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The article discusses geophysics research by N. Schmerr and colleagues within the issue. The author presents a brief overview of the theory of plate tectonics which posits that horizontal plates below the Pacific Ocean are moving laterally at a rate of approximately 10 centimeters (cm) per year above a weak layer called the asthenosphere. He notes that scientists are puzzled by how the plates, which are as large as 10 thousand kilometers (km), can maintain their rigidity while causing earthquakes at their edges. Topics include the use of high-resolution seismic maps by Schmerr's team to observe the process of plate tectonics, the role of the asthenosphere, which is a viscous layer below the lithosphere, in plate movement, and a diagram illustrating plate tectonics in the ocean.

The permeability of the upper mantle controls melt segregation beneath spreading centers. Reconciling contradictory geochemical and geophysical observations at ocean ridges requires a better understanding of transport properties in partially molten rocks. Using x-ray synchrotron microtomography, we obtained three-dimensional data on melt distribution for mantle peridotite with various melt fractions. At melt fractions as low as 0.02, triple junctions along grain edges dominated the melt network; there was no evidence of an abrupt change in the fundamental character of melt extraction as melt fraction increased to 0.2. The porosity of the partially molten region beneath ocean ridges is therefore controlled by a balance between viscous compaction and melting rate, not by a change in melt topology. [ABSTRACT FROM AUTHOR]

Cyclic sedimentary deposits link stratigraphic sequences that are now geographically distant but were once part of the same depositional environment. Some of these sequences occur at periods of 2 to 20 million years, and eustatic sea-level variations or regional tectonic events are likely causes of their formation. Using numerical modeling, we demonstrate that small-scale mantle convection can also cause the development of stratigraphic sequences through recurrent local and regional vertical surface movements. Small-scale convection-driven stratigraphic sequences occur at periods of 2 to 20 million years and correlate only at distances up to a few hundred kilometers. These results suggest that previous sequence stratigraphic analyses may contain erroneous conclusions regarding eustatic sea-level variations. [ABSTRACT FROM AUTHOR]

Bends in volcanic hotspot lineaments, best represented by the large elbow in the Hawaiian- Emperor chain, were thought to directly record changes in plate motion. Several lines of geophysical inquiry now suggest that a change in the locus of upwelling in the mantle induced by mantle dynamics causes bends in hotspot tracks. Inverse modeling suggests that although deep flow near the core-mantle boundary may have played a role in the Hawaiian-Emperor bend, capture of a plume by a ridge, followed by changes in sub-Pacific mantle flow, can better explain the observations. Thus, hotspot tracks can reveal patterns of past mantle circulation. [ABSTRACT FROM AUTHOR]

Cosmochemical, geochemical, and geophysical studies provide evidence that Earth's core contains iron with substantial (5 to 15%) amounts of nickel. The iron-nickel alloy Fe09Ni0.1 has been studied in situ by means of angle-dispersive x-ray diffraction in internally heated diamond anvil cells (DACs), and its resistance has been measured as a function of pressure and temperature. At pressures above 225 gigapascals and temperatures over 3400 kelvin, Fe09Ni0.1 adopts a body-centered cubic structure. Our experimental and theoretical results not only support the interpretation of shockwave data on pure iron as showing a solid-solid phase transition above about 200 gigapascals, but also suggest that iron alloys with geochemically reasonable compositions (that is, with substantial nickel, sulfur, or silicon content) adopt the bcc structure in Earth's inner core. [ABSTRACT FROM AUTHOR]

The article discusses geophysics research by P. Poli et al within the issue. The author notes that the Earth's thermal and chemical structure has historically been determined via the analysis of seismic waves excited by earthquakes, arguing that the resolution of those methods is limited because earthquakes occur along tectonic plate boundaries, resulting in large areas being seismically quiet. Topics include an imaging study of deep-Earth structures by Poli et al using improved processing methods for seismic noise data, the observation of body waves in ambient seismic noise, and diagrams illustrating surface and body waves in ambient noise tomography.

The article discusses the composition of pallasite meteorites in connection with the geophysical dynamo theory, with a focus on the article "Evidence for a Dynamo in the Main Group Pallasite Parent Body," published elsewhere in the November 16, 2012 issue by J. A. Tarduno et al. Topics include molten metals within the Earth's core, olivine crystals in pallasites, and paleomagnetic measurements. Additional information is presented on isothermal metallic cores and the generation of magnetic fields in asteroids.

The article discusses the use of precision isotope analysis to reveal details about the dynamic processes involved in the formation of planet Earth's mantle. Topics include a belief among geologists that evidence of the first few hundred million years of Earth's history had been erased by mantle convection and plate tectonics, a study within the issue regarding geophysics research by M. Touboul and colleagues reporting measurements of the isotopic composition of tungsten (W) in 2.8-billion-year-old basaltic rock, called komatiite, which is known to be derived from source regions deep within Earth's mantle, and the abundance of an tungsten isotope 182W, which forms from the decay of an isotope of hafnium (182Hf).

The article discusses four reports within the issue regarding geophysics research, including one by Sato and colleagues, Simons and colleagues, Ide and colleagues, and Vigny and colleagues. The teams illustrate the use of a network of global positioning system (GPS) detectors to show how the Earth's surface deformed before and after the Tohoku-Oki magnitude 9 (M9) earthquake in Japan on March 11, 2011 and the M9 earthquake in central Chile (Maule) on February 27, 2010, in which thousands of lives were saved as a result of early warning systems for tsunamis.

The article discusses a report within the issue regarding geophysics research investigating global plate tectonics. A brief overview of how convention within planet Earth's mantle affects geological activity, such as tectonic motions on the surface of Earth, is presented. Topics include an overview of plate tectonics and the team's creation of a numerical model, which uses adaptive mesh refinement algorithms on parallel computers to observe global mantle flows through simulation methods, and the behavioral influence of the oceanic lithosphere on plate driving forces.