# Seismic Risk Assessment of Chania, Greece, Using an Integrated Computational Approach
## 4 Seismic Risk Analysis Results
### Comparison of Quakeist Attenuation Models  
QuakeIST also has built-in attenuation models suitable for European countries. The results from the application of three of these models have been based on the expressions of (a)[PERSON] et al. [47], (b) CSO 2003 [53], and (c) Sabettaand Pugliese [50], and details can be found in [24]. The results using [PERSON] expression (Figure 7a) seem to relatively underestimate the risk of the city as all values are much lower than those of the external scenario shown in Figure 6b. There are mainly buildings with either quite high or very low risk. It is noted that some areas in the eastern part present a higher risk compared to the western parts, which is not consistent with the field observations. Similarly, the results presented in Figure 7b, obtained using CSO 2003 model, which has been basedon past earthquakes in Portugal, are not realistic, and this model is also not recommended. The risk indicators are particularly high, in contrast to the other QuakeIST models, but also with the external, i.e., local seismic scenario. Nevertheless, the spatial distribution seems to be quite reasonable.  
Lastly, the Sabetta and Pugliese [50] model, based on data from earthquakes in Italy, provides results (see Figure 7c) that are close to the results of the external scenario developed herein and in accordance with those obtained by [PERSON] et al. [27]. The risk levels appear to be slightly lower compared to the ones of the external scenario, while there is agreement on the distribution of risk. The urban complex can be divided into different zones analogously to the external scenario. This attenuation model seems to provide realistic results, and it is therefore recommended to further develop and incorporate the local attenuation model.  
Figure 8 displays the results of seismic risk analysis using an average attenuation relationship (i.e., the so-called, generic law), which is a combination of models available in the library of the QuakeIST software. This model is perhaps not so important from a scientific point of view, but these results have practical significance. The aim of the development of a \"synthetic\" relationship is to examine if the software can deliver reasonable results in any area of interest. It is observed that in the case of the city of Chania, the extracted results of the average model are particularly close to those of the external model and that of [PERSON] et al. [27]. There is good agreement on both quantitative and qualitative characteristics. Both methods provide the same results, and thus it enhances the generality of the application of QuakeIST software within the study area.  
Figure 9 presents the estimates of the average degree of damage that is likely to occur in the city of Chania if the external seismic model is based on the Gavdos earthquake data instead of the Kythira earthquake data. Similar risk distributions are presented as in all previous models that were examined. In the case of the Gavdos earthquake, however, the estimated damage rates were up to 40% less than the ones resulting from the Kythira earthquake, and did not actually affect much of the urban complex. Hence, comparing the two earthquakes and based on the fact that they are among the strongest events in recent years, it can be concluded that the risk is more pronounced due to earthquakes occurring in the north of Chania, as the one in Kythira, 2006, which is further examined in the sequence. Furthermore, it seems that the attenuation of seismic waves is higher for earthquakes occurring inthe south of the Chania Prefecture, similar to the one in Gavdos, 2012 (eventhough Gavdos's earthquake was closer to Chania than the earthquake of Kythira). This is also verified by seismological (horizontal PGAs) data and available laws (i.e., Ground Motion Prediction Equations (GMPE)), e.g., [PERSON] et al. [54] and [PERSON] et al. [55].