Technical Committee Geophysics
High Resolution Seismic Survey of the Seismicity near Rotenburg and Comparison of Survey Methods
Within the DGMK project 761, the Rotenburg region has been monitored for two years by a network of highly sensitive seismic arrays. Earthquakes of magnitude ML 0.2 and higher are reliably detected, but their number is far lower than the magnitude-frequency relation based on the 2004 ML 4.5 Rotenburg and 2012 ML 2.9 Visselhövede earthquake would suggest. The sensitivity of the network and validity of the completeness threshold could be verified by recording the Walsrode cluster 10-11/2014 despite the absence of quakes at Rotenburg.
This resulted in a first indication of earthquakes beyond the 5 km reservoir depth. By reprocessing additional BGR and WEG records, three further earthquakes beyond 5 km depth in the Rotenburg/Verden area could be identified in the period of the last 1.5 years. The high measurement effort by many stations allows an improved determination of the focal depth, which could be determined to 25-30 km. These deep earthquakes occur neither spatially nor temporally concentrated, while a clear clustering can be observed for the shallow earthquakes at 5 km depth.