This paper highlights the principal features of the M_w5.4 Zagreb earthquake. Located within the city limits at a depth of 10 km, the earthquake generated a peak ground acceleration of more than 0.2 g and a maximum spectral acceleration of about 0.6 g at 0.1 s in the historic downtown area. The situation was particularly challenging since the event occurred amid a partial Covid-19 lockdown at temperatures close to 0 °C, emphasizing the extensive and complex vulnerability of the local communities and individuals. 27 people were reported severely injured, one of which later died. The surprisingly high economic costs, needed to achieve a full reconstruction of damaged buildings and infrastructure in the affected area, are currently evaluated at more than 10B euros. Description of the organization of the emergency response in the first days and the observed damage to buildings is given with typical examples. The focus is on the performance of older masonry residential and cultural heritage buildings in the historic downtown, their inspection and evaluation of damage to structural and non-structural components. This information provides the basis for understanding of the negative impacts and clarifies the overall context identifying the enablers and barriers to the still ongoing recovery process. It also helps to increase the awareness of the seismic vulnerability of European cities with similar construction practices.

On December 29, 2020, nine months after the March Mw 5.4 Zagreb earthquake and amidst the COVID-19 lockdown, a devastating Mw 6.4 earthquake struck near the town of Petrinja, about 50 km SE from the country’s capital Zagreb. It was preceded by the Mw 4.9 foreshock from the day before. The main shock claimed 7 fatalities and caused widespread damage. Historical centers of nearby cities with invaluable heritage buildings were significantly affected as were the many residential buildings, built mainly of unreinforced masonry. Damage was observed as far as 60 km from the epicenter. This paper summarizes the seismological aspects of the Mw 6.4 Petrinja earthquake, the emergency response and the main impacts to people and buildings. The description and findings are based on the field observations and a series of post-earthquake activities led by the team of the Faculty of Civil Engineering, University of Zagreb. Typical damage to buildings and usability data are presented with examples based on 50,000 inspection results. By far the most affected were the unreinforced masonry buildings, followed by confined masonry, whereas reinforced concrete buildings were the least affected. The total direct and indirect losses are estimated to 4.8 billion EUR. The provided information represents a useful basis and impetus for improving emergency action and long-term disaster reduction plans in other regions with similar building exposure and seismotectonic settings.

Current regional seismic loss estimation models, for example, the United States Federal Emergency Management Agency’s (FEMA) Hazus, typically employ empirical functions for damage assessment of buried pipelines subjected to permanent ground deformation (PGD). These functions are based on a limited number of damage observations to pipelines during past strong earthquakes. They represent the repair rate per unit length in a brittle or ductile pipe segment under average structural and geotechnical conditions and ground failure phenomena. This study aims to propose an analytical method for assessment of vulnerability of ductile energy pipelines traversing permafrost regions and subject to active layer detachment (ALD) landslide hazard. Canadian ALD morphological statistics combined with the probability of pipeline exposure to transverse ALD-caused PGD and the extent of the potential PGD are used as input. A computer program is developed in order to analyze the structural behavior of pipelines and evaluate their vulnerability considering three damage mechanisms: tensile rupture, local buckling, and premature cross-sectional failure. The vulnerability functions associated with PGD, expressed in terms of repair rate, are obtained by applying Monte Carlo simulation to the structural analysis results. The novel vulnerability functions developed herein are specific to permafrost regions and can be incorporated in the Hazus-type platforms for regional seismic risk assessment.