著者

名和 一成 杉原 光彦 村田 泰章 風間 卓仁 西田 究 菅野 貴之 小山 悦郎 大久保 修平 奥田 隆

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.54, no.2, pp.59-67, 2008 (Released:2013-02-25)

参考文献数

17

被引用文献数

1

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We carried out continuous gravity observation with a Scintrex CG-3M gravimeter at Asama Volcano Observatory from September 4 to October 22 in 2007.We tried to detect hydrological gravity effects after heavy rainfall by Typhoon 200709 (FITOW). To detect hydrological gravity effects we supposed a simple tank model as proposed for the Matsushiro superconducting gravimeter observation, which model represented immediate gravity increase and gradual decrease after rainfall. Parameters of the tank model were estimated using an ABIC minimization iversion method and precipitation data as inputs. As a result, hydrological gravity effects were extracted from gravity residuals although gravity residuals included a large non-linear drift. And the extracted hydrological gravity effects corresponded to temporal gravity changes simultaneously observed with an FG5 absolute gravimeter. Our success promises expanding opportunities of continuous observation by using CG-3M gravimeters in the future.

著者

若林環 風間卓仁

出版者

北海道大学大学院理学研究院

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

vol.84, pp.11-20, 2021-03-26

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Campaign relative gravity measurement is one of the most powerful methods to monitor spatiotemporal mass variations associated with volcanic activities. In order to quantify volcanic gravity variations accurately, the systematic gravity error due to scale factor should be corrected from original gravity data. We therefore determined relative scale factors of portable relative gravimeters, using relative gravity values measured at six gravity points between Kyoto University and Mt. Hiei in 2020 frequently. We here calculated the relative scale factor of each gravimeter by dividing the gravity value of the LC-G534 gravimeter by that of the corresponding gravimeter. The scale factor of the LC-G680 gravimeter relative to the LC-G534 gravimeter was obtained to be 0.999900 ± 0.000067; although the gravity difference between Kyoto University and Mt. Hiei (about 167 mGal) was not so large for the scale factor calibration, we succeeded in determining the G680’s relative scale factor with small standard deviation because the measurement error of the gravity data became smaller thanks to the frequent gravity measurements. However, the relative scale factors for LC-G680 and D-58 as of 2020 were found to be different from those in 2018 by more than 0.0002. In addition, the standard deviations of the relative scale factors for LC-D58 and CG-5 were obtained to be greater than 0.0002. These results may be related to significant temporal variations in reading values, originating from the overhaul in 2019 (LC-G680), the manual adjustment of the reading range (LC-D58) and the large instrumental drift (CG-5). Our results also imply that scale factor values for LaCoste-type gravimeters can depend on their reading values, as mentioned in a previous study for Scintrex-type gravimeters.

著者

風間 卓仁

出版者

北海道大学大学院理学研究院

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

vol.83, pp.9-23, 2020-03-19

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Relative gravity data is continuously collected using different types of portable relative gravimeters on a trial basis, toward the future utilization of continuous relative gravity measurements for monitoring spatiotemporal mass variations associated with volcanic activities. The gravity data is first recorded using the Tera Term software installed to a Windows-based PC; although a typical LaCoste & Romberg gravimeter does not have any devices to transmit its gravity value digitally, its analog voltage output from its readout socket can be converted to serial data format using an appropriate analog-digital converter. The recorded gravity data is then sent to an Ubuntu-based computer periodically to draw graphs of gravity time series. The graphs are finally uploaded to a web server so as to monitor temporal gravity variations anytime and anywhere. The above system for continuous relative gravity measurement was applied to the LaCoste G680 gravimeter, which was installed at the Kyoto-A gravity point, Kyoto University in September 2017. The G680’s gravity data in 2018 clearly showed time variations in short-period tide and annual instrumental drift. In particular, the instrumental drift was expressed by the linear gravity decrease of about 10 mGal/year and the additional annual gravity variation of about 1.5 mGal amplitude. These results suggest that typical LaCoste gravimeters can be utilized for continuous relative gravity measurements without major instrumental remodeling.

著者

風間 卓仁

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.64, no.3, pp.189-212, 2019-09-30 (Released:2019-10-15)

参考文献数

107

著者

風間 卓仁 栗原 剛志 山本 圭吾 井口 正人 福田 洋一

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.61, no.4, pp.593-604, 2016-12-31 (Released:2017-01-13)

参考文献数

24

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Continuous time variations in relative gravity and tilt were observed by a CG-3 M relative gravimeter at Arimura, Sakurajima Volcano (Southern Japan) during the rapid inflation event on August 15, 2015. The gravity/tilt signals were retrieved from the original data by correcting several disturbances such as instrumental drift and tidal effect. The retrieved gravity change is -5.86±0.27μGal;its amplitude is smaller than the typical uncertainty of relative gravimeters (∼10μGal), but the continuous measurement of relative gravity in a one-minute interval contributed to the detection of the small gravity change in the case of Sakurajima Volcano. The tilt change of 55.9μrad is also retrieved from the CG-3 M’s tilt data. The success in detection of the tilt change shows that the gravimeters can be utilized as portable tiltmeters as long as significant tilt variations are expected at volcanic areas. The observed gravity change is consistent with one of the dike intrusion models provided by Geospatial Information Authority of Japan, if the density value in the dike of 0.98±0.37g/cm3 is assumed.

著者

風間 卓仁

出版者

京都大学

雑誌

特別研究員奨励費

巻号頁・発行日

2010

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本研究の最大の目的は、火山での重力観測を通して、火山内部におけるマグマ質量の移動プロセスを把握することである。また、マグマ移動起源の重力変化を検出するため、陸水起源の重力擾乱を適切に補正することも、本研究の大きな目的の1つである。本研究の最終年度に当たる平成24年度には、約2カ月に1度の頻度で桜島を訪問し、設置済みの相対重力計・気象観測装置・水分計のデータ回収およびメンテナンス作業を行った。この3年間、桜島では絶対重力計や相対重力計の連続データを大量に取得することができた。しかしながら、陸水擾乱によるノイズが大きかったために、現時点では火山起源の重力変化を十分には検出できていない。そこで本研究では、新たに八重山諸島とアラスカにて重力等の観測を実施し、陸水擾乱に関連して以下のような結果を得た。まず、八重山諸島では石垣島や西表島などで土壌採取を実施し、採取した土壌に対して透水試験を適用した。その結果、透水係数は空間的に均質ではなく、約4桁の範囲で変化していることが分かった。今回得られた土壌空間不均質を陸水シミュレーションに適用すれば、陸水擾乱を高精度に再現できるものと期待される。また、アラスカでは絶対重力計FG5による重力測定を実施した。その結果、絶対重力値は予想していた値よりも約10マイクロガル程度大きい'ことが分かった。これは2011~2012年冬季の異常降雪の影響と考えられ、今後積雪分布のデータなどを利用して重力変化を再現する予定である。今後は、陸水分布シミュレーションのプログラムを改編し、陸水擾乱の再現精度向上を目指す。そして、八重山諸島・アラスカ・南極地域(前年度に重力観測を実施)で取得した重力データに陸水擾乱補正を適用し、陸水分布シミュレーションの再現精度を評価する。その上で、桜島の重力観測データに対して高精度な陸水擾乱補正を適用し、火山起源の重力変化の抽出を目指す。