Earthquake: Sharp jolt triggers more damage

Source / www.google.co.nz/maps, Herald Graphic

Cantabrians may be subjected to frightening earthquake aftershocks for weeks yet, an expert has warned, after a big jolt yesterday caused damage to homes previously untouched by Saturday's big quake.

The magnitude 5.1 aftershock, which hit at 7.49am, caused residents and workers to flee their homes and offices. The state of emergency in Christchurch was extended for a further week and emergency services helped evacuate the city's central business district.

It was the largest of more than 15 aftershocks in the region yesterday and caused more structural damage.

"My guts are just churning up here. When will this thing end? It is like living in a maelstrom," Christchurch Mayor Bob Parker said on radio.

"We were starting to think, maybe, just maybe, we are over the worst of this, and now we have had this shocking event. This is a hammer-blow to the spirit of a lot of people."

The jolt occurred near Lyttelton Harbour, forcing the closure of the Lyttelton to Christchurch tunnel until 11.30am, after structural checks determined only superficial damage had occurred.

Families in suburbs near Lyttelton were evacuated from their homes, which were worse hit yesterday than the main quake on Saturday.

Hazel O'Leary, 94, left the home she built in 1950 and is unlikely to come back.

Her art deco house, in Cashmere, suffered no damage in Saturday's 7.1 quake, but cracks split open her walls yesterday.

A fracture circles the house along its foundations.

Her son, Jim O'Leary, who lives next door, said the cracks painted a clear picture of what had happened.

"It was huge, just a big bang up and down, boom boom," Mr O'Leary said.

"It was over in five seconds. The house was jolted up and fell back down again.

"This was the scariest one. We were just getting over it and this happens again. Saturday's went on rolling for a long time, but this was violent."

He said he didn't expect his mother to return to her house.

Mr O'Leary's wife, Karyn, said her workplace, the Southern Cross Hospital, was forced to close because of the aftershock.

Cracks had appeared for the first time there, with earthquake damage reaching new areas of the city.

An initial adrenalin rush that had carried Christchurch residents for the first few days was being replaced by exhaustion, she said.

"A lot of people are getting tired. We try to go to sleep and there's a shake at 12.30pm, then 3am, then 8am, or whatever it was. It just doesn't stop."

Almost 300 aftershocks have shaken Christchurch in the past five days.

Canterbury University geologist Dr Mark Quigley said big earthquakes like Saturday's, centred near Darfield, could trigger quakes in the Alpine fault or in Canterbury faults.

"We might still have aftershocks in the order of magnitude 6. That's a possibility, but it's also possible that we've had the biggest aftershocks already."

But in general, "The magnitude and frequency of aftershocks will diminish with time".

The WeatherWatch website reported a smell of sulphur, "similar to Rotorua" had been noticed in the east of Christchurch since Saturday. Civil Defence said it was not a gas leak.

Dr Quigley said earthquakes could cause the release of previously-trapped gases into the atmosphere from below the surface of the ground.

A water engineer said broken sewers could release hydrogen sulphide gas if there was a buildup of sewage.