Polygonal Fault System in the Great South Basin, New Zealand

Abstract

Polygonal faults are a network of layer-bound normal faults arranged in polygonal geometry. A polygonal fault system was identified from 3D seismic data in the Great South Basin, New Zealand. The lithology of the strata bounding the polygonal fault system is shale and siltstone which is typical for most polygonal fault systems identified globally.

This study applies an advanced fault skeletonization method to 3D seismic data of the Great South Basin. Seismic attributes such as coherence are used to delineate faults. A new fault advancement and skeletonization workflow is applied to sharpen structural and stratigraphic discontinuities and smear the incoherent noise on coherence. Fault images are co-render enhanced with the fault dip magnitude and dip azimuth to map the geometry of the polygonal fault system.

The tectonic control on the formation of the faults is studied by comparing the orientation of the faults to the NE-SW trending of the major structures in this study area. In addition, a 3D model of the polygonal faults is produced. The maximum displacement on polygonal faults and the displacement on a single fault are measured and analyzed which is showing that the displacement diminishes laterally towards the fault ends and the nucleation of the fault is near the base tip of the fault. Previous studies have attributed the formation of the polygonal faults to four main mechanisms: density inversion, syneresis, gravitational loading and diagenetically induced shear failure. In this study, the density inversion model is favored for the genetic mechanism for polygonal fault system because of folding of the hanging wall layer and the nucleation point near the base tip of the fault.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018