Hundalee Fault, North Canterbury, New Zealand: late Quaternary activity and regional tectonics

ABSTRACT The Hundalee Fault forms part of the southeastern margin of the 2016 Kaikōura Earthquake rupture zone. Its late Quaternary activity and structural character may offer insights to fault interrelationships associated with the 2016 rupture. Mapping of the Hundalee Fault revealed several pre-existing fault scarps. Trenching of a scarp across a fluvial terrace together with radiocarbon dating shows the occurrence of at least two, probably three, surface ruptures since 3.5 ka. The scarp records about 2.5 m of reverse-sense vertical deformation, mostly folding, of which ∼0.6 m occurred in 2016, along with subordinate sinistral slip. Fluvial terrace ages inferred from geomorphological relationships, together with the trenching results, indicate a long-term vertical slip rate of 0.2–0.4 mm/yr since at least 30 ka. Geological data indicate a relatively recently surface emergence of the Hundalee Fault from beneath a fault propagation fold. The 2016 Hundalee Fault rupture is interpreted as a break-out from an extensive blind thrust fault, whose motion triggered predominantly contractional rupture of an array of steeper near-surface faults. The thrust is hypothesised as having provided linkage in the 2016 rupture between the predominantly strike-slip ruptures of The Humps Fault to the southwest and the Kekerengu Fault to the northeast.