Summary On 29 December 2020, a shallow earthquake of magnitude Mw 6.4 struck northern Croatia, near the town of Petrinja, more than 24 hours after a strong foreshock (Ml 5). We formed a reconnaissance team of European geologists and engineers, from Croatia, Slovenia, France, Italy and Greece, rapidly deployed in the field to map the evidence of coseismic environmental effects. In the epicentral area, we recognized surface deformation, such as tectonic breaks along the earthquake source at the surface, liquefaction features (scattered in the fluvial plains of Kupa, Glina and Sava rivers), and slope failures, both caused by strong motion. Thanks to this concerted, collective and meticulous work, we were able to document and map a clear and unambiguous coseismic surface rupture associated with the main shock. The surface rupture appears discontinuous, consisting of multi-kilometer en échelon right stepping sections, along a NW-SE striking fault that we call the Petrinja-Pokupsko Fault (PPKF). The observed deformation features, in terms of kinematics and trace alignments, are consistent with slip on a right lateral fault, in agreement with the focal solution of the main shock. We found mole tracks, displacement on faults affecting natural features (e. g. drainage channels), scarplets, and more frequently breaks of anthropogenic markers (roads, fences). The surface rupture is observed over a length of ∼13 km from end-to-end, with a maximum displacement of 38 cm, and an average displacement of ∼10 cm. Moreover, the liquefaction extends over an area of nearly 600 km² around the epicenter. Typology of liquefaction features include sand blows, lateral spreading phenomenon along the road and river embankments, as well as sand ejecta of different grain size and matrix. Development of large and long fissures along the fluvial landforms, current or ancient, with massive ejections of sediments is pervasive. These features are sometimes accompanied by small horizontal displacements. Finally, the environmental effects of the earthquake appear to be reasonably consistent with the usual scaling relationships, in particular the surface faulting. This rupture of the ground occurred on or near traces of a fault that shows clear evidence of Quaternary activity. Further and detailed studies will be carried out to characterize this source and related faults in terms of future large earthquakes potential, for their integration into seismic hazard models.
We present a geomorphological map on a scale of 1:15,000, with detailed sedimentological descriptions, and a general relative spatio-temporal depositional reconstruction of Quaternary sediments in the Planica-Tamar Valley (NW Slovenia). After the Last Glacial Maximum, the retreating Quaternary glacier deposited large amounts of glacial sediments. These were followed by Holocene sediments, which differ in their sedimentological characteristics, transport mechanisms, and morphology. These sediments are deposited as sedimentary bodies with complex depositional geometries. They form areas of active, partly active, and inactive sedimentation in response to local/regional climate and bedrock geology. Previous research of the valley was mainly focused on bedrock mapping, while almost completely neglecting Quaternary deposits. This work is the first broader analysis of Quaternary sedimentary deposits in the research area, which offers an insight into the complex geomorphological and sedimentological processes, which shape the current mountainous landscape.
Alpine topography is formed by a complex series of geomorphological processes that result in a vast number of different landforms. The youngest and most diverse landforms are various Quaternary sedimentary bodies, each characterised by its unique landform features. The formation of Quaternary sedimentary bodies and their features derive from the dominant building sedimentary processes. In recent years, studies of Quaternary sedimentary bodies and processes have been greatly aided by the use of digital elevation models (DEMs) derived by airborne laser scanning (ALS). High-resolution DEMs allow detailed mapping of sedimentary bodies, detection of surface changes, and recognition of the building sedimentary processes. DEMs are often displayed as hillshaded reliefs, the most common visualisation technique, which suffers from the limitation of a single illumination source. As a result, features can be barely visible or even invisible to the viewer if they are parallel to the light source or hidden in the shadow. These limitations become challenging when representing landforms and subtle landscape features in a diverse alpine topography. In this study, we focus on eleven visualisations of Quaternary sedimentary bodies and their sedimentary and morphological features on a 0.5 m resolution DEM. We qualitatively compare analytical hillshading with a set of visualisation techniques contained in the Raster Visualisation Toolbox software, primarily hillshading from multiple directions RGB, 8-bit sky view factor and 8-bit slope. The aim is to determine which visualisation technique is best suited for visual recognition of sedimentary bodies and sedimentation processes in complex alpine landscapes. Detailed visual examination of previously documented Pleistocene moraine and lacustrine deposits, Holocene alluvial fans, scree deposits, debris flow and fluvial deposits on the created visualisations revealed several small-scale morphological and sedimentary features that were previously difficult or impossible to detect on analytical hillshading and aerial photographs. Hillshading from multiple directions resulted in a visualisation that could be universally applied across the mountainous and hilly terrains. In contrast, 8-bit sky view factor and 8-bit slope visualisations created better visibility and facilitated interpretation of subtle and small-scale (less than ten metres) sedimentary and morphological features.
