Title in Polish:
The article contains the results of kinematics analysis of the quake force to the building structure. Attention was paid to changes in the natural frequency of the object due to degradation of the structure during the forced vibrations of the load. The spectral power density map of the applied force and the course of the natural frequency variation of small mortar building were compared. Time-frequency analysis was performed using the Gabor transform. A clear correlation was found between the course and force changes in the value of natural frequency of the structure.