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Selected field photos of brittle faults studied within the WTBC. (A) Mesoscale brittle faults in outcrop from the footwall of the Kvaløysletta-Straumsbukta fault zone at Straumsbukta. Note the red-stained colour of the tonalitic gneiss bands due to hydrothermal alteration. (B) Outcrop of the Bremneset fault zone at Bremneset, showing a 2 m-wide, epidote-rich cataclastic zone that cuts the foliation of mafic gneisses at a high angle. Note splaying and deflection of fractures within the cataclastic core zone towards its boundaries, supporting a dextral component of displacement. (C) Small-scale brittle normal faults that offset foliated amphibolite gneisses within the Bremneset fault zone. The offsets indicate down-to-theESE fault motion. (D) Overview of the Tussøya fault zone localised at the lithological boundary between banded felsic and mafic gneisses and foliation-parallel granite. The height of the cliff is c. 300 m. (E) Calcite-rich breccia from the Hillesøya fault cropping out in a ~1.5 m-thick zone.
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Onshore-offshore correlation of brittle faults and tectonic lineaments has been undertaken along the SW Barents Sea margin off northern Norway. The study has focused on onshore mapping of fault zones, the mapping of offshore fault complexes and associated basins from seismic interpretation, and the linkage of fault complexes onshore and offshore by...
Contexts in source publication
Context 1
... They contain prominent cataclastic fault rocks and a hydrothermal alteration similar to that observed in Rekvika. The faults dip c. 60° southeast, largely parallel to the foliation of the host rock gneisses. At Bremneset, the fault zone occurs as a 0-3 m-thick, NNE-SSW-striking, E-dipping, cataclastic zone, c. 200 m long in the Kattfjord Complex (Fig. 5B). Fracture/fault surfaces commonly carry an epidote precipitate, and they are locally cut by younger faults/ fractures with hematite staining. The gneiss foliation is locally at a moderate angle to the fault zone ( Fig. 4F). Slickensided surfaces and minor fault offsets (Figs. 4F, 5C) suggest normal, down-to-the-ESE fault ...
Context 2
... Tussøya fault zone (Fig. 4G) strikes NNE-SSW, dips moderately southeast and juxtaposes granite in the footwall against banded gneisses in the hanging wall (Fig. 5D). Foliation in the gneisses is gently folded, but generally subparallel to the fault zone. The fault crops out as a 1-3 m-thick, proto-to ultracataclastic zone, characterised by altered granite in the host rock cut by dark bands of ultracataclasite. The granite in the footwall is red-stained through hydrothermal alteration, as observed ...
Context 3
... subvertical fold that may have controlled its location (Thorstensen, 2011). The fault zone is parallel to the foliation in amphibolitic gneisses and confined to granitic pegmatite sheets within the gneisses. Zones of breccia, 1.5-2 m wide with angular clasts of red pegmatite granite and amphibolite embedded in a matrix of calcite, are common (Fig. 5E). Clasts are cross-cut by epidotised veins, which, in turn, are cut by calcite-bearing veins. Other, less prevalent Other minor fault zones on Senja include the Grasmyrskogen and Nybygda faults (Fig. 2B), located within Caledonian rocks of the Upper Allochthon Lyngsfjellet Nappe Complex ( Zwaan et al., 1998) or close to the thrust ...
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Citations
... First, it forced the rift to assume another energy-effective mode of strain accommodation: strike-slip motion along a preexisting line of weakness. This explains the early Eocene development of the SFZ (Faleide et al., 2010), which is aligned with a Precambrian lineament (Indrevaer et al., 2013). Second, it caused a temporary increase in the strain rate at the SFZ. ...
The formation of paired extension-compression (PEC) postulated by rotational kinematics of rift propagation is demonstrated by analogue models but rarely observed in nature. In our study of the early Paleogene continental rift in the northeast Atlantic, a PEC is proposed based on the northeastward propagation and the coeval compression at the rift tip. The propagation is deduced from tectono-magmatic trends, including along-axis development of magmatism, and migration of tectonic faulting inward and toward the rift tip. Where this propagation terminated, we documented coeval extension and compression in the form of a horst-and-graben system (H&G) and V-shaped anticline (VA), respectively. Given their structural characteristics and spatiotemporal relationships with the rift, their origin is best illustrated by a three-stage model: (1) Rifting initiated at the site of mantle upwelling and propagated northeastward in the Paleocene. (2) The rift tip was stalled by an elevated mafic-ultramafic body at the Barents Shelf, which led to forward projection of the rift’s driving force to create the H&G and the VA (PEC), dissipating the along-axis force component. (3) Domination of axis-perpendicular components then promoted orthogonal extension and sheared margin development. Our study suggests that PEC has a crucial role in both termination of propagation and rift-mode conversion.
