Monitoring of geodynamic activity in the West Bohemia seismoactive region between 1993–1996

Abstract

The western part of the Bohemian Massif is characterized by repeated earthquake swarm occurrence, juvenile carbon dioxide waters, mineral springs, mofettes, Quaternary volcanics etc. To study the geodynamic activity of the region, repeated geodetic measurements of recent crustal movements, repeated gravity measurements and continuous recording of groundwater level have supplemented the seismological investigations since the fall of 1993. The December 4–5, 1994 weak earthquake swarm, the strongest seismic sequence between 1993–96, remarkably coincided with the absolute minimum of the groundwater level and a maximum of gravity. Repeated gravimetric measurements confirmed the existence of temporal variations of gravity, characterized by a certain correlation with the local tectonic setting. The results of GPS did not prove any displacement >5 mm–a in horizontal component. Precise levelling indicated small negative changes in elevation at several points of measurements.