Understanding the causal mechanisms of large devastating earthquakes in intraplate areas is a long-term challenge. Current seismic swarms and CO2 outflows in western Bohemia are often attributed to magmatic processes. Paleoseismic research at the Marianske Lazne fault, which crosses the focal zone, revealed the occurrence of two major earthquakes in the last 3 thousand. years, which broke the surface, the youngest of them around 1000 AD. To verify whether these large earthquakes were also the result of magmatic processes or of tectonic origin, the following approach will be used: 1) determination of long-term record of both large earthquakes, using standard paleoseismic survey and long-term δ13C record recorded in sediment-derived animal shells; 2) reconstruction of the plio-quaternary stress field and testing of its local or regional relation to volcanism. The results will allow an assessment of whether the current activity is "normal" for some time or whether it is increasing or decreasing, which may lead to a conclusion about the potential of future major earthquakes or volcanic events.