Seismicity and structural complexity of the Dinkelberg block, southern Rhine Graben

Abstract

A detailed analysis of the Dinkelberg seismicity is presented. The seismic activity of the central Dinkelberg block starts at about 10 km and increases with depth to a maximum between 18 and 20 km. Joint hypocentre determinations clearly prove that no hypocentres are located within the lower crust which starts at a depth of about 20 km according to results from recent reflection seismic surveys. The seismic activity is concentrated just above the top of the lower crust. Fault‐plane solutions of the Dinkelberg events show that the strike of the nodal planes is parallel to the directions of near‐surface tectonic features. A correlation also exists between the main fault directions and the spatial distribution of the hypocentres in the Pratteln earthquake cluster at the southern end of the Dinkelberg block. The occurrence of negative P residuals from local earthquakes for special propagation directions of waves crossing the Dinkelberg block is modelled by a westward‐dipping layer. This postulated upper crustal structure together with observations of preferred S‐wave polarizations are discussed in regard to recent tectonic models and geological findings. Copyright © 1994, Wiley Blackwell. All rights reserved