ACTA GEOGRAPHICA GEOGRAFSKI ZBORNIK SLOVENICA 2020 60 1 ACTA GEOGRAPHICA SLOVENICA GEOGRAFSKI ZBORNIK 60-1 • 2020 Contents Mojca POKLAR Comparison of the sonar recording method and the aerial photography methodfor mapping seagrass meadows 7 Vanja PAVLUKOVIĆ, Uglješa STANKOV, Daniela ARSENOVIĆ Social impacts of music festivals: A comparative study of Sziget (Hungary) and Exit (Serbia) 21 Péter János KISS, Csaba TÖLGYESI, Imola BÓNI, László ERDŐS, András VOJTKÓ,István Elek MAÁK, Zoltán BÁTORI The effects of intensive logging on the capacity of karst dolines to provide potential microrefugia for cool-adapted plants 37 Radu SĂGEATĂ Commercial services and urban space reconversion in Romania (1990–2017) 49 Kristina IVANČIČ, Jernej JEŽ, Blaž MILANIČ, Špela KUMELJ, Andrej ŠMUC Application of a mass movement susceptibility model in the heterogeneous Miocene clastic successions of the Slovenj Gradec Basin, northeast Slovenia 1 Andrej GOSAR Measurements of tectonic micro-displacements within the Idrija fault zone in the Učjavalley (W Slovenia) 79 Piotr RAŹNIAK, Sławomir DOROCKI, Anna WINIARCZYK-RAŹNIAK Economic resilienceofthe command andcontrolfunctionof citiesin Centraland EasternEurope 95 Mateja FERK, Rok CIGLIČ, Blaž KOMAC, Dénes LÓCZY Management of small retention ponds and their impact on flood hazard prevention in the Slovenske Gorice Hills 107 Gregor KOVAČIČ Sediment production in flysch badlands: A case study from Slovenian Istria 127 Vesna LUKIĆ, Aleksandar TOMAŠEVIĆ Immigrant integration regimes in Europe: Incorporating the Western Balkan countries 143 Mitja DURNIK Community development: LocalImmigrationPartnershipsin Canadaand implications forSlovenia 155 ISSN 1581-6613 9 771581 661010 MEASUREMENTS OF TECTONIC MICRO-DISPLACEMENTS WITHIN THE IDRIJA FAULT ZONE IN THE UčJA VALLEY (W SLOVENIA) Andrej Gosar Introductory figure caption: Left: A crack in the Idrija fault inner fault zone in the Učja valley on which the TM 71 extensometer is installed. Right: Outcrop of another fault plane located 50m to the east with clear striations indicating subhorizontal movements. DOI: https://doi.org/10.3986/AGS.7444 UDC: 551.242:551.34(497.47) COBISS: 1.01 Andrej Gosar1,2 Measurements of tectonic micro-displacements within the Idrija fault zone in the Učja valley (W Slovenia) ABSTRACT:Arecentslip-rateofanactivefaultisaveryimportantseismotectonicparameter,butnoteasy todetermine.Idrijafault,120kmlong,isaprominentgeomorphologicfeaturewithlargeseismogenicpoten­tial,stillneededtoberesearched.Measurementsoftectonicmicro-displacementscanprovideinsightinto its recent activity. The Učja valley extends transversally to the Idrija fault and was therefore selected for the installation of TM 71 extensometer. Measurements on the crack within its inner fault zone are con-ductedfromtheyear2004.In14yearsofobservationsasystematichorizontaldisplacementswithaverage rate of 0.21mm/year and subordinate vertical displacements of 0.06mm/year were established, proving the activity of this fault. An overview of methods of displacement measurements related to active faults and of newer interdisciplinary investigations of the Idrija fault is given. Displacement rates are beside for geodynamicinterpretationsimportantforimprovementofseismotectonicmodelsandthusforbetterseis­mic hazard assessment. KEY WORDS: tectonics, geodynamics, fault, extensometer, Idrija fault, Učja, Slovenia Meritve tektonskih mikro-premikov v prelomni coni Idrijskega preloma v dolini Učje (Z Slovenija) POVZETEK: Recentna hitrost premikov ob aktivnem prelomu je zelo pomemben seizmotektonski para­meter, ki pa ga ni lahko določiti. Idrijski prelom je z dolžino 120km pomembna geomorfološka struktura z velikim seizmogenim potencialom, ki pa ga je treba še raziskati. Meritve mikro-premikov lahko nudijo vpogledvrecentnoaktivnostpreloma.DolinaUčjepotekaprečnonaIdrijskiprelom,zaradičesarjebilaizbrana za namestitev ekstenziometra TM 71. Meritve na razpoki v notranji prelomni coni potekajo od leta 2004. V14letihopazovanjjebilougotovljenosistematičnovodoravnozmikanjespovprečnohitrostjo0,21mm/leto inpodrejenivertikalnipremikishitrostjo0,06mm/leto,kardokazujeaktivnosttegapreloma.Podanjepregled različnihmetodraziskovanjarecentnihpremikovobaktivnihprelomihternovejšihinterdisciplinarnihraziskav Idrijskega preloma. Ocene hitrosti premikov so poleg geodinamskih interpretacij pomembne predvsem za izboljšanje seizmotektonskih modelov in s tem boljše ocenjevanje potresne nevarnosti. KLJUČNE BESEDE: tektonika, geodinamika, prelom, ekstenziometer, Idrijski prelom, Učja, Slovenija The paper was submitted for publication on 5th June, 2019. Uredništvo je prejelo prispevek 5. junija 2019. 