Relation between seismicity and tectonic structures offshore and onshore Nordland, northern Norway

Janutyte, Ilma; Lindholm, Conrad; Olesen, Odleiv

doi:10.17850/njg97-3-02

Cited by 4 publications

(16 citation statements)

References 24 publications

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“…During the swarm activity there were recorded several hundreds of small earthquakes and most of them were shallow, 3 to 8 km deep (Janutyte et al, 2017), similar to the earlier reported earthquake swarms.…”

Section: Introductionsupporting

confidence: 87%

“…1 & 5). Gabrielsen et al (2002) around Steigen and Svartisen, where the most intense onshore seismicity was recorded (lower right). in the southwestern part clustered along well-defi ned NW-SE-trending lines, indicating that the earthquakes probably migrated along the structures, which were interpreted as active faults (Janutyte et al, 2017). e azimuths of nodal planes (Fig.…”

Section: Analysis Of the Focal Mechanismsmentioning

confidence: 96%

“…Using data from both the temporary and the permanent deployments 1242 earthquakes were located in the study area, including an earthquake swarm. In an earlier study (Janutyte et al, 2017) we used the seismological monitoring results to obtain the seismicity distribution and identify the relation between the observed earthquakes and the major tectonic structures in the area, while our current study is focused on the focal mechanisms of the earthquakes, and aims to reveal the underlying stress-generating mechanisms.…”

Section: Introductionmentioning

confidence: 99%

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Earthquake source mechanisms in onshore and offshore Nordland, northern Norway

Janutyte¹,

Lindholm²

2017

NJG

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In this paper we present a comprehensive database of 152 earthquake focal mechanism solutions for the Nordland area, northern Norway, and the adjacent offshore regions. 123 focal mechanisms are published for the first time. We developed an equation to objectively determine the quality of the focal mechanisms, while the equation was explicitly adjusted to the used dataset (not globally accepted). We used the equation to assign quality factors to the new focal mechanisms, while the quality of the earlier published focal mechanisms was kept as originally provided. About 20% of all focal mechanisms were set to the higher quality A and B, which was assigned to the onshore earthquakes only, whereas for offshore earthquakes the highest assigned quality was quality C, mostly due to larger azimuthal gaps. The results showed that seismicity onshore and offshore Nordland is different in type: with dominant shallow, normal-faulting earthquakes onshore and mostly deeper, mixed type faulting earthquakes offshore, while along the coast the faulting regime was mostly normal to strike-slip. The results indicated that maximum horizontal compressional stress, s H , directions in the offshore areas on a large scale originate from the plate-tectonic ridge push with NW-SE compression, whereas in the onshore regions s H directions are better explained through local stress-generating sources, such as topography. In our results we also recognised a possible relation between the Svartisen glacier massif and the enhanced seismicity in the surroundings, including an earthquake swarm activity to the west of the glacier. Moreover, in many onshore and offshore regions the nodal plane azimuths, obtained from the focal mechanisms, correlate well with the trends of geologically mapped onshore and offshore structures.

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Section: Introductionsupporting

confidence: 87%

Section: Analysis Of the Focal Mechanismsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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Earthquake source mechanisms in onshore and offshore Nordland, northern Norway

Janutyte¹,

Lindholm²

2017

NJG

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“…This procedure allows us to exclude most of the human‐induced seismicity from the correlation analysis of earthquake occurrence and atmospheric precipitation. The last, local catalog has been maintained in the framework of the NEONOR2 project “Neotectonics in Nordland – Implications for petroleum exploration” (Janutyte et al, 2017). The NEONOR2 catalog is also included in the NNSN catalog (NNSN, 2016) and is based on 27 seismological stations, which have been in operation during the period of 2013–2016 along the coast of the Nordland county, northern Norway (Janutyte et al, 2017).…”

Section: Methodsmentioning

confidence: 99%

“…The densest distribution of seismic events is observed near the shoreline, both onshore and offshore, in the Nordland area and Western Norway (Figure 1a). There is a tendency for deep earthquakes (deeper than 25 km) to occur far offshore (Janutyte et al, 2017), whereas shallow seismicity (shallower than 3 km) is concentrated onshore (NNSN, 2016). There is also a weak tendency for earthquakes with magnitudes greater than 3 to be located offshore.…”

Section: Introductionmentioning

confidence: 99%

Atmospheric Precipitation and Anomalous Upper Mantle in Relation to Intraplate Seismicity in Norway

et al. 2020

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Two enigmatic regions of high intraplate seismicity in Norway (Western Norway and the Nordland area) show a temporal correlation between the number of earthquakes within the upper crystalline crust and intensity of rain and snowmelt at the Earth's surface. This correlation is obvious in the Nordland area where detailed and reliable data on seismicity are available, whereas the correlation is weaker in Western Norway where detailed data on seismicity are missing. Moreover, these discrete zones of high seismic activity coincide spatially with prominent, low-velocity, and, most likely, thermally anomalous zones in the upper mantle. We propose that in addition to other causes, the high seismicity may be controlled by the anomalous upper mantle, along with topographically induced gravitational potential energy and crustal density variations. Precipitation-induced, seasonal increases in pore-fluid pressure within the fractured crystalline bedrock and changes in water loads may modulate the tectonically controlled seismicity.

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Crustal structure and intraplate seismicity in Nordland, Northern Norway: insight from seismic tomography

Shiddiqi

Ottemöller

Rondenay

et al. 2022

Geophysical Journal International

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Summary The Nordland region, Northern Norway, situated in an intraplate continental setting, has the highest seismicity rate in mainland Norway. However, the exact cause of seismicity in this region is still debated. Better understanding of factors that influence the seismicity in Nordland can help increase knowledge of intraplate seismicity in general. Here, we address this problem with the aid of a new high-resolution 3-D VP and VP/VS ratio images of the crust in Nordland using seismic travel-time tomography. These images show the existence of a localized, 10 - 15 km Moho step that runs parallel to the coast. The north-south extent of this step coincides with the region that exhibits the highest rates of seismicity. Focal mechanisms of selected earthquakes computed in this study are dominated by normal and oblique-normal, indicating a coast-perpendicular extension. The coast-perpendicular extensional stress regime deviates from the regional compression imposed by the ridge push from the North Atlantic. This deviation is thought to stem from the additional interference with local flexural stress caused by sediment redistribution and glacial isostatic adjustment, and possibly exacerbated by gravitational potential energy stress associated with the Moho step. The deformation due to the extensional regime is localized on pre-existing faults and fractures along the coastline. The tomography result shows that two distinct seismic swarms occurred in the coastal area with low VP and variable VP/VS ratio anomalies, pointing towards fractured crust and possibly the presence of fluids. The existence of fluids here can change the differential stress and promote seismic rupture.

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Relation between seismicity and tectonic structures offshore and onshore Nordland, northern Norway

Cited by 4 publications

References 24 publications

Earthquake source mechanisms in onshore and offshore Nordland, northern Norway

Earthquake source mechanisms in onshore and offshore Nordland, northern Norway

Atmospheric Precipitation and Anomalous Upper Mantle in Relation to Intraplate Seismicity in Norway

Crustal structure and intraplate seismicity in Nordland, Northern Norway: insight from seismic tomography

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