3-D STRUCTURAL ARCHITECTURE AND BLOCK ROTATIONS ALONG THE NORDLAND RIDGE, OFFSHORE MID-NORWAY

The Nordland Ridge is located in the Norwegian Sea on the western edge of the Trøndelag Platform and on the eastern flanks of the Vøring Basin. The primary episode of normal faulting in the area occurred in the middle Jurassic to early Cretaceous time, but some additional reactivation of some faults formed after the base Cretaceous unconformity. The area is marked by fault block rotations within a major graben. Regionally, the beds dip gently to the southeast toward the Helgeland Basin on the western edge of the Trøndelag Platform because of the structural uplift along the Nordland Ridge. The beds within the main graben appear to flatten out, change to a slightly northwesterly dip and switch back to a southeasterly dip after the graben terminates and overlaps with a second graben to the northeast. The possible mechanisms of block rotation within the graben were investigated using seismic interpretation, time to depth conversion, the construction of serial structural sections, structural restoration, and three-dimensional structural modeling. The structural architecture is defined by terminating faults with varying displacements along divergent, convergent, synthetic, collinear and collateral transfer zones, which result in changes in both the dip magnitude and direction along trend. Additional structural features include the large displacements of the Revfallet Fault Complex (RFC), large interacting grabens on the Nordland Ridge, drape folds at the tips of terminating faults, and strike ramps. The identification of these features and analysis of the variations in fault displacement provide an improved structural model for the area.