インドネシアMerapi火山の噴火機構に関する研究(序報)

Abstract

The eruptive activity of Merapi, the precursory phenomena and its magma supply system are summarized based on research made by the Volcanological Survey of Indonesia and are discussed in comparison with those at Mt. Unzen and Sakurajima.Although the output rate of lava and the type of magma at Merapi are much different from those at Mt.Unzen in 1991-1992, the sequence of eruptive activity and precursory phenomena are basically similar with each other: explosive eruptions at the intial stages of activity, pyroclastic flows due to collapse of lava domes, growth of lava domes by repeated domings, precursory seismic activity and remarkable ground deformation of summit area and so on. Magma supply system at Merapi inferred from the hypocentral distribution of volcanic earthquakes are quite similar with that at Sakurajirna: the vertically elongated distribution from the summit to 5 km in depth, a seismicity gap at 2-3 km deep and aseismic zone below 5 km. These suggest the vertical magma conduit of 5 km long from magma reservoirs to the summit and a magma pocket around 2-3 km deep at the both volcanoes.