An earthquake of magnitude 5.5 struck Croatia on March 22, 2020, at 6:24 a.m. The epicenter was near Markuševec, approximately 9 km from Zagreb. On the same day, shortly after this earthquake, another tremor of magnitude 5.0 occurred. The estimated intensity of the earthquake at the epicenter was VII on the European Macroseismic Scale (EMS). The area affected by the March 22, 2020 earthquake experienced many aftershocks, as can be seen here. The region hit by the recent earthquake is known for seismic activity. The Zagreb area lies at the junction of major tectonic units: the Alps to the northwest, the Pannonian Basin to the east, and the Dinarides to the south. Earthquakes in this region result from the relative movement of the Pannonian Basin and the Medvednica-Kalnik fault. The strongest previous earthquake in this area occurred in 1880, with its epicenter in Medvednica and a magnitude of 6.3. That earthquake caused damage or collapse to around 1,400 residential buildings, constituting more than half of the total building stock at that time, considering Zagreb then had about 30,000 inhabitants. Detailed information on the history of seismic hazard in Zagreb and its surroundings can be found here.
This earthquake occurred during the COVID-19 pandemic, which posed additional challenges both for the affected population and for the processes of damage assessment and recovery. The earthquake caused one human casualty and significant material damage, primarily in the epicentral area but also in the central part of Zagreb. Most damaged structures were masonry buildings, especially older ones (some over 100 years old). Among the damaged buildings were residential buildings, schools, hospitals, and structures of cultural and religious significance. According to data from the Croatian Centre for Earthquake Engineering, damage has so far been assessed on a total of 9,390 buildings. Based on inspections by engineering teams, buildings were classified into three categories: green (usable building), yellow (temporarily unusable but may become usable after urgent measures or detailed inspection), and red (unusable building with severe damage likely requiring reconstruction). Approximately 600 buildings were classified as red, about 2,600 in the yellow category, and the rest in green. Information on the condition of damaged buildings collected electronically can be found here.
Most damaged buildings were unreinforced masonry residential buildings that suffered both structural and non-structural damage. Structural damage was observed in facade and party walls, as well as roof structures. Many non-structural damages were noted, such as damage or collapse of chimneys and roof coverings (tiles). Seats of important national institutions were also damaged, such as the Croatian Academy of Sciences and Arts, the University of Zagreb, etc. Museums (e.g., the Modern Gallery and Museum of Contemporary Art) and religious buildings (e.g., the Church of the Sacred Heart of Jesus and Zagreb Cathedral) also suffered damage. More information about the damage to cultural and religious buildings can be found here.
Several hospitals within the Zagreb Clinical Hospital Centre (KBC Zagreb) also sustained structural and/or non-structural damage that disrupted their normal operation. For example, the maternity ward (Petrova Hospital) had to be evacuated immediately after the earthquake. More information on hospital damages can be found here.
Preparations for post-earthquake reconstruction are underway. One of the key activities is the development of a new Law on the Reconstruction of Damaged Buildings, which was prepared shortly after the earthquake. The Faculty of Civil Engineering at the University of Zagreb and the Croatian Chamber of Civil Engineers prepared and published a manual for urgent technical solutions for repairing chimneys and other parts of building structures, which can be found here.
We thank Dr. Marta Šavor-Novak, assistant professor at the Faculty of Civil Engineering, University of Zagreb, for valuable information regarding this earthquake.
More detailed information about the behavior of buildings during this earthquake can be found at the following websites:
