# Strong Ground Motion Sensor Network for Civil Protection Rapid Decision Support Systems
## 4 Results  
The installation of the SGMN's sensors on different geological formations to cover the broad area of a metropolitan city, the Chania in our case, provides a near real-time realistic delineation of the ground shaking in the monitoring area. The response spectra \begin{table}
\begin{tabular}{c c c} \hline \hline
**Station** & \(f_{0}\) **(Hz)** & \(A_{0}\) **(Unitless)** \\ \hline ABEA & 0.46 & 2.44 \\ ATEI & 0.40 & 2.27 \\ DEYA & 0.44 & 2.72 \\ GOLD & 0.42 & 4.08 \\ LENT & 0.40 & 2.44 \\ MULT & 0.36 & 2.27 \\ NERO & 0.63 & 1.99 \\ PASK & 0.33 & 3.00 \\ PERI & 0.46 & 3.51 \\ POLY & 0.55 & 2.50 \\ SOUD & 0.36 & 2.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The ground motion predominant frequency \(f_{0}\) and amplitude \(A_{0}\) at SGMN’s stations. from all stations after a major seismic event present valuable insight earthquake aftermath in different parts of the city which can be used by civil protection agencies, local authorities, and other stakeholders. Figure 2 illustrates the spectral acceleration plots in g-units for the events that brought on the largest values. The majority of buildings in the research area are of low structure height, typically exhibit natural periods much less than 1 s, thus all the panels on the Figure 2 are limited to periods up to 1 s. An exception to that is the Samos event panel (e) which depicts in the response spectra noticeable acceleration values for periods up to 2 s possibly related to the weak attenuation of low frequency part of spectrum with distance. The EQ.3, intermediate depth, event along with the EQ.4 event with epicentral distance less than 40 km from Chania were the two strongest recordings of the SGM network during the examination period. The spectral acceleration values are slightly above the 9% g for one station while the rest stations in alluvial deposits reported values more than 5% g. A similar behavior with slightly reduced acceleration exhibited the EQ.1 minor event with epicenter located southwest of Chania at very short distance from the city. The EQ.5 event had similar parameters (hypocenter and magnitude) with the EQ.4 one, but it presented considerably smaller acceleration values as the maximum was close to 4% g. The Samos strong event occurred very far away (about 365 km) from the Chania metropolitan area, but its magnitude was large enough to record almost 4% g at two strong ground motion stations. The EQ.8 is the most recent event felt in Chania in the same direction with the 2017's one (EQ.1), similar depth and larger magnitude but the factor of greater distance is the reason for the much smaller acceleration values which were less than 2% g.  
Figure 2: Spectral acceleration in g-units for the strongest events since 2017: **(a)** EQ.3; **(b)** EQ.4; **(c)** EQ.1; **(d)** EQ.5; **(e)** EQ.7 (Samos event); **(f)** EQ.8. For the case of Chania metropolitan city, where the sedimentary basin formations consist of materials with different stiffness and thickness from site to site, it is very interesting to examine the response spectra in each station for a number of strong shocks, as this can highlight the important footprint of local site effects. All events with significant ground shaking intensity since 2017, recorded from the majority of stations were examined. The spectral acceleration plot results point out that there are considerable variations in the reported values among some locations. From the results of this investigation, we extract and present in Figure 3 the three stations (GOLD, MULT, and SOUD) that systematically reported higher acceleration values, due to local subsurface geology, as opposed to the three stations (ATEI, LENT, and POLY) that consistently recorded lower values. The stations located in the Quaternary deposits demonstrated in most cases a clear peak between the periods 0.1 and 0.3 s. The EQ.3 and EQ.4 events generated significantly larger acceleration values at these stations.