A seismic reflection survey and a VSP (vertical seismic profiling) survey were conducted to obtain insight into the detailed characteristics of the fractured reservoir in the Kakkonda geothermal field, Japan. The geothermal reservoirs in this field are located in fractured Tertiary formations and a pre-Tertiary formation in contact with a younger Quaternary pluton. The seismic survey technique with a very long off-set distance proved to be effective at clearly imaging deeper reflective events that correlate with the top of the deep pre-Tertiary basement. Attenuation of the seismic signal (a very weakly reflective or dim zone) has been found to be much greater in areas where major geothermal reservoirs have been identified. The weakly reflective zone also corresponds to the concentration of microearthquake hypocenters. We suggest that such weakly reflective zones on the seismic reflection section may be favorable drilling targets; By combining the results of microearthquake monitoring (rate of occurrence, magnitude) with further case studies of seismic reflection data of different fractured reservoirs, such a hypothesis can be tested. The comprehensive seismic technique promises valuable insights into deep structures and fractured reservoirs for geothermal exploration.