Resonance frequencies of unconsolidated sediments of the Iška alluvial fan (Ljubljana Moor basin) were derived using microtremor method. Free-field measurements were conducted in a grid with point spacing of approximately 250 m. The sediments frequency-thickness relationship, h = 202.97 f -1.139, was obtained on the basis of 107 microtremor measurements, six existing boreholes that reached the Pre-Quaternary basement and two seismic reflection profiles. The reliance of the obtained relationship was evaluated with the R2 coefficient, which shows a very good level of determination. The resonance frequency map reveals the existence of an N-S oriented deeper buried valley (maximum depth 119 m) in the Western part of the alluvial fan. The microtremor HVSR amplitude map does not show any specific spatial distribution pattern, with the exception of a relatively narrow band of low amplitudes located north of Iška vas. This is probably related to an area of severely fractured bedrock along the Mišji Dol fault. Map of the Quaternary sediment thickness and map of the Pre-Quaternary basement topography were constructed on the basis of the established relationship. The basement topography map shows rather steep western slopes of the buried valley down to deepest part, followed by a gradually ascending basement towards the Eastern part of the fan. The comparison of the obtained parameters a and b in frequency-thickness relationship with other sedimentary basins around the world reveals a small variation of b values, and a rather large range of a values, which implies that the parameter a is characteristic for certain geological areas. The results of this research will find use in constructing more accurate hydrogeological models and for assessment of possible sediments-structure resonance effects in seismic microzonation., Lovro Rupar and Andrej Gosar., and Obsahuje bibliografii
Monitoring of tectonic movements along three active faults of Dinaric (NW-SE trending) fault system in W Slovenia using TM 71 extensiometers was set up in 2004. After two and a half years of measurements clear trends of displacement were recorded. The average left-lateral displacement along a crack in the inner fault zone of the Idrija fault in Učja valley was reading 0.38 mm/year. Short term (10 months) rates were even greater and reached the value of 0.54 mm/year. Since the Idrija fault is considered generally to be dextral strike-slipping, the observed left-lateral displacement can be explained by variations in principle stress. Raša fault monitoring site at the foot of Vremščica Mt. established an average reverse uplift of hanging wall (SW) block of 0.24 mm/year and left-lateral displacement of 0.16 mm/year. Short term (9 months) vertical displacements reached the value of 0.53 mm/year. The inclined displacement is in agreement with geological and seismological observations. In the Postojna cave system two instruments were installed at the fault which extends parallely to Predjama fault zone. The average vertical displacement rate at Postojna 1 site was 0.01 mm/year. Both devices recorded similar reaction which can be attributed to 12 July, 2004 (Mw=5.2) earthquake with an epicentre 70 km away from the measuring site. Since there were no other stronger earthquakes in the vicinity and time span of monitoring, no other correlations were established with earthquake activity. The observed displacement rates along all three monitored faults of up to 0.5 mm/year are consistent with the regional deformation rate in W Slovenia established from GPS measurements which is of the order of 2 mm/year., Andrej Gosar, Stanka Šebela, Blahoslav Košťák and Josef Stemberk., and Obsahuje bibliografii
UK-Slovenian collaborative research connected to EU COST-Action 625 began in 2003 and has involved interdisciplinary research into the current activity, structural architecture and landscape expression of the Ravne and Idrija strike-slip fault systems in NW Slovenia. The Ravne fault may be the best exposed actively propagating strike-slip fault system in Europe and through combined structural fieldwork, earthquake seismology and airborne LiDAR (Light Detection And Ranging) surveys, a new understanding of the fault’s along-strike segmentation, three dimensional geometry and stepover zone kinematics has been gained. The Idrija Fault in contrast, is poorly exposed, but defines a regional lineament with an intensely brecciated fault core; it may have been responsible for the largest historical earthquake to have ever affected the region. High-resolution LiDAR images recently obtained for both fault systems allow for efficient focussed fieldwork and future work will be devoted to documenting the timing of previous earthquakes and the connectivity and displacement transfer between active faults at the NE corner of the Adria microplate., Dickson Cunningham, Andrej Gosar, Vanja Kastelic, Stephen Grebby and Kevin Tansey., and Obsahuje bibliografii