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Open AccessArticle

The Zagreb (Croatia) M5.5 Earthquake on 22 March 2020

Department of Geophysics, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia
Faculty of Geotechnical Engineering, University of Zagreb, 42000 Varaždin, Croatia
Department of Geology, Croatian Geological Survey, 10000 Zagreb, Croatia
Faculty of Civil Engineering and Architecture Osijek, Josip Juraj Strossmayer University of Osijek, 31000 Osijek, Croatia
Author to whom correspondence should be addressed.
Geosciences 2020, 10(7), 252;
Received: 4 May 2020 / Revised: 26 June 2020 / Accepted: 28 June 2020 / Published: 1 July 2020
(This article belongs to the Section Geophysics)
On 22 March 2020, Zagreb was struck by an M5.5 earthquake that had been expected for more than 100 years and revealed all the failures in the construction of residential buildings in the Croatian capital, especially those built in the first half of the 20th century. Because of that, extensive seismological, geological, geodetic and structural engineering surveys were conducted immediately after the main shock. This study provides descriptions of damage, specifying the building performances and their correlation with the local soil characteristics, i.e., seismic motion amplification. Co-seismic vertical ground displacement was estimated, and the most affected area is identified according to Sentinel-1 interferometric wide-swath data. Finally, preliminary 3D structural modeling of the earthquake sequence was performed, and two major faults were modeled using inverse distance weight (IDW) interpolation of the grouped hypocenters. The first-order assessment of seismic amplification (due to site conditions) in the Zagreb area for the M5.5 earthquake shows that ground motions of approximately 0.16–0.19 g were amplified at least twice. The observed co-seismic deformation (based on Sentinel-1A IW SLC images) implies an approximately 3 cm uplift of the epicentral area that covers approximately 20 km2. Based on the preliminary spatial and temporal analyses of the Zagreb 2020 earthquake sequence, the main shock and the first aftershocks evidently occurred in the subsurface of the Medvednica Mountains along a deep-seated southeast-dipping thrust fault, recognized as the primary (master) fault. The co-seismic rupture propagated along the thrust towards northwest during the first half-hour of the earthquake sequence, which can be clearly seen from the time-lapse visualization. The preliminary results strongly support one of the debated models of the active tectonic setting of the Medvednica Mountains and will contribute to a better assessment of the seismic hazard for the wider Zagreb area. View Full-Text
Keywords: Zagreb earthquake; Medvednica Mountains; seismicity; amplification; structural modeling; building damage Zagreb earthquake; Medvednica Mountains; seismicity; amplification; structural modeling; building damage
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Markušić, S.; Stanko, D.; Korbar, T.; Belić, N.; Penava, D.; Kordić, B. The Zagreb (Croatia) M5.5 Earthquake on 22 March 2020. Geosciences 2020, 10, 252.

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