Creep, dike intrusion, and magma chamber deflation model for the 2000 Miyake eruption and the Izu islands earthquakes

Abstract

Analysis of Global Positioning System data shows shrinkage of Miyake Island and the widening between Nijima and Kozu Islands during the period of the Miyake island volcanic activity and the ensuing Izu islands earthquakes in 2000. The estimated time evolution of a model consisting of a dike, creeping faults, and a Mogi source suggests that a crack opening on Miyake Island occurred immediately after the start of the seismic activities on 26 June and ended within several days at the west coast of Miyake Island. After the seabed eruption on 27 June, magma migrated from Miyake Island to Kozu and Nijima Islands within several days. The estimated volume of intruded magma totals around 1.2 × 10 9 m 3 . Associated with the magma intrusion between Miyake and Kozu Islands, left‐lateral and right‐lateral creep motions occurred in regions off the west coast of Miyake Island and near Kozu Island. The accumulated moment energy is equivalent to an earthquake of M w 6.6 and 6.6 for right‐lateral and left‐lateral creeping faults, respectively. The estimated magma chamber continued deflation beneath the southwestern part of Miyake Island from 26 June, totaling around 0.12 × 10 9 m 3 in volume change, in addition to the collapse volume of 0.6 × 10 9 m 3 at the summit of Mount Oyama on Miyake Island. The volume change on Miyake Island can be compensated by the migrated magma toward Kozu Island from the deflation source beneath Miyake Island. The deflation speed of the magma chamber beneath Miyake Island decreased and increased before and after the eruption of 14–15 July and 18 August, suggesting a change in balance of mass influx and draining out rate of the magma chamber.