Full-waveform tomography reveals iron spin crossover in Earth's lower mantle.

Three-dimensional models of Earth's seismic structure can be used to identify temperature-dependent phenomena, including mineralogical phase and spin transformations, that are obscured in 1-D spherical averages. Full-waveform tomography maps seismic wave-speeds inside the Earth in three dimensions, at a higher resolution than classical methods. By providing absolute wave speeds (rather than perturbations) and simultaneously constraining bulk and shear wave speeds over the same frequency range, it becomes feasible to distinguish variations in temperature from changes in composition or spin state.

The origin of secondary microseism Love waves.

The interaction of ocean surface waves produces pressure fluctuations at the seafloor capable of generating seismic waves in the solid Earth. The accepted mechanism satisfactorily explains secondary microseisms of the Rayleigh type, but it does not justify the presence of transversely polarized Love waves, nevertheless widely observed. An explanation for two-thirds of the worldwide ambient wave field has been wanting for over a century.

Source encoding for viscoacoustic ultrasound computed tomography.

Ultrasound computed tomography (USCT) is a noninvasive imaging modality that has shown its clinical relevance for breast cancer diagnostics. As opposed to traveltime inversions, waveform-based inversions can exploit the full content of ultrasound data, thereby providing increased resolution. However, this is only feasible when modeling the full physics of wave propagation, accounting for 3D effects such as refraction and diffraction, and this comes at a significant computational cost.

Effects of Induced Stress on Seismic Waves: Validation Based on Ab Initio Calculations.

When a continuum is subjected to an induced stress, the equations that govern seismic wave propagation are modified in two ways. First, the equation of conservation of linear momentum gains terms related to the induced deviatoric stress, and, second, the elastic constitutive relationship acquires terms linear in the induced stress. This continuum mechanics theory makes testable predictions with regard to stress-induced changes in the elastic tensor.

Publisher Correction: Lithospheric foundering and underthrusting imaged beneath Tibet.

The original version of the Supplementary Information associated with this Article contained an error in Supplementary Figure 4 in which the colours on the maps rendered incorrectly. The HTML has been updated to include a corrected version of the Supplementary Information.

Tidal tomography constrains Earth's deep-mantle buoyancy.

Earth's body tide-also known as the solid Earth tide, the displacement of the solid Earth's surface caused by gravitational forces from the Moon and the Sun-is sensitive to the density of the two Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific. These massive regions extend approximately 1,000 kilometres upward from the base of the mantle and their buoyancy remains actively debated within the geophysical community. Here we use tidal tomography to constrain Earth's deep-mantle buoyancy derived from Global Positioning System (GPS)-based measurements of semi-diurnal body tide deformation.

Lithospheric foundering and underthrusting imaged beneath Tibet.

Long-standing debates exist over the timing and mechanism of uplift of the Tibetan Plateau and, more specifically, over the connection between lithospheric evolution and surface expressions of plateau uplift and volcanism. Here we show a T-shaped high wave speed structure in our new tomographic model beneath South-Central Tibet, interpreted as an upper-mantle remnant from earlier lithospheric foundering. Its spatial correlation with ultrapotassic and adakitic magmatism supports the hypothesis of convective removal of thickened Tibetan lithosphere causing major uplift of Southern Tibet during the Oligocene.

[A man with a skin condition on his trunk and extremities].

A 68-year-old man with a non-itching skin disease on his trunk and extremities was referred to the dermatologist. The patient had no medication changes, allergies or high-risk sexual contacts. The results of the laboratory tests revealed the diagnosis 'syphilis'.

Mapping tectonic deformation in the crust and upper mantle beneath Europe and the North Atlantic Ocean.

We constructed a three-dimensional azimuthally anisotropic model of Europe and the North Atlantic Ocean based on adjoint seismic tomography. Several features are well correlated with historical tectonic events in this region, such as extension along the North Atlantic Ridge, trench retreat in the Mediterranean, and counterclockwise rotation of the Anatolian Plate. Beneath northeastern Europe, the direction of the fast anisotropic axis follows trends of ancient rift systems older than 350 million years, suggesting "frozen-in" anisotropy related to the formation of the craton.

Seismic probes of solar interior magnetic structure.

Sun spots are prominent manifestations of solar magnetoconvection, and imaging their subsurface structure is an outstanding problem of wide physical importance. Travel times of seismic waves that propagate through these structures are typically used as inputs to inversions. Despite the presence of strongly anisotropic magnetic waveguides, these measurements have always been interpreted in terms of changes to isotropic wave speeds and flow-advection-related Doppler shifts.

Science and Engineering in the Petascale Era.

What breakthrough advances will petascale computing bring to various science and engineering fields? Experts in everything from astronomy to seismology envision the opportunities ahead and the impact they'll have on advancing our understanding of the world.

Adjoint tomography of the southern California crust.

Using an inversion strategy based on adjoint methods, we developed a three-dimensional seismological model of the southern California crust. The resulting model involved 16 tomographic iterations, which required 6800 wavefield simulations and a total of 0.8 million central processing unit hours.

Earth's free oscillations excited by the 26 December 2004 Sumatra-Andaman earthquake.

At periods greater than 1000 seconds, Earth's seismic free oscillations have anomalously large amplitude when referenced to the Harvard Centroid Moment Tensor fault mechanism, which is estimated from 300- to 500-second surface waves. By using more realistic rupture models on a steeper fault derived from seismic body and surface waves, we approximated free oscillation amplitudes with a seismic moment (6.5 x 10(22) Newton.

The spectral-element method, Beowulf computing, and global seismology.

The propagation of seismic waves through Earth can now be modeled accurately with the recently developed spectral-element method. This method takes into account heterogeneity in Earth models, such as three-dimensional variations of seismic wave velocity, density, and crustal thickness. The method is implemented on relatively inexpensive clusters of personal computers, so-called Beowulf machines.