Surface Versus Underground Measurements of Active Tectonic Displacements with TM 71 Exstensometers in Slovenia

Abstract

UDC 551.24(497.4-15) Andrej Gosar, Stanka Šebela, Blahoslav Košťák & Josef Stemberk: Surface versus underground measurements of active tectonic displacements with TM 71 exstensometers in Slovenia The tectonic setting of W Slovenia is characterised by NW-SE trending dextral strike-slip fault systems and moderate seismicity. Monitoring of tectonic movements along five presumably active faults or in their vicinity using TM 71 extensometers was set up in 2004. In five years of monitoring some clear trends of displacement were established. The morphologically most prominent fault in W Slovenia is Idrija Fault having a total length of more than 120 km. The average lateral displacement measured along a crack in its inner fault zone in Učja valley was 0.26 mm/year. Short-term rates were even greater and reached 0.54 mm/year. Raša Fault monitoring site at the foot of Vremščica Mt. established first an average uplift of SW block for 0.16 mm/year and left-lateral displacement of 0.16 mm/ year. It was followed by down-slip of the same block at the rate of 0.37 mm/year. In Postojnska Jama two instruments, 260 m apart, were installed at the fault zone, which extends about 1 km northeast from Predjama Fault. We detect small tectonic deformations, dextral horizontal movement of 0.05 mm in 5 years for Postojna 1 and extension of 0.03 mm in 5 years for Postojna 2. Both devices recorded similar reactions to some earthquakes with magnitude range 3.1-5.2 and epicentral distance of 12-95 km. The amplitude of individual peaks is in the order of 0.08 mm. The monitoring at Kneža Fault started at the end of 2006. In two years clear oblique displacement was established with left-lateral rate of 0.06 mm/year and uplift of SW block for 0.06 mm/year. Monitoring in Pološka Jama situated in vicinity of the Ravne Fault started in 2008. Preliminary results show 0.08 mm of horizontal displacement between two Izvleček UDK 551.24(497.4-15) Andrej Gosar, Stanka Šebela, Blahoslav Košťák & Josef Stemberk: Primerjava površinskih in podzemeljskih meritev aktivnih tektonskih premikov določenih s TM 71 ekstenziometri v zahodni Sloveniji Za tektonsko zgradbo zahodne Slovenije so značilni sistemi desnozmičnih prelomov usmerjeni NW-SE in zmerna potresna dejavnost. Leta 2004 smo pričeli z meritvami tektonskih premikov z ekstenziometri TM 71 ob petih domnevno aktivnih prelomih ali v njihovi bližini. V petih letih opazovanj smo ugotovili nekatere jasne trende premikov. Morfološko najmočneje izražen prelom v zahodni Sloveniji je Idrijski prelom, ki je dolg preko 120 km. Na razpoki v njegovi notranji coni v dolini Učje smo ugotovili povprečne zmične premike 0,26 mm/leto. Kratkotrajnejše hitrosti so še večje in dosežejo 0,54 mm/leto. Na Raškem prelomu v vznožju Vremščice smo ugotovili najprej dvigovanje SW bloka za 0,16 mm/leto in levozmične premike s hitrostjo 0,16 mm/leto. Sledilo je pogrezanje istega bloka za 0,37 mm/leto. V Postojnskem jamskem sistemu smo na razdalji 260 m namestili dva inštrumenta na prelomni coni, ki poteka okoli 1 km severovzhodno od Predjam...

The role of cave ventilation in governing cave air temperature and radon levels (Postojna Cave, Slovenia)

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The recognition of transient compressional fault slow−slip along the northern shore of Hornsund Fjord, Sw Spitsbergen, Svalbard

“…The advantages and limitations of the instrument are well defined given the protracted installation at a number of sites in, for example, the Czech Re− public, Slovenia, Slovakia, and Poland (Kontny et al 2005;Gosar et al 2009;Šebela et al 2009). It has been shown that seasonal and climatic variations can be detected and separated from the recorded movements (Briestenský et al 2010).…”

Reasons for large fluctuation of radon and CO<sub>2</sub> levels in a dead-end passage of a karst cave (Postojna Cave, Slovenia)

“…The complexity and size of Postojna Cave, with its numerous known and unknown entrances at different levels and a long and highly ramified cave system, makes this cave a fascinating study site for a variety of physical and environmental studies (Bezek et al, 2012;Gosar et al, 2009;Kobal et al, 1988;Mulec et al, 2012;Šebela et al, 2010;Šebela and Turk, 2011;Vaupotič, 2008). In general the ventilation of Postojna Cave is characterised by convective airflow, controlled mainly by the temperature difference between the cave and the outside atmosphere, as discussed by for one measurement location in the Velika Gora (Great Mountain) chamber of Postojna Cave.…”