## 4 Discussion
### Site Effect Differences
Therefore, at this moment, the presented observation cannot be treated as a constant and stable tendency for the rotational motion. Because translational amplification value depends on the arrangements of specific geological structures, their influence on the rotations might have occurred similarly. Nevertheless, some questions arose during this study: (a) Is the rotational amplification coefficient consistently lower than the corresponding translational one, or in some specific cases, is this trend opposite? (b) Can the translational and rotational site effect parameter relation be expressed with a mathematical function? Regarding the answer to the first question, some researchers [21] presented that the rotational H/V ratio was higher than the respective translational one. This leads to the conclusion that the local site conditions independently affect the rotational and translational motions, and therefore, the tendency to obtain a lower value of the amplification by rotational motion cannot be treated as constant. Thus, answering the second question, the potential mathematical expression between the rotational and translational site effect parameters probably does not exist because geological conditions affect the rotational and translational motions differently. Considering the parameters used in the H/V estimations, it is tough to ignore that the time window length (except in the case of the IMI station) should encompass the S-wave phase and the Rayleigh waves. However, the data sets from the IMI station exclude the presence of the Rayleigh waves on the 54 registered signals due to the meager epicentral distance. Considering that the analyzed seismic events were characterized by a double-couple source mechanism, the S-wave phase is dominant on the records. The minimum distance of the Rayleigh wave generation is given by the following formula [50]:  
\[s_{s}=\frac{V_{r}}{\sqrt{\beta^{2}-Vr^{2}}}d \tag{14}\]  
where \(V_{R}\) is the Rayleigh wave velocity (which is equal to 0.9 \(\beta\)), \(\beta\) is the shear wave velocity, and \(d\) denotes the depth of the event source. The depth of the events ranged from 1.0 km to 1.2 km, and the shear wave velocity of the surface layer was 2080 m/s, which caused the minimal distance of Rayleigh wave generation to range from 2.0 km to 2.4 km. Epicentral distances up to 2.0 km characterized the 54 analyzed events from the IMI station. The epicentral distance for the rest of the events was 4.0 km to 5.5 km. Consequently, the possibility of encompassing the Rayleigh wave in H/V spectrum analysis is significant. However, the influence of those events on the estimated H/V spectrum (Figure 4) was negligible. In the case of the PLA station, the epicentral distance did not exclude the presence of the Rayleigh wave on the signals, but time widow length should not encompass the S-wave phase and the Rayleigh waves. Nevertheless, regarding the type of data recorded by the IMI and PLA stations, one is obligated to pay attention to aspects connected with the SESAME criteria and definition of the cycle numbers, except in terms of the time window length. Considering the SESAME criteria, the time window length should be fulfilled in the following criteria:  
\[f_{0}>\frac{10}{l_{w}} \tag{15}\]  
where \(l_{w}\) is the window length and \(f_{0}\) denotes resonance frequency. Considering the data character of the IMI station, in the case of events from a longer distance than analyzed, the time window length of about 5s will encompass the surface waves. A similar situation occurs when the registered event is less distant at the PLA station--in that case, reducing the time window value and increasing the time window history. The natural consequence of that situation is the unfulfillment of the reliability criteria of the H/V curve from equation 15. In that situation, the estimation of the H/V spectrum of the registered microtremors may be treated as additional surveys, which can confirm the reliability of the spectrum obtained from the body wave analysis.