A Study of Groundwater Variations in Beppu Area by Means of the Precise Gravity Measurements.

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  • Fukuda Yoichi
    Beppu Geophysical Research Laboratory, Kyoto University
  • Mawatari Hideo
    Beppu Geophysical Research Laboratory, Kyoto University
  • Yusa Yuki
    Beppu Geophysical Research Laboratory, Kyoto University
  • Hunt T.
    Beppu Geophysical Research Laboratory, Kyoto University

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  • 精密重力測定による別府地域の地下水変動の研究
  • セイミツ ジュウリョク ソクテイ ニヨル ベップ チイキ ノ チカスイ ヘンド

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Abstract

The effects of groundwater variations upon gravity are one of the large noise sources which are generally removed from high-precision gravity measurements using superconducting gravimeters or absolute gravimeters. These effects, on the other hand, give us ;important information about the hydrological characteristics in the area concerned. Precise gravity measurements have been repeatedly carried out at Beppu, in order to detect the gravity changes associated with groundwater variations. Using a LaCoste & Romberg gravimeter (G-534), 31 microgravity surveys were made at about 1-monthintervals from February 1993 to February 1996, at 11 survey marks in the Beppu area . The observations were reduced using standard precise gravity techniques and the method of Principal Component Analysis (PCA) was employed to expand the observed gravity changes into the time-space domain. The result shows that; (1) the 1st and the 2nd components of PCA explain more than 85% of the variations, (2) the variations of the 1st component (58.3%) represent shallow unconfined water level changes, and (3) the 2nd component (27.4%) is possibly explained by deeper groundwater movements and associated ground level changes.

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