engleski

Analysis of the local site effects of the Međimurje region (North Croatia) and its consequences following the 1738 M5.1 Međimurje, 2020 M5.5 Zagreb and M6.2 Petrinja 2020 earthquakes

On 30 March 1738 the Međimurje region was struck by an earthquake with macroseismic intensity estimated in epicentre of 7.9 °MCS and magnitude of 5.1. Historical archives reported heavy earthquake damage for the entire region, especially of brick wall and wooden structures, churches and chapels. The famous Church of St. Jerome located in Štrigova was rebuilt in 1749 following the earthquake demolition as the original 15th-century-built chapel. Old Gothic architecture of the Zrinski Old Town Castle in Čakovec city was damaged. On 22 March 2020, the M5.5 earthquake struck the capital city of Zagreb and small damages to older churches were reported also in Međimurje (approx. 80 km from epicentre). However, moderate damages to churches and older buildings in the whole Međimurje region (approx. 100 km from epicentre) were reported following the destructive M6.2 Petrinja earthquake, which occurred on 29 December 2020. The Međimurje region is entirely a part of Tertiary basin that is distinguished by three major subbasins - Mura, Čakovec and Kotoriba, with relatively thick sedimentary sequences. Its elevations range between 120 and 344 meters, the latter being the elevation of the highest hill, Mohokos in the Međimurske Gorice, structure which is morphologically and topographically most pronounced in the Upper Međimurje. The aim of this analysis is to understand the local site effects of Međimurje region and damage after 1738 and 2020 earthquakes. We used Horizontal-to-Vertical Spectral Ratio (HVSR) method to estimate the local site parameters ; resonance frequency, sediment thickness, Vs30 and HVSR amplitude as an indication of the local site amplification. There is a reasonable indication that the analyzed earthquakes involved three local site effects ; strong amplification and probably potential nonlinearity due to hypothetically strong shaking or highly nonlinear soil behavior on soft soils, as well directional ground motion effects at sites with strong topographic features.

Local site effects, Međimurje 1738 earthquake, Zagreb 2020 earthquake, Petrinja 2020 earthquake

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