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

概要

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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.
社団法人東京地学協会の論文
2009-07-07