... The Norwegian Barents Sea is located along the paleo-Caledonian margin between Norway and Svalbard ( 1a) Despite a large number of studies focusing on the sub-surface geology of the southwestern Barents Sea (e.g., Gudlaugsson et al., 1987Gudlaugsson et al., , 1998Faleide et al., 1984Faleide et al., , 1993Gabrielsen et al., 1990;Indrevaer et al., 2013;Kairanov et al., 2021;Marín et al., 2021), the Precambrian-early Paleozoic tectonic evolution of the area is still largely unknown. This is mostly due to the limitation of current seismic datasets, which do not image pre-Devonian basement rocks well (e.g., Gudlaugsson et al., 1987;Faleide et al., 1984Faleide et al., , 1993Indrevaer et al., 2013), and to the rarity of exploration wells penetrating basement rocks (Slagstad et al., 2008). ...
... The Norwegian Barents Sea is located along the paleo-Caledonian margin between Norway and Svalbard ( 1a) Despite a large number of studies focusing on the sub-surface geology of the southwestern Barents Sea (e.g., Gudlaugsson et al., 1987Gudlaugsson et al., , 1998Faleide et al., 1984Faleide et al., , 1993Gabrielsen et al., 1990;Indrevaer et al., 2013;Kairanov et al., 2021;Marín et al., 2021), the Precambrian-early Paleozoic tectonic evolution of the area is still largely unknown. This is mostly due to the limitation of current seismic datasets, which do not image pre-Devonian basement rocks well (e.g., Gudlaugsson et al., 1987;Faleide et al., 1984Faleide et al., , 1993Indrevaer et al., 2013), and to the rarity of exploration wells penetrating basement rocks (Slagstad et al., 2008). The nature of basement rocks in the Barents Sea and their evolution in the Precambrian-early Paleozoic therefore remain elusive. ...
... The Triassic was tectonically quiet despite local occurrences of minor normal faulting in the Barents Sea and Svalbard (Anell et al., 2013;Osmundsen et al., 2014;Ogata et al., 2018). The Jurassic-Cretaceous, however, recorded renewed extension, which resulted in the formation of rift basins filled with several kilometers thick sedimentary successions in the western Barents Sea (Gudlaugsson et al., 1987;Faleide et al., 1984Faleide et al., , 1993Gabrielsen et al., 1990;Indrevaer et al., 2013;Kairanov et al., 2021;Marín et al., 2021). ...
The present study is a detailed structural analysis of 3D seismic data in the Selis Ridge in the western Loppa High in the Norwegian Barents Sea, to which seismic attributes and spectral decomposition were applied. The analysis reveals that pre-Devonian basement rocks are crosscut by a 40-50 kilometers wide, several kilometers thick, E-W-to WNW-ESE-striking fold-and-thrust belt, including a steep, kilometer-thick, top-SSW shear zone. The folds display dome-and trough-shaped geometries, the thrusts appear to have been reactivated dominantly as top-west structures, and the main shear zone warps over the top of the Selis Ridge. The fold-and-thrust belt is interpreted as part of the latest Neoproterozoic (ca. 650-550 Ma) Timanian Orogeny, which was reworked during E-W Caledonian contraction in the Ordovician-Silurian. The results are analogous to recent findings in the northern Norwegian Barents Sea and Svalbard. The presented interpretation provides the basis for discussing Neoproterozoic-Paleozoic plate tectonics reconstructions, the influence of Precambrian-early Paleozoic structures on post-Caledonian fault complexes, and the location of the Timanian and Caledonian suture zones.
... In addition, Skredkallen is bound to the north by a major brittle normal fault, the Skipsfjord-Slettnes fault (first mapped by Paulsen et al., 2020) which dips steeply SE. This fault is part of a regional system of Mesozoic NE-SW striking coast-parallel and NW-SE striking oblique normal faults and related steep fracture sets, linked to rifting and opening of the North-Atlantic Ocean (Indrevaer et al., 2013;Koehl et al., 2019). ...
