The decision by the Westland District Council to scrap a Plan Change to its District Plan in Franz Josef has been welcomed by businesses. However it has raised alarm among those familiar with the geological hazards under the town.
A Council has a duty of care to ratepayers, businesses and tourists alike. As such, when it makes a decision the consequences of that decision are legally binding on the Council in question. If something happens causing physical harm to people or damage to property that can ben traced back to the decision, then the Council opens itself to potentially massive litigation from businesses or people who have suffered.
The Alpine Fault is the tectonic plate boundary between the Australian and Pacific tectonic plates. It is 650 kilometres long and divided into four sections. Every 300-350 years this faultline ruptures in earthquakes that measure between magnitude 7.8 and 8.2. Each earthquake results in a movement between 8-10 metres long with up to 2-3 metres vertical displacement. Shaking intensity on the rupturing fault will be up to MMX and may last 2-4 minutes.The high intensity shaking combined with possibly quite high Peak Ground Accelerations mean the buildings currently straddling the Fault would be heavily damaged. An Alpine Fault earthquake is considered a certainty in the next 100 years as the last rupture was in or about 1717.
The Alpine Fault runs SW-NE through the township of Franz Josef in Westland District Council. Westland District Council introduced Plan Change 7 to their District Plan. This acknowledged the presence of the Alpine Fault in Franz Josef. It envisaged a zone through the town where people would relocate their businesses from to mitigate the risk posed by an Alpine Fault earthquake.
However the local business community have refused to accept the fault line poses a level of danger to their clients, to themselves whose probability of happening increases 1-2% each year. I find it frankly incredible that an elected council could succumb to a few business owners on something that has taken considerably more urgency following the Kaikoura earthquake. This quake was at the very lower end of what an Alpine Fault earthquake is expected to be in magnitude, but the high intensity shaking lasted a full 100-120 seconds and was MMV in Christchurch over 100km from the epicentre. Some of the faults that ruptured in this complex earthquake had 2-3 metres vertical displacement and over 6 metres horizontal displacement.