2019 | 72/3 | 179–193 | 13 Figs. | 1 Tab. | www.geologia-croatica.hr Journal of the Croatian Geological Survey and the Croatian Geological Society

Geological and structural setting of the Vinodol Valley (NW Adriatic, ): insights into its tectonic evolution based on structural investigations

Damir Palenik1*, Dubravko Matičec1, Ladislav Fuček1, Bojan Matoš2, Marijan Herak3 and Igor Vlahović2

1 Croatian Geological Survey, Department of Geology, Sachsova 2, HR-10000 , Croatia; (*corresponding author: [email protected]) 2 University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Department of Geology and Geological Engineering, Pierottijeva 6, HR-10000 Zagreb, Croatia 3 University of Zagreb, Faculty of Science, Department of Geophysics, Horvatovac 95, HR-10000 Zagreb, Croatia doi: 10.4154/gc.2019.13

Abstract Article history: The area of the Vinodol Valley and Bay represents a NW‒SE oriented valley in the NW Manuscript received January 28, 2019 Adriatic characterised by prominent historical and instrumentally recorded seismicity. As part of Revised manuscript accepted May 31, 2019 the greater geodynamic domain including the Ilirska Bistrica–– seismogenic fault Available online October 31, 2019 zone, new geological and structural data addressing the tectonic evolution of the area were col- lected in order to better understand the focal mechanisms of previous earthquakes and to en- able identification of potential seismogenic sources. Mapped informal lithostratigraphic units mostly correspond to the Upper Cretaceous, Palaeo- gene and Quaternary successions described in other parts of the External Dinarides. However, a shorter stratigraphic range of the Gornji Humac fm., the youngest Cretaceous unit in the study

area, was determined and suggests that the uplifted area in the central NW part of the Adriatic 2 Carbonate Platform already comprised several thousand km (from W and NW to and Vinodol area) at the end of the Turonian. Structural measurements of the fault planes in the study area generally correspond to the exist- ing structural model of the tectonic evolution of the Dinarides. However, in contrast to the SW

vergences typical of the Dinarides, NE-vergent reverse structures are common, especially along the SW margin of the Vinodol Valley. Cross-cutting relationships suggest that transpressional (NW–SE and NE–SW striking dextral and sinistral faults) and extensional features (NW–SE and NE–SW striking normal faults) are structurally concurrent or younger than the reverse faults, suggesting a change in the palaeostress field during the Neogene–Quaternary, with prevalent transpression and radial extension. Comparison of results of the palaeostress field analysis and the constructed synthetic focal mechanisms on one side, with available focal mechanism solu- tions for earthquakes within the Ilirska Bistrica–Rijeka–Senj seismogenic fault zone on the oth- Keywords: NW Adriatic, Vinodol Valley, Bakar Bay, SW and NE vergences, er, shows a favourable orientation of the observed NW‒SE and NE‒SW striking faults with re- compression/transpression, neotectonic activity, spect to the recent compressional/transpressional stress field (N‒S oriented P-axis), indicating focal mechanism solutions, seismicity these as potential seismogenic sources within the study area.

1. INTRODUCTION The Vinodol Valley is a 20 km long NW‒SE oriented valley which HERAK (1999), HERAK & HERAK (2017), and IVANČIĆ et runs parallel to the NE Adriatic coastline, stretching from Križišće al. (2018). These authors reported data on instrumental and his- in the NW to in the SE. The area of the Bakar torical seismic activity in the area and discussed the potential Bay represents its geomorphological and geological extension to- seismic sources. wards the NW (Fig. 1). Research presented here was performed in the framework of The most important geological investigation of the wider two ongoing scientific projects funded by the Croatian Science area of the Vinodol Valley and Bakar Bay was undertaken for the Foundation (HRZZ): VELEBIT (Grant no. IP-2014-09-9666) and Basic Geological Map of SFRY at a 1:100,000 scale (ŠUŠNJAR GEOSEKVA (Grant no. IP-2016-06-1854). The VELEBIT project et al., 1970). Accompanying explanatory notes (GRIMANI et al., represents a multidisciplinary research approach addressing cor- 1973) also include a review of previous studies. In addition to relation of seismological data and tectonic framework in the these geological investigations associated with the Basic Geo- neighbouring Velebit Mt. region, which is characterised by low logical Map and its explanatory notes, the most important geo- seismicity and weak to moderate magnitude (M ≤ 5) earthquakes logical and structural studies of the Vinodol Valley were those at shallow depths. The main research objectives of the GEO- by BLAŠKOVIĆ (1991, 1997, 1998, 1999, 2005), in which he pro- SEKVA project are the production of new geological maps (at posed a tectonic concept of the Vinodol Valley area. 1:25,000 and 1:50,000 scales) and 3D geological models of se- The area of the Vinodol Valley and Bakar Bay was investi- lected structures in the wider Kvarner region, as well as the gated as a seismotectonically active area by PRELOGOVIĆ et al. broadening of the seismic station network and construction of a (1981, 1982, 1995), HERAK et al. (1996, 2017), MARKUŠIĆ & relevant seismotectonic model of the Kvarner region. Geologia Croatica new geological map of the Vinodol Valley and its border areas areas border its Valleyand Vinodol the of map geological new the of production on focused was research the of phase first The 2.1. Geologicalmappingof thestudyarea METHODOLOGY2. ofCroatia oftheRepublic Map 1:300,000(HGI,2009). Figure 1.Location mapandschematic geological mapoftheinvestigated andwider areas ofthe Vinodol Valley Bay. andBakar from Geological Modified theBasic 180 kinematics and identification ofseismogenic structures. potential kinematics of standing the evolutiontectonic of the including study fault area, under greater to contribute could earthquakes of previous nisms mecha focal the on data new with together investigation, Such NW). the towards continuation (its Bay Bakar Valleyand nodol ofresearch by the accompanied Vistructural-geological detailed geological in the mapping from NW in Križišće to the Kričina SE The main focus of the research in the Vinodol Valley was the the was Valley Vinodol the in research the of focus main The - - - During analysis, for determination ofanalysis, for During fault in determination relation kinematics area, structural data on outcrop-scale fault slips were collected. Bay. Valley of Bakar Vinodol the the edges in well as as along SW the NE and were performed measurements Structural 2.2. Structural-geologicalinvestigation andanalysis areas. neighbouring from units lithostratigraphic contemporaneous with compared and tions were units from geological estimated lithostratigraphic cross-sec at1:25,000 mapped were scale. parts ginal Vi the of part mar the while 1:5,000 scale, central at mapped The been Valleyhas nodol principles. lithostratigraphic on based Within an approximately 30 km long and 1–5.5 km wide wide km 1–5.5 and long km 30 approximately an Within individual of thicknesses tectonics, intense the to Due Geologia Croatica 72/3 - - - Geologia Croatica - - - - - 181 , corresponding to the succession Milna fm. Milna – the island of Brač& JELASKA,(GUŠIĆ locus typicus On the basis of the geological map (Fig. 2) five transverse tures of the neighbouring Velebit Mt. and Krk island (VLAHOVIĆislandKrk and Mt. neighbouringtheVelebit tures of TOMLJENOVIĆ 2018). et al., 2018; et al., ŚRODOŃ 2012; et al., Inaddition to a completely new detailed lithostratigraphic subdi deposits,vision of this theis one of improvements key in respect 1970). al., et (ŠUŠNJAR areathe of map geological previousthe to geological cross-sections of the Vinodol have Valley been con structed 3). (Fig. Valley units of the Vinodol 3.2. Lithostratigraphic chronostratigraphicthe basedon were maps Previous geological approach so et (ŠUŠNJAR 1999), the al., BLAŠKOVIĆ, 1970; map presented here is the first one based on lithostratigraphic CretaceouslithostratigraphicUpperprinciples. named units were after, and compared to, the informal lithostratigraphic units al readydefined in other areasJELASKA, A total three of of 1990). Upper Cretaceous, the three Pal External Dinaridesaeogene (GUŠIĆ and four Quaternary& units have been described in the study area. those along the SW edge of the Vinodol Valley mostly indicate theindicate mostly Valley Vinodol the of edge SW the along those is,transport,tectonic which NE, directiontheof opposite towards although quite rare in the Dinarides, very common in the struc 3.2.1. Upper Cretaceous The oldest informal lithostratigraphic unit of theis Vinodolthe Cenomanian Valley at the 1990). It is composed of well-bedded limestones of a light brown- light a limestones well-beddedof of composed is It 1990). ------), ), intermediate 1 ) were calculated, whereas using 3 ) and minimum stress axes (σ 2 (σ LER, 1977) synthetic focal mechanisms for the analysed fault segments were determined, i.e., palaeo-synthetic focal mecha nisms as representations the palaeostress of fields. the computed Right Dihedra Method (ANGELIER & MECH Geological map and schematic geological column of the Vinodol Valley from Križišće Kričina. to from Valley Vinodol of the column geological map and schematic 2. Geological Figure 3. RESULTS Valley 3.1. Geological mapping of the Vinodol Vinodol thedetermined mappingmargins bothof Geological that Valley are in general fault-bounded, whereas earlier proposals suggested that only the et NEAlong al., 1970). the marginNE edge of the Vinodol reverseValley was fault boundedfaults are characterised (ŠUŠNJAR by tectonic transport to the while SW, urements of dip direction and dip angle of fault planes and orienand planes fault of angledirection dipdip and urements of tation of carbonate slickensides definedby azimuth andplunge, and, wherever possible, their sense of movement. Despite the relatively weathered outcrops and steep terrain, more than 120 sets of shear joint/fault planes data were gathered at stations 127 Bakar and Valley Vinodol the margins of SW NE and the along In Bay. some places, overlapping and crosscutting relationships between the observed striations enabled the relative temporal comparison of deformation. Based on kinematic criteria, the structuraldata separatedwere into compatibledatasets andpro cessed by FPTectonics software (ORTNER et Usingal., 2002). the P–T axis method (TURNER, MARRETT1953; & ALL MENDINGER, theoretical1990) maximum (σ to the past and present stress fields,we used dataof field meas Palenik et al.: Geological and structural setting of the Vinodol Valley (NW Adriatic, Croatia):insights into its tectonic evolution based on structural investigations Geologia Croatica ckina ckina BIGNY, d’OR foraminifera benthic the includes assemblage microfossil The environments. peritidal to subtidal and drodonts LLH deposition indicating in stromatolites, shallow are and/or relatively rudstones rare, as are chon layers containing floatstones Rudist shells. ostreid rare and debris rudist radiolitid of amounts variable with grainstones and packstones bioclastic peloid– ofand to colour wackestones composed grey mudstones Figure 3. Transverse 182 ( P. ) CHERCHI CHERCHI et balcanica al., Nummuloculina regularis PHILIPPSON, regularis Nummuloculina geological ofthe cross-sections Vinodol Valley. Pseudolithuonella reicheli Chrysalidina gradata gradata Chrysalidina Broe - - also characterised by the widespread Oceanic Anoxic Event 2 2 Event Anoxic Oceanic widespread the by characterised also Early Turonian (HAQ et al., 1987; et al., HARDENBOL 1998) was area). study the in out crop not does which unit of the lower part the including (not m 250 c. at estimated be may fm. Milna the of thickness The shells. chondrodont and rudists radiolitid minate nian age. Macrofossils are relatively by rare, represented indeter a Cenoma to Upper Middle indicating alveolinids, and MARIE Global relative sea-level rise during the Late Cenomanian‒ Late the during rise sea-level relative Global Geologia Croatica 72/3 - - Geologia Croatica ------183 ). active, unlithified rockfall deposits in in deposits rockfall unlithified active, –

