scholarly journals New insights into North Sea deep crustal structure and extension from transdimensional ambient noise tomography

2020 ◽  
Vol 224 (2) ◽  
pp. 1197-1210
Author(s):  
E Crowder ◽  
N Rawlinson ◽  
D G Cornwell ◽  
C Sammarco ◽  
E Galetti ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
North Sea ◽  
Crustal Structure ◽  
Shear Wave Velocity ◽  
Rift System ◽  
The North ◽  
Continental Rifts ◽  
Deep Crustal Structure ◽  
The North Sea

SUMMARY The deep crustal structure beneath the North Sea is poorly understood since it is constrained by only a few seismic reflection and refraction profiles. However, it is widely acknowledged that the mid to lower crust plays important roles in rift initiation and evolution, particularly when large-scale sutures and/or terrane boundaries are present, since these inherited features can focus strain or act as inhibitors to extensional deformation. Ancient tectonic features are known to exist beneath the iconic failed rift system of the North Sea, making it an ideal location to investigate the complex interplay between pre-existing regional heterogeneity and rifting. To this end, we produce a 3-D shear wave velocity model from transdimensional ambient seismic noise tomography to constrain crustal properties to ∼30 km depth beneath the North Sea and its surrounding landmasses. Major North Sea sedimentary basins appear as low shear wave velocity zones that are a good match to published sediment thickness maps. We constrain relatively thin crust (13–18 km) beneath the Central Graben depocentres that contrasts with crust elsewhere at least 25–30 km thick. Significant variations in crustal structure and rift symmetry are identified along the failed rift system that appears to be related to the locations of Laurentia–Avalonia–Baltica palaeoplate boundaries. We constrain first-order differences in structure between palaeoplates; with strong lateral gradients in crustal velocity related to Laurentia–Avalonia–Baltica plate juxtaposition and reduced lower crustal velocities in the vicinity of the Thor suture, possibly representing the remnants of a Caledonian accretionary complex. Our results provide fresh insight into the pivotal roles that ancient terranes can play in the formation and failure of continental rifts and may help explain the characteristics of other similar continental rifts globally.

Shear‐wave velocity and density estimation from PS-wave AVO analysis: Application to an OBS dataset from the North Sea

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1446-1454 ◽  
Author(s):  
Side Jin ◽  
G. Cambois ◽  
C. Vuillermoz
Keyword(s):  
Wave Velocity ◽  
North Sea ◽  
Random Noise ◽  
P Wave ◽  
S Wave ◽  
Data Set ◽  
Avo Analysis ◽  
The North ◽  
Avo Inversion ◽  
The North Sea

S-wave velocity and density information is crucial for hydrocarbon detection, because they help in the discrimination of pore filling fluids. Unfortunately, these two parameters cannot be accurately resolved from conventional P-wave marine data. Recent developments in ocean‐bottom seismic (OBS) technology make it possible to acquire high quality S-wave data in marine environments. The use of (S)-waves for amplitude variation with offset (AVO) analysis can give better estimates of S-wave velocity and density contrasts. Like P-wave AVO, S-wave AVO is sensitive to various types of noise. We investigate numerically and analytically the sensitivity of AVO inversion to random noise and errors in angles of incidence. Synthetic examples show that random noise and angle errors can strongly bias the parameter estimation. The use of singular value decomposition offers a simple stabilization scheme to solve for the elastic parameters. The AVO inversion is applied to an OBS data set from the North Sea. Special prestack processing techniques are required for the success of S-wave AVO inversion. The derived S-wave velocity and density contrasts help in detecting the fluid contacts and delineating the extent of the reservoir sand.

Near-surface shear-wave birefringence in the North Sea: Ekofisk 2D/4C test

2003 ◽  
Vol 22 (12) ◽  
pp. 1236-1242 ◽  
Author(s):  
Richard R. Van Dok ◽  
James E. Gaiser ◽  
Grant Byerley
Keyword(s):  
Shear Wave ◽  
North Sea ◽  
Surface Shear ◽  
Near Surface ◽  
The North ◽  
The North Sea ◽  
Surface Shear Wave

3-D crustal structure of the Iran plateau using phase velocity ambient noise tomography

2019 ◽  
Vol 220 (3) ◽  
pp. 1555-1568 ◽  
Author(s):  
R Movaghari ◽  
G Javan Doloei
Keyword(s):  
Phase Velocity ◽  
Shear Wave ◽  
Wave Velocity ◽  
Crustal Structure ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Velocity Model ◽  
Central Iran ◽  
Ambient Noise Tomography ◽  
Iran Plateau

SUMMARY More accurate crustal structure models will help us to better understand the tectonic convergence between Arabian and Eurasian plates in the Iran plateau. In this study, the crustal and uppermost mantle velocity structure of the Iran plateau is investigated using ambient noise tomography. Three years of continuous data are correlated to retrieve Rayleigh wave empirical Green's functions, and phase velocity dispersion curves are extracted using the spectral method. High-resolution Rayleigh wave phase velocity maps are presented at periods of 8–60 s. The tomographic maps show a clear consistency with geological structures such as sedimentary basins and seismotectonic zones, especially at short periods. A quasi-3-D shear wave velocity model is determined from the surface down to 100 km beneath the Iran plateau. A transect of the shear wave velocity model has been considered along with a profile extending across the southern Zagros, the Sanandaj-Sirjan Zone (SSZ), the Urumieh-Dokhtar Magmatic Arc (UDMA) and Central Iran and Kopeh-Dagh (KD). Obvious crustal thinning and thickening are observable along the transect of the shear wave velocity model beneath Central Iran and the SSZ, respectively. The observed shear wave velocities beneath the Iran plateau, specifically Central Iran, support the slab break-off idea in which low density asthenospheric materials drive towards the upper layers, replacing materials in the subcrustal lithosphere.

