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8 results on '"Nilsen, Espen Harris"'

1. 3D Prestack Fourier Mixed-Domain (FMD) depth migration for VTI media with large lateral contrasts

Author

Zhao, Hao, Gelius, Leiv J., Tygel, Martin, Nilsen, Espen Harris, and Evensen, Andreas Kjelsrud

Subjects
Physics - Geophysics, Physics - Computational Physics
Abstract

Although many 3D One-Way Wave-equation Migration (OWEM) methods exist for VTI media, most of them struggle either with the stability, the anisotropic noise or the computational cost. In this paper we present a new method based on a mixed space- and wavenumber-propagator that overcome these issues very effectively as demonstrated by the examples. The pioneering methods of phase-shift (PS) and Stolt migration in the frequency-wavenumber domain designed for laterally homogeneous media have been followed by several extensions for laterally inhomogeneous media. Referred many times to as phase-screen or generalized phase-screen methods, such extensions include as main examples of the Split-step Fourier (SSF) and the phase-shift plus interpolation (PSPI). To further refine such phase-screen techniques, we introduce a higher-order extension to SSF valid for a 3D VTI medium with large lateral contrasts in vertical velocity and anisotropy parameters. The method is denoted Fourier Mixed-Domain (FMD) prestack depth migration and can be regarded as a stable explicit algorithm. The FMD technique was tested using the 3D SEG/EAGE salt model and the 2D anisotropic Hess model with good results. Finally, FMD was applied with success to a 3D field data set from the Barents Sea including anisotropy., Comment: Accepted article in Journal of Applied Geophysics

Published
2019
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2. The High Arctic Large Igneous Province: first seismic-stratigraphic evidence for multiple Mesozoic volcanic pulses on the Lomonosov Ridge, central Arctic Ocean.

Author

Kristoffersen, Yngve, Nilsen, Espen Harris, and Hall, John Kendrick

Subjects
*IGNEOUS provinces, *MESOZOIC Era, *SEA ice drift, *VOLCANISM, *MAGNETIC flux density, *SEA ice, *OCEAN
Abstract

We use seismic reflection data acquired by an over-winter expedition on drifting sea ice in the central Arctic Ocean to explore a possible spatial and temporal magmatic relation between the sub-bottom geology of part of the deep Arctic Ocean and the Mesozoic volcanic rocks found on the islands and the bordering continental shelf of Franz Josef Land and Svalbard. The new dataset from the North American segment (85–90°N) of the Lomonosov Ridge, central Arctic Ocean documents several Mesozoic volcanic pulses over a distance of c. 600 km along the ridge. This volcanism borders a domain of high magnetic field intensity over the adjacent Alpha Ridge in the deep basin where the magnetic source rocks and recent seismic reflection data indicate extensive Mesozoic magmatism. We suggest that the Mesozoic volcanism on the Lomonosov Ridge in its palaeo-position at the former continental margin north of Franz Josef Land and Svalbard spatially links the Mesozoic magmatic pulses of the continental High Arctic Large Igneous Province (HALIP) of polar Europe to volcanism on the adjacent Alpha Ridge in the deep Arctic Ocean. Increased input of heat to the upper crust on the Lomonosov Ridge enhanced maturation of hydrocarbon source rocks as manifested by the presence of gas or fluid escape pipes restricted to the area of volcanism. [ABSTRACT FROM AUTHOR]

Published
2023
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8. Sediment deformation atop the Lomonosov Ridge, central Arctic Ocean: Evidence for gas-charged sediment mobilization?

Author

Kristoffersen, Yngve, Hall, John K., and Nilsen, Espen Harris

Subjects
*SEA ice drift, *GRABENS (Geology), *SEDIMENTS, *OCEAN, *CONTINENTAL margins, *SEA ice
Abstract

We have used a hovercraft platform drifting with the sea ice to acquire the first digitally recorded seismic reflection data transects across the Canada/Greenland (89°N-85°N) section of the Lomonosov Ridge, central Arctic Ocean. The flat-lying, laterally uniform Cenozoic sediment package on top of the ridge at 87°N, 60° W shows at least four sites with local seismic amplitude anomalies. The common feature is a column (<600 m wide) of partly discontinuous or chaotic bright reflection events at the center of a <1.5 km wide dome (amplitude <25 m) terminating at the seabed in a 8–12 m deep depression. The amplitude anomalies are interpreted as gas-charged fluid escape pipes marked by a pockmark at the seabed. Gas and fluids introduced from below have mobilized the overlying high porosity, low density Eocene bio-siliceous ooze causing the doming. The gas and fluids appear to originate from the top of rotated fault blocks and sub-basalt sediments of Mesozoic or older age deposited when the Lomonosov Ridge was part of the pre-Late Cretaceous continental margin north of Franz Josef Land. • Sediment deformation associated with seismic amplitude anomalies discovered in the central Arctic Ocean. • Amplitude anomalies represent gas-charged fluid migration. • Deformation is induced by mobilization of sediments. • Gas and fluids emanated from deep sources within Mesozoic or older rocks. • First evidence of hydrocarbon source rocks on the Mesozoic polar margin of Europe. [ABSTRACT FROM AUTHOR]

Published
2022
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