## 2 Instrumental Data  
Three strong motion records were selected for the main event on 11 September 2016--the acceleration recorded at the Seismological Observatory SKO, the seismograms at IZIIS Institute, and the film record at the FCE (Faculty of Civil Engineering--Gradezhen Fakultet). The station locations and epicenter are superimposed on the simplified geology map of the Skopje region (Figure 1). Figure 1: The recording station positions (triangles) and the epicenter (star) of the 11 September 2016 M\({}_{1}\)5.3 earthquake in respect to the geology around Skopje city (shaded area). Two records of the Zagreb 22 March 2020 earthquake from the closest stations coded QUHS and QARH, were used for our analysis. The stations' location and the epicenter superimposed over the geology map (detailed explanation in [7]) of the Zagreb region are displayed on Figure 2.  
Station coordinates, instrumentation, and soil type according to standard Eurocode-8 classification and using V\({}_{530}\) maps, are listed in Table 1.  
In the Seismological Observatory SKO at epicentral distance of approximately 7.2 km, the acceleration was recorded by the EpiSensor Kinemetrics instrument installed on bedrock. It is a multi-component set consisting of three force balance accelerometer modules mounted orthogonally and with full-scale recording ranges of \(\pm\)0.25 to \(\pm\)4 g, that is especially useful at near fault locations and in a variety of structure types. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Station Code** & **Latitude** & **Long** & **Altitude** & & \\
**Name** & **(deg)** & **(deg)** & **(m)** & **Instrument** & **Soil Type** \\
**SKO** & 41.9721\({}^{\circ}\) N & 21.4396\({}^{\circ}\) E & 346 & EpiSensor Kinemetrics & A \\ \hline
**FCE** & 42.0003\({}^{\circ}\) N & 21.4180\({}^{\circ}\) E & 269 & SMA-1 Kinemetrics & C \\ \hline
**IZIIS** & 41.9787\({}^{\circ}\) N & 21.4265\({}^{\circ}\) E & 376 & GGRALP GRM-T5 & B \\ \hline
**QUHS** & 45.8084\({}^{\circ}\) N & 15.9988\({}^{\circ}\) E & 115 & GURALP T5 GD0 & C \\ \hline
**QARH** & 45.6153\({}^{\circ}\) N & 15.9928\({}^{\circ}\) E & 100 & GGRALP T5 GD1 & C \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Selected station coordinates and instrumentation. Figure 2: The recording station positions (triangles) and the epicenter (star) of the Zagreb M\({}_{1}\),5.5 March 2020 earthquake with respect to the geology around Zagreb city. The 3-channels acceleration record of the 11 September 2016 magnitude M\({}_{\rm L}\)5.3 earthquake at the SKO location is shown on Figure 3. The maximum acceleration was on the Z-component; a measured zero-to-peak value of 555,000 counts or peak ground acceleration (PGA) of 0.140 g, the N-S component PGA was 0.10 g, and the E-W component PGA was 0.07 g.  
At the Faculty of Civil Engineering (Gradezen Fakultet) location, at an epicentral distance of approximately 6.5 km, the acceleration was recorded by the SMA-1 Kinemetrics instrument that was deployed at the site. It is a longstanding instrument that records on film and data had to be manually digitized. It was installed in the sub-basement of the faculty and the foundations consist of a few meters of sand, gravel, and quartz deposits 7 m deep. The 3-channel acceleration record of the 11 September 2016 magnitude M\({}_{\rm L}\)5.3 earthquake at the Faculty of Civil Engineering-Gradezen Fakultet location is shown in Figure 4. The maximum acceleration was recorded on the L-component and had a zero-to-peak value of 4.5 units or 0.121 g, while the V-component had slightly smaller values of 0.118 g and the T-component about 0.078 g.  
At the Institute of Earthquake Engineering and Engineering Seismology-IZIIS location at an epicentral distance of approximately 7.3 km, the acceleration was recorded by a broadband Guralp instrument that was deployed on the ground floor at that site. It is a non-anchored digital instrument positioned on a laminated concrete slab in the laboratory of the Institute [8].