Blar i NTNU Open på tidsskrift "Geophysical Journal International"
Viser treff 1-19 av 19
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Characterizing the acoustic properties of the cavity cloud generated close to an air-gun array as a time-dependent effective medium
(Journal article, 2018)A ghost cavity cloud consists of many small vapour cavities and appears above and around the air-guns in the source array a few milliseconds after the source is fired. Since there are dissolved gases and stable microbubbles ... -
Chemical and magnetic properties of rapidly cooled metastable ferri-ilmenite solid solutions - IV: The fine structure of self-reversed thermoremanent magnetization
(Journal article; Peer reviewed, 2014)Magnetic experiments, a Monte Carlo simulation and transmission electron microscopy observations combine to confirm variable chemical phase separation during quench and annealing of metastable ferri-ilmenite compositions, ... -
Chemical and magnetic properties of rapidly cooled metastable ferri-ilmenite solid solutions: II. Chemical changes during quenching and annealing
(Journal article; Peer reviewed, 2012)Chemical and microstructural evolution during quench and short-term annealing of a sample XFeTiO3= 0.61 is explored in the light of observations in Paper I. Ordering proceeds by (1) random appearance of ordered and ... -
Chemical and magnetic properties of rapidly cooled metastable ferri-ilmenite solid solutions: implications for magnetic self-reversal and exchange bias - III. Magnetic interactions in samples produced by Fe-Ti ordering
(Journal article; Peer reviewed, 2012)Paper II of this series described the chemical and microstructural evolution of ferri-ilmenite solid solutions during high-T quench and short-term annealing. Here we explore consequences of these Fe–Ti ordering-induced ... -
Diving-wave time-lapse delay for CO2 thin layer detection
(Peer reviewed; Journal article, 2024)We have derived an analytical approximate expression to estimate the delay in diving seismic waves due to thin layers of CO2. The expression is valid for high frequencies and can be used to estimate the delay in diving ... -
Experimental study of seismic dispersion: Influence of clay mineral content
(Journal article; Peer reviewed, 2023)We conducted an extensive study on the elastic properties of Opalinus Clay and the overlying and underlying rock formations, which range in the overall clay mineral content from nearly 0 wt.% to 60 wt.%. Our laboratory ... -
Finite-difference modelling of wavefield constituents
(Journal article; Peer reviewed, 2015)The finite-difference method is among the most popular methods for modelling seismic wave propagation. Although the method has enjoyed huge success for its ability to produce full wavefield seismograms in complex models, ... -
Frequency-depth-dependent spherical reflection response from the sea surface - a transmission experiment
(Journal article; Peer reviewed, 2018)In academia and the industry, there is an increasing interest in generating and recording low seismic frequencies, which lead to better data quality, deeper signal penetration and can be important for full-waveform inversion. ... -
Freznel zone in VTI and orthorhombic media
(Journal article; Peer reviewed, 2017)The reflecting zone in the subsurface insonified by the first quarter of a wavelength and the portion of the reflecting surface involved in these reflections is called the Fresnel zone or first Fresnel zone. The horizontal ... -
Higher-order Hamilton–Jacobi perturbation theory for anisotropic heterogeneous media: dynamic ray tracing in Cartesian coordinates
(Journal article; Peer reviewed, 2019)With a Hamilton–Jacobi equation in Cartesian coordinates as a starting point, it is common to use a system of ordinary differential equations describing the continuation of first-order derivatives of phase-space perturbations ... -
Higher-order Hamilton–Jacobi perturbation theory for anisotropic heterogeneous media: transformation between Cartesian and ray-centred coordinates
(Peer reviewed; Journal article, 2021)Dynamic ray tracing is a robust and efficient method for computation of amplitude and phase attributes of the high-frequency Green’s function. A formulation of dynamic ray tracing in Cartesian coordinates was recently ... -
Influence of lattice-preferred orientation with respect to magnetizing field on intensity of remanent magnetization in polycrystalline hemo-ilmenite
(Journal article; Peer reviewed, 2012)New experimental and computational approaches to interpret orientation and intensity of natural remanent magnetization (NRM) carried by lamellar magnetism are applied to historic magnetic measurements on a collection of ... -
Lamellar magnetism and exchange bias in billion-year-old metamorphic titanohematite with nanoscale ilmenite exsolution lamellae-III. Atomic-magnetic basis for experimental results
(Peer reviewed; Journal article, 2021)Lamellar magnetism is a source of remanent magnetization in natural rocks different from common bulk magnetic moments in ferrimagnetic minerals. It has been found to be a source for a wide class of magnetic anomalies with ... -
Magnetic petrology of the Devonian Achala Batholith, Argentina: titanohaematite as an indicator of highly oxidized magma during crystallization and cooling
(Journal article; Peer reviewed, 2008)Devonian magmatism in the Eastern Sierras Pampeanas (Córdoba, Argentina) is represented by elliptical, porphyritic, batholithic, late- to post-orogenic monzogranites emplaced in a metamorphic—plutonic basement. Two groups ... -
New interpretation of the spreading evolution of the Knipovich Ridge derived from aeromagnetic data
(Peer reviewed; Journal article, 2021)Insights into the spreading evolution of the Knipovich Ridge and development of the Fram Strait are revealed from a recent aeromagnetic survey. As an ultraslow spreading ridge in an oblique system located between the ... -
Size and shape dependence of the magnetic ordering temperature in nanoscale magnetic particles
(Journal article; Peer reviewed, 2012)Natural rocks and synthetic analogues can contain extremely small scaled magnetic minerals varying in shape from approximately equidimensional nanoparticles to lower dimensionally shaped lamellae resembling thin films or ... -
Stress-dependent elastic properties of shales—laboratory experiments at seismic and ultrasonic frequencies
(Journal article; Peer reviewed, 2018)Knowledge about the stress sensitivity of elastic properties and velocities of shales is important for the interpretation of seismic time-lapse data taken as part of reservoir and caprock surveillance of both unconventional ... -
Structural properties of the Southern San Andreas fault zone in northern Coachella Valley from magnetotelluric imaging
(Peer reviewed; Journal article, 2022)The Southern San Andreas fault (SSAF) poses one of the largest seismic risks in California. Yet, there is much ambiguity regarding its deeper structural properties around Coachella Valley, in large part due to the relative ... -
Wavefield reconstruction for velocity–stress elastodynamic full-waveform inversion
(Peer reviewed; Journal article, 2020)Gradient computations in full-waveform inversion (FWI) require calculating zero-lag cross-correlations of two wavefields propagating in opposite temporal directions. Lossless media permit accurate and efficient reconstruction ...