地学雑誌
論説
表面波探査による松代室野地区の泥火山の浅部S波速度構造調査
尾西 恭亮真田 佳典横田 俊之徳永 朋祥茂木 勝郎Jamhir SAFANIAdam O'NEILL
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118 巻 (2009) 3 号 p. 390-407

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 We investigated the geological structure below the Matsudai-Murono mud volcano, Tokamachi city, Niigata prefecture, Japan, using vertical distributions of S-wave velocities, estimated from surface wave inversion. From the surface to a depth of several meters, the S-wave velocity first increases, then decreases, and finally increases again. Below a depth of 10 m, there are two areas with high and low velocities in the horizontal direction. We found that the subsurface low-velocity layer is a mud layer produced by an eruption, and the deep low-velocity zone is a mudstone zone, some parts of which are transformed into soft clay by muddy water that drifts upward. The planar distribution of the S-wave velocity indicates that the deep low-velocity zone may be subdivided. The zone in which the velocity is particularly high corresponds to the area without surface uplift indicated by GPS; hence, this area is not influenced by the mud volcano. This study shows that it is possible to conduct subsurface geophysical investigations to clarify the eruption mechanism of the mud volcano.

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© 2009 公益社団法人 東京地学協会
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