terra rossa Deluvial-proluvial deposits areDeluvial-proluvial represented by chaotic Alluvial deposits – river and stream beds of the Vinodol Val Rockfall depositsRockfall Flyschdeposits are represented by the alternation of me 3.2.3. Quaternary Rockfall breccias cover marginal areasare of characterised the by Vinodol a variable but generally high degree Valley lith of and ification carbonateby cements. consistThey mainly of unsorted stratigraphictypicallyvariablealthough limestoneages, of debris some breccias contain clasts of only one lithostratigraphic unit, depending on their source area. The stratigraphic age of some thethan older even probably be lithified breccias may completely Quaternary. masses of angular to slightly rounded, unsorted limestone frag ments ranging in size from mm- to metre-sized blocks within a mostly reddish clayey matrix derived mostly from the Mediter ranean red soil ( ley are often filled with gravels characterised degreesvariable gravels by with filled oftenare ley roundnessdifferent and thesefragment of materialsizes. for The depositsmainlyoriginates carbonatefromthehinterland (Creta partlyandlimestones) sandstonefromPalaeogene theceousand horizons within the Flysch deposits. Flood plains are character ised the by deposition fine-grained of sands, silty mud clay. and resenting a gradual deepening, i.e. transition from shallow-ma rine Foraminiferal limestones to deep-marine Flysch deposits. They are mostclearly visible along the NE margin and in This unit characterised is the glauco by SE Valley. part the Vinodol of nite grains, both detrital and diagenetic in origin. In the lower part,upperparturchinsthebeds,seawhile some commoninare theof unit often contains irregular chert nodules. The estimated thickness of the Transitional deposits in the study area is about 60 m, and based on superpositional relationships they are prob Middle of Eoceneably age. the form of talus are located along the steep margins of the Vi the of margins steep the along located are talus of form the They nodol Valley. are more frequent and of larger dimensions margins.valleyTheir fragmentsNEthe angular areof along and differentsizes, being the resultofof erosion the steep carbonate Valley its and of Vinodolcliffsimmediate the hinterland. 3.3. Structural data analysis results within the Vinodol fault zone Within the structural field investigationsthe NEin andthe SW studymargins of area,the Vinodol joint/and Valley shearalong Bakar 120 than more Bay, 4) Fig. (VFZ; zone fault Vinodol the i.e. fault plane data on 127 geological stations have been collected (Fig. 4). According to the structural measurements, the area of the VFZ can be subdivided into the NE Vinodol Fault (NEVFZ)Zone and the SW Vinodol Fault Zone (SWVFZ) (Fig. 4). characterisedarestrike-slipdip-slipand both Faults kinemat by kinematicspredom oblique-slipcharacterised a as by well as ics, dium-sized,well-sorted carbonate/quartz/mica sandstones com However, marls.normalgradation showinggrey-blue andmonly more much areregularlydistributed they sincenot sandstones are common in the NW part of the Vinodol whileValley in its SE partmarls predominate. Thedeposits Flysch are usually consid ered to be the of Middle to Upper Eocene age (GRIMANI et al., although 1973), some studies in neighbouring areas indicate a possibly younger age (ŠPARICA et al., 2005; MIKES et al., 2008). Although the Flysch deposits are mostly coveredternary by Qua deposits their thickness in the study area probably does m, as estimated exceednot 350 from profiles. geological ------Decas (BONET) Thaumato (GUŠIĆ (GUŠIĆ & JELASKA, crop out along the slopes of

Pithonella sphaericaPithonella Pseudocyclammina sphaeroidea sphaeroidea Pseudocyclammina (RADOIČIĆ) and Sv. DuhSv. fm. are a succession of blueish to grey

(BONET)) rocks of this unit contain contain unit this of rocks (BONET)) kotori ) (KAUFMANN), (KAUFMANN), Aeolisaccus ( Foraminiferal limestonesForaminiferal (first established on the island of of island the on established The Gornji Humac fm. (first Transitional deposits Transitional Pithonella innominata Pithonella varies laterally from to around 70 m. c. 100

