Seismic Activity in the Ocean Area near Tokara Islands (near Kodakarajima Island)
After April 9, 2021 at about 23 o'clock, the seismic activity became rather high, in the ocean area near Tokara Islands (near Kodakarajima Island) and till April 30 at 24 o'clock, there occurred 265 earthquakes with maximum seismic intensity 1 or over (maximum seismic intensity: number of earthquakes, 4: 6, 3: 19, 2: 64, 1: 176). The largest were M5.3 earthquakes (maximum seismic intensity 4) occurring on April 10 at 07:07 (JST) and 12th at 23:01 (JST). These events occurred within the continental plate. The focal mechanisms showed a strike-slip fault type with a tension axis in an NW-SE direction.
For the seismic activity since October 1994, in the vicinity of the recent activity (Area a), there have sometimes been moderate activities. In December 2016 there occurred 55 earthquakes (including 2 earthquakes with maximum seismic intensity 4) with seismic intensity 1 or over, the largest being an M3.9 earthquake (maximum seismic intensity 2).
Also near Akusekijima Island the seismic activity became high, the largest being an M5.9 earthquake (maximum seismic intensity 5 Upper). This activity caused damage with 1 water pipe failure and so on (Fire and Disaster Management Agency).
For the seismic activity since January 1919, in the region around the recent activity (Area b), there have sometimes been earthquakes of M5.0 or over.
Japan Meteorological Agency
[Evaluation of Seismic Activities for April 2021 (May 14, 2021)]