On September 4 a magnitude 7.1 earthquake struck Christchurch, New Zealand's second largest city, shortly after 4.35am. An impressive four metres (13 ft) of sideways movement occured along a previously unknown faultline 30 kilometres west of the city. It was miracle that nobody was killed. Earlier in year an equally powerful earthquake in Hati killed more than 200,000 people. While no lives were lost in Christchurch an estimated NZ$4 billion of damage to homes, businesses and infrastructure has occurred. To date more than 86,000 compensation claims have been lodged with the New Zealand Government's Earthquake Commission, at least 70,000 in Christchurch alone.
A month later the city continues to be rattled by aftershocks. More than 1500 seismic events have been recorded since the main event, some large enough to cause their own damage. As recently as last Monday the city was jolted by magnitude five aftershock. This is the fifth such aftershock registering magnitude five or greater. As a child I experienced a 4.1 magnitude quake which was frightening enough. This particular quake stuck the southern New Zealand city of Dunedin on evening of April 4, 1974. I distinctly recall my bedroom shaking violently as my parents came racing down the hall yelling for us stand under a door frame.
For a nation that straddles two major Pacific Ocean faultlines, earthquakes are considered a fact of life in New Zealand. I recall being taught survival skills at school (climb under your desk indoors or seek shelter in a doorway) and the local phone book had pages of earthquake emergency information. However, speculation about earthquake damage generally focuses on Wellington, the nation's capital. The city is nestled in the shadow of steep hills that literally trace a series of faultlines for several miles. As a result, the Christchurch quake came as a complete surprise for most people.
This week the Christchurch quake struck a very sobering personal footnote. My mother was born in Christchurch and my father's family have equally strong ties to the area. I've visited the city many times, most recently in 2007. On this last visit I stayed with my Auntie Pam and caught up with cousins who live locally. I learnt today that my Aunt's house, in the suburb of Bexley, has been inspected by an insurance assessor and subsequently condemned. While deemed fit to live it, it's consider structurally compromised and will have to be demolished.
Bexley was scene of dramatic soil liquefaction during the quake. This spectacular phenomenon occurs whenever soil loses its natural stiffness when placed under extreme stress. Reclaimed coastal land and drained wetlands are particularly vulnerable to liquefaction as they generally retain a level of residual groundwater. Bexley is built on large tracts of drained swamp. This meant that at the height of the quake residents witnessed 'volcanoes' of silt and sewerage erupting from the ground or bursting through their floor boards.
More than one hundred homes, almost a quarter of the suburb, were rendered immediately uninhabitable as a result of subsidence and silt flows. Other homes, like Pam's, appeared to survive relatively unscathed. She had a few cracks to repair and interior doors needed a layer shaved off their top edge before they'd close. However, the building's entire foundation slab has tilted and thus the house is no longer stable. There is now talk of the entire suburb being demolished and future development banned. Poor Pam has my heart-felt sympathy.
UPDATE: October 13
Another 5.0 magnitude aftershock struck Christchurch overnight.
UPDATE: October 19
Yet another 5.0 magnitude aftershock has been reported in Christchurch today.
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