CRUSTAL REFLECTIVITY PATTERN AND ITS RELATION TO GEOLOGICAL PROVINCES1

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Abstract
The statistical treatment of deep seismic reflections from several different geological units has resulted in different reflectivity histograms. Reflectivity in old and cold shields differs significantly from that in younger, warmer areas. In the shields reflectivity is generally poor and concentrated in the upper crust whilst Caledonian and Variscan areas show strong reflecting lamellae in their lower crust. Also the length of the reflecting elements varies with age and heat flow. The lower crust in young areas is a zone of a strong viscosity minimum as derived from model studies with a temperature dependent rheology. The subhorizontal reflecting lamellae in the lower crust are considered to have been created in a large‐scale high‐temperature, low‐viscosity ordering process whose remnants are still preserved today. Local‐scale differences of reflectivity histograms define certain subprovinces which can be distinguished by their specific patterns.