In this study, we propose an analysis of the earthquake clusters that occurred in North-Eastern Italy and western Slovenia from 1977 to today. Given a mainshock generating alarm in the population, we ...are interested in forecasting if a similar magnitude earthquake will follow. We classify the earthquake clusters associated with mainshocks of magnitude Mm into two classes: if the strongest aftershock has a magnitude ≥Mm-1 (swarms or large aftershock seismic sequences) as type A, otherwise (smaller aftershocks seismic sequences) as type B. A large aftershock following a main shock can cause significant damages to already weakened buildings and infrastructures, so a timely advisory information to the civil protection is of great interest for effective decision-making. For the first time, we applied to a new catalogue a pattern recognition algorithm for cluster type forecasting that we developed for all Italy (Gentili and Di Giovambattista, 2017). Thanks to the lower completeness magnitude of the local OGS catalogue, compared to the national one, and to a new version of the algorithm, we were able to lower the threshold of the clusters mainshocks magnitude from 4.5 to 3.7. The method has been validated by rigorous statistical tests. We tested the algorithm on the 1976 highly destructive earthquake cluster (mainshock magnitude 6.5 – the strongest in the last 80 years in the region) and we retrospectively forecasted it as an A cluster. Successful results were obtained also on other three smaller earthquake clusters in 2019.
•We study the occurrence of large aftershocks for NE Italy – W Slovenia earthquakes.•NESTORE pattern recognition approach estimates of the probability of occurrence.•We use features based on the ongoing seismic activity after the mainshock.•We retrospectively forecast strong aftershocks for 1976 Friuli earthquake.
SUMMARY
Western Slovenia is part of an actively deforming region accommodating anticlockwise rotation of Adria and its continuous collision with Eurasia. The geometry of the active faulting system in ...this plate boundary is not well defined. In this study, detailed analysis of earthquake activity was performed with relocation of earthquakes in the period between 2006 and 2017. With inspection of the waveform data, slight temporal clustering of activity was observed. To increase the detection rate of microearthquakes we used a matched filter detection algorithm method. Templates of earthquakes were created and a database of continuous waveform data within the period 2006–2017 was investigated. As a result, high temporal correlation allowed us to identify swarms and earthquake sequences that affected the active fault system in the study region.
Relocated seismicity allowed us to constrain the geometry of 5 nearly parallel faults, namely: Ravne, Idrija, Predjama, Selce and Raša faults. All these faults do have an expression in the geomorphology and reach a seismogenic depth of up to 20 km. Vertical and along strike extents of these active faults can favour earthquakes of moment magnitude equal to 7 or larger. The most recent large earthquake that occurred in this region is the 1511 earthquake with a magnitude 6.8.
The leading fault in the system being the Idrija right-lateral strike-slip fault, experiences earthquake activity from 5 to 20 km on its northern segment, while on its southern segment no earthquake activity is detected over the decade of observations. We show that the interseismic loading on the southern segment of Idrija fault is likely unclamping the locked adjacent faults promoting the observed bursts of seismicity. Moreover, in 2009 the Predjama fault accommodated a sudden increase of the surface deformation at the extensometer accompanied by a simultaneous swarm activity at its seismogenic depth. This behaviour might correspond to velocity strengthening and weakening processes taking place at both the surface and depth terminations of a locked vertical fault. These processes can be driven by a slow-slip event on the deeper part of Idrija fault that would generate a temporary acceleration of the interseismic loading rate along with a change within the fluid circulation.
Spatial models are an effective tool for determining potential rockfall source, transit and deposit areas. The reliability of the final rockfall modelling results depends on the quality of the input ...data, which is mostly based on the digital elevation model (DEM). The spatial resolution of the DEM holds key information about the main morphological properties of the surface, which is crucially important when modelling this kind of geomorphological phenomenon. Therefore, this article studies the influence of DEM spatial resolution on the modelling of rockfall source, transit and deposit areas. Modelling was carried out at five different DEM spatial resolutions available for Slovenia (1 m, 5 m, 12.5 m, 25 m and 100 m). Rockfall source areas were identified using a geomorphometric approach based on a high resolution DEM and a geographical information system. Rockfall transit and deposit areas were modelled using the Conefall computer program, which is designed to estimate potential rockfall risk areas. The area of study was the municipality of Vipava (107.4 km2) in Slovenia, EU. A spatial resolution of 1 m was chosen as a reference layer to which all modelling results of the other spatial resolutions were compared. Validation of modelling included rockfall source area comparison with orthorectified aerial images and location collection of silent witnesses (rock deposits) in the field for estimating maximum runout zones. The modelling results indicate that a spatial resolution of 1 m is the most suitable for modelling on a local scale; resolutions of 5, 12.5 and 25 m can be used for modelling on a regional scale (depending on the purpose of the modelling results); and a resolution of 100 m should not be used for rockfall modelling. Major differences between spatial resolutions can be observed when modelling rockfall source areas, i.e. in areas with the most diverse topography, while in deposit areas the observed differences are smaller due to the less rugged surface.