Pithonellaovalis and rare indeterminate planktonic foraminifera, and in the lower and upper part shallow-marine ostracods and miliolids as as well bio Duh fm. was deposited The gastropods Sv. of clasts and bivalves. withintemporaryenvironments, transitionsdrownedplatform and fromtheunderlying andtotheshallow-marine overlying deposits are gradual. Based on the superposition, microfossil assemblage and similar deposits in neighbouring Istria (VLAHOVIĆ et al., estimatedDuhbe fm. may Upperas stratigraphic Sv. 2002) of age intensetoDue post-sedimentary Cenomanian Turonian. Lower to tectonics in the study area thickness of deposits cannot be meas ured directly, may be m. but approximated at 130‒150 Cre youngest representsthe JELASKA,1990) & GUŠIĆ by Brač taceous depositsin thestudy area, croppingout along the slopes of theVinodol Valley andrepresenting the footwallof the trans ForaminiferalPalaeogenegressive composedlimestones.of is It with benthic fenestral fo mudstone‒wackestones mudstones, raminifera, calcareous algae, ostracods, small bioclasts and pe benthicforaminiferaandrela and peloids packstones with loids, re-established in deposited were They rudistfloatstones. rare tively peritidal environments and in places contain numerous tronema porella parvovesiculifera (RAINERI), microfossils typical for this unit the entire over Adriatic Carbonate Platform area. Find foraminiferabenthicthe of ings indicatesGENDROT an Upper Turonian age for the deposits of this lithostratigraphic unit. In the study area, theofthe uppermostGornji Humac partfm. deposits is very karstified, intenselymore or less recrystallized and colouredstratigraphicvery long a hiatusestimatedduration be (its may at yellowish to reddishHumac dueGornji the thicknesstotal of tothe Therefore, 35–40My). c. fm. 1990). In the studied areabrownish the mudstones and mudstone‒wackestones. unit Besides a vari is composed of thick-bedded light able, able, but significant amountof pithonelomorphic calcispheres ( 3.2.2. The Palaeogene Eocene (OAE2; SCHLANGERJENKYNS,inwhich,areathe & of 1976) (OAE2; the Adriatic Carbonate Platform, is recognized as an informal lithostratigraphic unit – the Palenik et al.: Geological and structural setting of the Vinodol Valley (NW Adriatic, Croatia):insights into its tectonic evolution based on structural investigations the transgressivelyVinodol Valley, overlying the Upper Creta ceous deposits of the Gornji Humac fm. This unit is characterisedis unitThisfm. Humac Gornji the of depositsceous caused probably verticaldiversity, facies significant lateral and by organismsfrommixing of theresulting inpalaeorelief variable by general deepening- different environments. a although Therefore, upward trend is recognizable, Foraminiferal limestones in the study area cannot separated be into sub-units usually named af ter predominant benthic foraminifera older and(from shallower to younger and deeper facies zones the usual sequence is from Miliolid, through AlveolinidrepresentedlimestonesThese bearingby mostly are limestones). and Nummulitid towackestones Orthophragmidand/or packestones with variable amounts of fo raminifera tests and other bioclasts. Youngerare characterised part by ofthe the predominance deposits of orthophragmids con taining glauconite and a few other non-carbonate bioclasts. The areaForaminiferalstudyestimatedthe limestonesthickness inof 200is c. m, and they are Lower–Middle of Eocene age. marlstones with 20–30 cm limestoneclayey intercalations, rep Geologia Croatica group subsets i.e. conjugate fault pairs characterised by the NW‒ ofSW margins bythe VFZ. In it general two fault is characterised and NE the along both measured kinematics fault similar of data comprise (VFZ/RF1) faults reverse observed of group first The into three fault groups and separated six be group subsets can (Fig. planes 5 and fault Table reverse 1). observed that show SWVFZ (Fig.sets 5). were into subdivided compatible fault groups and fault group sub categories main aforementioned three the criteria, kinematic the ics, i.e. 18 and normal 18 reverse Taking kinematics. into account kinemat dip-slip 36 and with planes fault kinematics strike-slip with planes fault 36observed encompassed area SWVFZ the in and 21 exhibit measurements Fieldreverse kinematics. structural fault planes out with dip-slip kinematics, of which 8 have normal 29 and kinematics strike-slip show with 19 planes fault NEVFZ the along collected data kinematics, fault the to respect With planes show NW‒SE directions. and strike predominant NE‒SW and taceous SWVFZ; Palaeogene rocks, respectively.carbonate Those fault and (NEVFZ Bay Cre Upper the Bakar in measured were planes Fig. and 72fault 4), and 48 Valley Vinodol the of gins ible structural datasets. datasets. ible structural compat into data structural collected the separate to used were and SW Vinodol (SWVFZ) fault zones (Fig. 4) criteria kinematic (NEVFZ) Vinodol NE the In component. reverse dip-slip inant vided into theNE Vinodol Fault Zone whichiscoloured (NEVFZ), withablueishpolygon, andtheSW Vinodol Fault coloured Zone (SWVFZ) withareddish polygon. Figure 4.Topographic mapofthe Vinodol Valley Bay, andBakar i.e. the measurements. with127locations ofstructural Vinodol faultzone (VFZ) The VFZ issubdi 184 Results of structural analysis in the VFZ, i.e. NEVFZ and and NEVFZ i.e. VFZ, the in analysis structural of Results Within the Vinodol fault zone, along the NE and SW mar SW and NE the along zone, fault Vinodol the Within - - - - - using the P–T axis method (TURNER, 1953; MARRETT & 1953;MARRETT (TURNER, method axis P–T the using Fig. the in 5). diagram NE/RF1 group on directions SW-dipping with planes fault (see motions oblique-slip sinistral sition from pure reverse dip-slip motion to locally reverse, dextral/ tran fault’s the slickenside which and suggests orientation, strike cinity of Tribalj; Figs. 2 and 3) implies alsovi the (in a slightpart central change its in NEVFZ of of the the8).bending slight The (see Figs. deposits Flysch and 3 Eocene over the thrust are stones Palaeo the over SW of margin the Vinodol Valley lime Palaeogene Foraminiferal thrust are fm.) Milna and (the gene limestones clastic Foraminiferal rocks, whereas along the deposits Cretaceous Up older per Valley, Vinodol the of margin NE the along and part SE Table 1). the and Fig. 5 In the in VFZ/RF1 group the for diagrams structural Fig.3, the in cross-sections (see transport tectonic NE Valley,indicating Vinodol generally the of margin SW the along zone fault thrusting main the within measured was and transport tectonic NE-directed and direction dip SW average an by ised character is planes fault of subset second The details). Table for 1 for 3;diagrams the group in VFZ/RF1 the Fig.see structural 5 and (Fig. NEVFZ the of parts central and NW the in observed nanty predomi was It deposits. clastic Palaeogene younger over stones the Upper deposits and Cretaceous lime Palaeogene Foraminiferal of thrusting indicates 5–7) (Figs. transport tectonic SW-directed and direction dip NE average an with subset first (Table1). The SW and (dip NE the towards c. angle both 60°) dipping SE strike, Structural analysis of the representative palaeostress field palaeostress representative the ofanalysis Structural Geologia Croatica 72/3 ------Geologia Croatica - - - - - 185 81 T-axis 3 P-axis 63 02 158 70 222 10 121 12 250 80 175 11 266 05 221 06 131 04 018 03 288 02 338 77 234 03 193 68 79 09 246 76 339 01 9 0 Striation 82 43 93 51 216 54 106 60 200 47 202 37 297 43 111 11 268 124 32 112 144 12 185 25 135 64 229 55 223 23 208 51 258 48 Trend (°)Trend (°) Plunge (°) Trend (°) Plunge (°) Trend (°) Plunge

The second group of the observed reverse faults (NE/RF2) R R R N N N S-S S-S S-S type Fault within the VFZ, along the NE margin of the studygenerarea,themarginNE is within the of VFZ, along the ally characterised by twoThe fault first subset group is characterised subsets by an average (Fig. ESE dipand 5 WNW-directed anddirection tectonic transport, Table 1). whereas the second sub

