Structural aspect on the Slano blato landslide (Slovenia)

The active landslide Slano blato above Lokavec in the Vipava valley, Slovenia, is a complex phenomenon. The hinterland of the landslide consists of the large fossil block of Mala Gora that slid about 300 m down the slope of Mt. Čaven, and was tilted with respect to the slope. We presume that the corresponding failure surface is concavelyshaped. The block consist in its lower part of Eocene flysch beds and in its upper part of Triassic carbonate rocks that are thrust over the flysch. It is probable that due to gravitational slumping the flysch basement obtained a concave shape, that serves as a catchment structure for retaining the ground water. It slowly percolates throughthe crushed calcarenitic layers in flysch. According to available data the Slano blato was triggered in 1887 by earthworks, and in 2000 by natural erosion processes. The structural characteristics allow the assumption that movement occurs in crushed and weathered flysch beds that are percolated by a steady or periodical supply ofgroundwater from the structural reservoir in the Mala Gora fossil slumped block. Coexistence of the older structural and the younger active weathered material landslides can be observed also at other localities along the thrust front of the Trnovo and Hrušica (Nanos) nappe. Especially interesting in this respect are the Razdrto and Strane landslides

Geofizikalne raziskave na območju izvira reke Radovne (Julijske Alpe, SV Slovenija

The Radovna River Valley is located in the north-western part of Slovenia in the Julian Alps, where there is an extensive intergranular aquifer whose depth to pre-Quaternary bedrock is unknown. Therefore, to obtain information about the depth of the valley and the geometry of the aquif er two geophysical methods were used in our studyground penetrating radar (GPR) and seismic reflection method. The low-frequency GPR method has shown to be useful for determining the depth of the groundwater and the predominant groundwater recharge. Also, the high-resolution seismic method provided an insight about the morphology of the pre-Quaternary basement with the deepest point at 141 meters below surface. Measurements of hydrogeological parameters such as groundwater level and river discharge measurements were carried out in the study area. Both data analyses showed that groundwater level and river discharge are highly fluctuatingand rapidly changing, indicating a well-permeable aquifer, implying that such an aquifer is extremely sensitive and vulnerable to extreme climate events. Both the geophysical methods and the hydrogeological information have provided important information about the morphology of the valley and the alluvial aquifer, as well as increasing the knowledge about the Radovna springs system, which will contribute very important information for future hydrogeological studies.Dolina reke Radovne leži v severozahodnem delu Slovenije na območju Julijskih Alp, kjer se nahaja obsežen medzrnski vodonosnik, katerega globina do predkvartarne podlage ni znana. Zato smo v naši raziskavi za pridobitev podatkov o globini doline in geometriji vodonosnika uporabili dve geofizikalni metodigeoradar in metodo seizmične refleksije. Metoda nizkofrekvenčnega georadarja se je izkazala za uporabno pri določanju globine podzemne vode in smeri prevladujočega napajanja podzemne vode. Tudi seizmična metoda visoke ločljivosti je omogočila vpogled v morfologijo predkvartarne podlage z najglobljo točko 141 metrov pod površjem. Na območju raziskav so bile opravljene tudi meritve hidrogeoloških parametro v, kot so gladina podzemne vode in pretok v reki. Analiza obeh parametrov je pokazala, da nivo podzemne vode in rečni pretok močno nihata in se hitro spreminjata, kar pomeni, da je tak vodonosnik izjemno občutljiv in ranljiv za ekstremne podnebne dogodke. Tako geofizikalne metode kot hidrogeološki podatki predstavljajo pomembne informacije o morfologiji doline in aluvialnega vodonosnika, prav tako je znanje o sistemu izvirov Radovne večje, kar bo predstavljalo po memben doprinos pri hidrogeoloških raziskavah v prihodnje

Database of Active Faults in Slovenia: Compiling a New Active Fault Database at the Junction Between the Alps, the Dinarides and the Pannonian Basin Tectonic Domains

