有珠山2000年噴火における西麓の地表変形(<特集>2000年有珠山噴火 (3))

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From 31 March 2000, a series of phreatomagmatic and phreatic eruptions occurred at Usu volcano, located at the southwestern Hokkaido, northeast Japan. Surface ruptures, such as ground tilting, fault, crack, damage of structure, and surface muss movement occurred near and around the volcano from just before the initial eruption, and their formation continued for three months. Characteristics of surface ruptures are subdivided into compressional, tensional, and strike-slip regimes, based on by their deformation styles. Compressional deformations are most dominant in western flank of the volcano, and characterized by, buckling of kerbs, shortening of V-shape drain, asymmetrical pressure ridge of asphalt, and ground tilting. Tensional deformations consist of graben, ground subsidence, and open crack at road. Strike-slip deformation had appeared regionally. These are right-lateral or left-lateral strike slip faults, en echelon clacks and caused horizontal offset of tunnels. Four main zones and four sub-zones are recognized based on styles and superiority of the deformation. Compressional deformations are dominant in Zone 1-3. On the other hands, strike-slip and tensional deformations with ground uplift are remarkable in Zone 4. Zone 1 is characterized by severe compressional deformations. Eespecially, at far side from the volcano in Zone la, bending of rail, damages of house and bridge, and obvious ground uplift marked "Deformation Front." In this zone, first defonuations had appeared between 30 March evening and 31 March morning, prior to the first eruption at 31 March afternoon. Deformation rate decreased rapidly until the middle of April, and obvious deformation continued until the beginning of June. Although Zone 2 is also characterized by severe compressional deformations, deformations are more intense toward the volcano. Deformation rate was still in high level at the middle of June, and continued until July. In Zone 4, strike-slip fault and normal-fault grabens had grown from the last of March-April to June-July. Deep ground block (at least 60 m under the surface) also deformed by horizontal ground movement.
特定非営利活動法人日本火山学会の論文
2002-11-29

有珠山2000年噴火における西麓の地表変形(<特集>2000年有珠山噴火 (3))

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