- - – – – – – – – – – – – – (°) Strike 131–311

(°) 12 44–224 10 136–316 32 42–222 13 76–256 16 168–348 Pitch

(°) Dip angle –– –– –– 78 79 70 93 51 90 Dip 106 60 90 323 63 60 270 63 42 334 52 62 286 42 35 149 69 58 317 67 55 azimuth (°) , respectively. 5 3 2 2 3 – – 8 – – 0 8 – – 5 2 2 3 3 3 data No. of fault No. and σ 2 , σ 1 subset NE/RF2a NE/RF2b NE/NF2a SW/RF3a NE/NF2b SW/RF3b SW/NF3a VFZ/RF1a 12 55 55 67 NE/SSF2a SW/NF3b VFZ/RF1b 15 219 63 74 NE/SSF2b VFZ/NF1a SW/SSF3a 13 VFZ/NF1b 11 230 63 75 SW/SSF3b VFZ/SSF1a 12 VFZ/SSF1b 11 Fault group group Fault Structural diagrams for the Vinodol fault zone (VFZ), i.e. the NE and SW margins of the Vinodol Valley and Bakar Bay (NEVFZ and SWVFZ – see Fig. 4). The 4). and Bakar (NEVFZ Bay and SWVFZValley – see Fig. Vinodol (VFZ), fault zone Vinodol of the the NE and SW margins i.e. the for Structural diagrams

Fault group NE/RF2 NE/NF2 SW/RF3 SW/NF3 VFZ/RF1 NE/SSF2 VFZ/NF1 SW/SSF3 VFZ/SSF1 mal faults group 2; SW/NF3 – Normal faults group 3.Fault types: R – reverse; SS – strike-slip; N – normal. Orientation of the P and T-axis are based on constructed syn are T-axis SS – strike-slip; types: R – reverse; of the P and Orientation N – normal. 3.Fault 2; SW/NF3 – Normal faults group mal faults group thetic structural beach-ball diagrams. Mean geometric properties of the observed fault planes within the VFZ, i.e. along the NE and SW margins of the Vinodol Valley and Bakar (NEVFZ Bay and Valley Vinodol of the along the NE and SW margins 1. MeanVFZ, i.e. geometric properties of the observed fault planes within the Table their geometrical with respect properties to delineated were VFZ zone planes observed the in Fault SWVFZ) kinematic and parameters. with calculated indicators faults group SW/RF3 – Reverse faults group; – Reverse 1; NE/RF2 fault group VFZ/RF1 – Reverse 5): (see Fig. groups and kinematic within the following compatibility Nor – NE/NF2 1; Strike-slip- NormalVFZ/SSF1 – VFZ/NF1 group faults Strike-slip– NE/SSF2 E) 1; Strike-slip– SW/SSF3 2; group faults 3; G) 3; group faults group faults angles indicate σ angles indicate ALLMENDINGER, 1990) aspalaeostressobservedmechanisms, wellthecom indicated thatfocal as derived synthetic structuralpressional is associatedfield P-axiswith a predominantly trend ing NE‒SW, whereas the T-axis is subvertical, steeply dipping details). 1 for Table towards (see the NNW at an 81° angle of Figure 5. Figure 1 (VFZ/RF1); fault group Reverse A) tension. represent quadrants while the shaded compression, represent on the structural beach-ball diagrams quadrants white Strike-slip(SW/RF3); D) 3 2 (NE/RF2); C) 1 (VFZ/SSF1); fault group fault group Reverse fault group B) Reverse E) Strike-slip 2 (NE/SSF2); F) Strike-slip fault group fault blue tri and rectangles, dots, red The 1 (VFZ/NF1); 3 (SW/SSF3); G) Normal fault group 3 (SW/NF3). group 2 (NE/NF2); I) Normal fault group H) Normal fault group Palenik et al.: Geological and structural setting of the Vinodol Valley (NW Adriatic, Croatia):insights into its tectonic evolution based on structural investigations Geologia Croatica Figure 7.Photograph of i.e., three subsets group six and groups fault three into patibility and com to rated according kinematic properties their geometric sepa also were planes fault strike-slip observed The measured. were 9) and 5 2, (Figs. planes fault strike-slip 55 SWVFZ, and SE (see towards T-axis Table dipping is 1for details). the whereas NE‒SW, trending dominantly P-axis the with ated planes are related field,to the associ compressional palaeostress fault observed the that indicate field palaeostress representative trans of the analysis tectonic Table and 5 (Fig. 1). Structural subsets fault port) (SE-directed NW-dipping and transport) tectonic (E-directed W-dipping by characterised subsets group two into subdivided is group fault This planes. fault measured four only along the SW of margin the study area is by represented data from WSW the (Fig. Table towards 5and i.e. dipping steeply tical, 1). the T-axiswhereas NW‒SE, is trending subver dominantly axis a with P- fieldassociated palaeostress acompressional indicates field palaeostress representative the of analysis structural RF2), (NE/ faults of reverse group For this transport. tectonic directed SE- and direction dip NW average an with characterised is set the Vinodol Valley. Location: 45°13’22.4’’N, 14°42’14.5’’E. limestones oftheUpperCretaceous Humacfm.alongtheNEmargin Gornji of Figure 6.Photograph of the reverse fault plane (Fp=37/48) in recrystallized 186 Location: 45°16’15.5’’N, 14°36’14.2’’E. Humac fm. limestonesalong the NE margin of the Gornji of the Vinodol Valley. Besides the reverse fault planes observed along the NEVFZ along NEVFZ the observed fault planes reverse the Besides (SW/RF3)observed faults reverse the of group third The the reverse faultplane(Fp=24/62) intherecrystallized - - - - - occasional interchange of principal stress axes axes stress principal of interchange occasional the to poorly visible ofindicators opposite movement that may indicate addition in very by also characterised surfaces, were they movements fault predominant sinistral or dextral observed few movements (Fig. 10). sinistral and dextral both indicating overgrowths slickenside with reactivation, tural 45°15’32.1’ rockfallered anddeluvial–proluvial withtheQuaternary deposits. Location: with fm. Palaeogenenear the thrust contact ceous Milna clastic deposits cov three conjugate fault pairs (Fig. Table 5and pairs fault conjugate 1).three i.e. subsets, six and SW/NF3 and NE/NF2 VFZ/NF1, groups; fault three into separated be could motions slip oblique some and dip-slip pure both by characterised VFZ the within planes and part, less in the fault NW normal Measured and parts. central SE its in identified predominantly were planes fault ley,normal of the Vinodol Along margin Val the NE planes were observed. fault 18normal margin SW its along whereas measured, were ones. reverse the than probably younger are systems map in Fig. fault plane 2), strike-slip that the observed suggesting geological (see strike NW‒SE the of faults reverse the to angle WSWor at strikes) oriented perpendicular are an actually oblique ENE‒ and NE‒SW (with faults strike-slip where cases in able SWVFZ (see geological map in Fig. 2). notice This is particularly across, thereby reverse offsetting fault planes,especiallyalong the fault mostly planes cut show faults strike-slip that strike-slip and ficationtherelationships between mappedof reverse cross-cutting (see identi NW–SE Fig. and 5). Field trending observations axis T-a and P-axis trending NE‒SW the with associated one second the E–W, and trending T-axis the and P-axis, trending N–S the two slightlywithin different palaeostress formed fields:been have the firstmay one associated planes with fault identified the that indicating also the reactivation, supports concept of structural field. stress same the and ENE–WSW strike (SW/SSF3; strike ENE–WSW and Fig. Table 5and 1). strike- third VFZ the of slip fault resemble group a conjugate NNW–SSE fault with pair margin SW the along while 1), Table and NE/SSF2; Fig. and (VFZ/SSF1 5 NE–SW and NW–SE both ing strik were dominantly margins VFZ along the planes fault ured Meas 80°, of respectively. 65° and angles dip average with etry, geom dipping bysteeply Fig.characterised 5).are Fault groups SW/SSF3; and see NE/SSF2 (VFZ/SSF1, pairs fault conjugate Figure 8.Photograph of Along the NE margin of the VFZ, eight normal fault planes planes fault eight normal of VFZ, the margin NE the Along planes fault strike-slip observed the of analysis Kinematic Mapped strike-slip fault planes were characterised byfault planes struc were Mapped strike-slip characterised ’N, 14°37’7.8’’E. the

reverse faultplane(Fp=72/58) intheUpperCreta This implies that for a a for that implies This Geologia Croatica 72/3 σ 1 and σ 3 within within ------Geologia Croatica

