A silica long base tiltmeter with high stability and resolution

Abstract

In order to be able to provide valuable data in multiparameter measurement field operations, tiltmeters need to have a noise level better or equal than 10(-9) rad for a period range from a few minutes to a few years and a long term stability ranging from 10(-7) to 10(-8) rad/yr. Tiltmeter measurements should also be as much as possible insensitive to thermal disturbances, by taking great care of the horizontality of the base line tube first. Secondly, thermal responses have been assessed. We also took great care of the coupling of our tiltmeters with the bedrock. We've designed a long base tiltmeter with sensors in silica which has a low dilatation coefficient. The linear variable displacement transducer is based on coil coupling (powered by an alternative voltage). Finally we show the results of two 100 m silica water tube tiltmeters which were installed in a mine in the French Vosges massif in the framework of a hydrology research project. These instruments show a remarkably good stability (6.5x10(-9) rad/month) and a low noise level (of the order of 10(-11) rad). Toroidal and spheroidal free modes of the Earth were observed after the two last major earthquakes on Sumatra.

Modelling atmospheric and induced non-tidal oceanic loading contributions to surface gravity and tilt measurements

“…In fact, all these stations have been installed to study local or regional hydrology contributions (e.g. Longuevergne et al 2008). The station with the lowest noise level is Sainte-Croix-aux-Mines, where the about 100-m hydrostatic tiltmeters have been installed deeply in an old mine.…”

“…In order to have a better estimate of hydrological contributions, a regional model would be required (Longuevergne et al, 2008).…”

Inferring field‐scale properties of a fractured aquifer from ground surface deformation during a well test

“…In contrast, relative deformation instruments like tiltmeters and strainmeters were introduced in an innovative way to apprehend both short‐ and long‐term subsurface flow phenomena, first in volcanology where the signal is strong due to large inflating cavities [ Dzurisin , ] and later in hydrogeology thanks to technical improvement of these instruments [ Boudin et al , ; Hisz et al , ]. In particular, much effort has been dedicated into assessing how they can be used to characterize properties of groundwater flow, whether fluxes are man driven [ Chen et al , ; Barbour and Wyatt , ; Fabian and Kümpel , ] or natural [ Braitenberg , ; Jahr et al , ].…”

A phase-tracking fiber interferometer for seismologic applications

“…Further, if multiple sensor arrays are to be constructed to accurately monitor a selected site, the implications in costs, number of data channels as well as risk to lightning strikes might prove too prohibitive. In the case of tiltmeters, very longbase devices will have to be employed to achieve the desired nrad resolution [2]. Presently, GPSbased sensors offer a possible solution although their limited resolution might limit applications only to relatively largescale seismic perturbations [3].…”