How tectonic geomorphology can be used to find a hidden fault zone: a case study of the Te Tatua O Wairere fault zone, New Zealand

A series of complex fault systems have recently been discovered within the Hamilton Basin, New Zealand. Though the first zone was unexpectedly exposed during construction excavations, other zones have been discovered due to their influences on the local geomorphology. In this paper we present evidence for tectonic geomorphic features that were first observed via high-resolution LiDAR images of the Hamilton Basin, then confirmed by geologic and geomorphic mapping. Exposed fault traces show evidence of significant fault splaying within the soft sediments and tephra deposits contained within the basin, causing the fault zones to cover a wide area and create a geomorphic system of complex linear ridges. At Stubbs Road, tectonic geomorphological features including rectangular drainages, stream knickpoints, aggradational/degradational zones, linearly aligned ridges and drainage systems, and abandoned river channels and outlets were observed in the LiDAR and bathymetric data of the Waikato River and surrounding area. Field investigations revealed offset geological outcrops concurring with geomorphic features found in both the LiDAR and bathymetric data. At this site the Waikato River begins bending 82° from N to NE. Electrical resistivity data reveal a discontinuity in the geological material and seismic reflection indicates a fault crossing the river. These features are evidence for the Te Tatua o Wairere Fault Zone and are being presented to exemplify the use of tectonic geomorphology in aiding in the discovery of tectonic structures that are either concealed due to poor exposure within young, unconsolidated material, or that contain planes that have yet to daylight.