1 Slovenian Environment Agency, Seismology and Geology Office, Ljubljana, Slovenia 2 University of Ljubljana, Faculty of Natural Sciences and Engineering andrej.gosar@gov.si 80 1 Introduction A recent slip-rate of an active fault is among the most important seismotectonic parameters needed for realisticearthquakehazardassessment.However,itisnoteasytodetermineitandinterdisciplinaryapproach isneededforareliableestimate.ThemethodsappliedsofarontheIdrijafaultoritsvicinitycanbegrouped into a) geodetic (Kogoj9 2000; Rižnar, Koler and Bavec 2007; Weber et al. 2010), geological (Čar 2010), b) tectonic geomorphology (Moulin et al. 2014), c) paleoseismology (Bavec et al. 2013), d) outcrops dat­ing methods (Moulin et al. 2016) and e) seismological (Bajc et al. 2001; Živčić et al. 2011). Measurements of tectonic micro-displacements using extensometer represent an additional method (Stemberk, Košťak andVilimek2003),whichcancontributetothesolutionoftheproblem.Suchmeasurementswereenabled through invention of a crack-gauge instrument (Košťak 1991), which is installed on the crack which sep­arates two tectonic blocks. In Slovenia seven TM 71 extensometers were installed between 2004 and 2010 at or near the active faults,threeofthemonthesurface(Idrija,KnežaandRašafaults)andfourinsidekarstcaves(twoinPostojna cave, in Polog cave and in Kostanjevica cave) (Gosar et al. 2007, Gosar et al. 2011). Until 2011 the highest rates with stable sense of movements were observed on the Idrija fault (average horizontal displacement rateof0.24mm/year).Theobserveddisplacementrates(mainlyhorizontal)atallotherlocationsweremuch smaller(from0.006to0.05mm/year).OnlyontheRašafaultmoresignificantshort-termverticaldisplacement rateof0.16mm/yearwasobserved,atallotherlocationstherateswereanorderofmagnitudesmaller(Gosar et al. 2011). The fact that the monitoring on the Idrija fault showed with the leap the highest displacement ratesinSlovenia,additionaleightyearsofmonitoringtill2019andsignificanceoftheIdrijafaultforearth­quakehazardassessmentandtectonicgeomorphology,motivatedastudydedicatedonlytothemeasuring site in the Učja valley which is presented in this paper. Idrija fault is because of its length and prominent expression in topography one of the most impor­tant faults in Slovenia (Fig. 1) and it is supposed that it has a large seismogenic potential (Atanackov et al. 2014; 2016). However, its recent tectonic activity is not definitely proved yet by seismological monitoring or geodetic observations, but there are several indications for its activity from geological mapping, tec­tonic geomorphology, dating of outcrops and paleoseismological studies. TogetadditionalinsightintotheactivityoftheIdrijafault,weinstalledin2004theTM71extensometer on a crack within the inner fault cone which is exposed in the Učja valley (Figures 2 and 3). This location was selected as the best, because elsewhere along its trace there are no suitable outcrops. After 14 years of measurements,weprovidetheresultsofobservedtrendsanddisplacementrates.First,anoverviewofinter-disciplinary investigations of the Idrija fault is given. It is followed by description of different methods for displacement measurements and tectonic slip-rate estimates. The fault zone exposed in the Učja valley is describedtogetherwiththeselectionofthelocationfortheinstallationofextensometer.Observedmicro-tectonic displacements are evaluated and some possible interpretations indicated. 