Postglacial seismicity offshore mid-Norway with emphasis on spatio-temporal–magnitudal variations

Bungum, Hilmar; Lindholm, Conrad; Faleide, Jan Inge

doi:10.1016/j.marpetgeo.2004.10.007

Cited by 68 publications

(36 citation statements)

References 41 publications

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“…Observing the nomenclature used by Muir Wood (1993), Fenton (1994) and Olesen et al (2004Olesen et al ( , 2013, we conclude that the NVDF should be downgraded from its current status as "A (almost certainly neotectonics)" to "E (very unlikely to be neotectonics). " Because Norway's generalized recurrence estimates for medium-large (M w ≥ 6.0) range between a few to several hundred years (Bungum et al, 2005), and large earthquakes are known to trigger rock avalanches (Keefer, 1984), removing the NVDF from the catalogue of Norwegian paleoseismicity has some potential implications for society.…”

Section: Discussionmentioning

confidence: 99%

“…ent-day seismicity (e.g., Ahjos & Uski, 1992;Bungum et al, 2005;Redfield & Osmundsen, 2015) -it is a bit problematic to be removing neotectonic faults from the national map instead of adding them. Yet honest words best pierce the ear of grief.…”

Section: The Nvdf Enigmamentioning

confidence: 99%

“…1; see Osmundsen et al, 2009Osmundsen et al, , 2010. Because earthquakes in onshore Norway tend to be normal to normal-oblique Keiding et al, 2015), repeat intervals for medium-large (M w ≥ 6.0) events are uncertain in Scandinavia (e.g., Bungum et al, 2005), and such tremors are known to cause landsliding (see Keefer, 1984), its importance to Norwegian geology becomes that much the greater. Yet since 2000, no new work on the NVDF has been formally reported (e.g., Olesen et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Gravitational slope deformation, not neotectonics: Revisiting the Nordmannvikdalen feature of northern Norway

Redfield¹,

Hermanns²

2016

NJG

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A semicontinuous, lobate-to-linear, scarp-like feature slightly less than 1.3 km long strikes NW-SE across the northeast-facing slope of Nordmannvikdalen in Troms County, northern Norway. Its amplitude undergoes continuous decay from a maximum of slightly more than 1.25 m in the southeast to about 20-25 cm in the northwest. This 'Nordmannvikdalen feature' (NVDF) was previously interpreted as the trace of a recently active (e.g., neotectonic) normal fault. However, its greatest possible continuous surface rupture length is geologically constrained to no more than 6 km, and more probably zero. Its scarp length and displacement are incompatible with empirically derived magnitude/length and magnitude/height relationships for seismic surface ruptures. Shallow trenching near the southeastern end of the feature revealed an undeformed soil stratigraphy, a scarp composed entirely of topsoil, and no evidence of erosion typical of post-earthquake degradation or multiple offsets. Reinterpretation of three previously published Ground Penetrating Radar (GPR) profiles favors neither surface breaching nor 'blind' throw.Deep-seated Gravitational Slope Deformation (DSGSD) occurs at both ends of the NVDF. A plane through its scarp trace matching ca. 45° NE-dipping bedrock structures interpreted from GPR imaging projects through both DSGSD back-cracks. Low-angle foliation and thrust fabrics permit development of a complex basal failure surface below the NVDF. However, lower slope deformation typical of DSGSDs is not apparent and offset in the subsurface below the scarp cannot be unambiguously resolved by the GPR data. Signs of surface soil deformation, by freezethaw creep or other processes typical of periglacial environments, are rampant. Many of the NVDF's scarp morphologies are consistent with relict permafrost landforms such as short-and long-wavelength solifluction/gelifluction lobes and sheets, and appear controlled to a surprising degree by the along-strike change in dip of the underlying bedrock surface. We present one possible model conceptualizing how slope-parallel surface lineaments might form in mobilized permafrost soils. Nevertheless, a purely superficial origin of the NVDF cannot easily explain the spatial coincidence of the lineament with the trace of a structural plane describing both DSGSDs, and is therefore also incomplete.The NVDF is a unique landform which we do not fully understand. However, being certain that it was not formed by Holocene seismic surface rupture, we propose its status should be downgraded to "E (Very unlikely to be neotectonics)". Because Norway's paleoseismic and pre-instrument seismic records are poorly controlled, converting yet another onshore neotectonic fault commensurate with Mw > 5.8 surface rupture to the product of some sort of gravitational instability has relevance for better understanding medium-large earthquake recurrence intervals in Fennoscandia.

