On the Extensometer Whose Magnifier is a Zollner Suspension Type Tiltmeter, and the Observation of the Earth's Strains by Means of the Instruments

i. ozawa


In order to observe the ground-strain due to the tidegenerating force of the earth, it is necessary to record measurable the linearstrains, which are as large as 10-10. For that purpose, it should not onlymake longer the base line on the ground, but also magnify the relative displacementof the both edge-points of the base line extremely. A new typeof highly sensitive extensometer of which magnifier is a Zöllner suspensiontype tiltmeter is devised. In the mechanism of the extensometer, a superinvarrod whose the length is constant, is put parallel with the base line, andan edge of the rod is fixed 011 one edge of the line so that the relative displacementof the unfixed edge of the rod and the other edge of the line maybe transformed into the inclination of the support of the Zöllner pendulum.Consequently, the pendulum of the tiltmeter rotates magniloquently. Andalso the rotational angle of the pendulum is enlarged and recorded withan optical lever oil a photographic printing paper. The extensometer hasa sensitivity in the order that is higher than the formerly used one, andthe sensitivity is able to be perfectly controlled at will. As the sensitivityto the linear strain is more than 100 times as large as that of the extensometeras to the ground-tilting, the influence of the tilting may be neglected.The linear strains of the earth's surface in earth tide are observedwith this extensometer at Osakayama Observatory, and are obtained theanalyzed values that are subtracted the influence of the ground-tilting,in four directions N-S, E-W, S 38" W and S 52° E. Then, theearth-tidal constants Ii — 3 I, Ii and I are obtained as 0.440, 0.599 and0.053 respectively. And also the records (of the ground-strain) which areobserved with new type extensometer are compared with them which areobserved with other types'. In these records, the interesting phenomenawhich are generated within a short hour, are found.

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DOI: https://doi.org/10.4401/ag-5505
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X