A 6.4 magnitude earthquake struck the Sisak-Moslavina County in Croatia on December 29, 2020, in the early afternoon (12:20 PM). The epicenter was located about 3 km southwest of the town of Petrinja (50 kilometers southeast of Zagreb), with a hypocenter depth of 11 km. This was the strongest earthquake recorded in Croatia in the last 140 years. It was approximately 12 times stronger and released 45 times more energy than the earthquake that hit Zagreb and its surroundings on March 22, 2020. The earthquake was followed by over 2,000 aftershocks, some of which caused further damage to buildings. The quake affected a relatively large area of Croatia, especially the towns of Petrinja, Sisak, Dvor, Glina, and even Zagreb. Tens of thousands of people were temporarily or permanently displaced from their homes, and 7 people lost their lives. The maximum earthquake intensity was estimated at level VII on the Modified Mercalli Intensity (MMI) scale, and between VIII and IX on the European Macroseismic Scale (EMS-98). Mostly masonry buildings were damaged, especially older ones, some over 100 years old. Among the damaged structures were residential buildings, schools, hospitals, and buildings of cultural and religious significance. According to the Croatian Center for Earthquake Engineering (HCPI), around 30,000 buildings were reported for inspection due to potential damage. Of those inspected, 15% were marked red and deemed unfit for use, while 24% were marked yellow, making them temporarily unsuitable until a more detailed inspection and evaluation are completed. Five elementary schools in Sisak-Moslavina County require reconstruction, and nine others were severely damaged. Media reports indicate that 825 commercial buildings, 700 retail stores, and 13 high school buildings were damaged. More than 250 patients were transferred to other hospitals, as most of the Sisak hospital buildings had to be evacuated due to the earthquake.
Structural damage was observed on facade and party walls, as well as on ceilings and roof structures. Many damages were non-structural, such as damage or collapse of chimneys and roof coverings (tiles), and complete collapses of suspended ceilings were also recorded. Buildings housing state and local institutions were damaged, including the city hall in Petrinja, the Petrinja Craftsmen Society, the Teacher’s Faculty in Petrinja, and others. Religious buildings also sustained damage, such as the Church of St. Lawrence, the Church of St. Nicholas, and the Cathedral of the Exaltation of the Holy Cross. Additionally, damage was reported to infrastructure facilities, including bridges, electrical substations, and transformer stations.
More information about this earthquake can be found at the following links:
Information on the condition of damaged buildings: Hrvatski centar za potresno inženjerstvo (HCPI)
Article: Stein, R. i Toda, S. (2021). Stress analysis shows slight increase in seismic hazard near Zagreb, Tremblor
Article: Bijelić,N., Brzev,S., and Lazarević,D. (2020). Croatian earthquake causes significant damage, Tremblor
Photo sources: collapsed family house in the village of Prekope near Glina (Krešimir Micić) and damaged masonry building in the center of Petrinja (Joško Krolo)
