Abstract
In the Muka River, the Tokoro River system, if the outflow of small stones occurs, and the exposure of the soft rock and volcanic ash layer under them is accelerated, this will result in severe scouring and riverbed degradation. In this research, we worked on how to develop a tool that can reduce the effect of a water flow, to install a seismograph under water, and to excite vibrations in a river course. The results have told that underwater shear wave velocity measured with the method newly developed well represent the site conditions. In addition, the resulting shear wave velocity distribution has good continuity from the underwater river course to the land at a depth of up to 5 meters.
