3D FLEXURE AND INTRAPLATE COMPRESSION IN THE NORTH-SEA BASIN

We apply a recently developed 3D flexure model incorporating lateral v ariations in flexural rigidity (EET) and necking depth (z(n)) to study the 3D effects of intraplate stresses on Quaternary accelerated subsi dence and uplift in the North Sea Basin and adjacent areas. In the mod el approach lateral variations and magnitude of predicted Quaternary v ertical motions are largely dependent on the pre-existing Late Tertiar y flexural state of the area and the relative change in magnitude and orientation of intraplate stresses in the Quaternary. The Late Tertiar y deflections are reconstructed by incorporating lithospheric stretchi ng values calculated from the Mesozoic subsidence record, and by adopt ing admissible variations in necking depth (z(n)) and flexural rigidit y (EET) from earlier work. The 3D model results for the North Sea and adjacent areas indicate that an increase of compressive intraplate for ces with a magnitude of about 2.25 x 10(12) N/m can predict accelerate d subsidence values up to 700 m, largely in agreement with observed pa tterns of Quaternary isopach values corrected for effects of shallowin g waterdepth. The magnitude of the intraplate forces is 2 to 3 times l ower 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 rel ative increase in compressive forces is in agreement with observed com pressive stresses and the magnitude corresponds to characteristic valu es for plate boundary forces. The adopted values for z(n) and EET do n ot show a clear relation with the preceding basin history.