Seismic Exploration in the Fushime Geothermal Field, Kagoshima Prefecture

Abstract

A reflection seismic survey is a very effective tool to define the subsurface structure for petroleum exploration. However, it is often thought that good-quality seismic reflections can't be obtained through geothermal exploration especially in the non-sedimentary field. The following statements explain why its use is not widespread in geothermal exploration.

(1) the difficulty of working in a topographycally rough area
(2) the non~layered and complex geological structure
(3) the low transmission of seismic energy due 10 volcanic flow covering near the surface

In spite of these difficulties, a reflection seismic survey is expected to be able to detect the indications of faults and fracture zones that may serve as conduits for geothermal fluid.

A reflection seismic survey was conducted at the Fushime geothermal field in 1978, when conventional technic for petroleum exploration was applied. The results didn't provide any significant reflections and useful informations. After examining these data and wells data carefully, we carried out again an experimental reflection survey in order to find suitable field parameters using Yuatsu Impactor and Vibroseis at the same field in 1986(Fig. 1). We briefly present here the results of the reflection survey, compared with those of other geophysical investigations obtained in this field.