New Zealander’s have often been warned that their capital city Wellington, snuggly tucked at the bottom of the North Island, would likely be the place most in line to be thumped by a major earthquake - ‘The Big One.’
OUR SEISMICALLY VULNERABLE CAPITAL CITY
Those of us who grew up in the South Island’s east coast-hugging city of Christchurch, at the foot of the Canterbury plains, may recall the odd tiny seismic shudder that came our way over the decades. It may have rattled a tea cup in its saucer or sent the hanging ceiling lounge light into a little jig. But not much more. Mum may have glanced up from her knitting for a brief moment. No panic ensued.
So arguably some of the shock Cantabrians felt following the massive 7.1 magnitude September 4th 2010 event (that set in motion a sequence of sizable aftershocks for months to come) was caused not just from the earthquakes themselves, but that it was Christchurch devastated - not Wellington!
Our windy capital was always considered much more of an earthquake risk than the garden city for key reasons. The mighty Australian and Pacific tectonic plates, lock strongly together beneath Wellington. An abrupt rupture from the monumental accumulated strain is estimated to occur every 800 - 900 years, though evidence of the last event is tricky to pinpoint.
To boot, atop this plate boundary, four major active earthquake faults - the Ohariu, Shepherd’s Gully, Wellington and the Wairarapa – snake through the region and peel offshore. Of these major faults, the Wellington Fault holds the dubious honour of ‘biggest local seismic hazard for the city’ with GNS research suggesting it last ruptured between 170 and 370 years ago, with a 10 per cent chance it could rupture again within the next 100 years.
Needless to say, Wellington disaster planners are preparing the city for ‘when’ – rather than ‘if’ - a major earthquake could occur. The threat of a magnitude 7.5 or greater rupture along the Wellington Fault raises some major concerns. A fracture of this size has the potential to split the region into seven ‘islands,’ chunks of land separated by road damage that could cut off northern and western suburbs from the city’s central, eastern and southern suburbs with disruptions to water supply, power and access to medical care.
Major disruptions to flights in and out of the capital could occur following a major quake. Wellington airport is built on land understood to have risen out of the harbour in the Hao Whenua earthquake of the mid-1400s and there is a risk the runway length could drop away where it stretches onto reclaimed land. If a large shift occurred along the Wellington Fault it could also raise the sea-floor, potentially limiting the ability of large ships to enter and negotiate the harbour.
Then there would be the eye-watering cost of rebuilding and repairing our governing city to consider. Estimates put the total cost of the Canterbury quakes, including the disruption to business and rebuilding the city to higher building codes at the $30 billion mark. Meanwhile, Wellington is still paying the price for the 7.8 magnitude, 14 November 2016 Kaikoura shake. The ripple effect of which has been estimated to be costing the capital over $1 million a week in repairs.
It’s becoming more and more evident that it is not just one isolated region of New Zealand that is more seismically at risk than another. We are a young land geographically, exposed from top to toe to the violence and destruction of volcanoes earthquakes and tsunamis. Living some distance from the main divide alpine fault line that snakes the length of the South Island, by no means eliminated Christchurch from a walloping earthquake. And in fact new networks of previously undiscovered faults were unearthed beneath our Canterbury plains.
The Kaikoura earthquake, caused damage and in some cases closure to multiple multi-level buildings in Wellington - some 577.5 km to the North of the epicentre. It’s a timely wake up call and raises some big questions around the extent of damage and destruction should the predicted ‘big one’ rattle right under Wellington city high-rises.
An aptly named project, “It’s Our Fault” led by GNS Science and funded by government agencies aims to better prepare for, understand and define Wellington’s vulnerability to earthquake risk. The focus of the seven year, $3.5 million research project will be on how neighbouring seismic faults could effect each other if one or more were to snap. And to provide more information on the expected size, frequency and likelihood of large earthquakes in the region, as well as the physical, social and economic impacts to the city.
Wellington has been tightening building codes and strengthening key infrastructure to address it’s known earthquake risk with increased impetus since the 1980’s. Buildings that did not meet modern earthquake-resistant codes have been demolished, strengthened or flagged for attention. In light of recent events building owners have been given the more urgent time-frame of five-fifteen years to get their building earthquake code ducks in a row.
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