Construction of system for seismic observation in deep borehole (SODB) - Development of Deep Borehole Seismometer

The design and specifications of the seismometer specially developed for the SODB project were explained in detail. The seismometer used in SODB is a servo-type velocity seismometer, of which only the pendulum parts are placed in the borehole, and the electronic parts are placed on the ground. Seismometer probes were set at three depth levels in a cascade connection. In addition, an outline was given of several field experiments and in-house tests required for system development. Electric noise reduction at a high frequency range (above 10 Hz) is an issue in future and the durability of the optical fiber cables connecting the pendulum with the electronic parts under a high temperature environment (above 150 degrees Celsius) are required to be watched carefully. (author)