Lateral variations in crystal reflectivity beneath the Paris Basin

Abstract

The application of a new method of automatic extraction of reflections from a stacked Seismic section to the ECORS North of France profile highlights the lateral variations in crustal reflectivity observed beneath the Paris Basin. Five characteristic zones can be distinguished along the 228 km long profile. A complex pattern of spatially interfering dipping events occurs in the lower crust of the transition region between the zones of reflective and transparent lower crust. Modelling reveals that these events are diffractions from discontinuous subhorizontal scatterers concentrated near 8 s. Hyperbolic events at Moho level (12 s) may indicate that the 1 s increase in travel time to the Moho observed across the transition region is accommodated by a discontinuous step. There is no spatial correlation between the lateral variations in reflectivity observed within the upper and the lower crust. Neither is there evidence that any structure within the upper crust continues into the lower crust. We interpret these two observations as an indication of a younger origin of the lower crustal reflectivity and discuss the possibility that the early extensional phase of evolution of the Paris Basin has contributed to the lateral variations of reflectivity observed within the lower crust.