•The influence of the spatial resolution of the digital elevation model was observed at five different spatial resolutions.•Deviations between modelling results are greater for rockfall source areas than for rockfall runout zones.•High spatial resolutions (1 m) should be used for modelling on a local scale.•Lower spatial resolutions (5 m, 12.5 m and 25 m) can be used for modelling on a regional scale.•Spatial resolution 100 m should not be used for modelling rockfalls.
In this scientific article, the historical counterculture of Nature Worshippers in Western Slovenia is explained with emphasis on social functions of their oral tradition i.e. tales. The latter, ...recorded and published primarily by Pavel Medvešček – Klančar, were an important part of Nature Worshippers' educational concept. Cosmogonic myths, etiological explanations, animal tales and anecdotes introduced young children to the ethical norms and spiritual life of the community and played an important role in preserving the identity of Nature Worshippers. Detailed contextual and sociological analysis of Nature Worshippers' tales focuses on Pavel Medvešček's 1991 collection On a Red Cloud a Vineyard Grows and his 2015 book From the Invisible Side of the Sky. Revealed Secrets of the Old Belief.
Suspended matter (SM) plays an important role in the transport of mercury (Hg) in aquatic systems. Information about Hg-species in this material is crucial to understand risk potential, especially ...for Hg methylation and bioavailability. In the Idrija Hg mine (Slovenia) cinnabar (α-HgS) was mined and processed for centuries. These activities caused contamination of the Idrijca river system by dumping of ore roasting residues, as well as atmospheric Hg deposition in soils attributed to excessive Hg emissions from the roasting plant. Cinnabar is the dominant Hg-species in the coarse-grained sediments of the Idrijca river where Hg methylation is generally low, whereas natural-organic-matter-bound Hg (NOM-bound) has caused intense Hg methylation in the Gulf of Trieste (GT), the final sink for Hg released from the Idrijca catchment. Hydrology of the Idrijca river is characterized by high discharge events during heavy rains and snowmelt, which transports large amounts of SM towards the GT. However, the dominant Hg-species transported in SM and their specific source under varying hydrological conditions is largely unknown, yet crucial to predict future transport of bioavailable Hg forms from the mining area to the GT.
We analyzed Hg concentrations and Hg-species (Hg-thermo-desorption) in SM and different grain size fractions of soils from the Idrijca catchment to evaluate changes in solid phase Hg-species under low and high flow conditions. Concentrations of dissolved Hg did not change significantly during low and high flow (median: 21.3–28.1 ng L−1, respectively). Hg concentrations in SM in tributaries decreased with distance (∼30 km) from the mine from 32.7 to 0.47 mg kg−1 related to Hg concentrations in fine particulate soil fractions (0.45–20 μm) which ranged from 56.2 to 0.53 mg kg−1. Hg speciation in SM was dominated by NOM-bound Hg forms at low flow (median: 95.5%) which decrease during high flow conditions (median: 53.8%) attributed to increased mobilization of cinnabar from riverbanks and mine residues. Our results show that aqueous Hg transport in the Idrija mining area is dominated by heavy rain events and mobilization of NOM-bound Hg from soils indicating that the frequency of heavy rain events will control transport of bioavailable Hg to the marine environment.
•Idrija-soils are the main source of bioavailable mercury for the aquatic system.•Organically-bound Hg forms are transported as river-suspended matter.•Erosion of coarse-grain fractions increase the relative abundance of cinnabar.•Mercury speciation is grain-size dependent.•Weather conditions and hydrology predominantly control mercury species distribution.
