a2_The town of Litija was hit by four damaging earthquakes in the last 120 years which reached a maximum intensity of VII-VIII MSK. The town is located in a shallow sedimentary basin filled with relatively soft Quaternary sediments in which seismic site amplification is expected. On the other hand no borehole or geophysical data are available to support quantitative assessment of site effects. As a contribution to the first seismic microzonation of the area, we performed a free-field study based on the microtremor HVSR method in order to assess the resonance frequency of th e sediments. In ge neral clear spectral peaks were obtained for 57 measuring points which show distribution of frequencies in a broad range between 4.4 an d 22.7 Hz. The iso-frequency map was prepared by using natural neighbour interpolation algorithm. For soil-structure resonance assessment we considered large building stock from different Slovenian towns, because the building typology is similar in wider area. Low-rise masonry family houses with two or three floors prev ail. By microtremor measurements inside 45 such buildings their fundamental longitudinal and transver se frequencies were determined and statistically analysed in a complementary study. To assess the possible occurrence of soil-structure resonance in general, the average fundamental frequency +/- one standard devia tion interval is obtained for these two building heights, which give s the range 5.6-11.1 Hz. The free-field microtremor data shows that this frequency range occupies 37% of the urban area in the Litija basin. This study has shown that soil-structure resonance issue for low-rise buildings is frequently overlooked, but should be considere d seriously in shallow sedimentary basins, characterized by relatively high free-field frequencies, because many towns are located in such geological environment., a2_Second application of the derived iso-frequency map is to support soil classification, because recent investigations have shown that fundamental frequency of sediments can be used together with the average shear velocity in the upper 30 m to improve classi fications according to di fferent seismic codes., Andrej Gosar., and Obsahuje bibliografické odkazy
Two seismic sources were tested on different surfaces during acquisition of a 5.5-km long high resolution seismic reflection (HRS) profile on the Ljubljana Moor in central Slovenia. Maximum target depth range of the survey was 200 - 300 m. Nine different combinations of source-surface conditions were analysed. Seismic sources included a seismic shotgun and an accelerated weight dropper system. The HRS profile crossed different surfaces including: paved roads, gravel roads, ploughed fields, grasslands and marshlands. Seismic source performance on different surfaces was evaluated through frequency and S/N ratio analyses of seismic data, and analysis of source-generated coherent noise appearance on seismograms. Results show that both seismic sources are suitable for some of the surfaces found in the surveyed area. The accelerated weight dropper produced the best results on gravel road surface, but poor results were found on grassland and ploughed fields. The seismic shotgun produced the best results in water-saturated soil on marshlands. It performed less favourably in unsaturated soil, generating more coherent noise. Water-saturated marshland surface and gravel road surfaces were found to be the most favourable for acquisition of high-resolution seismic reflection data on the Ljubljana Moor., Jure Atanackov and Andrej Gosar., and Obsahuje bibliografii
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
At the end of 2010 seven TM 71 extensometers, installed at or near the active faults in Slovenia, were in operation. Three of them are on the surface and four inside karst caves. The highest rates with stable sense of movements were observed on the Idrija fault. Average horizontal displacement rate was 0.24 mm/year. Short term rates were even greater and reached 0.54 mm/year. The Raša fault first experienced an uplift of the SW block of 0.16 mm/year, which was followed by a short-term down-slip of the same block at the rate of 0.37 mm/year. Later the sense of movement returned to uplift with a rate of 0.05 mm/year. The average horizontal displacement was 0.07 mm/year. The Kneža fault experienced very small average displacements (y=0.035 mm/year, z=0.03 mm/year and x=0.02 mm/year). Similar rates were observed in nearby Polog cave (y=0.015 mm/year, z=0.027 mm/year and x=0.016 mm/year), which is located close to the seismically active Ravne fault. For Kostanjevica cave, located near the Brežice fault, small average rates are characteristic (y=0.006 mm/year, z=0.017 mm/year and x=0.012 mm/year). In Postojna cave, located close to the Predjama fault, two monitoring sites are very stable with small tectonic movements, including general dextral horizontal movement of 0.05 mm from 2004 to 2010 (Postojna 1) and two significant short-term peaks of 0.08 mm (Postojna 1-y and Postojna 2-z)., Andrej Gosar, Stanka Šebela, Blahoslav Košťák and Josef Stemberk., and Obsahuje bibliografii