Vertical displacement measurements in Central California with a long-baseline two-fluid tiltmeter

The need for a water-tube tiltmeter and the details of its operation were covered by Eaton [1] in 1959. Since that time more modern instrumentation has allowed modification and further development beyond the basic single-tube fluid tiltmeter with a mechanical surface sensor. A number of instruments are discussed in connection with thermal errors in a paper by Bevan and Bilham [2] including one due to Huggett, et al. [3]. This particular instrument, the two-fluid tiltmeter, is the subject of this project. A laboratory single leg prototype developed by Terra Technology Corporation [4] was modified and expanded for use in a field test site in central California.

The two major differences in this fluid tiltmeter are the use of two parallel tubes filled with fluids of different thermal properties experiencing the same thermal environment and the design of the level sensors in the reservoirs. The latter being piezoelectric acoustic drivers (sonar type transducers) submerged in the liquid which detect the change in the surface height in the reservoirs.