2 Idrija fault and measurements of tectonic displacements 2.1 Geology and geomorphology of the Idrija fault The Idrija fault is geomorphologically the most prominently expressed fault in W Slovenia and is clearly visible on satellite and aerial images or digital elevation models (Figure 1). Active tectonic movements are the only geological force which can influence the landscape in such a way. They can be studied by tec­tonic geomorphology methods or direct measurements along faults. The Idrija fault can be traced in the length of 120km from Friuli (Italy) on the NW (Figure 1) to Gorski Kotar in Croatia on the SE (Buser 1986).Itsaveragestrikedirectionis310o,andthedip85o(Atanackovetal.2014;2016).Inthesouthernpart there are several karst poljes of the Ljubljanica river system distributed along the fault. In the northern partthefaultextendsalongtheIdrijca,KanomljicaandSočarivervalleys(Figure1).Thehistoryofitsinves­tigationsisverylong(ČarandGosar2011),alsoduetotheimportanceoftheIdrijaHgoredeposits,because in the geological history part of the ore body (Ljubevč) was displaced along the fault for approximately 2.5km to its present position. Based on this fact and considering the supposed age of the fault of 10–12 million years, Placer (1971) estimated that the average slip-rate through the whole period was from 0.25 Figure 1: Mapofactivetectonicfaults inNWSlovenia(afterAtanackov et al.2014;2016) onshadedLiDAR 1mresolutiondigitalelevation model (ARSO 2015) with the location of TM 71 extensometer on the Idrija fault in the Učja valley. The rectangle indicates a detailed map shown in Figure 2. to0.16mm/year,andtheslipwasobliquewithverticaldisplacementof480m(Placer1982).Newerinves­tigationsalsoshownobliquedisplacement,whichistheresultoftwoseparatedtectonicphases(Čar2010). In middle Miocene, 12 million years ago, the area was under strong extensional forces and normal faults weredevelopedinNW–SEdirectiondippingtowardstheNE.AlongtheIdrijafaulttheNEblockwaslow­ered for up to 480m (Čar and Gosar 2011). Later the stress regime has changed to compression in approx. N–Sdirectionandthefaultwasreactivatedasadextralstrike-slip(Čar2010).Relatedtothischangesome new fault traces were developed. Due to this fact the whole fault zone is rather complex. In a newer study Placer, Vrabec and Celarc (2010) made an estimate that the apparent displacement along the Idrija fault in Tolmin area is around 10km. Because the Idrija fault runs mostly along river valleys and karst fields, there are very few outcrops suitable for detailed tectonic analyses. The best exposure of the whole fault zone is in the Učja valley at the far NW end of the fault (Figures 1 and 2), because it extends in a transverse direction to the fault and at the location of the fault zone it forms a small canyon (Čar and Pišljar 1993). In this canyon the structures of outer and inner fault zones are very good visible (Figure 2). The direct evidence of Quaternary to recent deformation in this area was described by Vrabec (2012). He found an outcrop of poorly sorted Quaternary breccia, which is dissect­ed by several NW–SE oriented subvertical faults and associated fractures. Activity of the fault is further indicated by dextral offsets of the Učja river coinciding with the strands of the Idrija fault zone. Using the tectonic geomorphology (e.g. Žibret and Žibret 2014) and detailed LiDAR digital elevation model, recent kinematics of the Idrija fault was studied by Moulin et al. (2014). Later they applied also thedatingmethodsbasedontheexposureofoutcropstocosmicrays(isotope36Cl)andestimatedtheaver-ageslipratealongthefaulton1.15mm/yearforlatePleistoceneonwards(Moulinetal.2016).Intheframe ofseismotectonicparameterisationofactivefaultsinSlovenia,Atanackovetal.