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

Abstract

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 β‐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.