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Report on Mikura Seamount (Japan) — December 1982

Bulletin of the Global Volcanism Network, vol. 7, no. 12 (December 1982)
Managing Editor: Lindsay McClelland.

Mikura Seamount (Japan) Earthquake sequence not volcanic

Please cite this report as:

Global Volcanism Program, 1982. Report on Mikura Seamount (Japan) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 7:12. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN198212-284043.

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Mikura Seamount

Japan

33.725°N, 139.408°E; summit elev. -321 m

All times are local (unless otherwise noted)


Beginning 27 December there have been many recorded earthquakes with epicenters in the ocean about 40 km S of Miyake-jima Island (~200 km S of Tokyo; figures 1 and 2). The first felt shock occurred at 1533. At 1537 on 28 December the largest, magnitude [6.4] on the JMA scale, originated at the N edge of the epicentral area. It was followed by gradually decreasing aftershock activity. Earthquake swarms or main shock-aftershock events in the sea around Miyake-jima occurred in July and September 1980, and . . . March 1981. The USGS/NEIS recorded four shocks of magnitude 5 or greater (table 1).

Figure (see Caption) Figure 1. Epicenters of earthquakes larger than magnitude 3, 27-31 December 1982. The epicentral area is 40 km S of Miyake-jima Island. The largest open circle is the main shock that occurred 28 December at 1537, 30 km S of Miyake-jima. Focal depths ranged from 0-20 km. The January 1983 earthquakes were located in the same area. Courtesy of JMA.
Figure (see Caption) Figure 2. Hourly and daily (inset) number of earthquakes in the Izu Islands recorded at Miyake-jima Weather Station, 27 December 1982-4 January 1983. Courtesy of JMA.

Table 1. Earthquakes of Ms >= 5 on 28 December 1982 in the Izu Islands, Japan. Courtesy of the USGS.

Time Magnitude Latitude Longitude Focal Depth
1024 5.0 33.74°N 139.46°E shallow
1053 5.5 33.70°N 139.44°E shallow
1112 5.1 33.70°N 139.52°E shallow
1537 6.1 33.77°N 139.51°E 20 km

Personnel from the Miyake-jima Weather Station visited the summit area (Oyama) on 29 December, but observed no unusual phenomena. The events were interpreted as having been too far from Miyake-jima to be precursors of volcanic activity. A group of shallow earthquakes occurred close to Miyake-jima a few months before the last eruption in 1962.

Geologic Background.

Information Contacts: JMA, Tokyo; USGS/NEIS, Denver CO, USA