Advances in seismic vulnerability assessment of historic masonry buildings: Insights from the Mw5.4 Zagreb (Croatia) earthquake of March 22, 2020

Abstract

The earthquake in Zagreb (Croatia) on March 22, 2020, despite its moderate magnitude of MW 5.4, demonstrated in a destructive way the high seismic vulnerability of historic masonry buildings from the era of the Austro-Hungarian Empire (≈ 1840–1918). European cities are largely composed of unreinforced brick masonry buildings (URM), making large-scale seismic risk assessment crucial for planning appropriate mitigation measures, particularly in urban areas. In this paper, a comprehensive damage analysis of selected building blocks representative of the historic URM in Zagreb's historic old town is carried out. The damage classification was conducted according to the European Macroseismic Scale (EMS-98). The statistical evaluation with empirical vulnerability functions enhances the still limited knowledge about the seismic structural behavior of the historic URM from the era of the Austro-Hungarian Empire and damage trends can be identified depending on specific building characteristics within the typological classification of the historic URM. The seismic vulnerability of the selected building stock is then assessed using a macroseismic method according to the EMS-98 scale. Based on the observed damage, a new approach for the assessment of the historic URM is proposed and vulnerability curves are developed as a function of specific building characteristics. Finally, fragility curves were estimated in relation to the macroseismic observation and the Peak Ground Acceleration (PGA).