Ground tilt observations at Syowa Station, Antarctica. Part 1. Borehole tiltmeter

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The first continuous observations of ground tilt in Antarctica were carried out at Syowa Station with a biaxial bubble-type borehole tiltmeter and a set of water-tube tiltmeter. The former was installed in a waterproof, steel-cased hole 196cm deep and 144mm in diameter. The observations began in April 1981. This paper discusses the borehole tiltmeter data from April to December. The signals were recorded on a 12-channel chart recorder in the data processing hut, 150m north from the observation hole. The maximum tilt fluctuation during nine months was 17μrad in the X-component (E-W) and 24μrad in the Y-component (N-S). As the data seem to be seriously affected by underground temperature variations, the observed data were corrected for temperature assuming a linear relation between the ground tilt and the underground temperature. The corrected records showed a trend of upward tilt on the west and north sides throughout the observation period. The cumulative change of ground tilt during nine months of observation was -1.5μrad in the X-component and 6μrad in the Y-component. These observations demonstrate that a true ground tilt can be detected by the borehole tiltmeter.
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