東京大学重力基準点の重力変化

抄録

Gravimetric comparisons have repeatedly made between the Tokyo and the Kakioka Fundamental Gravity Stations since 1963 by using LaCoste & Romberg gravimeters. The Gravity difference between them amounts to about 177 mgal. The gravity value at the Tokyo Fundamental Gravity Station relative to the Kakioka Station decreased at a rate of 11μgal/year till 1969, but afterwards it has turned increasing at a rate of 18, i gal/year during these three years. The gravity decrease is well coincident with the groundwater leveldown whichwas accompanied with the ground subsidence. On the other hand, the gravity in crease can be explained as the ground water level recovery. We estimate effective porosity of soil as about 20% in the gravity-decreasingperiod and 18% in the increasing one. Judging from these results, we conclude that the soil consolidation due to the ground subsidence has scarecely occurred throughout.