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Section: Discussionmentioning

confidence: 99%

Section: The Nvdf Enigmamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Gravitational slope deformation, not neotectonics: Revisiting the Nordmannvikdalen feature of northern Norway

Redfield¹,

Hermanns²

2016

NJG

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“…For Norway and adjacent areas the recurrence interval of a M5 earthquake is estimated to 10 years, while a M7 earthquake is suggested to occur every 1100 years (Bungum et al, 2005). The seismic activity is largely attributed to isostatic rebound after the last glacial maximum (LGM) and the retreat of the Fennoscandian Ice Sheet (FIS) (Byrkjeland et al, 2000).…”

Section: Geological Settingmentioning

confidence: 99%

“…Western Norway represents one of the most seismically active areas in Scandinavia (Ahjos & Uski, 1992;Bungum et al, 2005) and it is hence likely that earthquakes could have acted as the main trigger mechanism for such mass failures, as seen for other fjords along the Westand Mid-Norwegian coastline (Bøe et al, 2004). Other potential trigger mechanisms such as climate change and tsunami induced destabilisations are known to…”

Section: Sediment Distribution and Trigger Mechanismsmentioning

confidence: 99%

Detailed site survey examining the postglacial sediment succession and depositional processes within a Norwegian fjord system, Bjørnafjorden (West Norway)

Solli¹,

Vikebø²,

Søyland³

et al. 2017

NJG

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Based on a recently acquired dense grid of sub-bottom profiles and ultra-high resolution bathymetry, we have studied the postglacial depositional history of a West Norwegian fjord system. This dataset reveals a history of frequent mass failures taking place from all slopes surrounding the main studied sediment basin. The study also shows that present-day conditions may be subject to future mass wasting, as significant sediment volumes are retained on the basin margins. The overall sediment distribution seems to be largely governed by the underlying bedrock morphologies. Earthquakes are considered to represent the most dominant trigger mechanism in the area.

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Origin of shallow submarine mass movements and their glide planes—Sedimentological and geotechnical analyses from the continental slope off northern Norway

et al. 2014

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Submarine landslides are often characterized by a basal surface of rupture parallel to the stratigraphy, in which downslope movement is initiated. However, little is known about the sedimentology and physical properties of the sediments within these surfaces. In this study, we present a multiproxy analysis of the sediments collected from a giant piston core penetrating a shallow submarine mass transport deposit, in combination with high-resolution seismoacoustic data to identify and characterize the basal glide plane and the weaker sediments in which movement was initiated. The initial phase of instability consists of a single fracture that formed due to the downslope movement of a mostly intact slab of sediments. The 16 m long core, comprising mostly undisturbed massive and laminated ice-rafted debris-rich clay penetrated this slab. The base of the slab is characterized by a high-amplitude semicontinuous reflection visible on the subbottom profiler data at about 12.5 m depth, interpreted to originate from the glide plane on top of a plumite deposit. This plumite has dilative behavior with pore pressure decrease with increasing shear strain and high undrained shear strength. Movement probably started within contouritic sediments immediately above the glide plane, characterized by higher sensitivities and higher water contents. The occurrence of the mass movements documented in this study are likely affected by the presence of a submarine landslide complex directly downslope. The slide scar of this landslide complex promoted retrogressive movement farther upslope and progressive spreading of strain softening along the slide base and in the slide mass. Numerical models (infinite slope, BING, and retrogressive slope models) illustrate that the present-day continental slope is essentially stable and allow reconstruction of the failure processes when initiated by an external trigger.

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Postglacial seismicity offshore mid-Norway with emphasis on spatio-temporal–magnitudal variations

Cited by 68 publications

References 41 publications

Gravitational slope deformation, not neotectonics: Revisiting the Nordmannvikdalen feature of northern Norway

Gravitational slope deformation, not neotectonics: Revisiting the Nordmannvikdalen feature of northern Norway

Detailed site survey examining the postglacial sediment succession and depositional processes within a Norwegian fjord system, Bjørnafjorden (West Norway)

Origin of shallow submarine mass movements and their glide planes—Sedimentological and geotechnical analyses from the continental slope off northern Norway

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