Report on Kozushima (Japan) — June 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 6 (June 1992)
Managing Editor: Lindsay McClelland.
Kozushima (Japan) Earthquake and aftershocks
Please cite this report as:
Global Volcanism Program, 1992. Report on Kozushima (Japan). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 17:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199206-284030.
34.219°N, 139.153°E; summit elev. 572 m
All times are local (unless otherwise noted)
A M 5.2 earthquake, centered in the sea 8 km SW of the volcano at 9 km depth, occurred on 15 June at 1046. Island residents felt the shock at intensity 5 on the JMA scale of 0-7. Data from 30 stations of the Worldwide Standardized Seismic Network yielded magnitudes of 4.9 (mb) and 4.7 (Ms). One person was slightly injured by a rockfall, and wallrock collapse at 10 sites closed 5 roads to traffic. Aftershocks continued until 17 June off the island's SW coast. The event was the second largest since . . . April 1991 (figure 1). No surface anomalies were observed on the island or on the sea-surface nearby.
Geologic Background. A cluster of rhyolitic lava domes and associated pyroclastic deposits form the small 4 x 6 km island of Kozushima in the northern Izu Islands. Kozushima lies along the Zenisu Ridge, one of several en-echelon ridges oriented NE-SW, transverse to the trend of the northern Izu arc. The youngest and largest of the 18 lava domes, 574-m-high Tenjoyama, occupies the central portion of the island. Most of the older domes, some of which are Holocene in age, flank Tenjoyama to the north, although late-Pleistocene domes are also found at the southern end of the island. Only two possible historical eruptions, from the 9th century, are known. A lava flow may have reached the sea during an eruption in 832 CE. Tenjosan lava dome was formed during a major eruption in 838 CE that also produced pyroclastic flows and surges. Earthquake swarms took place during the 20th century.
Information Contacts: JMA; NEIC.