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Abstract: The high-frequency GPS analysis at Miyakejima volcano captured rapid deformation following the early stage of Miyakejima 2000 activity. Given a specified dike and spherical source geometry, we solve the opening distribution on each sub-dike that minimizes a linear combination of the norm of the weighted data residual and roughness of the opening distribution. The time dependence of dike intrusion and spherical source deflation shows that magma migrated laterally from the southern region to the west coast. Although the depth of the maximum opening does not change with time, a very shallow intrusion can be seen at the eastern part of the dike. This may explain why cracks and graben structures developed on the west coast. Most of the magma migrated northwest, with only a fraction coming to the surface in an eruption below sea level. [Copyright &y& Elsevier]

From June 26, 2000, an earthquake swarm started in Miyakejima, about 50 km south off Honshu, central Japan. Eruptions of Miyakejima and five large earthquakes with magnitudes 6.0 and above occurred for the following 2 months together with a large number of smaller earthquakes over 100,000. In this study, we focused on spatio-temporal crustal deformation observed at GPS stations in this area. In order to explain the seismicity and the crustal deformation, we considered a dike intrusion model placed between Miyakejima and Kozushima. Then, we attempted to obtain spatio-temporal distributions, the amount of the dike intrusion, deflation beneath Miyakejima, and fault slips of the seven large events by geodetic data inversion. For this purpose, we divided the time series of GPS data from June 12 to August 27 into 10 periods, which are related to significant events. In order to find location, depth, strike and dip of the dike plane and a depth of deflation beneath Miyakejima, we used the Monte Carlo method and tested 10,000 models for each period. As a result, we estimated that the total amount of the dike intrusion and the deflation beneath Miyakejima reached about 1.1×109 and 5.4×108 m3, respectively. The maximum amount of the dike intrusion and the deflation beneath Miyakejima reached over 3.5×108 m3 during the period from July 20 to July 28, 2000, and over 1.7×108 m3 during the period from June 15 to June 28, 2000, respectively. Temporal change of the amount of the dike intrusion corresponds well to that of the deflation beneath Miyakejima until the middle of July. However, since large amount of the dike intrusion from July 20 to 28 did not correspond to that of the deflation beneath Miyakejima, we deduced that the magma source changed from Miyakejima to Kozushima and the magma might come from sub-crustal magma pockets from the middle of July. If we assume the open crack associated with the dike intrusion and the deflation beneath Miyakejima are filled with magma with a density of 2500 kg/m3, the mass would be about 2.75×109 and 1.35×109 tons, respectively. We deduced that at least 1.4×109 tons of magma came from sub-crustal magma pockets. [Copyright &y& Elsevier]