## 4 Influence of Subsoil and Building Material Properties on the Natural Frequencies of Building
[MPa]), computed using the SM2 subsoil model: (**a**) induced by the mining tremor No. 1; (**b**) induced by the mining tremor No. 2. Similar analyses were performed for the subsoil model SM3. The influence of the Cz coefficient value on the transmission of vibrations from the free-field to the foundations in the horizontal x and y directions using the SM3 subsoil model and forcing with mining tremors No. 1 and No. 2 is shown respectively in Figures 15 and 16. Additionally, maximum values of foundation vibration (_a_) in the case of masonry building (brick load-bearing walls) depending on the material properties of subsoil (Cz) are compared in Table 5.  
By comparing the vibration courses of the foundations from Figure 13 and Table 5 (SM2 subsoil model, x direction), the significant influence of the Cz coefficient value on the calculated maximum vibration acceleration values is visible. It can be noticed that the larger the value of the Cz coefficient, the greater the maximum value of vibration acceleration. The maximum values of foundation vibrations are greater in the case of mining tremor No. 2, which is related to the greater intensity of this tremor compared with tremor No. 1. For example, in the SM2 model, the difference between the maximum vibration acceleration values related to mining tremor No. 1 and calculated for the Cz coefficient values of 35 MPa and Cz = 65 MPa was 44.1%. For the mining tremor No. 2, this difference was smaller and equaled 22.1%. In the case of y horizontal direction (see results for SM2 subsoil model presented in Figure 14 and Table 5), particularly the significant influence of the Cz coefficient value on the calculated maximum vibration acceleration and phases of the calculated records  
Figure 16: Masonry building (brick load-bearing walls) horizontal longitudinal (y) foundation vibration and the corresponding Fourier spectra depending on the material properties of subsoil (Cz [MPa]), computed using the SM3 subsoil model: (**a**) induced by the mining tremor No. 1; (**b**) induced by the mining tremor No. 2.  
were observed for mining tremor No. 2--comp. Figure 14b. The larger the value of the Cz coefficient, the greater the maximum value of vibration acceleration. For example, in the SM2 model and mining tremors No. 1 and No. 2, the difference between the maximum vibration acceleration values calculated for the Cz coefficient values of 35 MPa and Cz = 65 MPa was, respectively, 25.8% and 26.7%--comp. Figure 14 and Table 5.  
Comparing the FFT courses from the calculated foundation vibration courses induced by mining tremors No. 1 and No. 2, regardless of the value of the Cz coefficient, differences in the transmission of dominant frequencies in the band up to 17 Hz were observed, see, e.g., Figure 13. For mining tremor No. 1, the horizontal x component of vibrations with a frequency of approx. 5.3 Hz, corresponding to Cz values from 45 MPa to 60 MPa, were best transmitted from the ground to the foundations. Similarly, higher frequencies from the 9.7 Hz and 10.5 Hz bands transmitted without disturbances from the ground to the foundations for the whole assumed Cz values from 35 MPa to 60 MPa--comp. Figure 13a. For mining tremor No. 2, the horizontal x component of vibrations with a frequency of approx. 4.5 Hz, 7.75 Hz, 8.7 Hz, and 10.3 Hz, corresponding to Cz values from 35 MPa to 60 MPa, were best transmitted from the ground to the foundations--comp. Figure 13b. Results of the calculated FFT course in the horizontal y direction at foundation vibrations induced by mining tremor No. 1 indicate dominant frequencies in the range of about 5 Hz and 7.5 Hz regardless of the value of the Cz coefficient. Mining tremor No. 2 indicates slightly greater dominant frequencies in the calculated FFT course, referring to the transmitted vibration records from free-field to foundations--comp.