On the biannually repeating slow-slip events at the Ryukyu Trench, southwestern Japan

• Published in: Journal of Geophysical Research. B. Solid Earth 2008-11, Vol.113 (B11), p.n/a
• Main Authors: Heki, Kosuke, Kataoka, Takeshi
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; GPS; Ryukyu; Slow-slip event
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2008JB005739

Global positioning system data show that about 20 slow‐slip events occurred during 1997–2007 in the southwestern part of the Ryukyu Arc, Japan, where large interplate thrust earthquakes are not known to have occurred in spite of relatively fast plate convergence. They recur fairly regularly on one patch of the subduction fault, which is as deep as 20–40 km and mechanically isolated in an uncoupled subduction zone. They have time constants of a month or so and release seismic moment equivalent of Mw 6.6 on average. This is one of the best recorded sequences of repeating fault slips, with enough events for statistical analyses. They have fairly constant recurrence interval of ∼0.5 year but do not show preferred months of occurrence in a year, suggesting that they are not controlled by seasonal forcing. The correlation between intervals and amounts of fault slip show statistically significant time‐predictable recurrences. There is one significant disruption in the rhythm, but the stress perturbations due to nearby earthquakes do not appear to play a significant role. This part of the fault might be an altered asperity that used to rupture fast but now slips only slowly because of the increased ambient temperature.