A North Sea-southern Norway seismic crustal profile

Cassell, B. R.; Mykkeltveit, Svein; Kanestrøm, Reidar; Husebye, Eystein S.

doi:10.1111/j.1365-246x.1983.tb02830.x

Cited by 60 publications

(17 citation statements)

References 16 publications

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“…Refraction experiments indicate that crustal thickness may reach 35 km beneath both Scotland (Bamford et al 1978) and Norway (Cassell et al 1983). In this study it is imore appropriate to consider the results of refraction studies at the margin of the northern North Sea sedimentary basin which show Moho depths of 29-32 km W of the Central Graben (Barton & Wood 1984;, 30-32 km on the East Shetland Platform and 27-28 km on the SE margin of the Viking graben falling to 30 km at the Norwegian coast (Barton & Wood 1984;Cassell et al 1983). The value of 30 km chosen for the gravity modelling is a rough mean of these values and is considered to be a realistic value for the thickness of the crust beneath the Viking graben prior to Permo-Triassic rifting (Zervos & Reay, in prep).…”

Section: Initial Crustal Thicknessmentioning

confidence: 99%

A compilation and regional interpretation of the northern North Sea gravity map

Zervos¹

1987

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A Bouguer anomaly map of the northern North Sea between the Shetland Islands and Norway has been compiled based on four different data sources. The gravity effect of the Devonian to recent sediments was calculated along six published seismic profiles crossing the area and a regional gravity anomaly map produced on the assumption that the sedimentary basin structure is two dimensional. Regional.consideration of the gravity field revealed the presence of a mass excess beneath the low-density sediments within the Viking graben. This high-amplitude, long-wavelength anomaly is explained by thinning of the crust from 30 km beneath the flanks to 10 km beneath the centre of the graben, excluding the thickness of the sediments. Crustal thickness along the profiles was derived using the regional gravity field and from this a contour map of the Moho was produced. Predictions obtained from the gravity data confirm the crustal structure derived so far from seismic experiments in the North Sea. For comparison a threedimensional model of crustal thickness was constructed and a second contour map of the Moho was produced. The Moho contour maps derived from the two-dimensional and three-dimensional models show close agreement, demonstrating that a two-dimensional approach is justified in this case.

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Section: Initial Crustal Thicknessmentioning

confidence: 99%

A compilation and regional interpretation of the northern North Sea gravity map

Zervos¹

1987

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“…(Kinck et al 1993) and lithosphere thickness in km as deduced from surface wave dispersion analysis (Calcagnile 1982). (b) Present-day lithosphere structure along the modelled section A-A t as deduced from deep seismic data (Kanestrom 1971;Tryti & Sellevoll 1977;Cassel et al 1983;Lie et al 1990;Guggisberg et al 1991;Kinck et al 1993) and P-wave residual analysis (Plomerov~ et al 2001). Note that both surface-wave dispersion analysis and P-wave residuals analysis argue for base lithosphere deepening in the eastern part of section A-A'.…”

Section: Lithosphere Configurationmentioning

confidence: 99%

“…38 and 46 km below the western and the eastern parts of the models, respectively). The upper crust-lower crust boundary is not always well imaged on regional deep seismic profiles but seems to undulate at about 20km depth (Kanestrom 1971;Cassel et al 1983;Guggisberg et al 1991). For the sake of simplicity, the upper crust-lower crust boundary is modelled as a flat surface located at 20 km depth.…”

Section: Lithosphere Configurationmentioning

confidence: 99%

Asymmetric lithosphere as the cause of rifting and magmatism in the Permo-Carboniferous Oslo Graben

