Abstract: 3-D Oblique-Slip Fault Modelling: A numerical Solution

M. D. Renato de Matos

Three dimensional hanging wall roll-over geometry has been modelled using a 3-D numerical modelling that incorporates inclined simple shear to dip-slip and oblique-slip extensional faults. The model can handle slip of any direction (y = angle between the extension direction and the orthogonal to the rift axis) and magnitude (u = displacement vector), simulating orthogonal, oblique and even strike-slip movements on listric border faults. Fault planes are modelled as continuously curved listric surfates varying laterally in space. Similar to 2-D modelling, the process may be viewed as pulling away the hanging wall from the footwall (at any direction) and then allowing the hanging wall to collapse (subside) to fill the potential void (or uplift if some local compressional bend occurred). One of the major assumptions of 2D cross section restoration and balancing techniques is that the direction of the section has to be parallel to the direction of extension which is not always known. This technique helps to evaluate the importance of oblique extension on basin geometry, through a numerical solution to a 3D geometrical problem, assessing oblique extension and inclined simple shear during hangingwall collapse. Some key features of synthetic oblique-slip faults systems are discussed as an analogue to the seismic signature of natural oblique-slip fault systems. Dramatic changes in rollover geometry are observed in oblique-slip simulations, especially where significant lateral variations in fault geometry occur, leading to synthetic examples of 2-D oblique-slip cross sections, which are compared with 2-D seismic lines from NE Brazil, where oblique-slip faults are interpreted. Key 3-D synthetic models of transfer faults, extensional folds, local extensional and compressional "bend" structures are achieved by simulating lateral variations on the fault trace at the surface, near surface dip, as well as flat-ramp simulations on fault geometry of border rift faults, where oblique-slip fault displacement has occurred.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994