1st Croatian Conference on Earthquake Engineering 1CroCEE 2021

Following the damaging 2020 earthquake of 22 March 2020 (Mw 5.3), a question was raised if this was the largest event after the Great Zagreb earthquake of 1880 (Imax = VIII MSK). The counter-candidates are the events of 17 December 1905 and 2 January 1906. Relevant earthquake catalogues largely disagree when the magnitudes of the Zagreb earthquakes of 1905 and 1906 are concerned. The reported magnitudes range between 5.1 and 6.1 for the 1905 event, and between 5.3 and 6.1 for the earthquake of 1906. Epicentral intensities for both earthquakes are stated as either VII–VIII or VIII (MSK or MCS). To try to resolve the question, we propose to (re)analyse all available macroseismic data for the two historical events, in order to compare the observed intensity distribution with the one of the 2020 earthquake. Additionally, we shall analyse the seismograms of the 1905 and 1906 events recorded at the Göttingen observatory, in order to compute their magnitudes. To this end, we also plan to use reported amplitudes of the two events, as given in various station bulletins of the time. Initial analyses clearly put the 1905 event out of contest, but the challenge between the earthquakes of 1906 and 2020 is too close to call at the preliminary stage of investigations.