NEWS FEATURE 24 MAY 1998
THE DAY THE EARTH MOVED IN INANGAHUA
May 24 is the 30th anniversary of the magnitude 7 Inangahua earthquake.
It remains New Zealand's biggest on-land quake in the last three decades.
Many West Coasters remember the quake as the worst experience of their
lives. JOHN CALLAN of the Institute of Geological & Nuclear Sciences
Limited reports.
The Inangahua earthquake struck on a wintry morning 30 years ago -- the
furious and monumental shaking occurred without any foreshocks to warn
that something big was brewing.
Most New Zealanders had not even heard of Inangahua -- a tiny farming,
sawmilling and coal mining community 40km east of Westport on the South
Island's West Coast.
Inangahua dairy farmers Warren and Ruth Inwood remember hanging on to
their bed as it was tossed around the bedroom. Many Coasters have similar
memories as they were jarred violently out of their sleep by the 5.24am
quake.
'' I thought it was the end of the world,'' Mrs Inwood says.
'' The noise was horrendous. It was like nothing I've ever heard. Our
fridge was flipped on its side, a heavy three-seater sofa was thrown across
the lounge, ceilings were ripped open, windows exploded out of their frames,
cupboards were completely emptied, and broken ornaments and crockery littered
the floor.''
The Inwood's property, not far from the earthquake epicentre, took the
full force of the shockwaves.
'' It was like an explosion underneath us. The house was shunted up in
the air and then it shook violently. A lot of houses were knocked clean
off their piles.''
Duke and Ngaio Kingi, also near the epicentre, were thrown from their
collapsing bed just as a heavy wardrobe fell across it. Then roof tiles
rained down on them. People who ran from their beds cut their feet on
broken glass.
Wire fences on the Inwood's farm lay limply on the ground, not because
the wire had snapped but because it had been stretched so much.
When daylight came to Inangahua, it revealed a scene like the aftermath
of a military bombardment.
It was several hours before the outside world became aware of the plight
of the people living in the Inangahua Valley. Road access was cut off
in all directions and there was no electricity to send radio messages.
The first radio news bulletins reported that tremors had been felt throughout
New Zealand. There was initially no mention of the West Coast.
The earthquake left 70 percent of the houses in the township of Inangahua
uninhabitable. There were three deaths and 14 injuries. Two deaths occurred
in one of the many landslides, and the other occurred when a motorist
hit a bridge abutment in the dark. A further three people died when a
rescue helicopter crashed.
The main shock had a focal depth of 15km and there were 800 aftershocks
of magnitude 3.8 or greater in the following six weeks. Twelve of these
had magnitudes of 5 or greater. The main shock was felt from Kaitaia to
Invercargill and was recorded by seismometers overseas.
The earthquake damaged or destroyed 50 bridges and twisted railway track
so badly that about 100km of track had to be relaid. Property damage occurred
as far away as Christchurch and New Plymouth.
Brick chimneys were damaged and destroyed at distances of more than 150km
from the epicentre. Some chimneys in Inangahua, Reefton, Greymouth, Westport,
Murchison, and Granity crashed through roofs narrowly missing people in
their beds.
Brick walls and brick veneers commonly collapsed or were severely cracked.
It took several weeks to restore electricity, water supply, and telephone
and road links to some areas.
The entire population of the Inangahua area -- about 260 -- were ordered
to evacuate. Officials were worried that a large slip that had blocked
the Buller River at Dublin Creek might suddenly give way and cause serious
flooding downstream in Westport.
About 5pm, 12 hours after the quake struck, the Inwoods were among a group
of people who were told by officials to walk out of Inangahua ''towards
Reefton''.
'' There were about 50 of us and three torches. We were following the
railway line and gingerly crossing slips. You'd negotiate a tricky part
and pass the torch back to someone else so they could see where they were
going. We could feel the aftershocks and we could hear the rumble of the
hill sides slipping -- some people found it pretty scary.''
'While some residents walked out, others were taken by helicopter. They
were billeted in Reefton. Police and Civil Defence officials declared
Inangahua a no-go area for one month, although farmers were allowed to
return briefly to tend to stock.
Mrs Inwood says the people of Reefton were ''unbelievably generous'' in
accommodating all the evacuees at short notice. Some families stayed in
Reefton for over a month while services in Inangahua were gradually restored.
'' When we were ordered to evacuate, we only had the clothes we were wearing.
We were not even allowed to go back to get hand luggage -- some people
didn't even have their wallet or cheque book.''
Simon Nathan, a young geologist living in Greymouth at the time of the
earthquake, recalls it was about six hours before scientists established
where the epicentre was.
'' At first it was thought the earthquake was centred in Greymouth. There
was certainly a lot of damage to buildings and broken water pipes."
Later on the morning of the quake, aerial reconnaissance pointed to Inangahua
as the likely epicentre. This was backed up by recordings made by the
national seismograph network.
Dr Nathan says there was chaos as various official groups tried to cope
with the aftermath.
'' Because there hadn't been a big earthquake for at least two decades
no-one was quite sure how to react, and relationships between organisations
were unclear. Emergency response is better organised these days.''
The main objective of the first geologists on site was to assess ground
conditions and surface damage so that services could be restored. Geologists
also wanted to find out why and how the earthquake had occurred as there
were no known surface faults at the epicentre prior to the earthquake.
Geologists also found about 100 instances where farmers and residents
reported abnormal behaviour in domesticated animals in the hours before
the earthquake. They concluded that responses in animals may have been
triggered by an as yet unknown phenomenon associated with elastic ground
deformation prior to earthquakes.
Dr Nathan says Inangahua was the first earthquake in New Zealand to be
studied with modern analytical techniques.
There hadn't been a large earthquake since 1942, and we learned a lot
about damage to buildings, roads, bridges and other structures. Knowledge
gained at Inangahua helped significantly in improving building codes;
structures are safer as a result.''
In her book New Zealand Tradgedies -- Earthquakes, Anna Rogers
wrote: '' New Zealand was still reeling from the shock of the Wahine sinking
on April 10, which had left 51 people dead. The Inangahua earthquake...
mercifully took only three lives, but it caused immense physical and psychological
damage that was not easily repaired.''
contact:John Callan
Email: John Callan