ISHII Hiroshi and Yasuhiro ASAI,
Tono Research Institute of Earthquake Science (TRIES), Association for the Development of Earthquake Prediction (ADEP).
Tono Research Institute of Earthquake Science (TRIES) has developed a multi-component borehole instruments for continuous observation. The instrument is equipped with stress meters, strain meters, seismometers, tilt meters, magnetometers, and a thermometer, and we can choose the contents of the instrument as we like. At the present time about 15 borehole stations are in operation. The depth of the deepest borehole is 1030 m. There is a fault near our institute. We have investigated a relationship between a variation of underground water and a behavior of the fault by using geophysical data obtained from borehole observations.
Near our observation stations deep boreholes with diameters of 4m and 6.5m are under construction. And depth is about 500m at the present time. During the construction spring water sometimes happens and we analyzed the data caused by this. We also made experiments of water pumping out for a borehole near the stations and analyzed the data caused by this.
The main results obtained are as follows: 1: water level of TGR350 borehole station with 350m depth decreases by the pumping water and the spring water. Data of the strain meters installed at 350m depth indicate right lateral movements of the fault near TRIES. 2: data of the strain meters installed at 350m depth indicate left lateral movements of the fault in case of recovery of water level. 3: strain meters installed at shallower depth (165m) and extensometers installed in sedimentary layer do not indicate such fault movements. 4: we have considered a mechanism explaining the phenomena by using poroelastic understanding.
