東北地方における重力絶対測定

概要

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We made for the first time absolute gravity surveys at the Aobayama Earthquake Observatory, Tohoku University, for the period from January 30 to February 7, 1984, using a transportable absolute gravimeter completed at the International Latitude Observatory of Mizusawa. A cat's eye falls about 30 cm in vacuum and a Michelson interferometer, which is illuminated by an iodine stabilized He-Ne laser, measures its falling distance every 1 ms. Timing signals are synchronized with a rubidium frequency standard. The inside of the vacuum chamber, in which a dropping mechanism is installed, is kept at a high vacuum better than 2.6×10<SUP>-5</SUP> Pa. Piezo electric ceramics, which are attached to the feet of the absolute gravimeter, cancelled ground vibrations in order to stabilize the Michelson interferometer. The rotation of the cat's eye around its horizontal axis during free fall was monitored by an autocollimator and a two dimensional position sensor, and was proved to be within 10 seconds of arc. The arithmetic mean of results obtained by the present absolute gravity measurements was approximately 8.5 × 10-7m/s<SUP>2</SUP> (85 μgal) smaller than that obtained by two LaCoste and Romberg gravimeters referring to the IGSN 71 system.
日本測地学会の論文