Moho beneath the North Sea compared on normal incidence and wide-angle seismic records

Abstract

The Mohorovicic discontinuity (the Moho) is properly defined as the step in the velocity of horizontally travelling P waves from about 7 km s⁻¹ to about 8.1 km s⁻¹. Its detailed structure varies from place to place, but it is universally interpreted as the transition from crust to mantle. Normal incidence reflections originating at about Moho depth have been reported sporadi cally during the past 20 yr. During the past 10 yr continuous seismic reflection profiles have been obtained to this depth both on the continents and in the deep sea and, at the same time, striking improvements have been made in the methods available for interpretation of ‘refraction’ experiments. Here we report a comparison between the Moho determined by a long range refraction experiment across the North Sea and the results of a short normal incidence reflection profile shot along the same line (Fig. 1). We believe this to be the first time that such a direct comparison has been made.