Sur certains problèmes des observations des marées terrestres effectuées à l'aide des inclinomètres et sur leur précision

Skalský, Lumír; Pícha, Jan

doi:10.1007/bf02587817

Cited by 5 publications

(2 citation statements)

References 2 publications

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“…Since the tilt to be measured is in the nrad or µrad range, instruments like horizontal pendulums (Kato 1977) or folded pendulums (Wu et al 2002) can artificially amplify the actual tilt amplitude. Nonetheless, horizontal pendulums are astatic (Skalsky & Picha 1969) and the small structure of the folded pendulums lim-its their coupling surface. A tiltmeter measures the variation of the orientation of the instrument body with respect to the local gravity vector.…”

Section: Introductionmentioning

confidence: 99%

A simple pendulum borehole tiltmeter based on a triaxial optical-fibre displacement sensor

et al. 2015

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Sensitive instruments like strainmeters and tiltmeters are necessary for measuring slowly varying low amplitude Earth deformations. Nonetheless, laser and fibre interferometers are particularly suitable for interrogating such instruments due to their extreme precision and accuracy. In this paper, a practical design of a simple pendulum borehole tiltmeter based on laser fibre interferometric displacement sensors is presented. A prototype instrument has been constructed using welded borosilicate with a pendulum length of 0.85 m resulting in a main resonance frequency of 0.6 Hz. By implementing three coplanar extrinsic fibre Fabry-Perot interferometric probes and appropriate signal filtering, our instrument provides tilt measurements that are insensitive to parasitic deformations caused by temperature and pressure variations. This prototype has been installed in an underground facility (Rustrel, France) where results show accurate measurements of Earth strains derived from Earth and ocean tides, local hydrologic effects, as well as local and remote earthquakes. The large dynamic range and the high sensitivity of this tiltmeter render it an invaluable tool for numerous geophysical applications such as transient fault motion, volcanic strain and reservoir monitoring.

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Section: Introductionmentioning

confidence: 99%

A simple pendulum borehole tiltmeter based on a triaxial optical-fibre displacement sensor

et al. 2015

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“…by Instech (Austin, Texas), which uses a capacitive sensor; its small size (two pendulums fit in a capsule 7 cm across) makes it suitable for borehole use[Harrison and Levine, 1981].Because the bob of a horizontal pendulum moves in a circular arc, a full theory of its motion must allow for cross-coupling effects from tilts and accelerations[Skalsky and Picha, 1969;Rodgers, 1968] in directions other than the one it is sensitive to. This circular motion can be avoided by a different design.…”

mentioning

confidence: 99%

Strainmeters and tiltmeters

Agnew¹

1986

Reviews of Geophysics

230

125

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Despite steady effort over the last century, continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements. This article reviews the techniques and instrument designs that have been developed in this field. The continuous measurement of true tectonic motions, which have rates of 10−14 s−1, requires extremely high instrument stability, but more rapid motions (tides and seismic waves apart) are even smaller and not much more easily detectable. Much past effort has been spent improving the transducers used in these instruments, which usually measure small displacements; the commonest choices are optical (the most accurate), capacitive (the most sensitive), and inductive (the most rugged). Nowadays building a transducer is the easiest part; a much harder task, equally important to a good design, is attaching the instrument to the ground so that it can detect the signal wanted. This part of the design includes choosing a location. A large underground opening is thermally stable but distorting; a surface installation is easy to build but noisy because of soil weathering; and a borehole is inaccessible to weather but also to the operator. All such installations (and indeed the whole field of strain and tilt measurement) of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less; this is true for tides and seismic waves, but unproven for tectonic motions. Appropriate attachment techniques differ for each location, and many mundane details (such as cementing techniques for borehole instruments) remain to be worked out. The goal of measuring tectonic and tidal tilt has created many tiltmeter designs. Most are relatively small instruments that use some form of pendulum or bubble level; a few use a liquid surface to measure tilts over a long baseline. Repeated experience has shown the latter type, when well built, to be superior to the former, proving end‐monument motions to be a dominant source of noise. The same appears to hold true for strainmeters, the best results coming from long‐base laser instruments, though strainmeters using rigid or flexible material length standards are useful for special purposes, and borehole instruments show promise. Because achieving a good design has been so difficult, it is important to select the goals an instrument must meet and be prepared to compromise on others. The difficulty of validating results from this type of instrument makes comparison tests essential; such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details.

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Determination of azimuths of simple horizontal pendula

Skalský

1969

Stud Geophys Geod

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Sur certains problèmes des observations des marées terrestres effectuées à l'aide des inclinomètres et sur leur précision

Cited by 5 publications

References 2 publications

A simple pendulum borehole tiltmeter based on a triaxial optical-fibre displacement sensor

A simple pendulum borehole tiltmeter based on a triaxial optical-fibre displacement sensor

Strainmeters and tiltmeters

Determination of azimuths of simple horizontal pendula

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