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タイトル: 固有周期の安定な坑井用小型長周期地震計・傾斜計の開発
その他のタイトル: Development of the Borehole Easy-operation Long-period Seismometer (BELS Type 79) which has a Stable Period
著者: 安藤, 誠一
岡田, 義光
安芸 , 敬一
大工原, 保
鈴木, 喜吉
原, 智美
発行日: 1979年11月30日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第54冊第1号, 1979.11.30, pp. 135-146
抄録: The most troublesome factor in the observation of long-period oscillation or ground tilt is the problem of drift. As to the drift of zero-point, we can reduce it by the technique of negative feedback. On the other hand, we cannot avoid the drift of characteristic period (or drift of tilting sensitivity) as far as we use the principle of horizontal pendulum, which is the most popular way to construct the long-period seismometers. That is because the period of horizontal pendulum is essentially sensitive to the ground tilt. In this circumstance, we intended to device a long-period seismometer which has a stable period for the ground tilt. For the suspension of the pendulum we adopted the method originally suggested by Eomberg in 1961. This type of pendulum has the following features. (1) The change of characteristic period due to ground tilt is negligibly small. So, if we construct a long-period seismometer with this pendulum and combine it with negative feedback, we can obtain a very stable system which is free from both types of drift. (2) As adjustment of period and zero-point can be carried out independently, the settlement of this instrument is quite easy. (3) The shape of the pendulum is just adequate for the use in a borehole. The prototype model constructed in this study has dimensions of 120φ×540 (diameter × height in mm), a weight of 8kg and is equipped with two kinds of transducers. One signal is proportional to the displacement by use of the Magnesensor (SONY Inc.) while the other two are proportional to the velocity using ordinary moving coils. The characteristic period of the pendulum can be varied from 2 sec to 20 sec, by changing the position of the attachment point of the suspension spring. Total performance of this seismometer was found to be satisfactory through the test observation of natural earthquakes at a borehole site and earth tide observation in the vault.
URI: http://hdl.handle.net/2261/12722
ISSN: 00408972


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