Seismic activity in the area from Miyakejima to Niijima-Kozushima

However, along with the marked reduction in seismic activity, there have been changes in the forms of occurrence of seismic activity. Specifically,

1) The average daily incidence of M3.5 and greater events in Sea Zone 1 was 60 events per day in the period from June 26th to July 13th, 30 events per day from July 14th to August 8th, 10 events per day from August 9th to August 23rd, and has dropped to one per day since August 24th.

3) The seismic activity took the form of frequent burst activity (defined as multiple occurrences concentrated within the space of several hours) throughout July, but there have been only two such occurrences since August.

Also, looking at the occurrence of events of about M5 registering maximum seismic intensity of 5 lower or greater since August 3rd, there were, in the period from August 3rd to 5th (eight events), August 16th to 18th (three events), on the 29th (one event), September 11th (one event), showing a period of about ten days.

*The results of GPS observation of the area showed no marked changes from mid-July to mid-August to the trend in which Niijima moved to the northeast and Kozushima moved to the southwest, suggesting magma activity to the east of Kozushima. However, since that time the pace of change has slowed to the extent that movement has nearly stopped. Also, since about August 24th, the pace of change has slowed even in the southern tip of the Boso Peninusla, including changes in VLBI (very long baseline interferometry), which is thought to reflect movements of the magma activity in the sea east of Kozushima as a whole. However, some slight local crustal movement remains in the area between Niijima and Kozushima.

*In this way, the seismic activity and crustal movement are declining at the same time. Also, the crustal movement in the area between Niijima and Kozushima remains at the local level. Considering the above, although it is still not possible to rule out further events of about M5, it is believed that the seismic activity that began at the end of June is subsiding.

Crustal movement within the island of Miyakejima associated with the volcanic eruption there continues.

• Seismic activity in the area from the sea near Miyakejima to Niijima-Kozushima(entire period)
• September 11th M5.3 seismic activity (1)
• September 11th M5.3 seismic activity (2)
• Seismic activity in the area from the sea near Niijima-Kozushima to Miyakejima (M3.5 and greater events, by area)
• Seismic activity in Sea Zone 1 (Magnitude 3.5 and greater)
• For the present seismic activity, events that registered seismic intensity of 5 lower or greater (June 26th to September 11th)
• Vector map (horizontal)
• Continuous GPS observation of the Izu archipelago, baseline map
• Base-line-length variation graph(1)
• Base-line-length variation graph(2)
• Base-line-length variation graph(3)
• Base-line-length variation graph(4)
• Base-line-length variation(Kashima-Tateyama)
• Base-line-length variation graph(5)
• Base-line-length variation graph(6)
• Base-line-length variation graph(7)
• Base-line-length variation graph(8)
• Seismic activity movements and changes in the distance between southern Izu and Niijima (north-south)