抄録
Gravity survey has been carried out in Seikan tunnel, the world longest undersea tunnel in its completion which links Honshu with Hokkaido by railroad, for the purpose of clarifying gravity features in Tsugaru channel. Gravity values were obtained in the undersea tunnel, therefore, corresponding gravity values at sea surface were calculated in order to obtain free-air and Bouguer anomalies. The comparison between free-air and Bouguer anomalies at sea level indicates thedeiciency of mass which corresponds to the density difference between sea water (ρ=1.03 g/cm3) and rock (ρ=2.67 g/cm3) in Tsugaru channel Another interesting feature is increasing of Bouguer anomalies from center of Tsugaru channel toward Matsumae peninsula. It may be considered from some model investigations that the increasing is caused by lower crustal uplift in Matsumae penin sula. It also suggests a possibility of the relationship between geological structure and crustal structure in the region.