... The rock slope system at Skredkallen indicates an iterative and ongoing failure processes operating, with an active RSD and failure deposits shed below. The regional architecture of the thrust nappe (Paulsen et al., 2020) and younger brittle faults and fractures (Indrevaer et al., 2013) has clearly had a large imprint on the bedrock of Vanna, controlling how and where the bedrock destabilises at a local level. As the unstable Skredkallen mass evolved and deformed, it disintegrated along pre-existing brittle structures. ...
... We find a consistent alignment of morphostructures: e.g., backscarps, scarps, counterscarps and open fractures, all utilizing the mapped joint sets. These morphostructures also align well with the regional Mesozoic-age fault-fracture traces on Vannøya (Bergh et al., 2007;Davids et al., 2013;Indrevaer et al., 2013), including the NE-SW trending Skipsfjord-Slettnes Fault (Fig. 8). All of these brittle structures can be ascribed to Mesozoic and Cenozoic extension and opening of the North Atlantic Ocean along the Norwegian coastal margin (Indrevaer et al., 2013). ...
Large rock slope failures are temporal processes which act to modify the landscape after glacial retreat. The slope failure process often shows a lag time of thousands of years after deglaciation, with multiple failure events possible. While global datasets constrain this lag time from extensive mapping and dating of paraglacial rock avalanches, the timeline is poorly refined in northern Norway. We present a case study of multiphase failure at Skredkallen on Vanna, one of a group of coastal islands in Troms, northern Norway. The site contains an actively deforming rock slope above a large rock avalanche deposit. The rock slope deformation (RSD) is a system of fractured and dislocated blocks up to 3 Mm³, and is moving slowly ~5 mm/yr downslope to the north-east. The metasedimentary rock mass contains four pervasive joint sets and a foliation, contributing to a compound structure failure mechanism. The rock mass is further weakened by foliation-parallel sheared mylonite, and the presence of a brittle fault in the immediate area, with evidence of hydrothermal fluid flow though the RSD.
The rock avalanche deposit below the slope deformation is calculated to be 3 Mm³, and extends >1 km from the source area, displaying typical mobility for north Norwegian rock avalanches onto undrained sediments. The deposits showcase exceptional lobate morphology with elongated ridge-and-furrow features. Raised shorelines predating and postdating the deposit provide temporal constraints on the deposit and an opportunity to reconstruct a relative timeline for the slope evolution. The postglacial marine limit (>14 cal. ka BP) is obscured by the deposit, while shorelines corresponding to the early Younger Dryas (12.2 cal. ka BP) and the subsequent Tapes transgression maximum (7.6–7.2 cal. ka BP) are prominent across the deposits, implying that the avalanche was emplaced between 15 and 12.2 cal. ka BP. Failure occurred during a time of immense climate instability at the boundary to the early Holocene, consistent with global reports of mountain slope failure following glacial retreat. The avalanche was emplaced into what would have been the marine environment in the transition to the Holocene. The anomaly between the rock avalanche source area volume (35 Mm³), and the rock avalanche deposit implies previous failure events, the deposits of which were either removed due to failure of the underlying marine sediments into the fjord, or by retreating glacial ice. The initiation of movement at the RSD may be attributed to periods of local climate changes, such as the Holocene Thermal Maximum. Cosmogenic nuclide dating is suggested as the next step to fill gaps in the slope evolution story through the mid to late Holocene.
... This fault forms part of the Troms-Finnmark Fault Complex (TFFC), a basement-rooted, rift-related structure that accommodated several phases of Palaeozoic to Cenozoic extension (e.g. Gabrielsen, 1984;Indrevaer et al., 2013). Combining both 3D seismic reflection and borehole data enables us to study the temporal evolution of this fault system using age-constrained | 3 EAGE ALGHURAYBI et al. synkinematic stratigraphy. ...
... Crustal extension in the Late Devonian-Carboniferous created N-to NE-trending half-grabens and resulted in the formation of the TFFC (e.g. Faleide et al., 2008;Gabrielsen, 1984;Indrevaer et al., 2013). The TFFC is a basement-rooted normal fault system that represents a major structural element of the SW Barents Sea, separating recent shelf sediments offshore from onshore crystalline basement rocks (e.g. ...
... The TFFC is a basement-rooted normal fault system that represents a major structural element of the SW Barents Sea, separating recent shelf sediments offshore from onshore crystalline basement rocks (e.g. Gabrielsen, 1984;Indrevaer et al., 2013). The TFFC runs parallel to the present-day coastline of Norway, striking NE-SW in its southernmost part and NW-SE in its northern part (Gabrielsen, 1984). ...
