The Earth’s solid inner core consists mainly of iron (Fe), alloyed with lighter elements, such as silicon (Si). Interpretation of seismic anisotropy and layering requires knowledge of the stable crystal structure in the inner core. We report ab initio density functional theory calculations on the free energy and vibrational stability of pure iron and Fe–Si alloys at conditions representative of...

Ž . We investigate seismic layering i.e., discontinuities, regions of anomalous velocity gradients, and anisotropy and its Ž . lateral variability in the upper mantle by comparing seismic models from three tectonic regions: old ;100 Ma Pacific Ž . plate, younger ;40 Ma Philippine Sea plate, and Precambrian western Australia. These models were constructed by combining two data sets: ScS-reflecti...

Spatial variations in the rigidity of continental plates (expressed in terms of an effective elastic thickness, Te) can have a profound influence on the style of deformation of ocean–continent convergent margins. Depending on the spatial distribution of Te, strains related to plate boundary forces can become concentrated where Te is small. We calculate Te and Te anisotropy in western Canada by ...

Ethiopia is a region where continental rifting gives way to oceanic spreading. Yet the role that pre-existing lithospheric structure, melt, mantle flow, or active upwellings may play in this process is debated. Measurements of seismic anisotropy are often used to attempt to understand the contribution that these mechanisms may play. In this study, we use new data in Afar, Ethiopia along with le...

S U M M A R Y Measurements of seismic anisotropy are commonly used to constrain deformation in the upper mantle. Observations of anisotropy at mid-mantle depths are, however, relatively sparse. In this study we probe the anisotropic structure of the mid-mantle (transition zone and uppermost lower mantle) beneath the Japan, Izu-Bonin, and South America subduction systems. We present source-side ...

Ultrasonic velocities, densities and porosities for a set of coal and surrounding silty coal, silty shale, and shaly coal samples were measured in laboratory. The pressure effect, temperature effect, and saturation effect on velocities and anisotropy were evaluated. The results were compared and correlated with the well log data and discrepancies were analyzed. The potential influences of the c...

Surface waves propagating through a laterally inhomogeneous medium undergo wavefield complications such as multiple scattering, wavefront healing, and backward scattering. Unless accounted for accurately, these effects will introduce a systematic isotropic bias in estimates of azimuthal anisotropy. We demonstrate with synthetic experiments that backward scattering near an observing station will...

[1] Shear wave splitting observed in microearthquake data at the axis of the Mid-Atlantic Ridge near 35 N has a fast polarization direction that is parallel to the trend of the axial valley. The time delays between fast and slow S wave arrivals range from 35 to 180 ms, with an average of 90 ms, and show no relationship with ray path length, source-toreceiver azimuth, or receiver location. The a...

Seismic exploration is one of the main geophysical methods to extract quantitative inferences about the Earth’s interior at different scales from the recording of seismic waves near the surface. Main applications are civil engineering for cavity detection and landslide characterization, site effect modelling for seismic hazard, CO2 sequestration and nuclearwaste storage, oil and gas exploration...

LÕanalyse de la texture du sel gemme naturel et du halite dŽformŽ expŽrimentalement a montrŽ quÕil se produit une orientation prŽfŽrentiel le du rŽseau dans les cristaux de halite. Les paramtres dՎlasticitŽ pour une sŽrie dÕagrŽgats polycristallins de halite sont calculŽs en utilisant les fonctions de distribution dÕorientation. Ils sont alors utilisŽs pour Žlaborer des modles sismiques dans...