Thermally induced errors in fluid tube tiltmeters

Beavan, John; Bilham, Roger

doi:10.1029/jb082i036p05699

Cited by 21 publications

(4 citation statements)

References 10 publications

(3 reference statements)

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“…This uses a pot-and-tube geometry, but instead of measuring the level at each end, the differential pressure is measured at the center (Figure 19b). Beavan and Bilham [1977] show that the thermal effects are more complex for this design than for a level-sensing instrument, partly because the pressure transducer eliminates flow. Unless the slope of the tube, •, is kept very small (e.g, for Horsfall's prototype instrument 0.001ø), the second term is much larger than the first; neglecting the first term gives an expression similar to (25), except that the coefficient for the term involving differential pot temperature has become 2ae instead of/3.…”

Section: 23mentioning

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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Section: 23mentioning

confidence: 99%

Strainmeters and tiltmeters

Agnew¹

1986

Reviews of Geophysics

230

125

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“…The position of the liquid level on both sides of the instrument is monitored by the measurement of the float positions. 53 It also permits the discrimination of the motion of only one head from a real tilt. Another technique used is the central differential pressure sensor.…”

Section: Introductionmentioning

confidence: 99%

Very high resolution long-baseline water-tube tiltmeter to record small signals from Earth free oscillations up to secular tilts

d’Oreye

Zürn

2005

Review of Scientific Instruments

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Solving seismological problems using SGRAPH program: I-source parameters and hypocentral location AIP Conf.A 43 m long floatless water-tube tiltmeter has been in operation since 1997 at the Walferdange Underground Laboratory for Geodynamics in the Grand Duchy of Luxembourg. The absence of moving parts makes this instrument particularly simple but does not prevent it from measuring some very small geophysical signals such as the Earth tides with a very favorable signal-to-noise ratio or the successive passages of Love waves circling the globe after major Earthquakes. Its very low noise level and its high resolution up to the long-period seismic band ͑where for instance the resolution is better than 5 ϫ 10 −12 rad͒ also allows the successful recording of rarely observed grave toroidal and spheroidal free oscillations of the Earth excited by major earthquakes. In the environmental conditions of its installation ͑in a gypsum mine at 100 m depth͒, the instrument shows a high degree of reliability and a very low drift rate ͑Ͻ0.005 microrad/ month͒. The analytical tilt and horizontal displacement transfer functions computed for this instrument and its sensors can be used to calculate the best geometrical characteristics for the construction of prototypes which should respond to specific requirements for applications in geophysics or geotechnics.

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“…2). Currently, right-lateral slip on the Alpine fault accounts for about two-thirds of the strike-slip component of plate motion as seen at the surface (16,17). Such rates imply that localization of crustal strain on that fault began before 6 to 7 Ma.…”

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confidence: 99%

Continuous Deformation Versus Faulting Through the Continental Lithosphere of New Zealand

Molnár

Anderson

Audoine

et al. 1999

Science

146

135

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Seismic anisotropy and P-wave delays in New Zealand imply widespread deformation in the underlying mantle, not slip on a narrow fault zone, which is characteristic of plate boundaries in oceanic regions. Large magnitudes of shear-wave splitting and orientations of fast polarization parallel to the Alpine fault show that pervasive simple shear of the mantle lithosphere has accommodated the cumulative strike-slip plate motion. Variations in P-wave residuals across the Southern Alps rule out underthrusting of one slab of mantle lithosphere beneath another but permit continuous deformation of lithosphere shortened by about 100 kilometers since 6 to 7 million years ago.

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Thermally induced errors in fluid tube tiltmeters

Cited by 21 publications

References 10 publications

Strainmeters and tiltmeters

Strainmeters and tiltmeters

Very high resolution long-baseline water-tube tiltmeter to record small signals from Earth free oscillations up to secular tilts

Continuous Deformation Versus Faulting Through the Continental Lithosphere of New Zealand

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