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| Titel |
Comparison of a parallel installation of laser and quartz tube strainmeters at the Geodynamic Observatory Moxa in Thuringia, Germany |
| VerfasserIn |
Martin Kobe, Thomas Jahr, Nina Kukowski, Pascal Methe, Andreas Goepel |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250111801
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| Publikation (Nr.) |
 EGU/EGU2015-11945.pdf |
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| Zusammenfassung |
| High-resolution continuous deformation measurements provide an important data base for
studies on deformation of the solid Earth (e.g. due to tides or hydrologically-induced
deformation) that has strain amplitudes from μm to nm. Time series can be obtained by
different strainmeters that measure relative changes in length between two fixed points
on the Earth’s surface with a resolution up to 10-10 m. In order to improve the
signal-to-noise ratio strainmeters are installed in galleries or caves with a thick mountain
overburden.
The Geodynamic Observatory Moxa operates beside seismological and gravimetrical sensor
systems an extensive strainmeter array. It consists of a borehole extensometer, two quartz
tubes at right angles and one diagonally-installed laser strainmeter. In 2011, two new
laser strainmeters were added in cooperation with the company SIOS/Ilmenau.
They are installed parallel to the quartz tubes and fixed to the bedrock by the same
pylon.
This kind of parallel installation is unique in the world and allows the direct comparison of
measurements of horizontal length changes with different types of strainmeters for the first
time. For the comparison of the data we used mainly the tidal analysis of three-years long
time series, as well as the signal from a research borehole on the observatory’s perimeter. The
first results show a decrease of the long lasting device-specific drift by a factor of
2.3 - 2.5 x 10 of the laser strainmeters (LS) with respect to the quartz systems (QS).
Furthermore, the signal-to-noise ratio of the LS is significantly higher than for the QS, as can
be seen, for example, in the tidal amplitude factors (AF). In the north-south direction we
determined AFÂ≈ 1.0 (LS) and AFÂ≈ 0.6 (QS) that yields LS-
QS ≈ 1.66. In the east-west
direction we found AFÂ≈ 0.67 (LS), AFÂ≈ 0.16 (QS), and therefore -LS
QS ≈ 4.3. The tidal
parameters are used to evaluate the new laser strainmeter system. Furthermore the
determination of LS-
QS provides a method to calibrate the quartz tubes for the first time. The
comparison of other deformation signals in the time series reveals that LS-
QS changes with
the considered signal period. A transfer function is required to calibrate QS using
LS.
The new laser strainmeter array is a significant step towards the measurement of subsurface
deformation at the Geodynamic Observatory Moxa. Furthermore it is presently being used to
develop a transportable laser strainmeter system for areal applications, for example, across
fault zones. |
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