ABSTRACT
The occurrence of depression on the ground surface due to lignite pit has been observed at central southern area of Gifu prefecture, Central Japan. In order to prevent the ground surface depression caused by collapse of the tunnel due to the shaking of the Tokai and Tonankai earthquakes, which is expected to occur near future, the work on filling fluent earth materials to the underground cavity is proceeding. To clarify the distribution of lignite pits and to monitor the filling condition of fluent earth materials in the cavity, the seismic tomography is planned between ground surface and the borehole several meters below and parallel to the lignite layer, which is drilled by the directional drilling technology. We report the current status of the site, drilling and survey plan, and outline of the 3D simulation results of seismic tomography.
