Investigations about earthquake swarm areas and processes

Abstract

Earthquake swarms are observed worldwide, especially in connection with fluid movement and volcanism. Two regions are compared by numerical investigations using the finite element method: The Vogtland/NW-Bohemia area situated at the border between Germany and the Czech Republic and the Magadi region in the Kenya Rift. For the Vogt-land area a high-precision three-dimensional gravity model was developed. That modelling shows an interaction between geometries of geological structures and geodynamic processes and yields strong indications that a magmatic system at the crust mantle boundary is much more probable than an upwelling mantle as a source of the earthquake swarms. The geodynamic models for the two regions under investigation take into account the regional stress field and thermal stresses as well as creep and plasticity with a porous elastic rheology. The investigations are fo-cussed on the interaction between pore pressure variations, temperature changes, fluid movements, stress accumulation and deformations. It is suspected that these processes play an essential role in the generation of earthquake swarms. An essential result of the modelling is that the existence of the regional stress field alone neither explains the occurrence of the earthquake swarms in the Vogtland area nor in the Magadi area. Temperature changes and periodic pore pressure variations in the earth’s crust are most important for the geodynamic processes, although they are weighed differently in each focal area.