Extensional growth folds form ahead of the tips of propagating normal faults. These folds can accommodate a considerable amount of extensional strain and they may control rift geometry. Fold‐related surface deformation may also control the sedimentary evolution of syn‐rift depositional systems. Thus, by examining the stratigraphic record, we can constrain the four‐dimensional evolution of extensional growth folds, which in turn provides a record of fault growth and broader rift history. Here we use high‐quality 3D seismic reflection and borehole data from the SW Barents Sea, offshore northern Norway to determine the geometric and temporal evolution of extensional growth folds associated with a large, long‐lived, basement‐rooted fault. We show that the fault grew via the linkage of four segments, and that fault growth was associated with the formation of fault‐parallel and fault‐perpendicular folds that accommodated a substantial portion (10 – 40%) of the total extensional strain. Several periods of fault‐propagation folding occurred in response to periodic burial of the fault, with individual folding events (c. 25 Myr and 32 Myr) lasting a considered part of the c. 130 Myr rift period. Our study supports previous suggestions that continuous (i.e., folding) as well as discontinuous (i.e., faulting) deformation must be explicitly considered when assessing total strain in extensional setting. We also show that changes in the architecture of growth strata record alternating periods of folding and faulting, and that the margins of rift‐related depocentres may be characterised by basinward‐dipping monoclines as opposed to fault‐bound scarps. Our findings have broader implications for our understanding of the structural, physiographic, and tectonostratigraphic evolution of rift basins.
... After the Caledonian orogeny, an extensional phase began, leading to the opening of the Norwegian and Barents Seas. Bergh et al. (2007) suggest the rifting happened in several stages leading to normal faults and other tectonic structures which strike predominantly NW-SE, NNE-SSW and NE-SW (Indrevaer et al. 2013). Generally joints align with the fault orientations, with localized variations (Vick et al. 2020b). ...
A rainfall-induced debris flow disaster occurred in Shelong Gully on the 22th June, 2019. More than 26,300 m² of farmland and 14 houses were buried and transportation and power supply broke down in the worst catastrophe in the history of Shelong area. To investigate this disaster, a detailed interpretation was carried out using (Unmanned Aerial Vehicle) UAV-based images. Analysis of disaster characteristics based on images and field survey revealed that the disaster could be identified as a consequence of compound mountain hazards including mass movements and mountain torrent in Shelong Gully. Moreover, the dynamic process of debris flow was analysed by using the finite difference method. Its dynamic characteristics indicated that the structure of debris materials changed during the movement process of debris flow. The results reveal that the loose materials, steep terrain condition and abundant rainfall are the main causal factors of this disaster event. This research on the analysis of hazard formation conditions and dynamic process for debris flows is of guiding significance to the formulation of disaster risk assessment and disaster mitigation plans.
... After the Caledonian orogeny, an extensional phase began, leading to the opening of the Norwegian and Barents Seas. Bergh et al. (2007) suggest the rifting happened in several stages leading to normal faults and other tectonic structures which strike predominantly NW-SE, NNE-SSW and NE-SW (Indrevaer et al. 2013). Generally joints align with the fault orientations, with localized variations (Vick et al. 2020b). ...
Disasters Risks, generated by the interaction of complex human and natural systems, are more significant, more complicated, and more difficult to foresee. Silk Road spans Asia, Europe, and Africa, involving more than 140 countries and nearly 66% of the world population. Relevant studies show that the countries along the Silk Road area suffered from the most frequent natural hazards and the most severe losses in the world. In order to promote social and economic development in Silk Road areas, it is urgent to carry out comprehensive research on disaster risk and disaster reduction. This compels new conceptual and analytical approaches to improve understanding of disaster risk at different scales. This paper presents the Silk Road disaster risk assessment at four scales, which could serve a different purpose. It is a robust response to one of the prioritized areas of Sendai Framework on Disaster Risk Reduction for people to understand disaster risk better.
... After the Caledonian orogeny, an extensional phase began, leading to the opening of the Norwegian and Barents Seas. Bergh et al. (2007) suggest the rifting happened in several stages leading to normal faults and other tectonic structures which strike predominantly NW-SE, NNE-SSW and NE-SW (Indrevaer et al. 2013). Generally joints align with the fault orientations, with localized variations (Vick et al. 2020b). ...
