Faulting style and stress field investigations for swarm earthquakes in NE Baveria/Germany – the transition between Vogtland/NW-Bohemia and the KTB-site
A seismicity and stress field analysis of a region in NE Bavaria reveals a complex picture of seismic dislocation. The magnitudes are generally low, the strongest event recorded had a magnitude of 2.3. In the southern part of the area investigated, earthquakes occur very rarely. During the observation period of approximately four years, only four events, two of them forming a doublet, were recorded. Hypocentral depths in the southern part are considerably great (15 to 17 km) and indicate a mafic lower crust. The seismicity of the Marktredwitz area, located in the western extension of the Eger rift, is dominated by earthquake swarms that are strongly clustered in space and time. The swarms occurred at depths between 10 and 14 km. Precise relative relocations show clear planar arrangements of the hypocentres and enable to identify the orientation of active fault planes. A comparison of the structural and geomorphological settings reveals major similarities in the occurrence of earthquake swarms compared to the situation in the bordering Vogtland/NW-Bohemia swarm area.
Focal mechanisms cover a wide range of faulting styles. Normal fault, strike slip and reverse fault mechanisms as well as movements along sub-horizontal planes were found. The focal mechanisms were used to invert for the stress field. The inversion results reveal an ambiguity for the state of stress in the area of investigation and allow two different interpretations: A clockwise rotation of the stress field from North to South as well as a predominance of two slightly different stress regimes are possibilities.
Keywordsfocal mechanisms seismicity stress field swarm earthquakes Vogtland/NW-Bohemia
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