A high-amplitude post-critical reflection indicates the existence of a discrete reflecting interface dipping gently westwards between 40 and 50 km depth in the lithospheric mantle. A well resolved P-wave velocity structure for the lithosphere above the mantle reflectors is derived by inverting the seismic traveltimes to optimize the fit of the model to the data, and by generating synthetic seismograms from the model to match the relative amplitudes of the observed seismic phases. We report the results from an integrated seismic survey in which a series of explosive shots fired at sea were recorded by ocean bottom seismographs, land stations and a streamer towed by a second ship in an expanding spread configuration.
Wide-angle seismic reflection and refraction data are used here to constrain the P-wave velocity structure of the lithosphere in this region and to investigate the physical properties and geometry of these reflective structures. Both reflectors have a strong impedance contrast and are laterally coherent over tens of kilometres. The Flannan reflector dips eastwards from the Moho to a depth of 80 km at an angle of 0°, whilst the W-reflector is subhorizontal, lying 10-20 km beneath the Moho and terminating westwards against the Flannan.
The W-reflector and the Flannan reflector are two enigmatic planar structures in the lithospheric mantle north of Scotland, mapped in three dimensions using deep reflection profiling.
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