A recognised cluster of gravitational slope deformations in northern Norway is the result of a protracted geological history. A combination of nappe metamorphosis, strain localisation, basin extension, glacial loading and unloading and exposure to weathering has resulting in a significantly weakened rock mass. We present the engineering geology of one such site, the Jettan rockslide, compiled from existing studies and multiple field campaigns. We show that these geological processes manifest in the Jettan rockslide as mylonitic foliation, pervasive jointing and faulting, and ductile shear zones degraded by weathering. These structural factors accommodate the deformation at Jettan and contribute to the overall failure path. Channelised fluid flow through vertical joints and subhorizonal shear zones interplay with permafrost processes to reduce the strength of the presented failure path. These factors work together to form a failure hazard, which threatens to trigger a displacement wave, a scenario validated by the Holocene record and past performance.
... Timing and kinematics of major fault movements in these models are controversial, where for instance, the structural highs along the western margin (e.g. Senja Ridge and Veslemøy High; Fig. 2A) have either an extensional (Faleide et al., 1993;Indrevaer et al., 2013;Riis et al., 1986) or a compressional origin that resulted from strike slip tectonics along the Ringvassøy -Loppa and Bjørnøyrenna fault complexes (Gabrielsen and Faerseth, 1988). Later work, using potential field (magnetic and gravity) data, proposed a new crustal scale "boundinage" model for an entire SW Barents Sea (Gernigon et al., 2014). ...
... The TKFZ is characterized as a strike-slip fault that has an increasing component of extension toward the adjacent Hammerfest Basin (Berglund et al., 1986;Gabrielsen and Faerseth, 1989;Gabrielsen, 1984). This relationship has been well constrained with magnetic data (Gernigon et al., 2014); 2) The Bothnian-Senja Fault Complex (BSFC) and 3) The Bothnian-Kvaenangen Fault Complex (BKFC) are two major Precambrian NNW-SSE striking ductile shear zones that were periodically reactivated during Paleozoic and Mesozoic times ( Fig. 1A) (Doré et al., 1997;Indrevaer and Bergh, 2014;Indrevaer et al., 2013;Olesen et al., 1997). The Senja Shear Zone and Fugløya transfer zone have been proposed as offshore northward extension of the BSFC and BKFC, respectively ( Fig. 1A) (Faleide et al., 1993;Gabrielsen et al., 1997;Indrevaer et al., 2013). ...
... This relationship has been well constrained with magnetic data (Gernigon et al., 2014); 2) The Bothnian-Senja Fault Complex (BSFC) and 3) The Bothnian-Kvaenangen Fault Complex (BKFC) are two major Precambrian NNW-SSE striking ductile shear zones that were periodically reactivated during Paleozoic and Mesozoic times ( Fig. 1A) (Doré et al., 1997;Indrevaer and Bergh, 2014;Indrevaer et al., 2013;Olesen et al., 1997). The Senja Shear Zone and Fugløya transfer zone have been proposed as offshore northward extension of the BSFC and BKFC, respectively ( Fig. 1A) (Faleide et al., 1993;Gabrielsen et al., 1997;Indrevaer et al., 2013). Moreover, the Hornsund Fault Complex (HFC) and Billefjorden Fault Zone (BFZ) identified in Svalbard are suggested to be part of the same NNW -SSE structural trend ( Fig. 1A) (Doré et al., 1997). ...
This study presents an example of the extensional basin, namely Tromsø, which developed along the South-western Barents Sea (SWBS) transform margin. Three previous models have been proposed to explain the tectonic evolution and architecture of the basin, but there is no consensus on development of individual structures. In this study, we use 2D industry seismic reflection data, potential field and well data, as well as previously published information to understand the Early Cretaceous structural evolution of the Tromsø Basin in the context of the geodynamic processes in the SWBS. Mapping of the main seismic sequences and faults, time thickness map were integrated with modeled gravity anomalies along a composite 2D regional seismic section to facilitate the interpretation of crustal structures, which then were structurally restored. We propose a revised Early Cretaceous structural model for the Tromsø Basin, which involves oblique extension and formation of an intra-basinal transpressional transfer zone. This explains formation of the compressional faulting during overall extension in the SW Barents Sea. Basement heterogeneity most likely played an important role in localizing strain. The 2D sequential restoration of the composite regional seismic section yields an estimate of ca. 35 km of crustal extension in the SW Barents Sea margin, from the earliest Cretaceous until the present. Crustal thickness along the gravity modeled 2D regional section displayed a thinner crust below the Tromsø Basin as compared to the Sørvestnaget and Hammerfest basins favoring the interpretation of the Tromsø Basin as oblique rifting. This study illustrates the importance of detailed and regionally integrated analysis of rifted basins for reconstructing their evolution, as analysis of oblique rifted basins using two-dimensional plane strain can lead to erroneous assessment of faulting style and deformation
... In the northern part of Vanna island (Fig. 3), the Skipsfjord Nappe is down-faulted in the hanging wall by the VBF (Bergh et al., 2007;Opheim & Andresen, 1989). This fault is a splay fault to the regional, ENE-WSW-trending, zigzag-shaped, Vestfjord-Vanna Fault Complex (Fig. 2) that bounds the WTBC horst against Caledonian nappes to the east (Forslund, 1988;Olesen et al., 1997;Indrevaer et al., 2013Indrevaer et al., , 2014. Offshore to the northwest, the WTBC horst abuts against the Troms-Finnmark Fault Complex (Indrevaer et al., 2013) (Figs. 1 & 2). ...
