The Ravne Fault is an actively propagating NW–SE trending dextral strike-slip fault in the Julian Alps of NW Slovenia, which has been responsible for two moderate sized earthquakes in the last ...decade. Strike-slip displacements on moderate-steep fault planes are responsible for the recent seismic activity that is confined to shallow crustal levels. The fault is growing by interaction of individual right stepping fault segments and breaching of local transtensional step-over zones. The fault geometry is controlled by the original geometry of the NW–SE trending thrust zone, modified by successive faulting within the fault zone. In the modern N directed maximum horizontal stress regime, the segmented fault is lengthening by active growth at the fault's NW end. The spatial distribution of earthquake clusters shows that activity on strike-slip segments and thrust faults is contemporaneous. Detailed analysis of the spatial pattern of earthquake events and surface fault geometries suggests that for earthquakes of similar magnitudes and similar fault kinematics, the deciding factor for whether an earthquake rupture will breach a step-over zone is the relationship between the lengths of individual neighbouring fault segments and fault separation distances in the step-over-zones. The Ravne Fault represents an example of a tectonic structure that lies in an area subjected to multiple tectonic events under different regional stress conditions. At epicentral depths, the fault system is accommodating recent strain along newly formed fault planes, whereas in upper parts of the crust the activity is distributed over a wider deformation zone that includes reactivated brittle thrust faults.
We reconstructed the seismotectonic setting of the area comprising the northeastern Friuli Plain and the Julian pre-Alpine border (NE Italy) by integrating geological and seismological data. The ...study area represents the junction between the SSE-verging polyphase thrust-front of the south-Alpine Chain and the NW–SE-trending strike-slip faults of the eastern Friuli–western Slovenia domain. Following a multidisciplinary approach, the 3D geometry of the Susans–Tricesimo thrust system was reconstructed through the elaboration of four geological cross sections derived from the interpretation of ENI industrial seismic lines. In a second step, the seismogenic volume of the central-eastern Friuli area was investigated through hypocentral distribution analysis: the seismic events of the latest 50 years (1976–1977 and 1978–2019 time intervals) were plotted on four NE-SW-oriented seriated sections together with the fault plane’s geometry. Through this procedure, we were able to investigate the relationship between the NW-SE-striking high-angle faults, which characterize the northern Julian pre-Alps, and the WSW-verging medium-angle reverse fronts located at the piedmont of the Friuli plain, which experienced NW-SE- to NNW-SSE-oriented compression starting at least from the Pliocene. In detail, we examined the involvement of these structures during the seismic sequences of May and September 1976, in terms of activation and/or interaction. The resulting seismotectonic model highlights the interplay between transpressive/strike-slip and reverse planes. In particular, this study suggests that Predjama and Maniaglia transpressive faults strongly control the stress release and likely played a fundamental role both during the 6 May (Mw 6.5) and 15 September (Mw 6.0) Friuli earthquakes.
Various geodetic and lidar measurements performed on the Triglav Glacier (Julian Alps, Slovenia) make it possible to study not only the extent of the glacier but also changes in its thickness and ...volume. These measurements also make it possible to calculate the geodetic mass balance of the glacier. Thickness and volume changes were calculated using glacier area measurements from 1952, 1975, and 1992, and annually between 1999 and 2016. The mean thickness decreased from 39.2m in 1952 to 2.45m in 2012. The maximum thickness decreased from 48.3 m in 1952 to 5.2 m in 2007. The mean specific mass balance was calculated for the area of 1 hectare that the glacier covered in 2016. From 1952 to 2016, the annual specific mass balance was −0.45m w.e.a−1.
Various ice bodies are an important source of paleoenvironmental data, and their study improves the understanding of present and future environmental conditions. Their changes are an important ...indicator of climate change. This special issue of Acta geographica Slovenica draws attention to the changing and disappearing cryosphere across the globe, with an emphasis on the southeastern Alps, and the necessity to conduct research in this field before the ice disappears forever. This paper briefly summarizes the current body of knowledge on glaciers, permafrost, cave ice, lake and river ice, and snow in the southeastern Alps, and it presents the contribution of Acta geographica Slovenica to this research and the main highlights of all five papers included in this special issue.
