How communities will prepare for Alpine Fault line earthquake. Made with Funding from NZ On Air. Video / North and South
A series of news stories this week has again shed light on the risk posed by the Alpine Fault.
Experts are growing increasingly concerned that a devastating earthquake could be imminent, causing widespread chaos across the South Island and costing the economy billions of dollars.
"Based on the evidence, the Alpine Fault is towards the end of its seismic cycle," says Orchiston, who works closely with AF8, an organisation dedicated to ensuring the community along the Alpine Fault is prepared for an earthquake.
"Over the last 8000 years and longer, there's strong evidence of regular earthquakes happening over time with a sort of mean return period of around 250 to 300 years.
Evidence suggests that the last earthquake along the Alpine Fault happened in 1717, meaning that we are currently on the cusp of the next big one.
Research over the last year has shown that there's an 82 per cent probability that the next earthquake will be bigger than magnitude eight.
"The magnitude scale measures the amount of seismic energy released by an earthquake. It's what they call a logarithmic scale, which means that every .2 increment on that scale doubles the amount of seismic energy that's being released. And so, if you compare a magnitude six earthquake with a magnitude eight, that's almost a thousand times more seismic energy."
To put this into context, the earthquake that damaged Christchurch was a magnitude 6.3 (although that was in a concentrated and densely populated region).
"We're looking at around 750 to a thousand times more energy being released by this future Alpine Fault earthquake," says Orchiston.
"Of course, the Alpine Fault is very so long, and the impact and ground motion associated with this earthquake is going to affect a large area of the Southern Alps region. It will be felt widely across the South Island."
Orchiston explains that the impact of an Alpine Fault seismic event will differ quite markedly from what happened in Christchurch.
"We developed a scenario of how this earthquake might look in the future. Of course, scenarios are never exactly right. But the scenario from the AF8 programme suggests that the earthquake would start in the Milford Sound and push out the seismic energy up towards the northeast. And, of course, because it is a big, long fault, it takes time for that energy to move right across the South Island, so the footprint of a magnitude 8.2 earthquake will be much larger than the Christchurch earthquake."
Orchiston says this will lead to enormous ground shaking, which will trigger landslides and many other secondary consequences.
"That's going to disrupt the flow of people along state highways and across bridges. It will be significantly disruptive. We can expect a long period of recovery following this earthquake."
The expert says that steps are already being taken to prepare the community in this region for the likely impact of a major event.
Civil Defence and emergency management groups around the South Island are working with people in the community to ensure they are sufficiently prepared for an event.
"That starts with talking to your neighbours and making a family plan as to what you would do if you were separated from your kids, husband or grandparents," says Orchiston.
Asked whether politicians were doing enough to prepare for an event, Orchiston said the nation is doing the best it can with the available resources.
"I think our national emergency management agency is working really hard to build its capability and its capacity to support the nation in terms of dealing with these major events," she says.
"I think we've come a long way in the last two decades. Since I started doing my work in the space, we've come a huge way in terms of how we coordinate and work together to respond to these events."
The hope now is that the lessons learned from previous events will be enough to keep us safe in the event of the next big shake.
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