(2016)estimatedtherecent slip rate on 1mm/year. It is assumed that the Idrija fault is seismically active, although the number of earthquakes detectedso far in its vicinity is rather low (Živčić et al. 2011; Vičič et al. 2019). However, the fact that seismic sta­tionswereinthepastlocatedatrelatively largedistances,contributestothelargeextenttotheuncertainty of determinations. For the Idrija earthquake in 1511 with estimated magnitude of 6.8, it is supposed that it occurred in the wider area of the Idrija fault. However, the exact location of this event is still subject of investigations (Fitzko et al. 2005). Recently, the most important investigations of this subject are paleo­seismological(Bavecetal.2013).Inthe20th centuryinawiderareaoftheIdrijafaulttwostrongearthquakeshappened, the Cerknica one in 1926 and the 1998 in Krn Mountains (Živčić et al. 2011). 2.2 Measurements of tectonic displacements Estimatesonrecentslip-ratesareveryimportanttounderstandactivetectonicsandtectonicgeomorphol­ogy,aswellasforearthquakehazardassessments.Intheregionswithmoderateratesofdeformations,including Slovenia,tomeasurerecentslip-ratesisnotaneasytask,especiallyifstrongfaultsarecharacterisedbyrather wide fault zones. To accomplish the task the methods of terrestrial and satellite geodesy are used. In the past several repeated levelling measurements were conducted along various infrastructure. They usually measured only vertical deformations, but horizontal displacements can be measured as well. In the west­ern Slovenia vertical deformations were measured along the profile from Sečovlje to Bled (Rižnar, Koler andBavec2007) indicating fasterupliftoftheJulian Alpsnorth of the Idrija faultwith respecttothe terri­tory south of it. For detailed analysis of the activity of individual faults, geodetic measurements should be performed at locations where structural geological setting is well known and the fault zone is preferable nottoowide.OntheIdrijafaultitwasappraisedthatforterrestrialmeasurementsasuitabletransectisbetween DolenjaTrebušaandKanomeljskoRazpotje(ČarandGosar2011).Forthispurposeanetworkoffourpoints wasdeployedintheKanomljicavalleyalreadyin1985,butonlyinitialmeasurementswereconducted(Kogoj 2000). ForgeodeticmonitoringofactivefaultzonesPlacerandKoler(2007)proposeddeploymentofgeo­detic networks of points in both blocks outside the fault zones and long-term measurements. Some investigations which include repeated GNSS measurements were also conducted (Weber et al. 2010; Serpelloni et al. 2016) in W Slovenia. They provided velocity vectors for wider area indicating gen­eral movements in the north direction for 2–3mm/years. However, the density of measuring points was ingeneraltoolowtoenableassessmentofdisplacementsalongindividualfaults.BesidesGNSSmeasurements, fordetectionofverticalmovementsofthesurfaceSyntheticApertureRadarmethodofpersistentscatterers (InSAR PS) is also used. This method was applied also in the Julian Alps, but not evaluated for tectonicdeformations (Žibret, Komac and Jemec Auflič 2012). With respect to the scale of measurement, on the other end, compared to satellite geodesy, are micro-displacement measurements on individual fault planes or cracks inside the fault zones (Stemberk, Košťak andVilimek2003),whicharedescribedinthispaper.Bytheirapplicationwecanprovetheactivityofafault planeand thus activity of the fault, but we cannot assess the total deformation across the whole fault zone. 3 The Idrija fault zone in the Učja valley In the Učja valley the Idrija fault zone is approximately 750m wide (Figure 2). In the frame of COST pro­ject 3D monitoring of active tectonic structures it was geologically mapped by Igor Rižnar. The wider area isbuiltmainlyofupperTriassicDachsteinlimestone.Slightlytothenorth,thereisthemainthrustofKanin Mountains,alongwhichtheDachsteinlimestoneisoverthrustedtothesouthonCretaceousflysch(Buser 1986). To the SW of the main fault plane in the Učja valley there is a smaller area of Jurassic limestone, and in the canyon floor in some places Cretaceous flysch outcrops. The inner fault zone is approximate-ly260mwideandcomprisesoftwoborderfaults,themainandsidefaultplanes(Figure2).Alongthemain fault plane we didn’t find any suitable crack for micro-displacement measurements. On the other hand, thesidefaultplanewhichruns70mtotheeastacross50mhighcanyonwall,representsaprominentcrack (Figure 3a), which was found as the most appropriate for the installation of extensometer. Down the river to the east, there is another well exposed fault plane with striations which indicate subhorizontal move­ments (Figure 3b). However, the access to this narrow part of the canyon with equipment needed for the installation was not possible. Figure2:DetailedmapofouterandinnerfaultzonesoftheIdrijafaultintheUčjavalleyonshadedLiDAR1mresolutiondigitalelevationmodel(ARSO 2015) with the location of TM 71 extensometer. 