Outline of the Central North Sea overpressured zone based on chalk velocities

Due to overpressure below the Upper Miocene in the North Sea, seismic velocities below this level are low relative to depth in the central North Sea. The pronounced increase of chalk velocities with depth makes it possible to use deviations in velocities from a normal velocity-depth trend to outline the areal extent of overpressure in the tentral North Sea.