Seismicity had been quiet in the west to the Niijima Island till a M6.4 earthquake occurred in the sea near the Kozushima Island on July 1.

July 1 - July 14

Immediately before a M6.3 earthquake in the sea near the Niijima Island on July 15 It is apparent that earthquake swarms in the sea area between the Kozushima and the Miyakejima Islands have migrated toward northwest. Earthquakes in the west sea area of the Niijima Island had become active since a M.6 earthquake occurred in the sea near the Kozushima Island on July 1. Calculated stress change implies that a series of earthquakes in the west to the Niijima Island are induced by the earthquake in the sea near the Kozushima Island on July 1.

Hypocenter plot: Processed on ERI TSEIS by using JMA hypocenter catalog.