Seismic Activity in the Ocean near Tokara Islands (near Kodakarajima Island)
From December 4, 2021 at about 12 o'clock, in the ocean near Tokara Islands (near Kodakarajima Island), the seismic activity became rather high, and till December 31 at 24 o'clock, there occurred 308 earthquakes with maximum seismic intensity 1 or over (maximum seismic intensity: number of earthquakes, 5 Upper: 1, 4: 2, 3: 15, 2: 85, 1: 205). The largest was an M6.1 earthquake (maximum seismic intensity 5 Upper) occurring on 9th at 11:05 (JST). This event occurred within the continental plate. The focal mechanism showed a normal fault type with a tension axis in an NW-SE direction.
Although the recent seismic activity caused no human damage nor damage to the house, it caused landslide and so on at (Akusekijima Island) Toshima Village, Kagoshima prefecture (as of December 23, 2021, Kagoshima prefecture). Also half of the residents of Akusekijima Island sought refuge in Kagoshima City or Amami City. Japan Meteorological Agency dispatched JMA Emergency Task Team (JETT) to Kagoshima Prefectural Office and Toshima Village Office to assist by explaining the seismic activity and the meteorological situation. Moreover on December 14, Japan Meteorological Agency dispatched "JMA Mobile Observation Team (JMA-MOT)" to the seismic intensity observation points (Akusekijima Island) with seismic intensity 5 Upper in order to check the observing environments. No change was confirmed in observing environments, and the damage in the surrounding area and shaking situation was confirmed.
For the seismic activity since October 1994, in the vicinity of the recent cluster (Area a), there have sometimes been clusters. There was an active cluster, the largest being an M5.9 earthquake (maximum seismic intensity 5 Upper) on October 2, 2000, which caused damage with 1 water pipe failure and so on at Akusekijima Island, Toshima Village, Kagoshima prefecture (Fire and Disaster Management Agency). Recently there occurred 265 earthquakes with maximum seismic intensity 1 or over (including 6 earthquakes with maximum seismic intensity 4), the largest being 2 M5.3 earthquakes (maximum seismic intensity 4) on April 10 and 12, 2021.
For the recent seismic activity and the past major seismic activities, by comparing epicenter distribution diagram, hypocenter distribution in time and space diagram, M-T diagram and cumulative number diagram in 90 days period, we see that there are various forms of activity and it is difficult to identify the end time of a seismic activity (see next page).
Japan Meteorological Agency
[Evaluation of Seismic Activities for December 2021 (January 13, 2022)]