Search Results (30)

This paper presents a case study of an unreinforced masonry building in central Zagreb, which sustained moderate damage during the 2020 earthquakes. Situated within the Lenuci Horseshoe—a planned urban and landscaped space integral to Zagreb’s historic Lower Town—the building is part of a significant urban achievement, reflecting the city’s development from the late 19th to the early 20th century. The study explores the architectural and historical context of the building, its design features, and its role within Zagreb’s broader urban and cultural heritage, highlighting its value as a case study in balancing preservation and functional reuse. A multidisciplinary approach, including architectural documentation, archival research, laser scanning, damage analysis, and nonlinear modeling using 3Muri software, was employed to comprehensively assess its seismic behavior. Furthermore, the study examines retrofitting strategies that harmonize structural safety with cultural heritage preservation within the Croatian context. Full article

Background/Objectives: Previous works on the epidemiology of pediatric trauma during the COVID-19 lockdown observed a decrease in pediatric surgical emergency consultations and fracture referrals. None of those works describes a unique situation in which there is the coexistence of another opposing factor, like an earthquake, that influences the number of injured children’s referrals. Therefore, this study aimed to investigate the influence of earthquakes during the COVID-19 lockdown on pediatric injury pattern referrals at a tertiary care hospital in a urban setting. Methods: A retrospective single-center case-control study comprised a time interval at the time of the COVID-19 lockdown, starting with a day when the biggest earthquake happened and finishing at the end of the confinement period in Zagreb, Croatia (22 March–27 April 2020). The control group comprised the identical time interval in 2019. We identified all successive pediatric trauma patients referred to the Pediatric Emergency Department. Demographics and leading injury characteristics were analyzed. Results: We analyzed data from 1166 patients. In the case group, the median age was lower than in the control group but without gender differences. We detected a decrease in Pediatric Emergency Department referrals and a reduced proportion of pediatric trauma patients in the case group. Additionally, the proportion of shoulder/elbow injuries and head injuries was higher, and the proportion of foot/ankle injuries was lower in the case period than in the control period. Conclusions: Earthquakes during the COVID-19 lockdown changed the pattern of pediatric injuries. These data can be used to restructure health resources during similar conditions to provide optimal health care to children. Full article

Despite significant scientific and technological advancements in earthquake engineering, earthquakes continue to cause widespread destruction of the built environment, often resulting in numerous fatalities and substantial economic losses. Southeastern Europe, which includes Croatia, is part of the Mediterranean–Trans-Asian high-seismic activity zone. This area has recently experienced a series of earthquakes which had severe consequences for both populations and economies. Notably, the types of buildings that suffered significant damage or collapse during these events still constitute a large portion of the building stock across the region. The majority of residential buildings in Croatia and neighboring areas was constructed before the adoption of modern seismic standards, indicating that a considerable part of the building stock remains highly vulnerable to earthquakes. Therefore, the main goal of this study is to identify the building types which significantly contribute to seismic risk, with the focus on Zagreb as Croatia’s largest city and the capital; collect the documentation on the structural systems and occupancy; analyze the data; and carry out the initial vulnerability assessment. This serves as a first step toward developing a new exposure and vulnerability model for Zagreb that is also applicable to all urban areas in the region with similar building stock and seismotectonic conditions. Full article

The 2020 Zagreb earthquake caused extensive damage to historically significant buildings, including the Cathedral of the Assumption of Mary, a key monument of Croatian cultural heritage. The earthquake rendered the cathedral unsafe due to significant damage to its towers and numerous cracks in its vaults and walls. Urgent measures were necessary to ensure safety and facilitate planned reconstruction and strengthening efforts. A specialised scaffolding design was developed to support inaccessible and unstable areas, involving over 1000 tonnes of steel. This paper details the structural concepts and specific scaffolding design implemented for the urgent restoration and seismic retrofitting of Zagreb Cathedral, ensuring it meets high earthquake resistance requirements. Full article

The city of Zagreb, the national capital and economic hub of Croatia, is situated in a seismically active region and hosts a significant array of historical buildings, from the medieval to Austro-Hungarian periods. These buildings possess varying but generally high degrees of vulnerability to seismic loading. This was highlighted in the Zagreb earthquake of 22 March 2020, emphasizing the need for seismic retrofitting in order to preserve this architectural heritage. In this paper, the seismic capacity of one such unreinforced masonry building is considered through a number of analysis methods, including response spectrum, pushover, and out-of-plane wall failure analyses. Given the advantages and disadvantages of the individual methods, their applicability and value in a seismic analysis is considered. Ambient vibration measurements before and after the Zagreb 2020 earthquake, used for model calibration, are also presented. Conclusions are drawn from each individual analysis and later compared. In conclusion, no single analysis method considers all relevant failure modes, and a combination of nonlinear static or dynamic analysis and out-of-plane analysis is recommended. Due to the large volume of the material, it is published in two parts, with ground motion record selection, dynamic analysis, and a comparison of the results published in part two. Full article

