The 2000 eruption:
Stage 1: Intrusive stage (26 June - 8 July, 2000)
In this stage, magma intruded from the reservoir beneath the summit of Miyakejima towards the northwest, with numerous earthquakes. Seismic activity began on the evening of 26 June beneath the summit of the volcano, and migrated northwestward from 26 June to 1 July at about 5 km/day (Fujita et al. 2001; Sakai et al. 2001). Epicenters show a tabular distribution to the northwest of Miyakejima Volcano extending more than 20 km horizontally and 10 km vertically. GPS data showed the deflation of the summit area of Miyakejima Island and inflation of the western part of the island in the vicinity of the earthquake swarm, which was migrating westward during this stage. A series of open cracks and normal faults showing a N--S extension formed in the western coastal part of Miyakejima Island. These observations suggest the intrusion of a dike to the northwest of the volcano.
A minor submarine eruption occurred in the morning of 27 June about 1 km off of the west coast of Miyakejima Volcano. Eruption continued less than 3 hours and froms a chain of craters with small spatter cone align in WNW-ESE direction. During the submarine eruption, about 1--3*103 m3 of aphyric basaltic andesite spatter were issued.
(photo by Yomiuri Newspaper)
Seismic activity and ground deformation to the northwest of Miyakejima Volcano continued after the submarine eruption on 27 June. The seismic activity moved from Miyakejima to northwestward more than 30 km and formed a tabular distribution (Toda et al., 2002). Seismic activity continued till the middle of August, suggesting the continuous migration of magma from Miyakejima Volcano. Toda et al. (2002) suggests that the dike propagated in full length within the first week (26 June - 1 July) and, after then, continuously dilated for eseven weeks till middle of August.
There is no evidence for submarine eruption in the vicinity of the earthquake swarm, except for the submarine eruption of 27 June.
After the westward migration of the earthquake swarm, earthquake activity remained at a low level in Miyakejima Volcano. Earthquake activity beneath the summit area was reactivated from 4 July. The earthquakes showed a columnar distribution of about 2 km in diameter, and the top of the seismic swarm became shallower prior to the 8 July eruption.
Fujita E, Ukawa M, Yamamoto E, Okada Y, Kikuchi M (2001) Volcanic earthquakes and tremors associated with the 2000 Miyakejima volcanic eruption (in Japanese with English Abstract). J Geogr 156:191--203
Sakai S, Yamada T, Ide S, Mochizuki M, Shiobara H, Urabe T, Hirata N, Shinohara M, Kanazawa T, Nishizawa A, Fujie G, Mikada H (2001) Magma migration from the point of view of seismic activity in the volcanism of Miyake-jima Island in 2000 (in Japanese with English abstract). J Geogr 110:145--155
Toda S, Stein RS, T Sagiya (2002) Evidence fro the AD 2000 Izu islands earthquake swarm that stressing rate governs seismicity. Nature 419. 58-61.
(photo by Yomiuri Newspaper)