有珠火山2000年噴火における岩脈貫入過程と潜在ドームの形成メカニズム(<特集>2000年有珠山噴火)

概要

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Surface faulting is a common feature accompanied with dome (cryptodome) growth during 20th century eruptions of Usu volcano, northern Japan. Since the degree of fault development is a consequence of stress input from underlying intrusion of the magma, characterization of the faults is effective in understanding and estimating behaviors of magma. In the 2000 eruption of the volcano, the development of fault was traced by using high-resolution air-photographs. Temporal and sequential data of newly developed normal fault traces and fault-slip data were accurately measured. By using the stress inversion method, sixty fault-slip data clarified that stress regime and stress ratio (φ) for the intrusion are subvertical direction of stress σ_1 and the smallest magnitude of the φ. This indicates that a dike-like intrusion parallel to the azimuth of the faults is plausible as the intrusive magma body. The formation of initial dike beneath the Nishiyama region resulted in volcanic activity from the Nishiyama craters and induced the propagation of subsequent dike perpendicular to it. The second dike intrusion occurred beneath the region between the Nishiyama and Konpirayama craters, and presumably resulted in the activity of the Konpirayama craters.
特定非営利活動法人日本火山学会の論文
2002-07-10