In the Vipava Valley (SW Slovenia), various types of mass movements occur in a geologically and geomorphologically diverse setting. These comprise various types of landslides, creep, and Quaternary ...slope deposits of carbonate blocks and recent scree deposits. A general geological setting is represented as Mesozoic carbonate overthrust on Paleogene flysch (alternations of mostly sandstones and marlstones), resulting in steep slopes and mass movements. Our study is based on the automatic classification of various litho-geomorphological units including slope deposits, alluvial deposits, steep carbonate cliffs, flysch, two carbonate plateaus, and Quaternary deposits, based on supervised Maximum Likelihood Classification. Several polygons were used for training in the broader valley area, and later, the method was applied to automatically classify the complete area into the abovementioned six units. For input layers, we used data for elevation, slope, terrain ruggedness index (TRI), and curvature. Results show that generally, the method is suitable for classification of the litho-geomorphological units including slope deposits. However, comparison with a more detailed map, comprising mapped various mass movements indicated that the method correctly predicts high Trnovo plateau carbonates, steep carbonate slopes, translational carbonate blocks, and fossil rock avalanche deposits, and alluvial deposits, but is not able to clearly distinguish between flysch and more recent slope deposits of gravel and breccia due to their similar elevation, TRI, and slope values. The Slano blato mudflow and Stogovce landslide are not recognized. Therefore, this automatic classification can be carefully used to create a guidance map of general occurrences of litho-geomorphological units including slope deposits before going to the field, with the aim of delineation of slope deposits so they can be further studied in detail later in the field. However, such a map cannot be used as a direct substitute map for the geological and geomorphological map obtained in the field due to impossibility in distinguishing among the units with the same properties (elevation, slope, and TRI values).
The study focuses on the spatial organization of seismicity and the relation between fracture pattern and earthquakes in the Friuli (north-eastern Italy) and western Slovenia seismic regions. The ...structural setting is characterized by a complex structure resulting from the superposition of several tectonic phases that generated NW-SE trending Dinaric faults and about E-W trending Alpine faults. The upper crust is characterized by lithological and mechanical heterogeneities. The fractal analysis shows that, in general, the seismicity only partially fills a plane. Only in a few cases, the earthquakes distribute on planar structures. The orientation of planes that fit through the hypocentres shows a different disposition at the two depth intervals analysed. The shallower interval (0–10 km) is characterized by planes with highly variable orientations. The spatial seismicity is investigated in the context of a general damage model, represented by the crack density distribution. The results evidence that the seismicity appears mostly located along sharp transition areas from low crack density to higher crack density, i.e., from zones of low damage to zones of intermediate damage. These zones are characterized by high heterogeneity due to the superposition of different tectonic phases and by the maximum interference between Dinaric and Alpine domains. The orientation of the planes fitting the seismicity at 10–20-km depth appears less dispersed, coinciding with the trend of Dinaric sub-vertical faults in the northern and eastern parts of the study area, and with Alpine low-angle faults in the western and southern parts.
In the southern Julian Alps we described two communities whose tree layer is dominated by species from the genus
and noted two successional stages in the overgrowing of abandoned agricultural land ...(pastures, hay meadows). In the secondary succession on former subalpine pastures above the alp Planina Razor und under the Breginjski Stol ridge, where potential natural vegetation consists of subalpine beech forest, dwarf pine has been overgrown with mountain ash (
) whose stands are classified into the new association
. Whitebeam (
) has established itself on steep former hay meadows in the belt of altimontane beech forests under Mts. Jalovnik and Krikov Vrh, on gullied slopes on mixed geological bedrock dominated by chert, and these stands are classified into the association
. While occupying only small areas these two pioneer stages, as the sites of some rare or protected species, are nevertheless important biotopes and play a vital role in protection against avalanches.
