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Subducted slabs of oceanic lithosphere below the western Pacific tend to be stagnant in the transition zone with poorly known mechanical properties. Typical examples are the Izu-Bonin and Japan slabs that meet each other to form a cusplike junction beneath southwest Japan. Here, we show that these two slabs are torn apart at their junction when they bend to flatten over the 660-kilometer discontinuity, as is expected from a simple geometric argument. We present three lines of evidence for this ongoing slab tear. [ABSTRACT FROM AUTHOR]

The article discusses research that provides tomographic evidence for the development of a vertical tear in a slab underlying southwest Japan and shows that the plate is still rupturing. Measurements of stress revealed by active seismic sources were correlated with these images. The concept that slabs rupture as they move through the upper mantle has been used to explain geological observations in the past. In addition to knowing the location of an earthquake, high-resolution tomographic reconstructions and data collection networks are needed to distinguish slab rupture from sharp flexure.