scholarly journals Probabilistic neural network tomography across Grane field (North Sea) from surface wave dispersion data

2020 ◽  
Vol 223 (3) ◽  
pp. 1741-1757
Author(s):  
S Earp ◽  
A Curtis ◽  
X Zhang ◽  
F Hansteen
Keyword(s):  
Neural Network ◽  
Monte Carlo ◽  
Surface Wave ◽  
Shear Wave ◽  
Wave Velocity ◽  
North Sea ◽  
Shear Wave Velocity ◽  
Wave Dispersion ◽  
Surface Wave Dispersion ◽  
Dispersion Data

SUMMARY Surface wave tomography uses measured dispersion properties of surface waves to infer the spatial distribution of subsurface properties such as shear wave velocities. These properties can be estimated vertically below any geographical location at which surface wave dispersion data are available. As the inversion is significantly non-linear, Monte Carlo methods are often used to invert dispersion curves for shear wave velocity profiles with depth to give a probabilistic solution. Such methods provide uncertainty information but are computationally expensive. Neural network (NN) based inversion provides a more efficient way to obtain probabilistic solutions when those solutions are required beneath many geographical locations. Unlike Monte Carlo methods, once a network has been trained it can be applied rapidly to perform any number of inversions. We train a class of NNs called mixture density networks (MDNs), to invert dispersion curves for shear wave velocity models and their non-linearized uncertainty. MDNs are able to produce fully probabilistic solutions in the form of weighted sums of multivariate analytic kernels such as Gaussians, and we show that including data uncertainties as additional inputs to the MDN gives substantially more reliable velocity estimates when data contains significant noise. The networks were applied to data from the Grane field in the Norwegian North sea to produce shear wave velocity maps at several depth levels. Post-training we obtained probabilistic velocity profiles with depth beneath 26 772 locations to produce a 3-D velocity model in 21 s on a standard desktop computer. This method is therefore ideally suited for rapid, repeated 3-D subsurface imaging and monitoring.

Reconstruction of Salt Tectonics: Insights from the Mid North Sea High

2021 ◽  
Author(s):  
Chibuike Nnadi ◽  
Alexander Peace
Keyword(s):  
North Sea ◽  
Oil And Gas ◽  
Upper Permian ◽  
Rift System ◽  
Salt Tectonics ◽  
Driving Mechanism ◽  
The North ◽  
Driving Mechanisms ◽  
Structural Style ◽  
The North Sea

<p><strong>Abstract</strong></p><p>The North Sea is a complex rift system that has undergone a polyphase evolutionary history from the Palaeozoic to Recent, including the deposition, and subsequent mobilisation of Upper Permian Zechstein salt. This halokinesis has played an integral role in the geologic evolution of the North Sea, controlling the present-day structural style. The driving mechanisms and kinematics of salt deformation have gained widespread interest partly due to the potential role of salt in hydrocarbon systems, and also due to its potential uses for nuclear waste disposal. However, the primary driving mechanism for salt-related deformation in the North Sea is debated. Here, we focus on the Mid-North Sea High (MNSH), an area of the North Sea in which salt-related deformation is widespread. We interpret open access data made available by United Kingdom Oil and Gas Authority (OGA) including 2D seismic reflection, gravity, magnetic and well data in Petrel, followed by forward modeling and restoration in the MOVE software. The results show that, the style of salt-related deformation in the MNSH region is highly variable, with the influence of local stratigraphy, as well as basement structures, also contributing to the deformation style.</p><p><strong>Keywords:</strong> Salt tectonics, Halokinesis, North Sea, Mid North Sea High</p>

A reinterpretation of the ages and depositional environments of the lower and middle Miocene stratigraphic records in a key area along the southern margin of the North Sea Basin

2017 ◽  
Vol 156 (3) ◽  
pp. 525-532 ◽  
Author(s):  
JEF DECKERS ◽  
STEPHEN LOUWYE
Keyword(s):  
North Sea ◽  
Extreme Environments ◽  
Depositional Environments ◽  
Rift System ◽  
Short Pulses ◽  
Accommodation Space ◽  
The North ◽  
Southern Margin ◽  
The North Sea ◽  
Peat Formation

AbstractThe stratigraphic reinterpretation of the palynologically analysed Miocene succession of the Wijshagen borehole along the southern margin of the North Sea Basin allowed an age assessment – late Burdigalian to early Serravalian – for the Genk Sand Member of the Bolderberg Formation. The depositional environment varied during Burdigalian to Serravalian times from continental (peat formation) to open marine (glauconitic sands), respectively from south to north in the Roer Valley Rift System. The study area of the Wijshagen borehole is located in the central part of the Roer Valley Rift System between these extreme environments. During the Burdigalian, the glauconitic fine clayey sands of the Houthalen Sand Member were deposited in the study area. From the late Burdigalian onwards, the glauconite content decreased and lignite content increased as a result of high influx of clastic material in the Roer Valley Rift System, and marked the start of the deposition of the Genk Sand Member. The Genk Sand Member shows an overall coarsening-upwards trend, which is consistent with the gradual infill of the available accommodation space in the Roer Valley Rift System by northwest-prograding clastic delta sequences. Dinoflagellate cyst analyses indicate that the Genk Sand Member was largely deposited in a marginal marine environment with only short pulses of continental input. These pulses of continental input increase in a southerly or landward direction where they led to the development of thick lignite seams.

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