In order to investigate stream water, spring waters and water from a borehole facies, weathering processes, residence times and average recharge altitudes in the Radovna River valley were analysed ...for their concentrations of dissolved Ca
2+
, Mg
2+
, K
+
, Na
+
, HCO
3
−
, Cl
−
, NO
3
−
, SO
4
2−
and for the isotope compositions of hydrogen, oxygen and dissolved inorganic carbon (DIC). All water samples show a Ca
2+
–HCO
3
−
water facies with low contents of K
+
, Na
+
, Cl
−
, NO
3
−
and SO
4
2−
. Water–rock interaction and carbonate weathering are the significant contributors to water geochemistry. Analysis of the water chemistry indicates that waters drain a monolithological terrain and non-anthropogenically influenced watershed. The
δ
2
H and
δ
18
O values are seasonally dependent on the snowmelt, precipitation and evaporation. The average recharge altitudes for all sampling locations are between 1120 and 2130 m. The average residence time for the stream water is 2.4 years and for karst springs 1.2 years. The
δ
13
C
DIC
values in all samples are influenced by dissolution of carbonates, degradation of organic matter and by equilibrium with atmospheric CO
2
. All geochemical and isotope analyses show changes in stream water in the downstream direction and are highly dependent on the inflow of karstic spring. Based on hydrogeological mapping, geochemical and stable isotope results, a conceptual hydrogeological model of the Radovna system, in which karstic and alluvial aquifers are in contact, was determined.
The Triglav Glacier in the Julian Alps and the Skuta Glacier in the Kamnik-Savinja Alps are among the south-easternmost glaciers in the Alps. Historical data show that ice masses are undergoing mass ...loss as the overall climate warms. Glacier ice and cave ice contain a wealth of paleoclimatic information, and rapid sampling is needed if any such information is to be saved before the ice is completely melted. We present the first comprehensive geochemical and water isotope data from glacier ice, meltwater, spring water, and cave ice in the Mount Triglav area and glacier ice from the Skuta Glacier. The samples primarily reflect the initial precipitation signal that has been greatly modified by the input of local CaCO3-rich dust with lesser amounts of marine aerosol and vegetation debris.
The Alpine–Dinaric Transition Zone in Slovenia comprises the fold and thrust belt of the Southern Alps (South Karawanken Range, Julian Alps), Slovenian Basin and the Dinarides. The Slovenian Basin ...located between the Julian and Dinaric carbonate platforms evolved during Middle Triassic time and remained in a deep marine setting till the Late Cretaceous. The thermal history of Carboniferous to Eocene rocks in that area was investigated using vitrinite reflectance (VR) data, apatite fission track analysis and numeric 1D basin modeling. The study shows that maturity patterns are mainly controlled by the thickness of Upper Cretaceous to Eocene flysch deposits, filling the accommodation space. Therefore the thermal overprint reaches a maximum (>4%Rr) in Triassic to Cretaceous sediments of the Slovenian Basin and decreases towards the north and south. Minor sedimentary burial of the Adriatic Carbonate Platform and the Julian Alps results in a lower thermal overprint (<1.5%Rr). The thickness of flysch sediments was about 5km in the area of the Sava Folds, but significantly higher in the central part of the Slovenian Basin. Heat flow during maximum burial in Eocene time was in the order of the global average (60mW/m2). Cooling of Paleozoic and Mesozoic sediments below 110°C occurred between Late Eocene and Early Oligocene times in different parts of the study area. Nappe stacking due to Early (Dinaric) and Late Cenozoic (Alpine) compressional tectonics did not influence the thermal maturity of the sediments.
•Maturity of Mesozoic rocks in the Alpine-Dinaric transition zone is controlled by thickness of Cretaceous to Paleogene rocks.•Highest maturity is observed in the Slovenian Basin.•High vitrinite reflectance in Cretaceous sediments (up to 4.4 %Rr) is due to very thick Paleogene flysch sediments.•Uplift and cooling occurred between Late Eocene and Mid Oligocene time.•Thrusting postdates maturation.
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