Triaxial drill bit Vertical Seismic Profile (TAD-VSP), which utilizes the drill bit as a seismic source, was used during exploration of the deep portion of the Kakkonda geothermal system, Japan. The seismic signal associated with the bit was recorded continuously during the drilling of well WD-1a, from a depth of 1505 to 3000 m. The result of the TAD-VSP shows possible seismic reflectors at about 2.1, 2.2, 2.4 and 2.8 km below sea level. Based on drill hole lithology, these reflectors appear to correspond to the top of the Pre-Tertiary formation, the top of the Kakkonda granite and reflectors within the Kakkonda granite.