Abstract
On 28 December 2020, seismic activity in the wider Petrinja area strongly intensified after a period of relative seismological quiescence that had lasted more than 100 years (since the well-known M5.8 Kupa Valley earthquake of 1909, which is known based on the discovery of the Mohorovičić discontinuity). The day after the M5 foreshock, a destructive M6.2 mainshock occurred. Outcomes of preliminary seismological, geological and SAR image analyses indicate that the foreshocks, mainshock and aftershocks were generated due to the (re)activation of a complex fault system—the intersection of longitudinal NW–SE right-lateral and transverse NE–SW left-lateral faults along the transitional contact zone of the Dinarides and the Pannonian Basin. According to a survey of damage to buildings, approximately 15% of buildings were very heavily damaged or collapsed. Buildings of special or outstanding historical or cultural heritage significance mostly collapsed or became unserviceable. A preliminary analysis of the earthquake ground motion showed that in the epicentral area, the estimated peak ground acceleration PGA values for the bedrock ranged from 0.29 to 0.44 g. In the close Petrinja epicentral area that is characterized by the superficial deposits, significant ground failures were reported within local site effects. Based on that finding and building damage, we assume that the resulting peak ground acceleration (PGAsite) values were likely between 0.4 and 0.6 g depending on the local site characteristics and the distance from the epicentre.
Highlights
Introduction iationsThe active tectonics of the entire area of Croatia, which includes the wider PokupskoPetrinja epicentral area [1], are caused by the continuous movement of the Adriatic lithospheric microplate (Adria) to the north [2]
Peak ground acceleration and response spectra, with consideration of local site effects in the vicinity of the Petrinja M6.2 epicentre, were estimated from the engineering seismology aspect. This is highly important because the results indicate the type of impact the Petrinja M6.2 earthquake will have on future seismic hazard calculations in the epicentral area, and in Zagreb city, as discussed
Based on reported ground failures and building damage, the resulting PGAsite values were likely in the approximate range of 0.4–0.6 g depending on the local site characteristics and distance from the epicentre and are reasonably comparable with U.S Geological Survey (USGS) ShakeMap soil site predictions at the epicentre and at close distances (Figure 12)
Summary
The last week in 2020, for the citizens of Petrinja and its surroundings, along with. On Monday, 28 December 2020 at 05:28 (UTC), a strong M5 earthquake occurred with an epicentre 5 km southwest of Petrinja. The earthquake disturbed the population in the epicentral area and caused extensive damage, which was aggravated by the series of earthquakes that followed. 29 December 2020 at 11:19 (UTC), the wider area of Petrinja was hit by a destructive. A day later, it was readily observable that the material damage was enormous, with many destroyed or damaged buildings and structures in towns near the epicentre, especially Petrinja, Glina and Sisak. In those areas, the ground shaking reached intensities of almost VIII-IX ◦ EMS (European Macroseismic Scale).
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