The Greendale Fault lies in the Canterbury Plains of New Zealand's South Island, west of Christchurch, and is a right-lateral strike-slip fault about 30 kilometres long. Before 2010 it was completely unknown, buried beneath the flat farmland with no surface expression, making its discovery a landmark in earthquake science.
The fault ruptured in the September 2010 Darfield earthquake (magnitude ~7.1), tearing a fresh surface break across the plains with horizontal offsets of up to several metres visible in fences, roads and hedgerows. It sits within a diffuse zone of deformation far from the main plate boundary, where the Australian and Pacific plates interact across a broad region.
Although the Darfield quake itself caused no deaths, it triggered a prolonged aftershock sequence, including the deadly February 2011 Christchurch earthquake on a related nearby fault that killed 185 people. The Greendale Fault became a textbook example of the hazard posed by previously unrecognised faults.