Fault Plane Solutions for Small Earthquakes in SW Germany: Merzig, 17. Aug. 2007 and Osthofen, 13. Dec. 2007
Wagner, Michael; Ritter, Joachim R.R.
Routinely small earthquakes (local magitude Ml < 4) are only located by the state earthquake surveys and then listed in the bulletins. Further analysis such as fault plane solutions or more detailed analyses of dynamic parameters are not performed due to sparse data and low resources. However, the knowledge on detailed source parameters is very valuable, because these are necessary to understand the stress field in the lithosphere or for seismic hazard assessment. We gathered seismic waveforms from two small earthquakes(Ml~2.5) in SouthwestGermany that were recorded by 6 differentnetworks. A relocation with this dataset gives hypocentral parameters with error bars that are within the routine location errors given by the local earthquake surveys. Additionally we study the feasibility to calculate fault plane solutions with a widely used code called FOCMEC (Snoke, 2003a, b). For the Merzig earthquake (depth h=15 km) we find a thrust-faulting mechanism which we cannot relate to a known fault. The Osthofen earthquake (h=I-4 km) presumably has a steep normal-faulting mechanism which may be related to the extensional regime in the northern part of the Upper Rhine Graben.