Scientists reveal unknown fault behind quake
The killer Christchurch earthquake, which claimed 185 lives 10 years ago tomorrow, came from the violent rupturing of a previously unknown fault line pointing straight at the city, scientists have revealed.
The fault line underneath the Port Hills which overlooks Christchurch was aiming directly at the centre.
When it ruptured upwards to the northwest at 12.51pm on February 22, 2011, it stacked up energy as it went, releasing it towards the CBD, according to GNS Science researchers who have studied the worst natural disaster in modern New Zealand history over the past decade.
GNS Science seismologist Anna Kaiser said the extreme release of energy was “like a snowplough piling up snow as it moves along”.
Tomorrow marks the 10th anniversary of the magnitude-6.3 tremor, which caused the CTV building and PGC building to collapse, resulting in mass loss of life, as well as damaging thousands of other buildings, causing liquefaction, landsliding, rockfall, and cliff collapse.
Coming just months after the magnitude-7.1 Darfield earthquake of September 4, 2010, which caused widespread damage but no loss of life, it became known as the 2010 and 2011 Canterbury earthquake sequence, and resulted in huge changes around earthquake research in New Zealand.
The following quakes and thousands of aftershocks changed views about vulnerabilities to earthquakes in low seismicity regions.
And for many New Zealanders, Kaiser said it reinforced the fact that Kiwis live in a country where there are many unknown active faults.
She said several factors combined to produce extreme ground-shaking in the February 22 earthquake.
“Most important were the proximity to Christchurch, the amount of energy released, and the way it was directed towards the central city. The thick soils below Christchurch also played a role in amplifying and trapping seismic energy.”
The February 22 quake is also notable for its long — and continuing — aftershock sequence, mainly due to the strong and dense crust beneath Canterbury.
There have been more than 11,000 aftershocks since the deadly jolt — and aftershocks are still occurring every few days.
GNS Science seismologist Matt Gerstenberger said data collected after the quake provided many fresh insights that changed global scientific thinking about earthquakes.
The new knowledge has fed into a range of mitigation measures.
“The rupture of an unknown fault west of Christchurch that hadn’t ruptured for at least 20,000 years and subsequent quakes in Cook Strait and Kaiko¯ura have sparked major gains in the science of earthquakes and in resilience and preparedness.”