engleski

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

On 22 March 2020, Zagreb was struck by athe 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, immediately after the main shock extensive seismological, geological, geodetic and structural engineering surveys were conducted. Description of damage were provided, specifying the building performances, and they were correlated 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 modelling of the earthquake sequence was performed and two major faults were modelled 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 are amplified at least twice. The observed co-seismic deformation (based on Sentinel-1A IW SLC images) implies about 3 few 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 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 Medvednica Mountains active tectonic setting, and will contribute to a better assessment of the seismic hazard for the wider Zagreb area.

Zagreb earthquake ; Medvednica Mountains ; seismicity ; amplification ; structural modelling ; building damage

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