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; MLB5) 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 Maria´nske´ La´zne´ fault zone. The interpretation suggests an influence of the fluid system due to earthquake preparation processes.