The mechanism of deep low frequency earthquakes

Deep, non-volcanic low-frequency tremors, which consist of swarms of intermittent weak signals at relatively low frequencies (1 to 8 hertz) and last from days to a few weeks once activity begins, were first discovered along Japan's Nankai trough, a location known to generate great earthquakes.

Previous research has suggested that these low-frequency earthquakes (LFEs) represent shear slip on the boundary between the Pacific and Philippine Sea Plate and the Eurasian Plate. Ide et al. examined the mechanisms of low-frequency earthquakes along Nankai trough by comparing compilations of LFE waveforms with waveforms of earthquakes rupturing under known mechanisms within the Philippine Sea Plate. Through analyses of focal mechanisms and moment tensors from the two groups of earthquakes, they found that LFEs indeed represent shear slip on a low angle thrust fault at the plate interface that dips to the northwest. The authors suggest that deep tremor is generated directly by shear slip on the plate interface, and thus represents a seismic signature of the accompanying slow-slip events.-American Geophysical Union