4 Methods 4.1 Extensometer TM 71 TM 71 is a mechanic extensometer (Figure 4) aimed for installations on cracks to monitor relative micro-displacements of two tectonic blocks separated by the crack. It operates on the principle of Moire optical effect. Displacements are measured through interference pattern (Košťak 1977; Košťak 1991), formed by two optical grids engraved in two glass plates which undergo a relative shift. The instrument measures deformations in three dimensions as displacement vectors in two perpendicular planes (horizontal and vertical) and angular deviation (rotation). The accuracy of the instrument is 0.05–0.0125mm for dis­placements and greater than 3.2x10-4 rad (0.018o) for angular deviation (Stemberk, Košťak and Vilimek 2003; Stemberk, Košťak and Cacon et al. 2010). The main advantage of TM 71 is that it has no electric componentsandisthusveryrobustforoperationindifficultoutdoorconditions.Therefore,itisverysuit­ableforlong-termmonitoring.Adisadvantageisthatitrequiresmanualreadingsatregularintervals.However, this problem was recently solved for temperature stable and protected environments (for instance karst Figure 3: a) A crack in the Idrija fault inner fault zone in the Učja valley. Arrow indicates the location of the TM 71 extensometer. b) Outcrop of another fault plane located 50m to the east with clear striations indicating subhorizontal movements (after Gosar 2007). caves) by automated shooting images of interference pattern in selected intervals (Briestensky et al. 2010; Šebelaetal.2009).Instrumentreadingsarealwayscorrectedfortemperaturevariations.Todayalmost300 instruments are installed in the whole world. Beside measurements of tectonic displacements, it is used also in engineering geology for monitoring stability of rock blocks or landsliding. 4.2 Measurements of tectonic micro-displacements in the Učja valley Afterdetailedsurveyofthefaultzoneweselected,asthemostsuitableforinstallationoftheTM71,apromi­nentcrackintheinitialpartofthecanyon,whichcut50mhighsouthorientedface(Figure3a).Thecrack extends across the whole face, and the installation was realised at the foot of it, above a large scree cone (Figures 3a and 5). In this area seismically triggered rockfalls occurred during the 1976 Friuli earthquake (Čar and Pišljar 1993) and also during the 1998 earthquake in the Krn Mountains (Gosar 2012; 2019c).InstallationofTM71wasperformedinNovember2004(Šebelaetal.2005;Gosaretal.2007).Quiteachal­lengewasalreadyatransportofheavydrillingequipmentintothecanyonandacrosstheriver.Takinginto account configuration of the crack, a still rod is anchored in the western block in two points and in the eastern block in one point (Figure 5). Toguarantee a sustainable installation without exposureto damage, it was important that the instrument is located under the small overhang in the wall (Figure 3a) which protects it from falling rocks and ice. The instrument is protected with a metal case (Figure 5a). 5 Results The extensometer TM 71 records displacements for already 14 years. This is long enough period that it is possible to deduce on representativity of long-term displacements. The results of the first six years of measurements(endof2004–2010)werealreadypublishedinGosaretal.2011),butadditionaleightyears Figure 4: The TM 71 extensometer which measures tectonic micro-displacements in three directions. (2011–2018) of measurements allows much more firm interpretations and conclusions. The results (Figure6)showsespeciallysystematictrendofhorizontaldisplacements(y-axis)andrelativelysmallerdis-placements in vertical direction (z-axis). This