Pascal

Cloetingh

Davies

2004

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Compared to other Permo-Carboniferous rift basins of NW Europe, the Oslo Graben has two distinct characteristics. First, it initiated inside cold and stable Precambrian lithosphere, whereas most Permo-Carboniferous basins developed in weaker Phanerozoic lithosphere, and second, it is characterized by large volumes of magmatic rocks despite relatively little extension. Seismic reflection surveys show that the crust thickens from southern Norway to southern Sweden, the most significant Moho deepening occurring from the Oslo Region eastwards. Deep seismic studies also suggest that the base of the lithosphere deepens markedly eastwards from the Oslo Region. Such a long-wavelength lithospheric geometry cannot be explained by the Permian or post-Permian evolution of the area, hence the Oslo Graben appears to have evolved at the transition between two lithospheric domains with contrasting thickness. Numerical thermo-mechanical modelling is applied to test if this transitional position can influence the dynamics of rifting. Different models with varying lithosphere thickness contrast are considered. Model results show that a crust and lithosphere thickness contrast comparable to the Oslo Region can explain rifting and focusing of magmatism in a narrow zone with minor thinning of the crust. Models also account for the major characteristics of the Oslo Graben in terms of location and strain distributions in the crust.

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“…Fig. 2 a refraction profiling section CANOBE (Cassell et al 1983) is shown. The surprising feature here is that the dominant wavefield amplitude is associated with shear waves (Lg phase) on the transverse component, reflecting P-to-S conversions close to the source.…”

Section: Synthesizing W a V E P R O P A G A T I O N In The Crust A N mentioning

confidence: 99%

Seismic wave propagation in complex crust-upper mantle media using 2-D finite-difference synthetics

Hestholm

Husebye²,

Ruud³

1994

Geophysical Journal International

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SUMMARY A description is given of the numerical FD scheme used to solve the elasti wave equation, including a few remarks on the source functions used. Our FD method has been used for computing synthetic seismograms for 2‐D crust/upper mantle models of size 150 × 400 km2, with options for free‐surface topography. The strategy was to introduce successively more complex lithosphere models for generating the synthetics; the reference model was laterally homogeneous lithosphere. The interface scattering was visualized through displays of free‐surface synthetic waveforms and snapshots for models with a corrugated Moho only and free surface topography only. Near the free surface the latter seems to dominate, in the form of P‐to‐Rg and S‐to‐Rg conversions. Lithosphere randomizations were introduced through von Kármán functions of order n= 0.3, with rms velocity fluctuations of 3–4 per cent and correlation distances (horizontal and vertical) at 2.5 or 10 km. In case of a medium with only sub‐Moho heterogeneities, those with horizontal anisotropy (ax= 10 km; az= 2.5 km) produced relatively strong Pn and Sn phases. The respective codas were dominated as in most of our experiments by P‐to‐S and S‐to‐S scattering wavelets excluding Rg scattering at a free surface with topography. For a medium with crustal heterogeneities, the distortions of the P and S wave trains with distance were clearly demonstrated. For full‐scale heterogeneous lithosphere models, characteristic features of the synthetics were quantitatively similar to observational records of local events. Dominant attributes were a pronounced P coda consisting mainly of P‐ and Rg‐scattered wavelets, and a relatively strong S coda consisting mainly of P‐to‐S and S‐to‐S scattered wavelets. The P and S waveforms are severely distorted pointing at the futility of reliably picking many secondary arrivals in local event recordings. Most of the scattering wavelets are confined to the crustal waveguide and to surface waves, since coda excitations for sensors at a depth of 100 km were weak and, moreover, consisted mainly of S wavelets. This implies that a strong teleseismic P coda does not reflect scattering within the crust in the source region but, rather, a complex source. Observational results from analysis of NORESS and ARCESS local event recordings are also presented. Clearly the lithosphere is not isotropically inhomogeneous. The essence of our 2‐D FD synthetic seismogram experiments is that a simple lithosphere model, being moderately heterogeneous, gives rise to complex seismograms which are grossly similar to the observational recordings. In contrast, complex models derived from profiling surveys (but lacking the fine‐scale random variations) give simple,‘ray tracing’like synthetics, not necessarily similar to the observed records.

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A North Sea-southern Norway seismic crustal profile

Cited by 60 publications

References 16 publications

A compilation and regional interpretation of the northern North Sea gravity map

A compilation and regional interpretation of the northern North Sea gravity map

Asymmetric lithosphere as the cause of rifting and magmatism in the Permo-Carboniferous Oslo Graben

Seismic wave propagation in complex crust-upper mantle media using 2-D finite-difference synthetics

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