GEOLOGIC HISTORY
The Izu-Tobu volcanic group is scattered over more than
400 sq km area of the eastern Izu Peninsula. About 70
subaerial monogenic volcanoes formed during the last 40,000
years, and chemically similar ones lie offshore. Thirteen
eruptive episodes have been documented in the past 32,000
years.
Historic Activity: None.
Recent Activity:
- Two weeks of seismic swarm activity preceeded brief
eruption from July 13-16, 1989 which built submarine cone
at Teishi Knoll.
- Earthquake swarms during August 20-23, 1991 and
December 25-27, 1991 reported in nearby area (southeast
of Teishi Knoll).
- Earthquake swarm from Jan. 10, 1993 to Jan. 17, 1993
occurred in the same area as the 1991 swarms. The
strongest earthquake swarm since the 1989 submarine
eruption of Teishi Knoll occurred between May 28 and June
8, 1993. A total of 9,500 shocks were recored at a
seismic station 5 km SW of the source.
- Several earthquake swarms in Sept. and early Oct.
1995.
- Seismicity at the Izu-Tobu volcano group increased in
July 1996. There were 318 earthquakes recorded; and the
larges one was M 2.4. Another increase in seismicity in
October.
- A large earthquake swarm occurred between March 3 and
March 12, 1997.
Data Sources
- Smithsonian's SEAN Bulletin (V. 14, No. 6 to V. 14,
No. 7)
- Global Volcanism Network (V. 16, No. 12 to V. 23, No.
4).
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