observation is in agreement with the fact that Idrija fault is today mainly a strike-slip fault with minor vertical component of slip (Čar and Gosar 2011). This was so far known from geological observations only. Other source of information on the sense of displacements couldbeseismologicaldata.HoweverduringthelastdecadesofdetailedseismologicalmonitoringinSlovenia andFriuli,therewerenoreallystrongearthquakesontheIdrijafaultwhichwillallowcomputationoffocalmechanisms or detailed analysis of a coseismic slip along the faultplane (Živčić et al. 2011; Gosar 2019b). Suchanalyseswereperformedforthe1998and2004earthquakesintheKrnMountains,wherefocalmech­anisms show on almost pure dextral slip along the Ravne fault with only minor vertical component (Bajc et al. 2001; Živčić et al. 2011; Gosar 2019a). Since Ravne and Idrija faults are parallel and both exposed to thesamestressregime(compressioninN–Sdirection),wecandeducethatalsoalongtheIdrijafaultrecent displacements are predominantly dextral strike-slip. However, this is not necessarily valid for all cracks within the wide fault zone (e.g. Twiss and Moores 1992). In fact measurements with TM 71 on the crack which is parallel to the main fault plane shows predominantly left-lateral strike-slip with minor vertical component. Although sucha result is a surprise, a thorough discussion on possible causes at this moment is not possible. This would perhaps become possible, if detailed geodetic measurements in a dense net of points would be performed for several years. Such a survey should include a measuring points that are definitely located in a stabile blocks far outside from the fault zone, as well as within the blocks separat­edbyindividualfaultplaneswithintheouterandinnerfaultzones.Localpermutationsofthestressdirection withincomplexfaultzonesarealwayspossible,andtheycanresultinunequalsenseofmovementsofindi­vidual blocks also due to rotation of blocks (Twiss and Moores 1992). Therefore, in spite the whole Idrija fault clearly expresses right-lateral strike-slip movements, a displacement on a crack inside the fault zone composed of several blocks and fault planes can show opposite sense. Large scale neotectonic rotations of rigid blocks in the Adria-Eurasia collision strike-slip zones in W Slovenia were recently revealed from paleomagnetic data of Pliocene-Quaternary cave sediments (Vrabec et al. 2018). However, this large scale observation cannot be directly transferred to the local scale situation within the complex fault zone. Average displacement rate of left-lateral slip in the first ten years (2004–2014) is 0.21mm/years (Figure 6). Inthefirsttenmonthsafterinstallationthevelocitywasevenmuchhigher(y=+0.54mm/year) (Gosar et al. 2011). It was followed with anomalous reading at the beginning of 2006. Although there are nodirect proofs,this outlieris most probably a result ofanoutermechanical influenceontheinstrument, which can be a falling rock or ice. This explanation is likely, because outlying reading was later completely recovered. In the first 2.5 years the average displacement rate was 0.31mm/year, and in the first six years 0.24mm/year (Gosar et al. 2011). This can be an indication of gradually diminishing of displacement rate 2.8 2.6 2.4 y 2.2 2.0 1.8 Displacement (mm) +0.21 mm/yr +0.18 mm/yr 1.6 1.4 1.2 +0.24 mm/yr 1.0 0.8 +0.31 mm/yr 0.6 +0.54 z 0.4 +0.06 mm/yr 0.2 mm/yr +0.03 mm/yr 0.0 x –0.2 –0.4 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Year Figure 6: Displacements observed with TM 71 on the Idrija fault; +x indicates closing of the crack, +y indicates left-lateral displacement, +z indicates lowering of the SW block. 35 0.3 Temperature +x – crack opening 0.2 30 0.1 0 25 –0.1 Temperature (°C) 20 15 10 5 0 –0.2 –0.3 –0.4 –0.5 –0.6 –0.7 –0.8 –0.9 Displacement (mm) 12.11.2004 6.01.200510.03.200515.04.200512.06.2005 5.08.200524.09.200511.11.200520.01.200611.03.2006 2.04.200612.05.200624.06.200626.07.2006 9.10.200614.11.200617.02.200713.05.200718.08.200725.11.2007 2.03.200814.05.200829.06.200810.11.2008 7.05.200928.08.200923.11.2009 1.09.201014.10.201019.04.201118.11.201122.11.201223.07.201323.07.201324.07.201419.07.201619.10.201622.03.2017 5.10.201723.04.201824.07.201826.09.2018 Date Figure 7: Correlation between temperature variations and opening (-x extension) or closing (+x compression) of the crack on the Idrija fault. 