- - - - - 187 ientation of bedding is 30/33. ientation The Group 3 and group subsets of the normal fault planes Or Photograph of the normal fault plane with the NW–SE strike strike of the normal fault plane with the NW–SE 11. Photograph Figure limestones NW) ls=80° from Foraminiferal (Fp=214/75; within the Palaeogene 14°44’56.5’’E. 45°9’23.7’’N, Location: Valley. Vinodol of the along the SW margin nary rockfall material and gravitational slides in the vicinity of con potentialgenetictheir suggest planesmeasured normalfault nection. were1) Table (SW/NF3; observed along the VFZ SW margin (Fig. 5). These conjugate strikingSW fault dipping fault plane both subsets to 5 (Figs. and 11) pairs are characterised by the NE‒ characterised by a general N‒S strike (locally NNE‒SSW or NNW‒SSE),dipping to theW (WSW) and E with a dipangle of approx. 40–50° Kinematic(see 1). Table analysis of collected structural data indicated that these fault planes were formed within the palaeostress field associated with the subverticalP- axis (orientation of P-axis is see 193/68; Table 1), and T-axis trending ENE‒WSW 1 (see Table for details), resulting in the NE–SW and E–W extension. Due to poor outcrops resulting in ambiguous structural relationships between the Cretaceous and cross-cutting the of relationshipsunits, identification Palaeogene strike-and reverse and planes observednormalfault betweenthe slip fault planes was rather unclear. Large bodies of the Quater - - - - - Group 1 (VFZ/NF1; Fig. 5) is characterised by predomi The Group 2 and group subsets of the normal fault planes vement indicators probably represents a reactivated older fault. Location: older fault. Location: a reactivated represents probably indicators vement Photograph of the strike-slip in the recrystal 10. Photograph fault plane (Fp=54/85) Figure Gornji Humac fm. along the SW mar of the Upper Cretaceous limestones lized Strike-slip dextral both with plane fault sinistral and Valley. Vinodol the of gin mo 14°42’4.4’’E. 45°11’27.6’’N, acterised by the N–S trending P-axis, and E–W oriented T-axis. B) Detail of the fault plane – subhorizontal striations indicate dextral movement. Recrystallized dextral lime movement. striations indicate B) Detail of the fault plane – subhorizontal T-axis. oriented and E–W P-axis, acterised the N–S trending by 14°42’4.9’’E. 45°11’27.4’’N, Gornji Humac fm. Location: of the Upper Cretaceous stones A) Photograph of the fault plane with NW–SE orientation (Fp=55/81) mapped along the SW margin of the Vinodol Valley; the fault is probably formed in formed the fault is probably Valley; Vinodol of the margin mapped along the SW (Fp=55/81) orientation NW–SE of the fault plane with Photograph 9. A) Figure field char as a dextralreactivated fault within the palaeostress and subsequently NW–SE, T-axis trending and NE–SW, P-axis trending with the field the palaeostress Palenik et al.: Geological and structural setting of the Vinodol Valley (NW Adriatic, Croatia):insights into its tectonic evolution based on structural investigations nantly NW‒SE striking Kinematic fault plane 1). subsets that are Table steeply and dip 11 (Fig. SW and NE both towards ping withinformed were planes normalfault thesethat shows analysis the palaeostress field characteriseddipping towards the WSW (P-axis orientationby a subvertical is 338/77; Table 1) and subhorizontal T-axis trending P-axis NE‒SW 1 (see Table for de steeply thattails) in overall resulted in the NE–SW directed extension. (NE/NF2; Table 1) observed along the NE margin of the VFZ are Geologia Croatica relatively large, probably covering several km thousand end-Turonian the was before uplifted AdCP the of part NW tral cen the in area the that evidence additional provides area study the in au emergence early Such lower, Mt. Učka the the of in part as tochthonous well as 1994), al., et (ĆOSOVIĆ Krk of island Istria N the and of neighbouring island the of part in N the 1996), al., et than (MATIČEC later bit a Ma), 90 (c. nian Turo Late the relativelyearly, during probably started area this in Platform) Carbonate Adriatic the of parts all almost in corded and Palaeogene (re the Cretaceous between regional emergence mac are exclusively fm. of Turonian age the in study since area, its of the Gornji Humac fm. are consequently in the Vinodol Val Vinodol the in consequently are fm. Humac Gornji the of its and the Vinodol area).to Krk Depos W Istria from and NW ing Brač (GUŠIĆ 1990).Brač &JELASKA, al., et of island the on (KORBAR unit, Vis the of of typicus 2012) locus 110 c. or island the at m the on m 40 2015), al., et (FUČEK Cres of island the on m 30–100 1996), al., et (JURKOVŠEK NW in m 2017),70–200 al., et BRČIĆ – (Ćićarija Istria 110–140Northern areas: in m other in determined nesses thick with fits also and area study the in 130–150m at mated esti was boundary Cenomanian/Turonian the near event ing of the Sv. Duh fm., a drown deposited during regional temporary 1990).LASKA, on ofthe island the fm. determined ofMilna Brač (GUŠIĆ & JE 2012) (FUČEK and c. 400 m limestones shallow-marine Unije thick Cenomanian of al., et (KORBAR island Vis of island the the on on 2015),m al., m 300–350 et 300–350 2015), al., et (FUČEK Cres of island the on deposits Cenomanian shallow-marine of m in NW Slovenia (JURKOVŠEK et al., 1996), more 400 than m & VLAHOVIĆ,(VELIĆ 1994), Istria 300–400 Northern in unit entire forthe determined >320succession the thick m wellwith oftherefore its thickness more estimated than 250 m corresponds and area, study the out in not crop does fm., Milna Cenomanian al., et 2005).distances (VLAHOVIĆ AdCP the across significant over correlated resulted less or more be can blocks teristics different charac general their but between units, the of variation tec thickness the the in subsidence in Changes controlled therein). tonically references and 2018 al., (see et con Plate ŚRODOŃ European and continuous Microplate the by Adria the caused of was vergence dynamics Cretaceous Late its (AdCP), and Platform Carbonate Adriatic Mesozoic the of part represents area, study the including domain, Adriatic NW The Valley andBakarBay 4.1. GeologyandpalaeogeographyoftheVinodol struc geological recent the of of area. the formation ture the to led which ternary, togenesis of the this area through Palaeogene, Neogene - and Qua tec complex the indicate area Bay Bakar and Valley Vinodol the in investigations structural and geological of the results The DISCUSSION 4. extension. directed NW–SE (see Table 1 for details). Such a palaeostress field resultedinthe towards the SW, whereas T-axisthe subhorizontal NW‒SE trends dipping steeply P-axis subvertical a with field palaeostress the Fig.(NW‒SE; 5). fault planes were normal These within formed Dinarides the of strike general the to normal is strike NE–SW The 5).Fig. in (SW/NF2)diagrams (seeSE and NW the wards 188 The youngest Cretaceous rocks belonging to the Gornji Hu Gornji the to belonging rocks Cretaceous youngest The ofThe thickness overlying with pelagic limestones influence the unit, Cretaceous Upper oldest the of part lower The 2 (stretch ------NW and SE (c. 60° and 63°), indicating NW- and SE-directed SE-directed and NW- 63°),indicating and (c. 60° SE and NW the towards dipping strike, NE–SW general a conjugate with by planes fault characterised was VFZ the of margin NE the along Fig. the in 3). (see cross-sections transport tectonic directed the SW of margin the Vinodol Valley suggest predominant NE- along zone fault thrusting main the along planes fault measured and 3) (Fig. units lithostratigraphic the of position structural while the show margin transport, tectonic SW-directed dominant verse fault group subsets, i.e. conjugate fault along pairs the NE re 5, (Fig. Tablestrike, see NW‒SE A; forthe details).1 With diagram respectively transport tectonic NE-directed SW- and ing (c.planes SW, 55° and NE 63°) the and indicat towards dipping group fault (VFZ/RF1)reverse first the that shows analysis A).Kinematic gram was characterisedof (Fig. by both and pure dip-slip oblique-slip kinematics 5, see dia steep conjugate by striations which along served are characterised both margins, faultob planes fault reverse the by represented is (VFZ/RF1) group field. stress recent the to respect in activity along the mapped fault systems but also their potential neotectonic recorded field changes palaeostress of information basic only not provided area study the in identified relationships overlapping the of of analysis Vinodol the Valleyfault and planes Kinematic area. which may evolution be also the used Quaternary in understanding area, study the of evolution Cretaceous tectonic the of evidence field Upper vided the between contact and and the clastic limestones carbonate Eocene deposits and pro tectonic the along 120 collected than more in mostly were data resulted structural These 5) 127stations. at (Fig. measurements SWVFZ and prolon NEVFZ NW the its and within Valley Vinodol the in gation BayBakar data collected on based on fault planes structural investigations Structural Bakar Bay 4.2. StructuralrelationshipsintheVinodol Valley and al., et 1969).