Empirical observations and mechanical implications of fault displacement vectors within a complex fault system in the Taranaki Basin, New Zealand

Fault networks often consist of multiple, simultaneously active fault segments of varying orientations. Subject to a single regional stress direction, it is often assumed that strain on these fault systems must be accommodated by resolving varying degrees of dip-, oblique-, and strike-slip displacement on individual faults as a function of their orientation; however, empirical observations well-suited to testing this assumption are limited. We present observations from a 3D seismic reflection dataset off the west coast of the north island of New Zealand. In these data, a series of slope channels associated with a prograding shelf margin depositional system have been later offset by a system of normal faults with varying local orientation, providing piercing point constraints on fault displacement vectors. Detailed mapping of stratigraphic horizons and several dozen offset individual slope channels provides offset constraints across faults of various orientations relative to the regional stress field; we observe that the offsets are nearly pure dip-slip, regardless of the local orientation of the fault. We have constructed a detailed 3D fault and horizon framework model that permit utilization of structural surface restoration methods. By comparing surface restorations without piercing point constraints with those that are forced to comply with the observed fault displacement vectors, we are able to infer that the observed fault displacements require significant off-fault deformation in specific regions. Further comparison with analog and mechanical models allow us to explore the mechanical implications of the geological observations. We conclude by discussing the potential implications of these results for common assumptions in structural interpretation and fault mechanics.