Periodic slow slip triggers megathrust zone earthquakes in northeastern Japan

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Science  29 Jan 2016:
Vol. 351, Issue 6272, pp. 488-492
DOI: 10.1126/science.aad3108

A silent and periodic earthquake trigger

Large earthquakes that hit places such as Japan seem to be preceded by subtle and silent deformation. Uchida et al. show that these “slow-slip events” are quasi-periodic in the megathrust zone in Japan. Slow-slip events occurred every 1 to 6 years and frequently were correlated with large earthquakes, including the great 2011 Tohoku-oki earthquake. The quasi-periodic behavior stretches back to at least 1930 and provides an important constraint for seismic hazard assessment in the region.

Science, this issue p. 488


Both aseismic and seismic slip accommodate relative motion across partially coupled plate-boundary faults. In northeastern Japan, aseismic slip occurs in the form of decelerating afterslip after large interplate earthquakes and as relatively steady slip on uncoupled areas of the subduction thrust. Here we report on a previously unrecognized quasi-periodic slow-slip behavior that is widespread in the megathrust zone. The repeat intervals of the slow slip range from 1 to 6 years and often coincide with or precede clusters of large [magnitude (M) ≥ 5] earthquakes, including the 2011 M 9 Tohoku-oki earthquake. These results suggest that inherently periodic slow-slip events result in periodic stress perturbations and modulate the occurrence time of larger earthquakes. The periodicity in the slow-slip rate has the potential to help refine time-dependent earthquake forecasts.

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