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In order to investigate an often-quoted coincidence of an intracrustal velocity jump (the Conrad discontinuity) and lower crustal reflections (found in tectonothermally young areas), 54 reflection seismic profiles have been analysed and combined with 50 refraction seismic profiles adjacent to the reflection lines.

Variable parameters of the continental crust are: crustal age, heat flow, reflectivity, thickness and velocity. While heat flow and reflectivity decrease, crustal thickness increases with age. For stable crustal regions we present a correlation between crustal thickness and mean crustal velocity. The evaluation is based on more than 270 data points. It is shown that mean crustal velocity is higher in thicker crusts. An attempt is made to relate this observation to crustal growth by accretion from below.