Seismic analysis of polygonal fault systems in the Great South Basin, New Zealand

Abstract

Abstract Polygonal fault systems (PFS) consisting of networks of layer-bound normal faults are analyzed for Eocene strata in the Great South Basin, New Zealand. An advanced fault enhancement and skeletonization method is applied to delineate faults using 3D seismic data from the Great South Basin. The process sharpens structural and stratigraphic discontinuities and smears the incoherent noise on coherence to obtain a skeletonized fault probability volume which can be directly used to extract and map fault geometries. The characteristics of the polygonal faults in cross-section, planform, and 3D space were studied. The faults dip approximately 50°, with displacements on a single fault ranging from tens of meters to a hundred meters. The fault planform patterns are polygonal but also related to the regional horizontal stress anisotropy caused by slope changes of the basal unit. The patterns vary from linear for high slopes, rectangular for moderate slopes and polygonal for low slopes. Two preferred orientations may reflect the superposition of deep Cretaceous trends on the polygonal system in the Eocene strata. A local concentric pattern with outward dipping normal faults is related to passive or active draping above a circular plutonic-volcanic structure. The genetic mechanism of the polygonal fault systems is interpreted to be related to volume loss and shear failure related to Opal A/CT transition within the sediments.