Editor's Summary

13 July 2006

Tremor on a plate

Non-volcanic seismic tremor, seismic activity resembling that created by magma moving under volcanoes, but taking place well away from any volcanic activity, was first observed six years ago in the Nankai trough subduction zone in southwest Japan and subsequently in the Cascadia subduction zone and beneath the San Andreas fault. The mechanisms causing this 'new' form of seismic activity are still unclear. Seismic monitoring data from southwest Japan have now been used to locate lowfrequency events associated with nonvolcanic tremor. These earthquakes occur at the plate interface, which suggests that they and the associated tremor are generated by fluidenabled shear slip on the plate interface, rather than directly by fluid flow.

Letter: Low-frequency earthquakes in Shikoku, Japan, and their relationship to episodic tremor and slip

David R. Shelly, Gregory C. Beroza, Satoshi Ide and Sho Nakamula

doi:10.1038/nature04931

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