12:35 PM - 12:38 PM
[SVC46-P14] NW-SE trending graben structure and crater row on Teishi Knoll, off Izu Peninsula
3-min talk in an oral session
Keywords:Higashi-Izu monogenetic volcano group, bathymetry, multibeam echo sounder, graben, crater row, dike
The survey was conducted in December 2014. Multibeam echo sounder EM302 installed on S/V Kaiyo and interferometric sonar GeoSwath Plus on AUV GondouS were used.
The graben formed just southeast of the main crater. The length is 120 m, width 70 m and 1.5 m deep. The four small craters formed inside the main crater associated with 1989 eruption. The craters are aligned in the NW-SE direction and each crater has 20?50 m in diameter. NW-SE trending linear topographic high also formed between the graben and craters.
Yamamoto et al 1991 concluded that magma intrusion into the sediment blanket caused the eruption, vapor explosion. Okada and Yamamoto 1991 concluded that the tensile fault, N125E strike (?NW-SE) caused the magma intrusion to sedimentary layers. The relationship between magma intrusion and surface deformation and the depth of the top of the dike is approximately equal to half the width of graben (Mastin and Pollard 1988; Chadwick and Embley 1998). The relationship was applied to our result in the Teishi knoll. The graben width 70 m implies that the top of the dike beneath the graben was at about 35 m depth. There are no direct evidences that the graben formed associated with 1989 eruption. Considering that the crater row is aligning in same NW-SE direction, same width 70 m and lying on the same line as graben, the graben might be formed in the identical environment, that is 1989 eruption with dike intrusion.