Mike Coward¹

(1) Ries-Coward Associates Limited, Reading, United Kingdom

ABSTRACT: 3D Fault Restoration and Kinematic Analysis, Viking Graben, North Sea

3D restoration and forward modelling has been used for several fields in the Viking Graben to determine the fault shape, both at depth and from the eroded section. The software 3D Move has been used to model hangingwall geometries of Jurassic and base Cretaceous horizons, mapped from 3D seismic data. The faults are not planar. In some areas, e.g. Statfjord, hangingwall geometries indicate that the faults originally shallowed upwards from Triassic rocks into the Jurassic section, aiding degradation of the footwall. Where the footwall comprises largely crystalline basement, it has often slumped or been eroded, so that during the latest Jurassic-early Cretaceous inversion, the hangingwall moved upwards from a fault scarp onto a shallow erosional terrace, producing a hangingwall anticline. The shape of the footwall terrace can be defined in 3D allowing sediment input to be mapped. Similarly the shape of the basin floor can be modelled, showing the evolution of local depocentres and channelways with time.

In the third dimension the faults are corrugated on all scales. The cusps point towards the original displacement direction. Changes in fault kinematics cause the hangingwall rocks to move across these cusps, producing irregular hangingwall fold structures. The 3D-4D analyses indicate that fault kinematics changed with time, with localized block rotation and inversion. Variations in 3D-4D kinematics will be related to basin development in the Viking Graben and its relationship to regional Jurassic-Cretaceous structures in the North Atlantic.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado