Seismology in Croatia, 2003–2006

Report submitted to the International Association of Seismology and Physics of the Earth’s Interior of the International Union of Geodesy and Geophysic

Fault plane solutions for earthquakes (1956-1995) in Croatia and neighboring regions

The study presents (re)evaluation of fault-plane solutions for 40 earthquakes that occurred in the period 1956-1995 in Croatia and neighboring regions. All events were analyzed in the same manner, using the best available velocity models and the most recently updated earthquake catalogue for that region. For the most important earthquakes our solution is briefly discussed and compared to the results of previous studies when they were available. The results are presented with all related data thus enabling estimation of each solution’s reliability

Which one of the three latest large earthquakes in Zagreb was the strongest – the 1905, 1906 or the 2020 one?

Following the damaging earthquake of 22 March 2020 (ML = 5.5, Mw = 5.3, Imax = VII EMS) in Zagreb, a question was raised whether this was the largest event after the Great Zagreb earthquake of 1880 (Imax = VIII MSK). The countercandidates are the events of 17 December 1905 and 2 January 1906, for which relevant earthquake catalogues mostly report larger or comparable magnitudes as for the earthquake of 2020, with their maximum intensities mostly within a narrow margin between VII and VII–VIII in various intensity scales. In order to resolve the question, we have (re)analysed all available macroseismic data for the two historical events, collected readings from station bulletins, and analysed available historical seismograms. Macroseismic proxy for the local magnitude (MmR) was estimated on the basis of modelled radii of isoseismals V EMS and VI EMS using the regressions derived for a set of 12 earthquakes in NW Croatia and the neighbouring areas. Macroseismic magnitude was found to be the largest for the 1906 event (MmR = 5.3), followed by MmR = 5.1 for the 2020 quake. Considering the magnitudes computed after Wiechert seismograms from the Göttingen (GTT) station, and from the amplitude/period readings reported from the German stations JEN and HOH for the earthquake of 1906, as well as the magnitudes calculated from broad-band records of the GTTG station and the stations of the Croatian network for the event of 2020, a unified local magnitude of ML = 5.3 is found for both events. The magnitudes of the 1905 earthquake were consistently the lowest of the three. Taking the uncertainties into account, the events of 1906 and 2020 should be considered approximately equal in size. However, the strongest shaking in the centre of Zagreb was caused by the 2020 event. It occurred on the reverse North Medvednica boundary fault, while the macroseismic epicentres of earthquakes of 1905 and 1906 lie practically on the trace of the nearby strike-slip Kašina fault. That Kašina fault could have been the source of the 1906 earthquake is also hinted at by the elongated region of the strongest shaking along its strike

ESR Study of the Reaction Sites in the Barbituric Acid Derivatives

ESR spectroscopy has been used to analyse free radicals in the barbituric acid derivatives exposed to thermal H atoms or to excited Ar atoms. Reaction with both types of atoms leads to the same products, demonstrating that the most probable reaction sites in these molecules do not depend upon whether the chemicai or physicai type of energy is transferred to the molecules. In all the barbituric acid derivatives studied the reaction takes place at the 5-substituent of the compound. The reaction observed is either the loss of the substituent or a change in the substituent. The former reaction is observed in the pharmacologically inactive barbituric acid derivatives, the latter in the active ones

ESR Study of the Reaction Sites in the Barbituric Acid Derivatives

ESR spectroscopy has been used to analyse free radicals in the barbituric acid derivatives exposed to thermal H atoms or to excited Ar atoms. Reaction with both types of atoms leads to the same products, demonstrating that the most probable reaction sites in these molecules do not depend upon whether the chemicai or physicai type of energy is transferred to the molecules. In all the barbituric acid derivatives studied the reaction takes place at the 5-substituent of the compound. The reaction observed is either the loss of the substituent or a change in the substituent. The former reaction is observed in the pharmacologically inactive barbituric acid derivatives, the latter in the active ones

Racism - roots and recovery : creating and teaching a two-component introductory curriculum on unlearning racism

This study involves the responses of Salish Kootenai College students to racism

Tectonic Interrelation of the Dinarides and the Southern Alps

The study focuses on northwestern Croatia which, including the Zumberak (Zumberacka Gora), Medvednica (Zagrebacka Gora), Kalnik, Ivanscica, and Ravna Gora mountains, make a cross area of the Slovenian “Sava Folds”, Southern Alps, Mid-Transdanubian Zone, Tisia, and the Inner Dinarides. This is a complex structural region and cannot be attributed merely to one of the units. Therefore, a geotectonic interpretation is proposed which respects the diversification and multiple superposition of basinal and platform elements. This concept allows linkage of the Slovenian Trough with the Bosnian Zone and its southeastern prolongation as a major coherent tectonic unit overlain by different nappe elements. The possible linkage with the Budva Zone beneath the carbonate nappe is also discussed