In Slovenia, rainfall-induced landslides lead to considerable damages, even causing human losses. In order to reduce the impact of this kind of landslide, several researchers analyzed ...rainfall-induced landslides in this country, but to date, no rainfall thresholds have been developed for a landslide warning system at national scale. In this paper, the definition of rainfall thresholds for rainfall-induced landslides in Slovenia is presented. The thresholds have been calculated by collecting approximately 900 landslide data and the relative rainfall amounts, which have been collected from 41 rain gauges. To define the thresholds, an existing procedure characterized by a high degree of objectiveness has been used. This approach is based on a software that was developed for a test site with very different characteristics (Tuscany, central Italy). At first, a single national threshold has been defined; subsequently, the country was divided into four zones, on the basis of the major river basins. The effectiveness of the thresholds has been verified by the use of several statistical parameters and it resulted in quite good performances, even if with some uncertainties, probably due to the quality of the available data. Besides the setting of a threshold system, usable for civil protection purposes at national scale, an additional outcome of this work was the possibility of applying, with good results, a methodology defined for another region, therefore testing its degree of exportability in different settings.
•We study eight seismicity populations with the Shannon entropy and fractal analysis.•The seismicity sets are characterized by fluctuations of entropy and fractal dimension.•Aftershock sequences are ...characterized by a marked decrease of the Shannon entropy.•Entropy and fractal fluctuations are interpreted as variations of crustal strain energy.
The spatio-temporal evolution of eight seismicity populations, preceding and following moderate earthquake sequences occurred in NE-Italy and W-Slovenia, are investigated by means of the normalized Shannon entropy and the fractal dimension. Three phases are recognized in the temporal seismic series. The period preceding the mainshock is characterized by oscillations of the Shannon entropy around a nearly constant level and by fluctuations of the fractal dimension. The phase of mainshock and aftershock sequences is characterized by a significant decrease of the Shannon entropy. A simultaneous marked decrease of the fractal dimension is observed in five cases. After the sequence, the entropy recovers the nearly constant trend before the mainshock and the fractal dimension is characterized by fluctuations. We interpreted the fluctuations of the normalized Shannon entropy and the fractal dimension caused by the coupling between the stress field and the mechanical heterogeneities of the crust that results in spatial and temporal fluctuations of the strain energy.
Upper Permian and lowermost Triassic strata of the Masore section in western Slovenia have been restudied by means of bio- and lithostratigraphy. This section is mainly characterized by a carbonate ...succession of the Bellerophon Formation deposited in a shallow marine ramp environment that was located in the western part of the Paleotethys. The Permian-Triassic boundary (PTB) transition is marked by laminated microbialites – stromatolites interpreted to reflect a deeper ramp environment. The conodont elements recovered enabled the recognition of the Hindeodus praeparvus Zone of the uppermost Permian (Upper Changhsingian) in the Bellerophon Formation. Gondolellids are documented in the PTB transitional interval with microbial microfacies, whereas the Isarcicella isarcica Zone (Lower Griesbachian, Lower Triassic) is recognized in the tectonically separated Werfen Formation just above the microbial microfacies part of the section. The lowermost part of the microbialites is characterized by Late Permian species of foraminifers indicating that at least this part of the section is still Upper Permian.
•The Masore section in Slovenia has been restudied.•The PTB transition is marked by laminated microbialites – stromatolites.•Three conodont faunas are recognized based on Clarkina, Hindeodus and Isarcicella.•Abundant and diverse Changhsingian foraminifers are documented.•The Masore area was located in the western Paleotethyan carbonate ramp-like edge.
In some rainfall-triggered landslides, intensity-duration thresholds can have limited prediction ability; therefore, investigation of alternative approaches that can be used for temporal prediction ...of rainfall-induced landslides is needed. This paper presents a methodology for predicting rainfall-induced shallow landslides based on a lumped conceptual hydrological model. The production storage level during the rainfall event and the rainfall sum during the event are used for landslide prediction. Based on these two hydro-meteorological variables a threshold is defined that could be used for rainfall-induced landslides prediction as part of an early warning system. The presented methodology is tested using the meso-scale Selška Sora River catchment case study in western Slovenia where 20 active landslides from the Slovenian National Landslide Database are used to calibrate and evaluate the methodology performance. The results are compared to three different (i.e. local, regional, and global) intensity-duration thresholds. The results of the presented approach are superior in terms of several goodness-of-fit criteria compared to tested local and global ID thresholds. Because only daily rainfall, evapotranspiration, and discharge data are needed to calibrate the selected hydrological model and only daily rainfall and evapotranspiration to run the model, the presented approach could also be useful for data-scarce areas where detailed physically based landslide prediction models that require many data cannot be constructed. Moreover, we have also derived the probabilistic version of the proposed threshold for triggering of shallow landslides using copula functions.
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