– MAMUŽIĆ m m, Fd – et ŠIKIĆ al.,400–650 1972; : Td 150 m, Fd 600 m Td 200 Bistrica: 1969; Ilirska al., et Fd ŠIKIĆ 450 – m 300–700, Td (Labin: maps neighbouring on represented thicknesses age aver the 1970),than al., ŠUŠNJAR et less – much m but 200 at Basic Geological Map (the of thickness was both units estimated greater of the sheet the on presented values significantly average is the than which m, >350 at (Fd) deposits Flysch ing overlyof thickness and m, 60 at estimated Valley Vinodol was area. The ofKotari thickness the Transitional deposits (Td) in the (1991) 230 between thicknesses and measured 280 m in the Ravni of 255 DROBNE and thickness m, (2017) al. et their determined – e.g.hiatus graphic in the Čikola river ŠPANIČEKsection et al. strati the of duration and subsidence local palaeorelief, the on depending variable, very locally is limestones Foraminiferal of Geologi Basic the of Map (120cal ŠUŠNJARm, sheet et al., 1970). However, thickness the Crikvenica the on presented deposits ofthese thickness average the than thicker is m 200 ofc. stones Brač (GUŠIĆ 1990).Brač &JELASKA, of island the on locality type their at m 500 almost to 250 from e.g. – deposits thicker much in consequently resulting age, in ally muchor even younger,Campanian Santonian mostly Upper mac fm. is in other ofareas Platform the Carbonate usu Adriatic probably 35 hiatus, to graphic 40 My). top The of the Gornji Hu strati long relatively the during karstification intense to due is c.70 100 thickness to (them from variable leyrelatively thin, The second reverse fault plane group (NE/RF2) observed observed (NE/RF2) group plane fault reverse second The fault first the Bay Bakar and Valley Vinodol the of area the In The estimated thickness of Palaeogene Foraminiferal lime Foraminiferal ofPalaeogene thickness estimated The Geologia Croatica 72/3 ------Geologia Croatica ------189 Fur . during the late Cretaceous–Oligocene,lateduring the late Cretaceous–Oligocene, simultaneously or the during Mapped normal faults in the Vinodol Valley and Bakar Bay However, at the same time, due to their subverticaltheirgeometryto duetime, same the at However, Results of the structural study conducted and presented in tween mapped reverse and strike-slip fault planes, we believe that believe we strike-slipplanes, andfault reversemapped tween probably areareastudy the inobservedstrike-slip planesthe fault younger than the reverse faults because most of them cross-cut and laterally displace measured reverse fault planes At (Fig. 3). the same time, the geometry of mapped strike-slip faults and NNE‒characterisedand N–S, NE‒SW, stressby field computed strike- observed the with accordance in is P-axis trending SSW slip and reverse fault planes in the NW External Dinarides of Slovenia, where N–S oriented compression during the Pliocene andQuaternary has also been indicated (ŽIBRET the & VRABEC, 1995), 1982, (1981, al. et PRELOGOVIĆ Accordingto 2016). mapped NW‒SE and NE‒SW striking strike-slip faults in the Vinodoland Valley Bakar Bay are parts of the Ilirska Bistrica– neotectonicallyresemble and zone fault Rijeka–Senjseismogenic active faults in the study area. were characterised by NW‒SE SSW and NNW‒SSE) striking and planes that NE‒SW accommodated Table seepure 5; (locally Fig. in I and H G, (diagramsmotions dip-slip/oblique N–S, NNE‒ and 1) NE‒SW and NW‒SE (locally E‒W) trending extension. Though the structural relationships between reverse and strike- it groups faultwithrespect normaltheclear, slip to faultsarenot assumedcanbe andNW‒SEdirected E‒W that NE‒SW, exten may sion be considered as a local feature associated with gravi tational collapse of the hanging wall structural sequence, i.e. hostingtheanticlines. hinge of zonesInouropinion,gravi such ref and 2012 al., et TAVANI (cf. extensiontationallyconditioned erences therein) may be either potentially concurrent to active folding and formation of the Vinodol Valley and Bakar Bay area during the Late Cretaceous and Palaeogene or it was associated characterisedradialextensiontectonicphase younger by the with compressional/transpressional structure after/before folded the of Quaternary.and Ac Pliocene the commenced intectonics which cording to VAN UNEN etal. (2019) andarea of the their Internal Dinarides, observations the extension of folded structures in the in the Dinarides occurredsimultaneously or slightly after the main orogeny build up, but definitely before thePliocene–Quaternary transpression. and present fieldobservations of cross-cutting relationships be thermore, in the vicinity of the observed normal fault planes, large bodies of Quaternary rockfall material and gravitational slides have been mapped, which according to BLAŠKOVIĆ suggestmay their potentialin the increasing role (1997) inrock stability and failure. on existingknowledge the with accord ingenerally are paper this the local/regional tectonic evolution in this part of BLAŠKOVIĆ, the External1995; 1982, 1981, al., Dinarideset (PRELOGOVIĆ 2005; ŽIBRET & VRABEC, UNENVAN 2016; et al., 2019). structuralourcompres of presenceaddressresultstheHowever, sional structures characterisedtonic transport. Our observations field of bythe cross-cutting both rela SW and NE-directedtionships between mapped reverse tecand strike-slip fault planes studythe inobservedstrike-slip planes the faultthat suggest also thanAlternaplanes.youngerreversefault thearea are probably the measuredtively, normal fault planes may be associated with gravitationalwithincollapsehosting the antihingethezonesof clines slightly after orogeny build up, before however, the Pliocene– Quaternary transpression ------BLAŠKOVIĆ, 2005 and references therein), which sensu Though typical NW‒SE striking, NE-dipping structures The second observed reverse fault plane group in this work Beside the measured reverse fault planes in the area of the Palaeostress field analysisof measured reverse faultplanes were previously observed within the Vinodol and Valley Bakar 2005; PRELOGOVIĆ1999, 1997, et Bay 1991, (BLAŠKOVIĆ, planes thisstudynumerousidentified fault 1995), 1982, 1981, al., within the VFZ that are steeply 60°) towards dipping the (c. SW and are characterised by NE-directed tectonic transport. These new findings confirm that duringthe tectonicevolution of trans the tectonic NE-directed with structures Dinarides, External neighbouringtheVel in areas(as some informed been porthave ebit Mt. area – VLAHOVIĆ et et ŚRODOŃ al., al., 2012; 2018; TOMLJENOVIĆ along et with al., 2018) the predominant SW- directed tectonic transport. Such structures were formed either concurrently withDinaridic SW-vergent structures or their for principalDinaridicwithinsubstagethetec a present may mation tonic phase. directionsdip(diagrams NE,ESE characterised(W)andNW by results with correlates details) for 1 Table see 5; Fig. in C and B reportedIn reported by (1998). BLAŠKOVIĆ study author de scribed existing Dinaridic structures as refolded and Dinaridicphase’faulted structuresduring‘late deformed the were which NE‒SW change from trend stressfield regional the of result a as ing compression to WNW–ESE trending compression andBakar numerous Bay strike-slipValley Vinodol planesfault accordanceIngeomet thewith observed thisstudy. inalso were ric properties and kinematics within the Vinodol fault zone de characterisedsubverticallineatedwere strike-slipgroups by fault geometry and slickensides showing structural reactivation, i.e., both dextral and sinistral motions.strike Characterised (dipping towards both NE and SW) byand the perpendicular NW‒SE strike NE‒SW (dipping towards both NW and SE), kinematic analysis of the observed strike-slip fault planes indicated a similar palaeostress field to theobserved reverse faultplane groups, being characterised by N–S, NE‒SW, and NNE‒SSW trending P-axis (diagrams D, E, and F in Fig. 5; see 1 Table for details). These results may suggest that at least some observedof strike- slip fault planes in the study area resemble structurally reacti vated inherited reverse fault planes within the transpressional/ transtensional stress field. duringthe Late Cretaceous and Palaeogene resulted in the build up of the major fault and fold related NW‒SE strikingin the Dinarides, structures being characterised by NE-dipping geometry SW-directedand tectonic transport 1981, al., (PRELOGOVIĆet ŽIBRET 2005; & VRABEC, 2016). BLAŠKOVIĆ, 1995; 1982, ally towards the NW (W) and ESE 63° and (c. 52°), with the tec (diagramrespectively WNW, andtransport (E)tonic SE towards details). 