We study the sub-ionospheric VLF transmitter signals recorded by the Austrian Graz station in the year 2020. Those radio signals are known to propagate in the Earth-ionosphere waveguide between the ground and lower ionosphere. The Austrian Graz facility (geographic coordinates: 15.46°E, 47.03°N) can receive such sub-ionospheric transmitter signals, particularly those propagating above earthquake (EQ) regions in the southern part of Europe. We consider in this work the transmitter amplitude variations recorded a few weeks before the occurrence of two EQs in Croatia at a distance less than 200 km from Graz VLF facility. The selected EQs happened on 22 March 2020 and 29 December 2020, with magnitudes of M_w5.4 and M_w6.4, respectively, epicenters localized close to Zagreb (16.02°E, 45.87°N; 16.21°E, 45.42°N), and with focuses of depth smaller than 10 km. In our study we emphasize the anomaly fluctuations before/after the sunrise times, sunset times, and the cross-correlation of transmitter signals. We attempt to evaluate and to estimate the latitudinal and the longitudinal expansions of the ionospheric disturbances related to the seismic preparation areas. Full article

The largest earthquake (Mw 6.4) in northwestern Croatia ruptured the faults near the city of Petrinja on 29 December 2020, at 11:19 UTC. The epicenter was located ~3 km southwest of Petrinja, ~40 km southeast of Zagreb, the capital of the Republic of Croatia. Here we investigated the geometric and kinematic properties of the 2020 Mw 6.4 Petrinja earthquake using a joint inversion of ascending and descending interferograms from three tracks of Sentinel-1 Single-Look Complex (SLC) images. The coseismic and early postseismic surface displacements associated with the Petrinja earthquake were imaged using standard DInSAR and SBAS time-series InSAR methods, respectively. The distributed slip model was inverted based on the ground surface displacements with maximum slip patch in 5 km depth. The early postseismic deformation occurred on the northwestern extent of coseismic slip, and it cannot be well modeled by the coseismic model. We thus suggested that the postseismic deformation was caused by a combined effect of the postseismic afterslips and aftershocks occurring in this area. Based on the inverted slip model, we calculated the Coulomb stress change in the region, and found a good correlation between positive Coulomb failure stress ∆CFS and the distribution of aftershocks. Based on these results, we identified which faults are more active, and then better estimated the seismic hazards in the region. Full article

In this article we present a space–time epidemic-type aftershock sequence (ETAS) model for the area of Hungary, motivated by the goal of its application in insurance risk models. High-quality recent instrumental data from the period 1996–2021 are used for model parameterization, including data from the recent nearby Zagreb and Petrinja event sequences. In the earthquake-triggering equations of our ETAS model, we replace the commonly used modified Omori law with the more recently proposed stretched exponential time response form, and a Gaussian space response function is applied with a variance add-on for epicenter error. After this model was tested against the observations, an appropriate overall fit for magnitudes $M\ge 3.0$ was found, which is sufficient for insurance applications, although the tests also show deviations at the $M=2.5$ threshold. Since the data used for parameterization are dominated by Croatian earthquake sequences, we also downscale the model to regional zones via parameter adjustments. In the downscaling older historical data are incorporated for a better representation of the key events within Hungary itself. Comparison of long-term large event numbers in simulated catalogues versus historical data shows that the model fit by zone is improved by the downscaling. Full article

The differential interferometric synthetic aperture radar (DInSAR) method is based on phase variation between the complex value of pixels of timely separated scenes in interferometric SAR pairs. This phase variation has five components: surface topography, curvature of planet’s surface, terrain displacement, volume scatterers, and atmospheric propagation effects. The terrain displacement is the main product of the DInSAR method, while the last two effects are unpredictable and bring inaccuracy into the terrain displacement measurements. In this work, the propagation conditions in the troposphere and ionosphere were studied during two DInSAR measurements examining the Zagreb 22 March 2020 earthquake, with terrain raising of up to +3 cm at the epicenter. For the troposphere, the vertical profile of the modified refraction index, which incorporates local curvature change with height, was reconstructed using aerological balloon probing data. Ionospheric conditions were determined based on total electron content (TEC) calculated from the Croatian positioning system (CROPOS) and global navigation satellite system (GNSS) reference stations’ measurements. One of the DInSAR measurements was conducted in unfavorable tropospheric refractive conditions, which resulted in an overall bias of −2 cm. The variability of propagation conditions indicates the need for examining the atmospheric propagation effects when calculating terrain displacements using the DInSAR method. The results of DInSAR indicate slight displacements, comparable with the amplitude of atmospheric variations, and should therefore be approached with caution. Full article

Following the Zagreb earthquake in March of 2020, a destructive 6.2 magnitude earthquake struck Croatia again in December of 2020. The Sisak-Moslavina county suffered the most severe consequences; many historical and cultural buildings were badly damaged. In the education sector, 109 buildings were damaged. One such building is the case study of this research. The heritage-protected building of the First Primary School in Petrinja is an unreinforced masonry structure, constructed using traditional materials and building techniques. The historical background of the building and the results of the post-earthquake assessment are presented. A numerical calculation of three strengthening methods was performed in 3Muri software: FRCM, FRP, and shotcrete. Non-linear pushover analysis was performed for each model. Finally, the strengthening methods are compared based on the achieved earthquake capacity, cost, and environmental impact. Full article

