Logo link to homepage

Report on Niijima (Japan) — October 1985


Scientific Event Alert Network Bulletin, vol. 10, no. 10 (October 1985)
Managing Editor: Lindsay McClelland.

Niijima (Japan) Submarine earthquake swarm

Please cite this report as:

Global Volcanism Program, 1985. Report on Niijima (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 10:10. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198510-284020



34.397°N, 139.27°E; summit elev. 432 m

All times are local (unless otherwise noted)

Local seismicity increased in the sea NW of Nii-jima on 21-22 September. Residents measured no significant changes in temperatures of the island's hot springs during this period. Because epicenters were close to the island, more than 20 events were felt, the largest of magnitude [3.5 (JMA)]. Earthquake swarms are common around Nii-jima; the most recent was in August-September 1983 [when the largest event was M 4.2].

Geological Summary. The elongated island of Niijima, SSW of Oshima, is 11 km long and only 2.5 km wide. Eight low rhyolitic lava domes are clustered in two groups at the northern and southern ends of the island, separated by an area of flat-topped domes and a low isthmus of pyroclastic deposits. The Mukaiyama complex on the south and the Atchiyama lava dome on the north were formed during eruptions in the 9th century CE, the last known activity. Shikineyama and Zinaito domes form small islands immediately to the SW and W, respectively, during earlier stages of volcanism. Earthquake swarms occurred during the 20th century.

Information Contacts: JMA, Tokyo.