1 for see Table 5; C in Fig. CretaceousthrustUpperPalaeogenethethe and along contactof Palaeo younger the over limestones) (Foraminiferal carbonates gene clastic deposits suggest the compressional stress field and structures formed within Table see both 5; NE‒SW Fig. in C trending and B A, and (diagrams NW‒SE compression trending StructuresNE‒SWtrendingthe details). compresto related for 1 sion probably correlate with the principal ‘Dinaridic tectonic phase’ ( tectonic transport (Fig. 5, diagram B; see Table 1 for details). The details). for 1 Table see diagram B; tectonictransport5, (Fig. third reverse of faults fault plane group along the SW (SW/RF3) reversethe resemble BakarBay and Valley Vinodol the margin of fault plane group NE/RF2 observed along the NE margin. The SW/RF3 fault group is characterised by subsets dipping gener Palenik et al.: Geological and structural setting of the Vinodol Valley (NW Adriatic, Croatia):insights into its tectonic evolution based on structural investigations Geologia Croatica tion tion and as the unreliable. The magnitude large earthquake Bakar the glagolitic so from Grižane), document we both treat the loca only exists about very information sparse it (merely a sentence in that it unfortunate is damage, considerable caused and occurred probablyindeed earthquake this Although MSK. IX° as (the high as 1323 of that been have could ‘Vinodol them of earthquake’) which is strongest often listed The 1916. as causingand intensity the point of view of study)this are the events (fromof ones 1323, important 1750, most The 1870,past. the in here occurred have 2017 therein). references HERAK, and IVANČIĆ 1999; et al., 2006, 2018; HERAK, KASTELIC et al., & 2013; & HERAK MARKUŠIĆ (e.g. studies micity-related seis numerous by and thereafter) annually 1996,al., updated et (CEC,Catalogue Croatian byEarthquake firstdescribed HERAK the in entries corresponding the in It is 20well km. documented than shallower mostly crust, upper the in hypocentres with ity, Bakar, Vinodol, Krk and Senj) is expressed by moderate seismic Rijeka, Bistrica–, Ilirska of areas epicentral the cluding pr gion. occurrenceThe year isindicated ofearthquake by eachepicentre. The events of1323,1648,and1776are Magnitudes ofthe (seetext). considered uncertain the wider study area. area. study wider the from data seismological available the with analysis field ostress palae of results our compare hereby we field, stress recent the within the VFZ and their possible faults of favourableactivity neotectonic orientation potential within the address to order In seismological data 4.3. Comparisonofpalaeostressfieldanalysisand annually thereafter). Figure 12. 190 e-instrumental earthquakes are estimated intensities. from earthquakes Catalogue theobserved After etal., theCroatian (firstdescribed by HERAK 1996,updated e-instrumental Earthquake Figure 12 shows that significant earthquakes are known to to known are earthquakes significant that shows 12 Figure The ongoing tectonic activity in the greater Vinodol area (in area Vinodol greater the in activity tectonic ongoing The Historical seismicity (1323–1908)andepicentres seismicity Historical ofinstrumentally recorded (until 1995)withmagnitudes M earthquakes - - - - - of November 28, 1750 (I been computed by inverting the observed spatial distribution of distribution spatial observed the inverting by computed been of faults. active geometry the about more tion (e.g.methods 2017) & HERAK, HERAK were used to learn inverted been have for could a ofevents small (Fig.number rather 13), loca and advanced polarity P-wave first the of distribution spatial observed the particular, In activity. low of periods their during even properties faults seismogenic of details on mation it made possible to collect infor 1.0 turn, in This, some in areas. enabled lowering the detection threshold well below seismological in stations Croatia magnitude and Slovenia in this time period, densification Nevertheless, decades. significant of thenetwork of two over for 4.8 magnitude exceeding event no however,with Fig. ‒see 4). area nodol Fault (NEVFZ) Zone Vi NE the within Valley, Vinodol the of part ENE the (in Bribir and (overdamaged) 100houses Grižane from reported was age lowing it. The Klana mainshock of 1870 (March 1, 1870, I 1870, 1, (March 1870 of mainshock Klana The it. lowing fact that about 3000 aftershocks were felt in the three years fol et al. (2017), by HERAK detail the so mention only wehere will nodolski, with the epicentral intensity I intensity epicentral the with nodolski, Vi Novi of east 1916 12, 10km about March on occurred one recent most The area. Rijeka greater the in hazard seismic ing and is one ofby keythe local inhabitants, events for understand remembered vividly still It is area. Bistrica–Klana Ilirska the in earthquake significant last 2018) al.,the et was HERAK MSK, Focal mechanism solutions (FMS, shown in Fig. 13)Fig.have in shown (FMS, solutions mechanism Focal followsseismicity (Fig. the Contemporary same 13),pattern o = VII–VIII MSK) has been studied in o = VIII MSK. Most dam Most MSK. VIII = L >4.5inthewider Vinodol re Geologia Croatica 72/3 o = VIII VIII = ------Geologia Croatica - - 191 Upper Cretaceous informal lithostratigraphic units mapped Synthetic focal mechanisms constructed by applying the 5. CONCLUSIONS 5. and geological Bay Bakar and Valley Vinodol the of area the In structuraltectonicevolution complex highlighttheinvestigations of this area not only through the Palaeogene and Neogene, but also during the Quaternary period. in the study area can be well correlated with units proposed by equality of resistance to sliding on both faults and the angle of convergence between50° andfaulting 35°will (as be ispreferred the over oblique faulting case for thrusts here),with decoupleddip angles lower than 20–30°. BECK’ssteeperfaults.(1983) dipping estimates for even decoupling favour permissiveand are more Thisprocess in casessome beplausible may here, especially for focal depths exceeding about 5 km or if the strike-slip fault is considerably weaker than the thrust. Right Dihedra Method (ANGELIER & MECHLER, (see 1977) mech focal correspondenceavailable thegood with show 5) Fig. anism solutions Both (Fig. 13). synthetic focal mechanism and instrumentally mechanismfor focal solutions available recorded Kvarner and area Rijeka‒Vinodol larger the within earthquakes NE‒SWstrikingand principalNW‒SE theseis that suggest Bay mogenic sources (definedby mapping as reverse and strike-slip are faults) and compressional transpressional structures, which are recently tectonically active within the compressional stress characterised field, generallyby a N‒S orientedP-axis. - - - - principal 3 and σ and 2 > 0.0). The hypocentral depth is represented by the symbol colour according to the colour scale on the right. the colour to according the symbol colour by depth is represented hypocentral The > 0.0). L The suggested types of faulting, on the other hand, are far Only events located by at least 8 reported phase onsets, and having azimuthal gap of reporting stations smaller than 120° are