The Seddon Earthquake

At 6.25 pm on Saturday 23rd April. 1966, an earthquake of magnitude 6.1, originating in Cook Strait at a depth of about 22km, shook the Marlborough area and the southern part of the North Island. ³² In Marlborough the earthquake appeared to come from the northeast, striking first Blind River and Seddon and then tailing off to the west, south to Ward and north towards Blenheim.

The worst hit populated area was the town of Seddon, about 35km from the epicentre of the earthquake, although fortunately no one was injured. Residents had a similar story to tell, of breaking kitchen crockery and crashing of utensils, of windows shattering and the noise of chimneys collapsing on roofs, television sets being overturned and plaster showering from the ceilings, of floors heaving, wallpaper splitting and the crying of frightened children, followed by an uncanny silence as people waited for the next shock that never came. ³³ , ³⁴

At least one house was moved a good half inch out of plumb, with consequent damage to walls and ceiling. In other buildings, including the church, cracks appeared in concrete walls, brickwork was cracked, timbers split and paint flaked. Settlement on house piles also occurred. About 150 chimneys were shattered and dozens more were damaged. Windows in shops, houses and the local hotel were broken; water mains fractured, leaving most of the town without supplies for the greater part of Sunday. Power and telephone lines were broken, with the whole area blacked out for up to half an hour and telephone services out of operation for seven minutes.

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The road seal was cracked. In most houses the contents of kitchen cupboards, shelves and bookcases were emptied and floors were strewn with broken crockery, glassware; mirrors and pictures fell from walls. In the Seddon Hotel dozens of bottles of spirits crashed from the shelves in the bar to form a mixed cocktail over the floor. Door hinges snapped and lavatory pans cracked. A number of space heaters were pulled from the wall and rotated, although none were alight at the time.

A large slip, bringing down thousands of tons of the grey mudstone (papa) rock that forms the cliffed banks of the Awatere River, occurred upstream of the combined rail-road bridge. At the Cape Campbell lighthouse a glide roller to the light prism weighing two and a half tons was sheared off by the movement of the prism during the earthquake shaking. The roller hit the prism, bounced off and went through an outside window. ³³

It almost appeared that the earthquake had selectively damaged parts of the town, while leaving other parts relatively little affected. For instance, it shattered the chimney of the house of the head teacher, but left the school only 50 meters away almost unscathed. Only two or three chairs that had been placed on top of the desks had fallen, although most of the books in the school library had been thrown from the shelves.

The house of Mr and Mrs George McNulty in the middle of Seddon was the worst hit. They were in Nelson at the time, and arriving home on Sunday found doors wrenched from their hinges, windows shattered, the floor covered with the contents of cupboards and shelves, and mirrors which had been thrown from the walls lying broken on the floor.

Many of the Railway houses in the town were also badly damaged. All of them, together with the station, lost their chimneys. Heavy goods wagons in the railway yards were derailed. Mr and Mrs Marfell, who were driving home from Blenheim, did not feel the earthquake although Mr Marfell, the civil defence controller, noticed that there were an unusually large number of stones on the highway in the vicinity of Dashwood and Weld passes. Arriving about half an hour later, their home looked such a mess that they thought it had been ransacked by thieves.

In Blenheim 180 guests, including two Members of Parliament, the Hon. T. Shand and W. Rowling, the Mayors of Blenheim and Picton and the Chairmen of the Awatere and Kaikoura County Councils, were just about to begin a dinner in the Marlborough Centennial Hall to mark the 100th anniversary of The Marlborough Express when the earthquake struck. This page 29was the first big event to be held in the Hall, and the earthquake caused a dramatic start to things when the large building clanged alarmingly. The power failed and the caterers had the unenviable task of trying to keep the meal hot. Car lights were directed through the front of the building to give sufficient light. In Picton the earthquake was preceded by a large rumbling noise, followed by a severe jolt that frightened many people.

Initially there was hardly any damage reported outside the general area of Blind River and Seddon. In Blenheim there were reports of a window in Woolworth's building in Market Street being cracked, of stock on shelves and in windows being upset in a few shops and some plaster being shaken from a few other buildings, including the Palace Theatre which also suffered cracks in its facade, necessitating its closure for repairs. In homes in and around Blenheim items in cupboards and on walls were disturbed, and some breakages occurred. One television was reported to have "blown up". In Picton, a chimney was reported to have been damaged.

About 1km south of Seddon, distortion of the Main Trunk Railway Line over a distance of 60m was discovered when the line was checked by a railway ganger shortly after the earthquake. It was found that the inner rail of a 20m radius was found to have bulged upwards by 76mm, while the outer rail had buckled downwards by 25mm. The buckling caused a reverse in the cant of the railway line, from being 82mm to the east before, to 19mm to the west after the earthquake.

Careful inspection of the railway line between Blenheim and Ward showed that there was no other ground distortion. The area of damage is situated where the Hogg Swamp Fault intersects the railway. This fault trends east-north-east along the Hogg Swamp Stream, but has no surface break such as the Awatere Fault. Its presence is deduced from geological and geophysical evidence. ³² It appears that the fault moved during the earthquake, and the damage to the railway line is consistent with horizontal movement on the fault at depth having caused distortion of the surface sediments.

At Ward the damage was scattered, with some houses being unaffected. Seven chimneys of Railway houses were damaged and had to be dismantled, while other residents reported furniture, mirrors and ornaments cracked or broken.

The following day was both clean-up time and a chance for detailed damage inspection to be made. Close inspection of buildings and homes in Seddon revealed extensive, although not always severe structural damage to page 30interior walls and ceilings. Many chimneys, although still standing, had been sheared through at roof level or fractured. Thirty eight chimneys considered to be a dangerous state were quickly demolished. Claims began to come in and by Tuesday the number had reached 160.

Earthquake damage assessors in Blenheim received more claims than anticipated, with most relating to chimneys and several for stock and the contents of shops and homes. Many older-type buildings in the town had suffered minor earthquake damage, with cracked plaster interiors, parapets and other ornamental fixtures, and in general had their weaknesses shown up by the shaking. For example, at Farmers in Queen Street the main flagpole had fallen on the veranda and cracks were found in second floor walls and ceiling.

The main shock on Saturday evening was followed by smaller intensity shock registering 4.1 on the Richter magnitude scale at 8.28 pm on Sunday. Over the weekend 11 other minor shocks occurred, although a large number were only identified by the seismograph at the Seismological Office in Wellington. Within the week following the earthquake about 40 aftershocks took place.

An interesting phenomenon was observed a few hours before the earthquake struck. This was a large area of pure white foam in Cook Strait seen over an interval of one hour by Mr and Mrs G. Woolley of Seddon from their parked car at the mouth of the Wairau Diversion. They described the foam as being about five miles out from the coast, covering perhaps several acres aligned in a north-easterly direction.

The area of the foam appeared like some kind of disturbance within an otherwise calm sea. There is no way of knowing if this phenomenon was a precursor, related to the earthquake that was to follow, but the description suggests that it may have been the result of a significant release of gas from the sea floor.