88 withtime.Possiblereasonsforthisarenotknown.However,on12July,2004astrongearthquakewithmoment magnitudeof5.2occurredintheKrnMountains(Gosar2019b)atthedistanceof10–12kmfromUčja,only fivemonthsbeforeinstallationofTM71. Itiswellknownthatlargeearthquakescauseastaticstresschange on neighbouring faults. Therefore also the Krn Mountains earthquake definitely had an influence also on theIdrijafaultwhichrunsonly8kmtotheSW.Coulombstaticstresschangefor1998and2004earthquakes wascomputedbyGanas,GosarandDrakatos(2008)andshowsslightunloadinginthepartoftheIdrijafaultnear Žaga. Although this can be only a hypothesis, the stress change can have an influence on the slip-rate withdiminisheswithtimeaftertheearthquake.Moreover,aftertheyear2004uptonowtherewerenoother strong earthquakes in the area which exceed magnitude 3.5 (Gosar 2019b). In the last years a smaller dis­placement rate of 0.08mm/year was measured with TM 71 from mid-2014 up to the end of 2018. Taking intoaccountthewhole14-yearsofobservation,theaveragehorizontaldisplacementratewas0.18mm/year. Ontheverticalaxis(z-axis)duringfirstsixyearsofobservationsverystablepositivedisplacementrates wereestablished+0.06mm/year(Gosaretal.2011),whichmeansrelativesubsidenceoftheSWblockwith respect to the NE block (Figure 6). After 2010 this rate has diminished and for the whole 14-years period it is only +0.03mm/year. For the Idrija fault prevailing strike-slip tectonics, subordinated vertical com­ponent was expected also from geological data. The horizontal x-axis extends in transverse direction to the crack and reflects opening or closure of the crack. As expected it shows only seasonal variations, which are in general well correlated with mea­suredtemperaturesatthetimeoftakingreadings(Figures6and7).Positivevalues(compression)corresponds to higher temperatures in summer months and negative values (extension) to lower temperatures in win­ter months. Observed displacements do not exceed 0.2mm. Angular deformations (rotations) in both measuring planes are small (Figure 8). In the xz plane they reach maximum of +0.4 ./200 and in the xy plane maximum of -0.2 ./200. The largest deformations in the xz plane were in years 2007, 2009 in 2011, but they were later mostly recovered and there is no sys-tematictrendoverthewholeperiodofobservation.Onthexyplanethereisonlyaslighttrendtonegative values over the whole period. 0.5 0.4 0.3 0.2 gama xz 0.1 0.0 gama xy 0.1 0.2 0.3 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Angular deviation ( /200) . Year Figure 8: Angular deviations observed with TM 71 on the Idrija fault in two planes. 6 Discussion of results and conclusions Displacement measurements with TM 71 extensometer on the crack in the inner fault zone of the Idrija fault proved that this is an active fault. This is a very important result, because no direct geodetic (Kogoj2000) or seismological (Živčić et al. 2011) proofs of its recent activity are available so far, although it was deduced from the geologic (Čar 2010), tectonic geomorphological (Cunningham et al. 2006; Moulin et al. 2016) and paleoseismological (Bavec et al. 2013) investigations that Idrija fault is an active fault. AmongallsupposedactivefaultsmonitoredwithTM71extensometersinSlovenia(Gosaretal.2011) the observed horizontal displacement rates on the Idrija fault are with the leap the highest (average rate of 0.21mm/year) and with the most stable and consistent trend. The measured displacement rates on the Raša, Kneža, Predjama-Avče (Figure 1) and Brežice faults (from 0.006 to 0.05mm/year) are for one order of magnitude smaller. Only measuring location on the Raša fault showed for 2.5 years a higher vertical displacement rate (0.16mm/years), but later the sense of the movements has changed and the long-term