Detection of triggered deep low-frequency events from the 2003 Tokachi-oki earthquake

We show the level of increased/decreased seismicity mapped across Japan immediately following the 2003 Tokachi-oki earthquake (M-w 8.1) of September 25, 2003 (UT) by use of the beta-statistic. Significant dynamic triggering of events is found near the Nankai subduction zone 900 - 1400 km from the earthquake. The events are inferred to be dynamically triggered deep low-frequency earthquakes, of a type that often occur in this region. The triggering appears to be caused by the long-period oscillations of the surface waves, which may be effective in triggering fluid-related events. The region that showed the highest level of triggered events, was an area of elevated activity in the Bungo strait where a slow-slip event was in progress.