Slug flow - A possible explanation for hydrogeochemical earthquake precursors at Bad Brambach, Germany

Extensive hydrogeological, geochemical, radiometric and hydro-isotope investigations in the Vogtland region, Germany, since 1989 suggest a fluid connection between a special epicentral area (focal depth: 3-15 km; M-L < 5) and a mineral spring at Bad Brambach. Twenty-six hydrogeochemical anomalies are related to earthquakes/swarmquakes of that epicentral area near Novy Kostel (CZ) during the last 9 years. The anomalies were originated by a slug-flow process in the fluid-filled fracture system near the surface. The gas component of the observed fluid (99 vol. % CO2) is of upper mantle/crustal origin. The fluid transport pathway to the surface is the seismically active Marianske Lazne fault zone. The interpretation suggests an influence of the fluid system due to earthquake preparation processes.