The fact that the little West Coast town of Franz Josef is built on the Alpine Fault has been known for years. Despite this, people there have managed to put it in the back of their minds and have continued to develop there almost as though the fault did not exist.
OPINION: Last week that changed with the public notification by the Westland District Council of its intention to alter its district plan to prevent development where the risk is greatest. Critics of the move complain that it will ruin their businesses and sentence the town to a slow decline. That is very likely true but the council's move is merely belated recognition of reality and failure to act would be dangerously complacent.
The district council's plan is recognition of the high risk to the region created by the Alpine Fault. The fault has been marked by large-scale ruptures on a remarkably regular pattern, on average once every 330 years. The last big quake on the fault occurred in 1717 which enables geologists to calculate that there is a roughly 30 per cent chance there will be another major event within the next 50 years. It is a risk that cannot be ignored.
The district council's plan will create two new zones - the Franz Josef/Waiau fault rupture avoidance zone and the general fault rupture avoidance zone. The Franz Josef zone creates a 135-metre-wide swathe through the town where landowners will be able to carry on their existing activities but will be prevented from erecting new buildings, extending their properties or developing new subdivisions.
It is necessary because Franz Josef is right on the fault line. The town's service station, a motel and other buildings sit directly astride the gap. Although geologists, local politicians, residents and others have been aware of the dangers, it has not been written into local maps or planning policies, with the result that building across the fault has continued even during the past 15 years. The police station, put up only a few years ago, is right on the lip of it.
According to two recent GNS Science reports, a rupture of the fault could be expected to move the land up to 9m horizontally and 2m vertically. As Christchurch residents are well aware, movements of that magnitude would be catastrophic.
New Zealand has always been known as a seismically active landscape but the absence until September 4, 2010, of any large urban tremors since the Napier earthquake in 1931 had enabled it to be treated at the level of mildly flippant remarks about the "shaky isles" and a less than rigorous approach to making buildings that were earthquake resistant.
Complacency had crept in and proved hard to eradicate. Even after September 4, many objected when the Christchurch City Council tightened the building code to take account of the sharply exposed reality that this is an earthquake-prone country.
Franz Josef is not the only area in which risks that have for too long been ignored are now being properly recognised. Wellington, too, sits on a fault line and new assessments of the hazards created by old buildings are causing dismay to some property owners. The reassessments are unavoidable, however. As Canterbury's experience has shown, the risk does not disappear by being ignored.