A tensioned-wire strain seismometer

Sydenham, Peter H.

doi:10.1088/0022-3735/2/12/322

Cited by 15 publications

(7 citation statements)

References 11 publications

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“…In May 1969, it was demonstrated in the Queensbury Tunnel (operated an an experimental Earth strain studies laboratory by the Department of Geodesy and Geophysics, Cambridge University) that a two-point mounted, flexible mechanical standard (in the form of a thin invar wire) could produce useable solid-tide records with extreme simplicity. The devices used at that time (King et al 1969;Sydenham 1969a) were not designed for this application and considerable room for improvement existed.…”

Section: Introductionmentioning

confidence: 99%

Progress in the Design of Tensioned-Wire Earth Strainmeters

Sydenham

1972

Geophysical Journal International

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Section: Introductionmentioning

confidence: 99%

Progress in the Design of Tensioned-Wire Earth Strainmeters

Sydenham

1972

Geophysical Journal International

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“…This motion was recorded with an optical lever. More recent instruments stem from the design bySydenham [1969] of a strainmeter in which the wire is fixed at one end and at the other is free to move but kept under constant tension.…”

mentioning

confidence: 99%

Strainmeters and tiltmeters

Agnew¹

1986

Reviews of Geophysics

231

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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“…The deflection was monitored with the displacement probe. The following stiffnesses were recorded: The value for the three-point plate is considerably lower than reported for the Queensbury plates (Sydenham 1969 reported 1000 N m-') probably because the latter used larger bolt sizes and shorter projections. The plates laid on the sand moved permanently for forces approaching 10 N. There is a marked correlation between the number of interfaces and the stiffness as would be expected.…”

Section: Experimental Methodsmentioning

confidence: 71%

“…The three-point mount in Fig. 3(b) has been used for the Invar wire strain meters installed in the Queensbury Observatory in Yorkshire (King et al 1969;Sydenham 1969) and for the experimental quartz-tube strain meter built in the Cooney Observatory. (Sydenham et al 1972).…”

Section: Description Of the Mounts Investigatedmentioning

confidence: 99%

Stability of Strain-Meter Mounts

Jeffery

Sydenham

1973

Geophysical Journal International

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As the mounts of an Earth strainmeter are part of the measurement loop it is advantageous to know their short and long-term drift characteristics.Presented are the drift rates recorded for six mounting methods over a several month period. It has been clearly shown that the sand and plate mount is the better where a horizontal surface is available. Expanding bolt methods take longer to stabilize but do achieve a similar low and adequate drift rate. Allowance for the non-linear nature of mount drift in Fourier analyses is discussed.

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A tensioned-wire strain seismometer

Cited by 15 publications

References 11 publications

Progress in the Design of Tensioned-Wire Earth Strainmeters

Progress in the Design of Tensioned-Wire Earth Strainmeters

Strainmeters and tiltmeters

Stability of Strain-Meter Mounts

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