Incidence of M4.0 and greater major seismic events and earthquake swarm activity in the Japanese archipelago and surrounding area

The current seismic activity in the area of Miyakejima, Niijima and Kozushima has faetured a pronounced number of M4 and greater events, and has a large scale for an earthquake swarm. There have already been around 500 events of M4 or greater in a little over one month.

This easily surpasses the approximately 250 such events that occurred over the course of nearly two years in the Matsushiro earthquake swarm, as well as the number of aftershocks following major M7 class events such as Nihonkai Chubu Earthquake or Earthquake off the Southwest Coast of Hokkaido.

There are typically about 1000 aftershocks to Earthquake off the East Coast of Hokkaido at the juncture of massive tectonic plates on the Pacific Coast. Kanto Earthquakes and Nankai Earthquake are also of the same order. Only events on this scale occasion a greater total number of M4 and greater events than the current activity.

The earthquake swarm activity in the sea east of the Izu Peninsula which occurred over the space of more than ten years was on the order of 100 events of M4 or greater, which gives an indication of the difference in scale from the current activity.

Japan Meteorological Agency