## 5 Conclusions  
This study highlights the significance of examining a building's dynamic behavior under actual seismic loading, utilizing real accelerometric data from the Mw 5.6 Pernik earthquake (22 May 2012). The selected recordings, from the basement and sixth floor of a mid-rise RC building in Sofia, reveal significant vertical and horizontal amplification phenomena. The resulting data form a basis for understanding site-specific seismic performance and informing both retrofit strategies and instrumentation planning. The findings show that the structure remained largely within elastic limits; however, amplified responses at the top floor (e.g., PGA ratio up to 3.27) highlight critical demands on non-structural components and the necessity for careful attention to seismic detailing. Natural period estimates derived from RSA (0.25 s in the basement and 0.42 s on the sixth floor) confirm an increasing flexibility and deformation with building height, consistent with the modal behavior observed in similar structures. The applied methodology--combining recorded motions, spectral analysis, and the Kanai-Yoshizawa (KY) linear modal estimation--demonstrated suitability for rapid seismic vulnerability assessment in reinforced concrete buildings. Significantly, this framework may also be adapted to other construction typologies, such as unreinforced masonry, steel-frame, or hybrid systems, provided the following conditions are met:  
* Sufficient sensor deployment for meaningful modal extraction. * Reasonable knowledge or estimation of structural properties. * Consideration of soil-structure interaction effects where applicable. Regarding methodological refinement, we acknowledge that incorporating non-linear constitutive models--such as the Kent model for concrete and the Kent-Park model for reinforcement, as illustrated by [PERSON] et al. [64] in their study on RC chimneys with tuned mass dampers--could offer improved realism in capturing post-yield behavior and damage evolution. While this would introduce computational complexity, particularly in finite element or fiber-based frameworks, it may lead to significantly different results regarding residual drifts and localized damage. Although this study focuses on system-level metrics and employs linear elastic assumptions due to data limitations, future work should explore non-linear extensions to enhance risk characterization and support informed retrofit decision-making. The Mw 5.6 earthquake in the Pernik region serves as a critical case study for assessing seismic risk in Sofia, a region prone to earthquakes. The seismic response analysis of a six-story building highlights the importance of utilizing real accelerogram data to comprehend structural behavior under earthquake loading. Using records from the basement and sixth floor during the 2012 Pernik earthquake, the study evaluated key parameters, including PGA, PGV, PGD, PFA, PFV, PFD, and displacement distributions. The results emphasize the increasing flexibility and deformation of the structure with height, reflected in the natural periods of the RSA: 0.25 s in the basement and 0.42 s on the sixth floor. These findings align with the typical dynamic responses of multi-story buildings, where displacements on the top floor are amplified. The findings support the use of simple predictive models, such as KY, combined with spectral analysis to assess seismic building vulnerability [15; 16]. These insights inform design codes, retrofitting strategies, and urban seismic risk management approaches. In summary, the conclusions affirm the value of strong-motion monitoring, the effectiveness of simplified spectral models for vulnerability analysis, and encourage broader methodological application with future integration of non-linear structural response modeling. Conceptualization, L.P. and I.P. ; methodology, L.P., E.O. and I.P. ; software, L.P., E.O. and I.P. ; validation, R.I.; formal analysis, L.P., E.O., R.I. and I.P. ; investigation, L.P., E.O., R.I. and I.P.