The 2014–2015 earthquake series in the northern Upper Rhine Graben, Central Europe

• Published in: Journal of seismology 2017, Vol.21 (1), p.83-98
• Main Authors: Homuth, B., Rümpker, G.
• Format: Article
• Language: English
• Subjects: Aftershocks; Alignment; Clusters; Dating; Earth and Environmental Science; Earth Sciences; Earthquakes; Geophysics/Geodesy; Geotechnical Engineering & Applied Earth Sciences; Graben; Historical account; Hydrogeology; Measurement; Movements; Original Article; Seismic activity; Seismic phenomena; Seismology; Sequences; Series (mathematics); Structural Geology
• ISSN: 1383-4649; 1573-157X
• DOI: 10.1007/s10950-016-9584-6

Since March 2014, an unusually large amount of earthquakes occur southeast of the city of Darmstadt in the northern Upper Rhine Graben. During the period, until April 2015, we have recorded 356 earthquakes with magnitudes ranging from M L  = −0.6 to 4.2. We identified two source clusters separated laterally by about 5 km. The hypocentres within these clusters are aligned vertically extending over a depth range from 1 to 8 km with a lateral extent of about 1 to 2 km. Focal mechanisms show left-lateral strike-slip movements; b values are changing with time between b  = 0.6 and b  = 0.9. This is the first time in almost 150 years that such high earthquake rates have been observed in the region. Historical accounts dating back to the nineteenth century report of over 2000 felt earthquakes over a time span from 1869 to 1871. From these, maximum intensities of VII have been estimated. Other seismic activities in the region were reported in the 1970s. The observations of the 2014–2015 earthquake series do not completely match a typical main shock–aftershock sequence or a typical earthquake swarm. Especially the activity at the beginning of the earthquake series may be considered as a mixture of a main shock–aftershock sequence and a short-lasting swarm event. Whether or not the time gap between the current seismic activity, which actually takes place at the same locations as parts of the seismic swarm in 1869–1871, and the seismic activity in the nineteenth century or the seismic activity in the 1970s can be interpreted as a seismic cycle remains unclear.