... Therefore, we favour a model involving a successive and/or repeated supply of over-pressurised hydrothermal fluids, from a variety of sources (Fig. 20C), in a tectonic environment characterised by crustal extension and normal faulting (cf., Indrevaer et al., 2013Indrevaer et al., , 2014 to explain the complex Cu-Zn mineralisation in the VBF. ...
... Such an age contrasts with previous workers arguing for a Palaeoproterozoic VMS stringer zone origin of the Cu-Zn mineralisation, linked with the 2.4 Ga mafic dyke swarm (Ojala et al., 2013;Monsen, 2014) and a subsequent spread of metals into sediments now present in the Skipsfjord Nappe (Opheim & Andresen, 1989). The K-Ar dating results are consistent with formation of the VBF and enclosed Cu-Zn mineralised fault rocks/veins as part of an Early Permian rifting event in the North Norwegian continental margin producing NE-SW striking brittle normal faults and associated fracture sets (Gabrielsen et al., 1990;Faleide et al., 2008;Smelror et al., 2009;Hansen et al., 2012), which later on evolved to major fault zones like the Vestfjord-Vanna and Troms-Finnmark fault complexes (Olesen et al., 1997;Indrevaer et al., 2013Indrevaer et al., , 2014Koehl et al., 2018b). Most of these Permian faults, including the VBF, contain features that indicate complex fluid flow and fault-rock interactions; ...
... Major rift-related offshore and onshore faults and smaller-scale discontinuities within the fault damage zone align with one another (Roberts and Lippard 2005;Bergh et al. 2007;Indrevaer et al. 2013Indrevaer et al. , 2014Davids et al. 2013;Koehl 2018;Fig. 3). ...
... 3). These structures are characterised by rhombic, zigzag-shaped structures (in map view) striking variably NNE-SSW, NE-SW and NW-SE (Bergh et al. 2007;Eig 2008;Eig and Bergh 2011;Hansen and Bergh 2012;Indrevaer et al. 2013). Most mapped onshore structures display steep to near-vertical dip angles, i.e. rarely dip < 60°, while lowangle structures (listric extensional fault geometries) occur at greater depth in the crust (Indrevaer et al. 2013(Indrevaer et al. , 2014. ...
... These structures are characterised by rhombic, zigzag-shaped structures (in map view) striking variably NNE-SSW, NE-SW and NW-SE (Bergh et al. 2007;Eig 2008;Eig and Bergh 2011;Hansen and Bergh 2012;Indrevaer et al. 2013). Most mapped onshore structures display steep to near-vertical dip angles, i.e. rarely dip < 60°, while lowangle structures (listric extensional fault geometries) occur at greater depth in the crust (Indrevaer et al. 2013(Indrevaer et al. , 2014. ...
Gravitational forcing of oversteepened rock mass leads to progressive failure, including rupture, creeping, sliding and eventual avalanching of the unstable mass. As the point of rupture initiation typically follows pre-existing structural discontinuities within the rock mass, understanding the structural setting of slopes is necessary for an accurate characterisation of the hazards and estimation of the risk to life and infrastructure. Northern Norway is an alpine region with a high frequency of large rock slope deformations. Inherited structures in the metamorphic bedrock create a recurring pattern of anisotropy, that, given certain valley orientations, causes mass instability. We review the geomorphology, structural mechanics and kinematics of nine deforming rock slopes in Troms County, with the aim of linking styles of deformation. The limits of the unstable rock mass follow either foliation planes, joint planes or inherited faults, depending on the valley aspect, slope angle, foliation dip and proximity to fault structures. We present an updated geotechnical model of the different failure mechanisms, based on the interpretations at each site of the review.
