Seismic Activity in the Ocean Area near Niijima and Kozushima Islands

In Area a of the ocean area near Niijima and Kozushima Islands, from May 22, 2023, the seismic activity became high and till 31 there were 61 earthquakes with seismic intensity 1 or over observed (maximum seismic intensity: number of earthquakes, 5 Lower: 1, 4: 1, 3: 4, 2: 13, 1: 42). On May 22 at 16:42 (JST), there was an M5.3 earthquake (maximum seismic intensity 5 Lower, recent event ①) at a depth of 11 km, and on the same day at 19:46 (JST) there was an M5.1 earthquake (maximum seismic intensity 4, recent event ②) at a depth of 11 km. These earthquakes occurred within the Philippine Sea plate. The focal mechanism of the recent event ① showed a strike-slip fault type with a compression axis in an NW-SE direction and the focal mechanism of the recent event ② showed a strike-slip fault type with a compression axis in an NNW-SSE direction.
For the seismic activity since October 1997, in Area b extending from Niijima and Kozushima Islands to Miyakejima Island, during July and August when the volcanic activity was high, there were 6 earthquakes of M6.0 or over. Of these an M6.5 earthquake on July 1 caused damage with a fatality and so on (Fire and Disaster Management Agency).
For the seismic activity since 1919, in the region around the recent event (Area c), there have sometimes been earthquakes of M6.0 or over.

Japan Meteorological Agency
[Evaluation of Seismic Activities for May 2023 (June 9, 2023)]