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Gravity at sea--A memoir of a marine geophysicist.

Tomoda Y - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2010)

Bottom Line: Professor Chuji Tsuboi made a number of unsuccessful attempts at developing a gravity meter that can be operated on a normal surface ship by reducing the noise by minimizing the motion of the gravity meter through a mechanical design.I have chosen a new approach toward the measurements of gravity on a surface ship by simplifying the mechanical part using a string gravity meter that was installed directly on a vertical gyroscope in combination with the numerical and/or electronic reduction of noises.The results reveal the fine structures of gravity field in and around trenches that provide important clues as to a number of geodynamic issues including the nature of the trench-trench interaction and the interaction of trenches with seamounts.

View Article: PubMed Central - PubMed

Affiliation: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. fujimoto@aob.gp.tohoku.ac.jp

ABSTRACT
A history of studies on the gravity measurements at sea in Japan is reviewed with an emphasis on the contribution of the author. The first successful measurements at sea were made in 1923 by Vening Meinesz in the Netherlands using the pendulum apparatus installed in a submarine. However, the gravity measurements using a submarine are not convenient because the access to a submarine is limited. Professor Chuji Tsuboi made a number of unsuccessful attempts at developing a gravity meter that can be operated on a normal surface ship by reducing the noise by minimizing the motion of the gravity meter through a mechanical design. I have chosen a new approach toward the measurements of gravity on a surface ship by simplifying the mechanical part using a string gravity meter that was installed directly on a vertical gyroscope in combination with the numerical and/or electronic reduction of noises. With this gravity meter TSSG (Tokyo Surface Ship Gravity Meter), we firstly succeeded in measuring gravity at sea onboard a surface ship in July 1961 and the measurements have been extended to the northwestern Pacific and beyond. The results reveal the fine structures of gravity field in and around trenches that provide important clues as to a number of geodynamic issues including the nature of the trench-trench interaction and the interaction of trenches with seamounts.

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Cross sections of trenches. “Positive free-air anomalies seaward of the trench” indicating the interaction between seamounts and the trench: ΔG′: free-air anomalies, ΔG″: Bouguer anomalies, and D: bottom topography. (a), Gravity profile when a seamount is located far from the trench. (b), Gravity profile when a seamount is located near the trench. (c), An example of cancellation of the outer gravity high seaward of the trench by the low gravity around the seamount.
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fig9d: Cross sections of trenches. “Positive free-air anomalies seaward of the trench” indicating the interaction between seamounts and the trench: ΔG′: free-air anomalies, ΔG″: Bouguer anomalies, and D: bottom topography. (a), Gravity profile when a seamount is located far from the trench. (b), Gravity profile when a seamount is located near the trench. (c), An example of cancellation of the outer gravity high seaward of the trench by the low gravity around the seamount.

Mentions: Though not so large as the positive gravity anomaly in the island arc, there is a positive gravity anomaly seaward of the trench. Its amplitude is usually about 50 mgals, and the horizontal extent is as much as 300 km from the profile in Fig. 18a. “The positive anomaly seaward of the trench” is an important phenomenon related to the origin of “subduction” of the oceanic plate. The following features are related to this phenomenon.


Gravity at sea--A memoir of a marine geophysicist.

Tomoda Y - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2010)

Cross sections of trenches. “Positive free-air anomalies seaward of the trench” indicating the interaction between seamounts and the trench: ΔG′: free-air anomalies, ΔG″: Bouguer anomalies, and D: bottom topography. (a), Gravity profile when a seamount is located far from the trench. (b), Gravity profile when a seamount is located near the trench. (c), An example of cancellation of the outer gravity high seaward of the trench by the low gravity around the seamount.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3037522&req=5

fig9d: Cross sections of trenches. “Positive free-air anomalies seaward of the trench” indicating the interaction between seamounts and the trench: ΔG′: free-air anomalies, ΔG″: Bouguer anomalies, and D: bottom topography. (a), Gravity profile when a seamount is located far from the trench. (b), Gravity profile when a seamount is located near the trench. (c), An example of cancellation of the outer gravity high seaward of the trench by the low gravity around the seamount.
Mentions: Though not so large as the positive gravity anomaly in the island arc, there is a positive gravity anomaly seaward of the trench. Its amplitude is usually about 50 mgals, and the horizontal extent is as much as 300 km from the profile in Fig. 18a. “The positive anomaly seaward of the trench” is an important phenomenon related to the origin of “subduction” of the oceanic plate. The following features are related to this phenomenon.

Bottom Line: Professor Chuji Tsuboi made a number of unsuccessful attempts at developing a gravity meter that can be operated on a normal surface ship by reducing the noise by minimizing the motion of the gravity meter through a mechanical design.I have chosen a new approach toward the measurements of gravity on a surface ship by simplifying the mechanical part using a string gravity meter that was installed directly on a vertical gyroscope in combination with the numerical and/or electronic reduction of noises.The results reveal the fine structures of gravity field in and around trenches that provide important clues as to a number of geodynamic issues including the nature of the trench-trench interaction and the interaction of trenches with seamounts.

View Article: PubMed Central - PubMed

Affiliation: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. fujimoto@aob.gp.tohoku.ac.jp

ABSTRACT
A history of studies on the gravity measurements at sea in Japan is reviewed with an emphasis on the contribution of the author. The first successful measurements at sea were made in 1923 by Vening Meinesz in the Netherlands using the pendulum apparatus installed in a submarine. However, the gravity measurements using a submarine are not convenient because the access to a submarine is limited. Professor Chuji Tsuboi made a number of unsuccessful attempts at developing a gravity meter that can be operated on a normal surface ship by reducing the noise by minimizing the motion of the gravity meter through a mechanical design. I have chosen a new approach toward the measurements of gravity on a surface ship by simplifying the mechanical part using a string gravity meter that was installed directly on a vertical gyroscope in combination with the numerical and/or electronic reduction of noises. With this gravity meter TSSG (Tokyo Surface Ship Gravity Meter), we firstly succeeded in measuring gravity at sea onboard a surface ship in July 1961 and the measurements have been extended to the northwestern Pacific and beyond. The results reveal the fine structures of gravity field in and around trenches that provide important clues as to a number of geodynamic issues including the nature of the trench-trench interaction and the interaction of trenches with seamounts.

Show MeSH
Related in: MedlinePlus