Seizmičnost Hrvatske u 1989.godini i potres od 6. prosinca u blizini planine Kamešnice

The seismicity of Croatia and its surrounding areas in 1989 was analysed on the basis of the earthquake catalogue consisting of 361 earthquakes. Its completeness threshold was estimated to be MLC ≥ 3.0. Seismically the most active was the coastal part of Croatia, where the strongest earthquake in 1989 occurred on December 6 with the focus beneath the hill-sides of the Kamešnica Mt. The fault plane solution for this event indicates the presence of a tectonic stress-field directed approximately SW-NE, which is compatible with the assumed anticlockwise rotation on the Adriatic microplate around the pole in Northern Italy, and the associated subduction of the Adriatic plate under the Dinarides. The aftershocks of the Kamešnica Mt. event were numerous, with hypocenters at depth up to 20 km. Macroseismic investigations confirm the frequently observed fact that seismic energy is much more efficiently absorbed perpendicularly to the direction of the Dinaric belt than along it

Pregled nedavnih mjerenja mikroseizmničkoga nemira u Hrvatskoj na otvorenom terenu i u zgradama

The paper describes some recent applications of the measurements of ambient vibrations (microseismic noise) in Croatia. They include free-field measurements, as well as those done within buildings. Data obtained in the field at the studied localities are consistent with the properties of shallow geological structures known to exist there. In Zagreb, Horizontal-to-Vertical Spectral Ratios (HVSR) indicate thick alluvial cover (over 100 m) that gradually gets thinner towards the slopes of the Mt. Medvednica. A similar situation – on a smaller scale – is also encountered in Ston, where HVSR profiles reveal several tens of meters thick sedimentary cover over the bedrock which gets exposed at the Bartolomija hill. Analyses of records from Ston and Dubrovnik suggest that soil-building resonance must be seriously considered. Measurements in the buildings were analysed by a newly developed software package FREDA – a suite of Matlab routines. Based on tests on synthetic and real data it is concluded that spectral methods are in general more robust and less dependent on parameters of the algorithm employed, than time-domain analyses. Spectral algorithms are also better in resolving higher modes. Applications to real buildings proved that analyses of shaking induced by ambient vibrations in most cases lead to well constrained, reliable, and time independent estimates of frequencies and damping of the buildings’ vibrational modes for small excitation levels.Prikazani su rezultati i interpretacija nedavnih mjerenja mikroseizmičkog nemira u Hrvatskoj, kako onih na terenu, tako i u zgradama. Terenski podaci prikupljeni u Zagrebu, Stonu, Dubrovniku i na drugim lokacijama konzistentni su sa spoznajama o građi površinskih slojeva. U Zagrebu HVSR spektri ukazuju na postojanje debelih aluvijalnih naslaga debljine veće od 100 m koji se stanjuju s približavanjem Medvednici. Slična je situacija, samo na manjoj skali, i u Stonu, gdje se nekoliko desetaka metara duboka osnovna stijena sasvim približava površini na brdu Bartolomija. Analiza mjerenja u Stonu i Dubrovniku ukazuje na mogu}nost nastajanja rezonancije između tla i zgrade tijekom potresa. Mjerenja vibracija građevina uzrokovanih mikroseizmičkim nemirom analizirana su pomoću novorazvijenog programskog alata FREDA. Rezultati testova sa sintetičkim i realnim signalima ukazuju na to da su algoritmi bazirani na analizi spektara mnogo stabilniji u odnosu na analizu u prostoru vremena. Oni su bolji i u razlučivanju viših modova, te manje ovise o odabranim parametrima. Mjerenja u zgradama jeftina su i u velikoj većini slučajeva omogućuju pouzdane procjene vlastitih frekvencija te prigušenja vibracijskih modova pojedine građevine za oscilacije malih amplituda. Usporedbom izmjerenih dominantnih frekvencija osciliranja zgrade s vlastitim frekvencijama tla na kojem se ona nalazi, može se procijeniti opasnost pojave rezonancije zgrada-tlo za vrijeme potresa