Comparison of two extensometric stations in Hungary

Quartz-tube extensometers are used to measure rock deformations in two geodynamic observatories in Hungary in order to contribute to the investigation of recent tectonic movements on the area of the Pannonian Basin. One of the observatories is situated on the border of the Alps at Sopronbánfalva and is set in the metamorphic (gneiss) material of the mountains. The other station is in the basically karstic environment of the Mátyáshegy (Mátyás Hill) near Budapest. The aim of this paper is to investigate how the local conditions, such as structure of the observatory, topography or geologic features of the surrounding rocks, lead to additional or modified deformations of the extensometric stations. Data collected over eight years were processed and analysed to compare the observatories taking into account geologic, lithologic and topograpic properties of the measurement sites. Tidal and coherence analysis of the continuous strain measurements revealed that the instrument at Sopronbánfalva is more sensitive to atmospheric pressure loading than the extensometer at Mátyáshegy. Signal to noise values from the data processing of the short period variations support the higher stability of tidal strain measurements at Mátyáshegy. The strain rates measured by extensometers in both observatories are in good agreement with the strain rates inferred from GPS measurements of the Hungarian GPS Geodynamic Reference Network and the Central European GPS Reference Network.