The crustal velocity and density structure of Northwest Europe : a 3D model and its implications for isostasy

A new seismic P-wave velocity model has been constructed for a region of northwest Europe encompassing Britain, Ireland and the surrounding marine sedimentary basins. This model has considerably higher resolution than previously published velocity models for the region and is unique in being quantitatively constrained. The velocity model provides a tool for future work in seismology, allowing crustal correction for teleseismic arrivals recorded in Britain and Ireland, refined local earthquake location and provides a starting model for local and regional seismic tomography. The velocity model has been developed in conjunction with a crustal density model. The new models indicate that: the mean crustal velocity and density are related to the near-surface geology; the near-surface velocity is well correlated with the near-surface geology; there may be a regional trend from high velocity crust near the northwest continental margin to lower velocity crust under continental Europe; there may be a weak trend of increasing density with increasing crustal thickness; and that the crustal structure beneath the sedimentary basin varies from basin to basin. In addition to the geological interpretation, the density model has been used to investigate isostasy in the region using a newly developed method for estimating the elastic thickness of the lithosphere. This approach uses the relationship between the predicted height of topography for local isostatic equilibrium and the true topography to estimate the degree of compensation, which is in turn related to the elastic thickness. However, the results of this investigation are inconsistent across the different wavelengths tested and so the elastic thickness is resolved with less constraint than the range in published values for the region.