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Volume
98
Journal of Research of the National Institute of Standards and Technology
Abstract
A borehole tiltmeter with a sensitivity of a few nanoradians is described. It is composed of two orthogonal horizontal pendulums with free periods of 1 s. The pendulums are insensitive to barometric pressure fluctuations, and the measured temperature coefficient is less than 30 nrad/degrees-C. The range of the pendulums is about +/- 5 micro rad, and their response is linear within 1% and stable over several years. The performance of the tiltmeter in the field was evaluated using tidal data obtained from a closely spaced array of boreholes in Southern California. The long-term stability of the tiltmeter is generally better than 1 micro rad/yr. The data also indicate that instruments in boreholes at least 24 m deep are independent of surface effects. Several different capsules designed to couple the instrument to the surrounding material have been tested. In addition, an experimental method for estimating the magnitudes of local perturbation in the regional tilt field is described.
Addeddate
2011-08-30 19:37:53
Cite
J. Res. Natl. Inst. Stand. Technol. Vol. 98, No. 2, p. 191
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