Rainfall-triggered shallow landslides represent a major threat to people and infrastructure worldwide. Predicting the possibility of a landslide occurrence accurately means understanding the trigger mechanisms adequately. Rainfall is the main cause of slope failures in Slovenia, and rainfall thresholds are among the most-used tools to predict the possible occurrence of rainfall-triggered landslides. The recent validation of the prototype landslide early system in Slovenia highlighted the need to define new reliable rainfall thresholds. In this study, several empirical thresholds are determined using an automatic tool. The thresholds are represented by a power law curve that links the cumulated event rainfall (E, in mm) with the duration of the rainfall event (D, in h). By eliminating all subjective criteria thanks to the automated calculation, thresholds at diverse non-exceedance probabilities are defined and validated, and the uncertainties associated with their parameters are estimated. Additional thresholds are also calculated for two different environmental classifications. The first classification is based on mean annual rainfall (MAR) with the national territory divided into three classes. The area with the highest MAR has the highest thresholds, which indicates a likely adaptation of the landscape to higher amounts of rainfall. The second classification is based on four lithological units. Two-thirds of the considered landslides occur in the unit of any type of clastic sedimentary rocks, which proves an influence of the lithology on the occurrence of shallow landslides. Sedimentary rocks that are prone to weathering have the lowest thresholds, while magmatic and metamorphic rocks have the highest thresholds. Thresholds obtained for both classifications are far less reliable due to the low number of empirical points and can only be used as indicators of rainfall conditions for each of the classes. Finally, the new national thresholds for Slovenia are also compared with other regional, national, and global thresholds. The thresholds can be used to define probabilistic schemes aiming at the operative prediction of rainfall-induced shallow landslides in Slovenia, in the framework of the Slovenian prototype early warning system.
Monitoring is important for assessing the stability of the ground and for confirming the validity of the design during the construction and operation of structures. The ideal monitoring system for projects in Rock and Geotechnical Engineering would be able to monitor the behavior of small to extensive areas continuously and automatically with high accuracy. In addition, the costs would be low and the system would be easy to handle. Satellite technology has the potential to realize the above monitoring system by combining it with conventional geotechnical instruments. In this paper, satellite technology for displacement monitoring, i.e., GPS and SAR, is firstly outlined and then the concept of spatiotemporal continuous displacement monitoring is introduced. The use of both satellite technology and geotechnical instruments is effective for geotechnical monitoring. Practical applications of GPS for landslide monitoring and collaborative researches using DInSAR with Balkan countries are described.
Automatic landslide classification based on digital elevation models has become a powerful complementary tool to field mapping. Many studies focus on the automatic classification of landslides’ geomorphological features, such as their steep main scarps, but in many cases, the scarps and other morphological features are difficult for algorithms to detect. In this study, we performed an automatic classification of different litho-geomorphological units to differentiate slope mass movements in field maps by using Maximum Likelihood Classification. The classification was based on high-resolution lidar-derived DEM of the Vipava Valley, SW Slovenia. The results show an improvement over previous approaches as we used a blended image (VAT, which included four different raster layers with different weights) along with other common raster layers for morphometric analysis of the surface (e.g., slope, elevation, aspect, TRI, curvature, etc.). The newly created map showed better classification of the five classes we used in the study and recognizes alluvial deposits, carbonate cliffs (including landslide scarps), carbonate plateaus, flysch, and slope deposits better than previous studies. Multivariate statistics recognized the VAT layer as the most important layer with the highest eigenvalues, and when combined with Aspect and Elevation layers, it explained 90% of the total variance. The paper also discusses the correlations between the different layers and which layers are better suited for certain geomorphological surface analyses.
We analyse systematic fractures occurring in sandstone beds in Eocene flysch of the Slovenian coastal area. Two nearly perpendicular fracture sets were identified: fractures F1 are generally NW-SE oriented, wellexpressed and predominately planar, whereas fractures F2 are NE-SW-striking, shorter, more irregular in shape, and terminate against the F1 set. The average orientation of both sets does not change significantly in a coastal transect crossing all principal structural domains of the area. We analysed fracture spacing with respect to layer thickness and determined fracture spacing index for both fracture sets. We interpret both fracture sets as tensional (Mode I) joints originating in two distinct extensional episodes. Set F1 is older and formed in NE-SW directed tension which we correlate with the well-documented regional post-Dinaric orogen-perpendicular extension of presumably mid-Miocene age. Set F2 formed in NW-SE oriented tension, which is compatible with previously documented NE-SW-striking normal faults occurring in the area, but was so far not documented elsewhere. We interpret that F1 fractures predate folding and thrusting in the coastal belt. Earlier, Eocene-Oligocene Dinaric thrusting therefore did not significantly affect the coastal area, whereas post-F1 shortening, associated with northward indentation and underthrusting of the Adria microplate, did not commence before late Miocene. IzvlečekRaziskali smo sistematične razpoke, ki se pojavljajo v plasteh peščenjaka v eocenskem flišu Slovenske obale. Pojavljata se dve, medsebojno skoraj pravokotni družini razpok: razpoke družine F1 so generalno usmerjene v SZ-JV smeri in so dobro izražene in pretežno planarne, razpoke družine F2 pa imajo smer SV-JZ in so krajše, bolj nepravilno oblikovane in se zaključujejo na ploskvah razpok F1. Povprečna orientacija razpok obeh družin se bistveno ne spreminja vzdolž raziskanega profila, ki preči vse glavne strukturne domene ob Obali. Analizirali smo medsebojno oddaljenost razpok glede na debelino plasti in obema družinama določili indeks oddaljenosti razpok (fracture spacing index). Obe družini interpretiramo kot natezne razpoke tipa I, ki so nastale v dveh ločenih fazah natezne tektonike. Družina F1 je starejša in je nastala v SV-JZ usmerjeni tenziji in jo povezujemo z dobro poznano regionalno fazo post-Dinarske ekstenzije, ki je domnevno srednje miocenske starosti. Družina F2 je nastala v SZ-JV usmerjeni tenziji in je skladna z SV-JZ usmerjenimi normalnimi prelomi, ki so bili že prej dokumentirani v območju Obale, ni pa še bila odkrita v ostalih delih Slovenije. Po naši interpretaciji so razpoke družine F1 starejše od narivanja in gubanja v območju Obale. Zato sklepamo, da predhodno Dinarsko narivanje eocensko-oligocenske starosti ni bistveno prizadelo obalnega območja. Krčenje ozemlja po nastanku razpok F1, ki ga povezujemo s podrivanjem Jadranske mikroplošče proti severu, pa se ni začelo pred mlajšim miocenom.
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