Geologic Background:
The elongated island of Nii-jima is 11-km long
and only 2.5-km wide. It is comprised of eight low
rhyolitic lava domes in two groups at the northern and
southern ends of the island. The Mukai-yama complex at
the southern end of the island and Achi-yama lava dome at
the northern end were formed during Nii-jima's only
historical eruptions in the 9th century AD. Shikine-yama
and Seto-yama domes form small islands immediately to the
SW and west of Nii-jima.
Historic Activity:
- The Mukai-yama complex at the S end of the island and
Achi-yama lava dome at the N end were formed during
Nii-jima's only historical eruptions in 886 AD.
Earthquake swarms, were most recently recorded in
Aug.-Sept. 1983 and Sept. 1985.
Recent Activity:
- An earthquake swarm occurred on January 3-4, 1992,
centered 10 km SW of Nii-jima near Shikine-jima, a dome
of the Nii-jima complex. Another earthquake swarm
occurred on March 19, 1992 with 10 quakes beneath and
around island. A third weak earthquake swarm occurred on
August 28-29. Additional swarms occurred on Sept. 16 and
Sept. 22, 1992. An earthquake swarm occurred midway
between Nii-jima and Kozu-shima during Oct. 17-20,
1992.
- A weak earthquake swarm occurred on March 23, 1993 in
the north part of Nii-jima island. An earthquake swarm
occurred near Nii-jima island on Sept. 9, 1993.
Earthquake swarm on Dec. 4, 1995.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 11, No. 8 to V. 13,
No. 8)
- Global Volcanism Network (V. 15, No. 6 to V. 21, No.
7).
|