3D Flexure and intraplate compression in the North Sea Basin

We apply a recently developed 3D flexure model incorporating lateral variations in flexural rigidity (EET) and necking depth (zn) to study the 3D effects of intraplate stresses on Quaternary accelerated subsidence and uplift in the North Sea Basin and adjacent areas. In the model approach lateral variations and magnitude of predicted Quaternary vertical motions are largely dependent on the pre-existing Late Tertiary flexural state of the area and the relative change in magnitude and orientation of intraplate stresses in the Quaternary. The Late Tertiary deflections are reconstructed by incorporating lithospheric stretching values calculated from the Mesozoic subsidence record, and by adopting admissible variations in necking depth (z,) and flexural rigidity (EET) from earlier work. The 3D model results for the North Sea and adjacent areas indicate that an increase of compressive intraplate forces with a magnitude of about 2.25 × 10 ~2 N/m can predict accelerated subsidence values up to 700 m, largely in agreement with observed patterns of Quaternary isopach values corrected for effects of shallowing waterdepth. The magnitude of the intraplate forces is 2 to 3 times lower than predicted by earlier 2D studies. It is believed that the 2D model results actually overestimate required stress levels, since they do not take into account the effect of out-of-plane stresses.The relative increase in compressive forces is in agreement with observed compressive stresses and the magnitude corresponds to characteristic values for plate boundary forces. The adopted values for Zn and EET do not show a clear relation with the preceding basin history.