Maps showing depth to the Moho, the 6 km/s and 7 km/s isovelocity surfaces and the thickness of the crust with a velocity greater than 7.0 km/s for the UK and surrounding continental crust have been generated from a compilation of wide-angle/refraction data. The data show that the crust beneath northwestern Scotland is thinner and of higher velocity than that beneath southern Britain. The lower crust beneath the East Irish Sea and parts of the southern North Sea is formed from thick layers of high velocity rock. The lateral extent of these layers cross-cuts the downward projection of major structures mapped at the surface. This suggests that the major structures do not bound regions of lower crust with contrasting properties at depth. Instead these structures may be overprinted by modification of the lower crust, for example, by magmatic underplating, which is not observed directly at the surface. Mapped variations in crustal thickness do not mirror the variations in surface topography, which appears to contradict the view that the crust is in Airy isostatic equilibrium.

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