axis. The obtained results of the distribution of local velocities are consistent with the previously obtained geological structure of the study area and indicate the presence of higher velocities in the area of the anticlinal fold passing through the volcano zone.