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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 mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics, and thus the understanding of the processes at the [ithosphere-asthenosphere boundary (LAB) is fundamental to understand how our planet works. It is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the LAB. Data from borehole broadband ocean bottom seismometers show that the LAB beneath the Pacific and Philippine Sea plates is sharp and age-dependent. The observed large shear wave velocity reduction at the LAB requires a partially molten asthenosphere consisting of horizontal melt-rich layers embedded in melt-rich mantle, which accounts for the large viscosity contrast at the LAB that facilitates horizontal plate motions. [ABSTRACT FROM AUTHOR]

We report seismic evidence for the transportation of water into the deep mantle in the subduction zone beneath northeastern Japan. Our data indicate that water is released from the hydrated oceanic crust at shallow depths (≤100 kilometers) and then forms a channel of hydrated mantle material on top of the subducting plate that is the pathway for water into the deep mantle. Our result provides direct evidence that shows how water is transported from the ocean to the deep mantle in a cold subduction zone environment. [ABSTRACT FROM AUTHOR]

Discusses the monitoring of volcano activity. How broadband seismometers deployed at Aso volcano in Japan have detected a hydrothermal reservoir that continually resonates with periods as long as 15 seconds; How the hydrothermal reservoir appears to help control the surface activity at Aso volcano.

The article is a report on global surface wave telegraphy using seismic hum. Earth's seismic hum signals, which are background free oscillations, are continuously excited by the ocean and atmosphere. The authors used cross-correlation (CC) analysis of hum signals that showed background Rayleigh waves which were propagated globally. Topics include how the waves open the possibility for global surface wave tomography without references to earthquakes.