After a long period of no excessive ground shaking in Croatia and the region of ex-Yugoslavia, an earthquake that woke up the entire region was the one that shook Croatia on 22 March 2020. More than 25,000 buildings were severely damaged. A process of reconstruction and strengthening of existing damaged buildings is underway. This paper presents proposed strengthening measures to be conducted on a cultural-historical building located in the city of Zagreb, which is under protection and located in zone A. After a detailed visual inspection and on-site experimental investigations, modeling of the existing and strengthened structure was performed in 3Muri. It is an old unreinforced masonry building typical not only for this region but for relevant parts of Europe (north, central, and east). The aim was to strengthen the building to Level 3 while respecting the ICOMOS recommendations and Venice Charter. Some non-completely conservative concessions had to be made, to fully retrofit the building as requested. The structural strengthening consisted of a series of organic interventions relying on—in the weakest direction—a new steel frame, new steel-ring frames, and FRCM materials, besides fillings the cracks. Such intervention resulted in increasing the ultimate load in the X and Y directions, respectively, more than 650 and 175% with reference to the unstrengthened structure. Good consistency was obtained between the numerical modeling, visual inspection, and on-site testing. Full article

The Međimurje region (North Croatia), situated between the Drava and Mura rivers with a slightly elevated hilly area, can be generally characterized as a low-seismicity area. However, macroseismic observations from historical and recent earthquakes indicate that some localities in this region are more prone to damage than others. Significant damage and the observed higher intensities in the Međimurje region after the historical earthquakes of 1738 M_Lm5.1 (Međimurje) and 1880 M_L6.3 (Zagreb), and events that occurred in the instrumental era, 1938 M_L5.6 (Koprivnica), 1982 M_L4.5 (Ivanec), and the most recent 2020 M_L5.5 Zagreb and 2020 M_L6.2 Petrinja earthquakes, point to the influence of local site effects. There is a reasonable indication that these earthquakes involved several localized site effects that could explain the increased intensity of half a degree or even up to one degree at certain localities compared to macroseismic modeling for rock condition. To better understand the influence of local site effects in the Međimurje region, the single-station microtremor Horizontal-to-Vertical Spectral Ratio (HVSR) method for subsurface characterization was used. Based on individual measurements, microzonation maps were derived for the Međimurje region to better understand the behavior of ground motion and the influence of local site conditions in comparison to macroseismic intensities and past damage observations. Several local site effects could be interpreted as a main contribution to site amplification and resonance effects due to variations in deep soft-deposit thicknesses overlayed on hard deposits and directional variations in topographical areas that could localize earthquake damage patterns. Correlations of microtremor analysis with intensity observations from historical earthquakes as well with recent earthquakes could help to distinguish local site zones prone to the possible occurrence of higher earthquake damage from nearby and distant earthquakes. Full article

In 2020, Croatia was struck by two catastrophic earthquakes, resulting in more than 50,000 damaged structures. The majority of these are masonry buildings, but there are a number of reinforced concrete structures that suffered moderate to extensive damage. In this paper, the seismic condition assessment and upgrading of existing RC structures are presented with a case study building in Zagreb. The assessment procedure includes initial visual inspection, rapid preliminary evaluation, detailed in situ measurements, and non- and semi-destructive methods. New technologies were applied and followed by numerical modeling and verifications. Strengthening proposals are made that respect owner needs and the needs for the energy retrofitting of the existing RC building. As the integrated approach should be respected in the renovation of existing buildings, this case study can represent an example of good practice in the process of seismic and energy retrofitting. Full article

After the Zagreb earthquakes in March 2020, around 25,000 buildings were estimated damaged, most of them being in the historic city center. This fact is not that surprising since most of the city center buildings are unreinforced masonry structures that have not been assessed in quite some time and usually no retrofitting methods were ever applied. The rapid post-disaster assessment began the same day after the first earthquake occurred. Through mostly visual assessment methods, the basic idea is to identify the safety and usability of buildings in general. This type of assessment was also conducted in one of the oldest Croatian cultural institutions, Matica Hrvatska. It is a building of great historical significance and cultural value, as is most of the city center. Accordingly, this building was constructed with no consideration given to seismic events and with the use of traditional materials and building techniques. In the scope of this paper, urgent actions that were taken are shown with problems and challenges that occurred. Furthermore, the decision-making process after an earthquake is elaborated. In addition, a numerical model is developed in 3Muri software for structural modeling. A non-linear static pushover analysis is performed, and possible failure mechanisms are examined. Furthermore, real-life damage is compared to the software results, and a conclusion process of the building’s usability is explained. In the end, the results obtained are analyzed and conclusions regarding the efficiency of the used software are drawn. Full article