We present the compilation of a new database of active faults in Slovenia, aiming at introducing geological data for the first time as input for a new national seismic hazard model. The area at the junction of the Alps, the Dinarides, and the Pannonian Basin is moderately seismically active. About a dozen Mw > 5.5 earthquakes have occurred across the national territory in the last millennium, four of which in the instrumental era. The relative paucity of major earthquakes and low to moderate fault slip rates necessitate the use of geologic input for a more representative assessment of seismic hazard. Active fault identification is complicated by complex regional structural setting due to overprinting of different tectonic phases. Additionally, overall high rates of erosion, denudation and slope mass movement processes with rates up to several orders of magnitude larger than fault slip rates obscure the surface definition of faults and traces of activity, making fault parametrization difficult. The presented database includes active, probably active and potentially active faults with trace lengths >5 km, systematically compiled and cataloged from a vast and highly heterogeneous dataset. Input data was mined from published papers, reports, studies, maps, unpublished reports and data from the Geological Survey of Slovenia archives and dedicated studies. All faults in the database are fully parametrized with spatial, geometric, kinematic and activity data with parameter descriptors including data origin and data quality for full traceability of input data. The input dataset was compiled through an extended questionnaire and a set of criteria into a homogenous database. The final database includes 96 faults with 240 segments and is optimized for maximum compatibility with other current maps of active faults at national and EU levels. It is by far the most detailed and advanced map of active faults in Slovenia

Revealing subtle active tectonic deformation: integrating lidar, photogrammetry, field mapping, and geophysical surveys to assess the Late Quaternary activity of the Sava Fault (Southern Alps, Slovenia)

We applied an interdisciplinary approach to analyze the late Quaternary activity of the Sava Fault in the Slovenian Southern Alps. The Sava Fault is an active strike-slip fault, and part of the Periadriatic Fault System that accommodated the convergence of Adria and Europe. It is one of the longest faults in the Southern Alps. Using high-resolution digital elevation models from lidar and photogrammetric surveys, we were able to overcome the challenges of assessing fault activity in a region with intense surface processes, dense vegetation, and relatively low fault slip rates. By integrating remote sensing analysis, geomorphological mapping, structural geological investigations, and near-surface geophysics (electrical resistivity tomography and ground penetrating radar), we were able to find subtle geomorphological indicators, detect near-surface deformation, and show distributed surface deformation and a complex fault pattern. Using optically stimulated luminescence dating, we tentatively estimated a slip rate of 1.8 ± 0.4 mm/a for the last 27 ka, which exceeds previous estimates and suggests temporal variability in fault behavior. Our study highlights the importance of modern high-resolution remote sensing techniques and interdisciplinary approaches in detecting tectonic deformation in relatively low-strain rate environments with intense surface processes. We show that slip rates can vary significantly depending on the studied time window. This is a critical piece of information since slip rates are a key input parameter for seismic hazard studies

Seismogenic fault and area sources for probabilistic seismic hazard model in Slovenia

The Slovenian Environment Agency (ARSO) and Geological Survey of Slovenia (GeoZS) jointly developed a new seismic hazard model for the 2021 Slovenian probabilistic seismic hazard assessment (PSHA) in the scope of a seven-year project starting in 2014. Fault and area source parameters and their uncertainties were estimated, using all available seismological, geological, and seismotectonic data, models, and interpretations. A fault source is a 3D structure, which is described by a fault trace, dip, seismogenic depth, and parameters that describe its kinematics (activity, fault source type, rake, slip rate values) and maximum magnitude the source can generate. An area source is represented by a polygon described with characteristic structural domain (faults, fault systems) and its style of faulting, seismogenic/hypocentral depth, activity rate, and maximum magnitude. The database contains 89 seismogenic faults and 18 area sources in Slovenia and its surroundings. Data includes shapefiles describing the geometry of seismogenic sources, and Excel parametrization tables, linked through source ID and name. Shapefiles provide fault surface traces and polygons for area sources. Both fault and area parametrization tables include two Excel sheets: the first level (sheet names Fault sources and Area Sources) describes all estimated source parameters, and the second (sheet names FS_PSHA and AS_PSHA) consists of parameters that were used in the 2021 Slovenian PSHA model and calculation of national seismic hazard maps. The owner of the database is ARSO, which led the PSHA and financed the seven-year project on active faults in Slovenia, carried out by GeoZS and ARSO. Seismogenic source delineation and estimation of many source parameters were done in the scope of this project. Other parameters were estimated by ARSO based on seismological data

