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S U M M A R YA detailed analysis of the Dinkelberg seismicity is presented. T h e seismic activity of the central Dinkelberg block starts a t about 10 km and increases with depth t o a maximum between 18 and 20 km. Joint hypocentre determinations clearly prove that no hypocentres are located within the lower crust which starts a t a depth of about 20 k m according t o 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 a n d the spatial distribution of the hypocentres in the Pratteln earthquake cluster at the southern end of the Dinkelberg block. T h e 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 t o recent tectonic models and geological findings.

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