shown. The beach-ball diagrams diagrams beach-ball The shown. are 120° than reporting of smaller gap azimuthal stations having and reported 8 onsets, least phase at by located events Only focal sphere the first motion onto projection P-wave of the sense of the stereographic hemisphere, as lower mechanism solutions (FMS) focal (1986–2017) represent each FMS. for of the P-axes orientation inferred Red colour-coding of the mechanism type. lines show shaded). See the legend for are quadrants (compressive the firstlongitudinal polarity wave for the bestfit double-couple source geometry (FMS-Database, The P-axes 2019). computed from FMS are often taken as the first order(within proxy about Judgingtectonicdirectionthelocalfrom movement. for of ±15°) tectonicstressthe 13, Fig. distributionpresentedinspatialtheir as field is relativelyhomogeneous andhorizontal (averageplunge with a mean1.5°), orientation close to N–SIndividual (N13°E). deviations from this direction may be a consequence of local stresses,pre-existing weakfractures small earthfor (especially quakes), variationsquakes), in pore pressure, influenceof friction during faulting, the or simply inversion uncertainty. thestudyfrom homogeneousover region.While inthe NW part with consistent are FMS all Slovenia) (in area sub considered striking the SE–NW of the along faulting strike-slip right-lateral vertical faults the (e.g. Raša furtherfault), to the SE there is a mixture of transpressive, almost pure dip-slip, and strike-slip faulting. In a compressional tectonic setting this is indicative of a generally transpressive regime, where the σ Figure 13. Seismicity in the period 1996–2017 (M Figure Palenik et al.: Geological and structural setting of the Vinodol Valley (NW Adriatic, Croatia):insights into its tectonic evolution based on structural investigations mine which one is vertical. Indeed, our study area (and the greaterthe (and areastudyvertical.Indeed,our is one which mine transitionalthezone asregarded be may region) Kvarner‒Velebit into switch In transpression predominantlyof gradually where thrustand reverse mecha Slovenia. Dinarides External southern southern of the of nisms Dinarides NW the in strike-slip pure environments,such faulting,stressthe release oblique instead of may also be decoupled between parallel striking thruststrike-slip faults.and According to MICHAEL assuming(1990), stresses are of similar magnitude, and often only details deter Geologia Croatica dominant strike-slip motions. strike-slip dominant with transpression ter, however before Pliocene–Quaternary the ing the orogen build up (VAN UNEN et al., 2019)et (VAN up build orogen UNEN the ing of the (TAVANIanticline zones et al., hinge 2012 the in and references therein) dur structures wall hanging of collapse itational grav by caused been have may and extension) directed NW‒SE and planes (NE‒SW striking by NW‒SE and NE‒SW generally ones. younger probably the are fault and planes strike-slip suggests that structures the strike-slip reverse mapped between relationships cross-cutting and ometry ge subvertical fault the time, same the At planes. fault reverse older reactivated structurally resemble area study the in planes fault strike-slip mapped that suggest may field stress stensional of Orientation the P-axis with associated the transpressional/tran NNW‒ a and N‒S SSE P-axis, to NE‒SW, similar the trending reverse observed fault by planes. both characterised field (dipping palaeostress a striking NW‒SE indicate planes fault motions. striking NE‒SW and SW) and NE towards sinistral and dextral both i.e. reactivation, show by geometry structural subvertical terised charac groups fault Strike-slip observed. also were planes fault stress regional in compression. ing change a to due field structures from NE‒SW trending compression Dinaridic toWNW–ESE existing trendof phase’ ofthe ‘latein formed the refoldingDinaridic and faulting were structures Dinaridic (1998)these BLAŠKOVIĆ to ing both and within NE‒SW compression. NW‒SE Accord trending formed pairs fault conjugate resemble subsets plane fault These respectively. transport tectonic directed WNW and (E) SE and ESE directions, dip and (W) NW by both characterised are area area. study the in existed also that phase Dinaridic principal the within sub-stage separate a with associated were or SW-vergentstructures the to concurrent either formed tures struc NE-vergent Dinarides, the in structures SW-vergent inant Newly predom the beside 2016). that indicate structures VRABEC, & SW-dipping mapped ŽIBRET 2005; (BLAŠKOVIĆ phase tectonic Dinaridic the within formed probably that field stress are related to compression a dipping trending structures NE‒SW Both NE and SW NE-vergent structures. as predominantly tures struc faulted Valleyaddress we Vinodol the of margin SW the relationships graphic of along units the mapped lithostratigraphic strati and Valley. Vinodol structural the to However, according the of margins SW and NE the both along within determined structures mapped was transport tectonic NE-directed The respectively. transport tectonic NE-directed SW-and dicating planes steep (c. 60°) either dipping towards the NE or the SW in by characterised were groups fault reverse first the that shows analysis Kinematic kinematics. oblique-slip and dip-slip pure ity of the observed reverse fault planes by were both characterised ered several thousands km thousands several ered new findings. findings. new important several including Dinarides, evolutionofthe tectonic the about knowledge existing and studies previous of those to area). Vinodol and Adriatic Carbonate Platform at covofend the Platform Turonian already Carbonate Adriatic Valley suggest that the area uplifted in the NW ofcentral part the Vinodol the in rocks Cretaceous Upper youngest fm. the of age Turonian Humac Gornji the unit, youngest the of range graphic strati (1990), shorter much GUŠIĆthe forJELASKA except & 192 Measured normal fault normal Measured planes in the study area characterised Bay, Valley strike-slip Vinodol Bakar of the and area the In study the in groups plane fault reverse mapped second The In the area of the Vinodol Valley and Bakar Bay, major Valley the Vinodol Bakar of the and area the In correspond in investigation general ofResults the structural 2 (from W and NW Istria to the Krk Krk the to Istria NW and W (from or slightly af ------pressional/transpressional stress field (N‒S oriented P-axis) sug area. P-axis) study oriented the within (N‒S sources seismogenic field potential be may they stress gesting pressional/transpressional NE‒ and NW‒SE observed of orientation favourable the shows zone fault genic seismo Bistrica–Rijeka–Senj Ilirska the within solutions nism mecha focal on data available with mechanism focal synthetic and Dr. Ajka ŠORŠA (CGS) for preparation of the Vinodol Valley Valley Vinodol the of map. geological preparation for (CGS) ŠORŠA Ajka Dr. and would also like to Dr. thank Georg KOCH (CGS) for Weuseful team. mapping geological Valleyarea Vinodol the of part KORBAR from the Croatian Geological Survey (CGS), who were Tvrtko Dr. and OŠTRIĆ Nenad colleagues thank to like would We manuscript. this of quality the improved considerably that s (University of Belgrade) and Professor Marko (Univer VRABEC research. The authors would like to thank Dr. Ana MLADENOVIĆ and the authors for are grateful all in support the fieldand cabinet IP-2016-06-1854,SEKVAno.KORBAR), Tvrtko (Grant Dr. PI GEO and HERAK) no.IP-2014-09-9666, Marijan PIProfessor (Grant VELEBIT (HRZZ): Foundation Science Croatian the by work from resulted paper onThis two scientific funded projects ACKNOWLEDGEMENT GRIMANI, I., ŠUŠNJAR, M., BUKOVAC,M., ŠUŠNJAR, I., MILAN, CRNOLATAC,GRIMANI, J., A., ŠIKIĆ, I., FUČEK, L., MATIČEC, D., VLAHOVIĆ, I., OŠTRIĆ, N., PRTOLJAN, B., KOROLI- De- the of Solutions.– Archives Mechanism Focal of Database (2019): FMS-Database DROBNE, K., VLAHOVIĆ, I., TRUTIN, M., PAVLOVEC, R., ĆOSOVIĆ, V., BABAC, I. GUŠIĆ, A., MORO, T., MARJANAC, M., KOIĆ, D., BALONČIĆ, V., ĆOSOVIĆ, BRČIĆ, V.,GRIZELJ, L., FUČEK, B., GLUMAC, HORVAT,A., H. POSILOVIĆ, M., BLAŠKOVIĆ, I. (2005): Geologija Vinodola (Geology of Vinodol).‒ In: BIONDIĆ, R., BLAŠKOVIĆ, I. 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