中部日本における重力潮汐の地域的変化に関する観測的研究〔英文〕
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概要
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Tidal gravity observations have been conducted at ten stations in Central Japan with two LaCoste & Romberg gravimeters for the purpose of investigating regional variations of gravity tides. Analyses of the obtained data have revealed remarkable regional heterogeneities of tidal gravity parameters. These heterogeneities cannot be eliminated by ocean tide corrections. After ocean tide corrections the obtained δ-factors show a tendency to decrease from the south-eastern part of this area toward the north-western part by 1.5% for M2 constituent and by 3% for O1 one. The obtained phase differences after ocean tide corrections also show systematic variations associated with the δ-factor variations. Such large lateral variations in the δ-factor, occurring within a range of about a few hundred kilometers, have never been clearly obtained in previous studies. We have examined several possible causes of these δ-factor variations, such as correction errors of ocean tide effects, meteorological disturbances, groundwater perturbations and topographic effects, but none of them can explain the δ-factor variations. The area of a lower δ-factor corresponds approximately to the center of negative Bouguer gravity anomaly and beneath that area exists an attenuative and low velocity layer. Therefore, the lateral heterogeneity of the earth which has both elastic and anelastic properties seems to be a likely cause, but a satisfactorily quantitative explanation cannot be given at present. Improvements of an earth tide theory including effects of lateral heterogeneities are required for quantitative explanations.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地震研究所の論文
東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地震研究所 | 論文
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