engleski

The Međimurje earthquake of 1738 – from historical data to macroseismic parameters

The earthquake that we describe occurred in 1738 in Međimurje, a province situated between the Mura and the Drava rivers in the northernmost Croatia, bordering with Slovenia to the west and northwest and Hungary to the northeast. It is located in the western part of the Pannonian Basin, in the contact area with the eastern Alps and the north-western Dinarides. Contemporary seismicity is very low – the two largest instrumentally recorded earthquakes in the greater Međimurje region in the last 110 years (M = 4.7) occurred in 1919 (M = 4.7) and 1943 (M = 4.8). Only 7 events with magnitudes M ≥ 3.0 are listed in Međimurje in the instrumental era. Historical seismicity of this region is poorly known. These facts heavily influenced the assessed seismic hazard in Međimurje, which is currently mostly controlled by seismicity in the neighbouring epicentral areas. However, the two strong events of 1738 and 1838 that are either missing from the relevant catalogues or are listed with the wrong parameters, indicate that significant earthquakes in Međimurje are not as rare as it may seem from the instrumental data. Herewith we present the first detailed macroseismic study of the most important known event in Međimurje – the Čakovec earthquake of 1738. We describe all the sources used – from the monography by Bedeković (1752) and diverse documents from the mostly Pauline monasteries, to reports from canonical visitations and various historical, archaeological and art history studies. We also measured the HVSR of ambient noise at several localities from where we had reports on the damage, in order to characterize the soil and assess possible amplification and/or building-soil resonance effects. The data collected enabled us to resolve the problem of the date of the earthquake (30 March 1738, around 1 am UTC), and to estimate intensity (MSK) for 13 localities. Those intensity data points were inverted for the hypocentral coordinates and the epicentral intensity by the modified R. Musson’s MEEP 2.0 program, using the MEEP, centroid (Boxer), and Bakun-Wentworth methods. The representative location was taken as the barycentre of 3000 bootstrap solutions (with replacements), 1000 for each method used. The 68% and 90% confidence limits ellipses centred at the macroseismic epicentre were estimated obeying the minimum area and minimum ellipticity constraints. The epicentre is located about 4 km from the city of Čakovec, close to the Čakovec fault, which we thus identify as an active one capable of producing very strong and destructive earthquakes. This fact has the potential to significantly influence seismic hazard in Međimurje.

The Međimurje earthquake of 1738 ; seismic hazard

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