Moho-offset beneath northern Scotland

Summary. Independent sets of LISPB data are presented, having as a common feature a local lateral variation in the Moho beneath northern Britain.
The evidence for this step-like feature on the Moho is taken from P and S travel times and from PS reflection times and phase velocities.
Another important observation is that a high-frequency Moho refraction is generated north of the step, whilst the refraction from the step region and south of it contains only low frequencies. This leads to the assumption that a change in the Moho structure exists in the same region as where the step has been deduced from travel-time interpretation. A numerical model is presented which generates a high-frequency refracted wave from an input signal which contains low- and high-frequency spectral energy.
The significance of this offset on the Moho, in particular its relationship to surface tectonics, is critically discussed.