The FSU Jena Geodynamic Observatory Moxa (Thuringia, central Germany): Instrumentation, observations and results from different sensor systems

The Geodynamic Observatory Moxa of Friedrich-Schiller University Jena, assigned to the Chair of General Geophysics of the Institute of Geosciences, is located about 30 km south of Jena in the Thuringian slate mountains. Due to its isolated location and the possibility of subsurface installations in a gallery or in boreholes, Moxa observatory provides excellent conditions for long term observations.
Moxa observatory is equipped with various geophysical sensor systems to observe transients signals of the local gravity field (superconducting Gravimeter CD-034, LCR-ET-18), deformation (altogether three laser strain meters with base length of 28 and 36 m, respectively, which also enable to estimate areal strain; ASKANIA borehole tilt meters, Ilmenau tilt meter,) and of subsurface temperatures (optical glass fibre in a 100m deep borehole). These systems are complemented e.g. through temperature sensors placed within the gallery, water level gauges and a climate station to record environmental parameters. Most sensor system are recording with a resolution in the nano- or subnano range, which allows to study very small parameter changes and thus to identify even very faint natural signals. All recorded time series show high signal to noise ratios for a large range of frequencies.
Some of our long-term observations already have led to more than two decades of continuous time-series, whereas other sensors now have been recording for about five to ten years. Here we provide a  concise overview about important goals and results of the records of the individuals instruments at Moxa: The analyses of Earth tides over the last 20 years show variations of the tidal parameters for the main tidal constituents, which may be caused by changes of the ocean loading effect, due to a worldwide redistribution of water masses probably linked to the increase of the sea surface hight (SSH). Investigations regarding gravity effects of storm surges show that e.g. for the North Sea a significant gravity signal which is detectable in the data of the superconducting gravimeter at Moxa observatory. Both results are based observations independent of satellite data and therefore they are an important complement to findings e.g. from satellite altimetry. Deformation signals like tilt and strain are very sensitive to hydrological signals, e.g. pore pressure fluctuations, and enable to detect both, global and local groundwater flow effects. However, as it is often difficult to clearly identify the cause of hydrological signals, these records need to be complemented by independent observations. This is done via recording temperature along a borehole which enables to detect local thermal anomalies, which can be related to groundwater movements. Further, the temperature-depth time series also mirror seasonal solar contributions to the subsurface thermal inventory as well as environmental effects. Besides contributing to geophysical research topics, the improvement and further development of sensor technology and the configuration of data acquisition systems, with emphasis on tilt, strain, and temperature recording sensor systems is a further important goals of our group, which is realised in cooperation with other institutions and companies in and close to Jena.