Geodynamic modelling of the recent stress and strain field in the Vogtland swarm earthquake area using the finite-element-method

The study of several swarm earthquake regions led us to the assumption that swarm quakes mostly occur in combination with fluid migration and often in the neighbourhood of volcanoes. Observations of the strong carbon dioxide flux and investigations of Weinlich et al. (1999) about recent volcanism in the Vogtland/ Western Bohemia are the linking part to global observations of swarm earthquakes. This idea and the theoretical modelling of Yamashita (1999) were the starting point to develop a model using the finite-element-method with the software package ABAQUS concerning stress field, pore pressure, temperature and deformation in the Vogtland swarm quake area. The model is intended to reveal the interaction between fluid migration, temperature changes and deformation in this area. Its horizontal dimensions are 55 km×60 km and 30 km in depth. The main geological units include the Marianske Lazne Fault Zone and the Eger Rift. We focus on that part of the Vogtland/Western Bohemia region where these two fault zones cross. The model takes into consideration the stress field, Mohr–Coulomb failure, thermal stresses as well as creep and poro-elastoplastic rheologies. The results show that the rate of deformation and the stress accumulation caused only by the regional stress field is not high enough to generate the swarm earthquakes. But periodic change of pore pressure (which includes fluid migration) in combination with temperature changes has a severe influence on the rate of deformation and is in the dimension to cause swarm quakes.