Insights on the European Fault-Source Model (EFSM20) as input to the 2020 update of the European Seismic Hazard Model (ESHM20)

European Geosciences Union (EGU) General Assembly 2020, 4-8 May 2020The H2020 Project SERA (WP25-JRA3; http://www.sera-eu.org) is committed to updating and extending the 2013 European Seismic Hazard Model (ESHM13; Woessner et al., 2015, Bull. Earthquake Eng.) to form the basis of the next revision of the European seismic design code (CEN-EC8). Following the probabilistic framework established for ESHM13, the 2020 update (ESHM20) requires a continent-wide seismogenic model based on input from earthquake catalogs, tectonic information, and active faulting. The development of the European Fault-Source Model (EFSM20) fulfills the requirements related to active faulting. EFSM20 has two main categories of seismogenic faults: crustal faults and subduction systems. Crustal faults are meant to provide the hazard model with seismicity rates in a variety of tectonic contexts, including onshore and offshore active plate margins and plate interiors. Subduction systems are meant to provide the hazard model with both slab interface and intraslab seismicity rates. The model covers an area that encompasses a buffer of 300 km around all target European countries (except for Overseas Countries and Territories, OTCs), and a maximum of 300 km depth for slabs. The compilation of EFSM20 relies heavily on publicly available datasets and voluntarily contributed datasets spanning large regions, as well as solicited local contributions in specific areas of interest. The current status of the EFSM20 compilation includes 1,256 records of crustal faults for a total length of ~92,906 km and four subduction systems, namely the Gibraltar Arc, Calabrian Arc, Hellenic Arc, and Cyprus Arc. In this contribution, we present the curation of the main datasets and their associated information, the criteria for the prioritization and harmonization across the region, and the main strategy for transferring the earthquake fault-source input to the hazard modelers. The final version of EFSM20 will be made available through standard web services published in the EFEHR (http://www.efehr.org) and EPOS (https://www.seismofaults.eu) platforms adopting FAIR data principlesThe SERA project received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No.730900Peer reviewe

Surface faulting during the 29 December 2020 Mw 6.4 Petrinja earthquake (Croatia)

International audienceThe 29 December 2020, Mw 6.4 Petrinja earthquake nucleated at a depth of ~10 km in the Sisak-Moslavina County in northern Croatia, ~6 km WSW of the Petrinja town. Focal mechanisms, aftershocks distribution, and preliminary Sentinel-1 InSAR interferogram suggest that the NW-SE right-lateral strike-slip Pokupsko-Petrinja fault was the source of this event.The Croatian Geological Survey, joined by a European team of earthquake geologists from France, Slovenia and Italy, performed a prompt systematic survey of the area to map the surface effects of the earthquake. The field survey was guided by geological maps, preliminary morphotectonic mapping based on 1:5,000 topographical maps and InSAR interferogram. Locally, field mapping was aided by drone survey.<br>We mapped unambiguous evidence of surface faulting at several sites between Župić to the NW and Hrastovica to the SE, in the central part of the Pokupsko-Petrinja fault, for a total length of ~6.5 km. This is probably a minimum length since several portions of the fault have not been explored yet, and in part crossing forbidden uncleared minefields. Surface faulting was observed on anthropic features (roads, walls) and on Quaternary sediments (soft colluvium and alluvium) and Miocene bedrock (calcarenites). The observed ruptures strike mostly NW-SE, with evidences of strike-slip right-lateral displacement and zones of extension (opening) or contraction (small pressure ridges, moletracks) at<br>local bends of the rupture trace. Those ruptures are interpreted as evidences of coseismic surface faulting (primary effects) as they affect the morphology independently from the slope direction. Ground failures due to gravitational sliding and liquefaction occurrences were also observed, mapped and interpreted as secondary effects (see Amoroso et al., and Vukovski et al., this session). SE of Križ, the rupture broke a water pipeline with a right-lateral offset of several centimetres. Measured right-lateral net displacement varies from a few centimetres up to ~35 cm. A portion of the maximum measured displacement could be due to afterlisp, as it was mapped several days after the main shock. Hybrid surface ruptures (shear plus opening and liquefaction), striking SW-NE, with cm-size left-lateral strike-slip offsets were mapped on the northern side of the Petrinja town, ~3 km NE of the main fault. Overall, the rupture zone appears discontinuous. Several factors might be inferred to explain this pattern such as incomplete mapping of the rupture, inherited structural discontinuities within the Pokupsko-Petrinja fault system, or specific mechanical properties of the Neogene-Quaternary strata

