抄録
The feasibility study is under way for the tunnel construction under the Hoyo straits to connect the Shikoku and the Kyushu islands. Several serpentinite bodies crop out in the Saganoseki Peninsula which would be the exit of tunnel in the Kyushu.
Tunnels in serpentinite are often deformed by ground squeezing and heavy earth pressure. Magnetic prospecting was carried- out to obtain more detailed information about serpentinite in the northern part of Saganoseki Peninsula where small serpentinite outcrops are scattered along Sambagawa metamorphic belt.
The following results have been obtained from this prospecting:
(1) Virtually all magnetic anomalies in this area are caused by serpentinite and the three-dimensional structures of serpentinite have been clarified by the analysis of magnetic anomalies.
(2) Serpentinite bodies are distributed almost continuously beneath the earth's surface in the east-west direction which is parallel to the axis of the Saganoseki Peninsula.
(3) Serpentinite in this area had been inferred to have thin sheet shape, but it was clarified by this prospecting that most serpentinite bodies have subsurface dikelike roots.
(4) The subsurface shapes of exposed or concealed serpentinite bodies have been inferred from the magnetic anomalies.
(5) Magnetic prospecting is very effective method for the survey of serpentinite bodies.
