Observation of local tectonic movements by a quartz-tube extensometer in the Sopronbánfalva Geodynamic Observatory, in Hungary – Validation of extensometric data by tidal analysis and simultaneous radon concentration measurements

Abstract

In 1990 a quartz tube extensometer was installed in the Sopronbánfalva Geodynamic Observatory (SGO) of the Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences. On the basis of the 20 year data series, an average strain rate of −5.36μstr/y was determined. Because the instrumental drift can also cause a slow change in the output signal of the sensor similar to the tectonic movements, a lot of efforts were made to determine the drift of the extensometer. The instrument has no detectable drift according to the instrumental calibrations (regular calibration, parallel recording by more displacement sensors, etc.). Since autumn of 2008, the radon concentration has been continuously monitored by an AlfaGuard instrument in the SGO. The investigation of the relationship between strain and radon concentration also showed the absence of instrumental drift, so the instrument measures real tectonic movements. The results of the extensometric measurements show that the rate of tectonic movement is not constant. During the period 1993–2001, the strain rate accelerated to a maximum of −8.6μstr/y in 2001, and then decelerated again between 2002 and 2010 to approx. −2.5μstr/y in 2010.