## 4 Evaluation of Design Response Spectra
In addition, in the case of Bucharest, a comparison between the design acceleration response spectra computed based on the current Eurocode 8 draft revision [1] (mean return period of 475 years), the seismic design code P100-1/2013 [29] (mean return period of 225 years) and the envelope of the spectral acceleration from the ground motions recorded during Vrancea earthquakes is shown in Figure 7.  
Figure 4: (**a**) A comparison between the control period T\({}_{\text{C}}\) from P100-1/2013 [29] and based on Eurocode 8 draft revision [1] for category B sites; (**b**) a comparison between the maximum spectral acceleration from P100-1/2013 [29] and based on Eurocode 8 draft revision [1] for category B sites. Another comparison between the ground motions recorded at the Banloc station during the crustal earthquake of December 1991, and the design response spectra based on the Eurocode 8 draft revision [1] and the seismic design code P100-1/2013 [29] is shown in Figure 8. It has to be highlighted that this particular ground motion recording can be characterised as being pulse-like [16] and it therefore contains significant long-period spectral amplifications. Figure 5: (**a**) A comparison between the control period T\({}_{\text{C}}\) from P100-1/2013 [29] and based on Eurocode 8 draft revision [1] for category C sites; (**b**) a comparison between the maximum spectral acceleration from P100-1/2013 [29] and based on Eurocode 8 draft revision [1] for category C sites. Figure 6: (**a**) A comparison between the control period T\({}_{\text{C}}\) from P100-1/2013 [29] and based on Eurocode 8 draft revision [1] for category F sites; (**b**) a comparison between the maximum spectral acceleration from P100-1/2013 [29] and based on Eurocode 8 draft revision [1] for category F sites. Figure 8: **(a)** A comparison between the design absolute acceleration response spectra from P100-1/2013 [29], the Eurocode 8 draft revision [1] and the spectral accelerations of the ground motions recorded at the Banloc station during the 1991 crustal earthquake; **(b)** a comparison between the design relative displacement response spectra from P100-1/2013 [29], the Eurocode 8 draft revision [1] and the spectral displacements of the ground motions recorded at the Banloc station during the 1991 crustal earthquake. Figure 7: **(a)** A comparison between the design absolute acceleration response spectra from P100-1/2013 [29] (mean return period of 225 years), the Eurocode 8 draft revision [1] (mean return period of 475 years) and the envelope of the spectral accelerations from the ground motions recorded in the Bucharest area during Vrancea intermediate-depth earthquakes; **(b)** a comparison between the design displacement response spectra from P100-1/2013 [29] (mean return period of 225 years), the Eurocode 8 draft revision [1] (mean return period of 475 years) and the envelope of the spectral displacements from the ground motions recorded in the Bucharest area during Vrancea intermediate-depth earthquakes. It is clearly visible from both Figures 6 and 7 that the design response spectra derived based on the relations provided in the Eurocode 8 draft revision [1] fail to capture the intermediate- and long-period spectral amplifications observed in the response spectra of the ground motions recorded at Bucharest. It can also be observed that there are period ranges in which the envelopes of the spectral accelerations or displacements are superior to the ordinates computed according to the Eurocode 8 draft revision [1]. It has to be emphasised that the mean return periods of the Vrancea intermediate-depth earthquakes and the crustal event in western Romania, which was recorded at Banloc, is less than 80 years. The two seismic sources that produced the earthquakes (Vrancea intermediate-depth and Banat) are capable of producing much larger earthquakes [25]. The source for these differences are mainly attributed to the site amplification factors proposed in the Eurocode 8 draft revision [1] and were derived considering crustal seismic events.