Detection of active crustal structures in the Upper Rhine Graben using local earthquake tomography, gravimetry and reflection seismics

This paper presents a case study, in which three different geophysical methods are combined to link the large-scale seismically active deformation of the basement to the deformation of the sedimentary cover in the seismically active southern end of the Upper Rhine Graben. Local earthquake tomography shows velocity contrasts related to large-scale faulting in the basement. The observed faults coincide with the discontinuities in the Bouguer anomaly map for the upper part of the basement and the sedimentary cover. Reflection seismic profiles show distinct faulting in the sedimentary cover at the position of the structures observed in the local earthquake tomography and the Bouguer anomaly maps. They provide the link of the seismogenic structures at depth and the near-surface geology. It is shown that the structure of the southern end of the Rhine Graben is dominated by faults that have a NNE-SSW trend, slightly oblique to the graben axis. The presence of earthquake hypocenters nearby the faults indicate their present-day activity.