averagedisplacementtrendis0.06mm/year(Gosaretal.2011),whichisthesameasmeasuredinthewhole 14-years period on the Idrija fault, but the trend on the later was stable and the sense of movements con­sistent in the whole period. DuringthewholeperiodthedisplacementtrendsontheIdrijafaultwereconsistent,howevertheslip-rate diminishes with time. This can be only hypothetically related to the static stress changes on the Idrija fault after the strong 2004 earthquake (Ganas, Gosar and Drakatos 2008). Prevailing are left-lateral hor­izontaldisplacementswithaveragerateof0.21mm/year,andsubordinatedverticaldisplacementswiththe rate of 0.06mm/year. For observed left-lateral displacements within dextral strike-slip fault we can only guess that they are caused by local permutation of the stress field within a complex and very wide fault zone or by rotations of the blocks. Measured displacement rates can be compared with long-term dis­placementsestimatedfromthegeologicaldata,whicharefrom0.25to0.16mm/year(Placer1971).Based on tectonic geomorphology and cosmic rays exposure dating, the slip-rate of the Idrija fault for post late Pleistocene period is assessed on 1.15mm/year (Moulin et al. 2016). In the frame of seismotectonic para­meterisation of active faults Atanackov et al. (2014) estimated the recent slip-rate on 1mm/year. GNSS measurements performed in W Slovenia revealed general movements of the territory in the north direc­tion with velocity of 2–3mm/year(Weber et al. 2010; Serpelloni et al. 2016). Deformations related to this movementsaredistributedovernumerousfaultsofDinaricdirectionwhichprevailintheWSlovenia(Moulin et al. 2016). In a recent study on the present-day kinematic behaviour of active faults in the Eastern Alps in Austria using TM 71 extensometers (Baroň et al. 2019), it was found that annual displacement rates of the monitored faults were mostly about an order of magnitude smaller than the rates of the entire crustal wedges revealed from GNSS measurements. This is consistent with our observations on the Idrija fault. Comparison of deformation rates on various faults is very important for earthquake hazard assess-ment,especiallyintheWSlovenia,whereactiveDinaricstrike-slipfaultsprevail.Themostintriguingabove all is the Idrija fault, due to rather low recent seismic activity in the last decades of instrumentally seis­mological monitoring (Živčić et al. 2011). This fact rises a question which of Dinaric faults could be a seismogenic sources of the strongest known historical or paleoseismological earthquakes in the region, for instance the Idrija 1511 earthquake (Fitzko et al. 2005), because these earthquakes to large extent con­trol the seismic hazard in W Slovenia. Results of TM 71 measurements on the Idrija and Raša faults and in vicinity of the Predjama-Avče fault in the Postojna cave revealed that observed deformations are much higher on the Idrija fault, although the seismic activity in the last decades was higher in the vicinity of the Raša and Predjama-Avče faults especially with several earthquake swarms or aftershock sequences in the Ilirska Bistrica, Pivka-Knežak and Vipava valley areas (Vičič et al. 2019). AlthoughinvestigationsontheactivetectonicsoftheDinaricfaultsystemhavebeenmoreintensivein thelastdecadeandcomprisestectonicgeomorphology,paleoseismology,satellitegeodesy,seismology,micro-displacement measurements etc., they still do not provide sufficient data for reliable estimates on recent slip-ratesoftheIdrijafault.Therefore,itwouldbeveryimportanttosupplementthemwithsystematicand long-term geodetic measurements in a well designed and dense network of measuring points installed on stableoutcropsonbothtectonicblocksseparatedbythefault,outsideofitshighlyfracturedfaultzone(Placer andKoler2007).RealisticdataonrecentratesoftectonicdeformationsalongtheIdrijafaultandotherDinaric faults in the W Slovenia are beside geodynamic interpretations very important for improvement of seis­motectonic models and thus for better seismic hazard assessment in this earthquakes prone area. 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