A database of the environmental effects associated to the December 29th, 2020 Mw 6.4 Petrinja earthquake (Croatia)

International audience<p>On December 29th, 2020, a strong Mw 6.4 earthquake hit central Croatia. The epicenter was located approximately 3 km southwest of Petrinja, and the intensity was estimated to VIII-IX EMS. The earthquake led to significant environmental effects related to earthquake magnitude, focal depth, and geological and geotechnical properties of the affected area.<br>The Croatian Geological Survey (HGI-CGS) conducted extensive geological and geodetic surveys starting a few hours following the main shock to measure the earthquake’s effects,<br>including those on infrastructures. Ten geologists from the Department of Geology carried out surveys from Decmber 31st, 2020 to January 7th, 2021 along the potential seismogenic source (inferred from geological maps and InSAR data) and in the wider epicentral area that suffered significant damage (e.g., Glina and Sisak).<br>During a second phase, researchers from the University of Zagreb (PMF UniZG), Slovenia (GeoZS), Italy (INGV, ISPRA, U. Chieti) and France (CEREGE, IRSN) were mobilized to complete the observations. The collaboration with these geologists allowed to deepen the investigations and to bring further detail to quantify the effects. The surveys were then compiled based on data formats used by the European Community, namely those of the INGV EMERGEO team (Villani et al., 2017; for environmental effects including surface ruptures and liquefaction) and those of the SURE group (Baize et al., 2019 for surface ruptures).<br>These observations revealed that the earthquake triggered a discontinuous, few km-long surface rupture with a maximum displacement of about 20 cm, which is consistent with the lower average of observations made on similar events (Wells and Coppersmith, 1994). Liquefaction spread over several tens of square kilometers mostly in river plains, the most distant being about 20 km from the epicenter (to be confirmed!). Other observed effects include lateral spreading, landslides, groundwater regime changes, rockfalls, and various infrastructure damage.<br>The compilation of the acquired dataset into a unified database, consistent with database of other historical and recent events, is essential for establishing reliable empirical relations between geological effects and physical characteristics of earthquakes (magnitude, depth). This forms the basis for seismic hazard assessments, whether for “surface rupture”, “liquefaction”, or “ground-shaking” potential.</p&gt

European Fault-Source Model 2020 (EFSM20): online data on fault geometry and activity parameters

The European Fault-Source Model 2020 (EFSM20) is a product of the EU H2020 Project SERA (WP25-JRA3). It is designed to fulfill the requirements related to active faulting of the 2020 update of the European Seismic Hazard Model (ESHM20) following the probabilistic framework established for the 2013 European Seismic Hazard Model (ESHM13). EFSM20 has two main categories of seismogenic sources: crustal faults and subduction systems. Crustal faults are meant to provide the hazard model with seismicity rates in various tectonic contexts, including onshore and offshore active plate margins and plate interiors. Subduction systems are intended to provide the hazard model with slab interface and intraslab seismicity rates. The model covers an area encompassing a buffer of 300 km around all target European countries (except for Overseas Countries and Territories, OTCs) and a maximum 300 km depth for slabs. It extends beyond this area to include the main tectonic plate boundaries as much as possible