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A Closer Look at a Seismic Bump in the Road

Caption: The generation of partially molten rock locally sharpens the lithosphere-asthenosphere boundary (LAB), allowing seismic waves to reflect from the interface. Shear waves from an earthquake (star) travel through the Earth and reflect from the surface, and also where melt has ponded at the base of the lithosphere. The waves are recorded by seismometers (blue inverted triangle) deployed around the globe, providing a complete view of the LAB beneath the Pacific. Regions without melt will not produce a deeper reflection, signifying that melt is not the primary mechanism for weakening of rock in the asthenosphere. This image relates to a paper that appeared in the March 23, 2012, issue of Science, published by AAAS. The paper, by Nicholas Schmerr at Department of Terrestrial Magnetism, Carnegie Institution of Washington in Washington, D.C., and colleagues was titled, "The Gutenberg Discontinuity: Melt at the Lithosphere-Asthenosphere Boundary."

Credit: Image courtesy of Nicholas Schmerr

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