The Rebrnice area in the Upper Vipava Valley, SW Slovenia, is covered by Quaternary slope deposits that are very complex in their genesis and composition. Some of the sediments are deposited in the form of heterogeneously composed fossil landslides. One of these landslides in the Rebrnice area is the Lozice fossil landslide located above the village of Lozice. Analysis of this landslide includes geological mapping of the fossil landslide, classification of different sedimentary facies, 3-D modelling of the landslide, and transverse and longitudinal cross-sections. The geological mapping of the fossil landslide is based on field work mapping and analysis of shaded digital terrain models (DTMs) with a resolution of 1 × 1 m obtained by airborne laser scanning. Lithological data from boreholes and excavation trenches have been classified into eight specific sediment facies that had been defined in previous studies. The 3-D model of the landslide was made using the ArcScene application in the program ESRI ArcGIS. For each sediment facies, a surface was made in the form of a Triangulated Irregular Network (TIN), which gave us a wireframe object. TIN nets were merged in Multipatch objects and exported to 3-D Analyst, where a 3-D model was created. In addition, a shaded DTM image was added for a better placement of the 3-D model in space. Previous findings indicate that deposition of fossil landslides in the Rebrnice area was influenced by palaeotopography. Based on borehole data, transverse and longitudinal cross-sections of the fossil landslide were made and indicate concave depressions under the Lozice fossil landslide. Analysis of the Lozice fossil landslide indicates its complex structure of intertwined heterogeneous sedimentary facies. IzvlečekObmočje Rebrnic v Vipavski dolini v jugozahodni Sloveniji prekrivajo kvartarni sedimenti, katerih izvor in sestava sta zelo kompleksna. Nekateri sedimenti so združeni v večkompozitne fosilne plazove, med katerimi je fosilni plaz Lozice, ki se nahaja nad vasjo Lozice v Vipavski dolini. Analiza fosilnega plaz Lozice vključuje geološko karto, klasifikacijo sedimentnih faciesov, izdelavo 3-D modela fosilnega plazu ter vzdolžnega in prečnega profila plazu na podlagi podatkov vrtin. Geološko karto smo izdelali na podlagi terenskega dela ter senčenega digitalnega modela višin, ločljivosti 1 × 1 m, pridobljenega iz lidarskih posnetkov. Litološke opise sedimentov iz vrtin in sondažnih jaškov smo kategorizirali v osem sedimentnih faciesov. 3-D model fosilnega plazu smo izdelali z aplikacijo ArcScene v programskem okolju ESRI ArcGIS Analyst. Za vsak sedimentni facies smo naredili ploskev v obliki nepravilne trikotniške mreže (TIN), s katero smo dobili žičnati model površja. 3-D model smo v prostor umestili tudi z uporabo senčenih digitalnih modelov višin. Dosedanje raziskave kažejo, da so fosilni plazovi na območju Rebrnic vezani na paleotopografsko podlago. Na podlagi podatkov vrtin smo izdelali vzdolžni in prečni profil plazu, ki kažeta na konkavne zajede na območju fosilnega...
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