Not a single person was killed when a 7.0-magnitude quake hit the city last year, in what experts hailed as a miracle after 220,000 were killed when a tremor of the same intensity struck Haiti in January 2010.

But University of Canterbury seismologist John Townend said there were a variety of reasons why the 6.3 quake that rocked Christchurch Tuesday was more destructive than last September's tremor, even though it had a lower magnitude.

The latest quake was closer to the city centre, just five kilometres (three miles) compared to 30 kilometres in September, and hit at a depth of four kilometres rather than 16 previously.

Townend said it was also fortunate that the September quake occurred in the pre-dawn hours, while Tuesday's tremor hit at lunchtime when streets and office buildings were packed.

The earlier tremor also weakened structures, making them less resistant to the latest big shake.

"We were very lucky in September and perhaps we were a little bit complacent because the damage was limited to buildings, roads and infrastructure," he told Radio New Zealand.

"The fact that it happened at 4:05am also meant that very few people were out to be exposed to it... in general an earthquake of this size happening so close to a city, even a well-prepared one, is always going to cause major damage."

Christchurch has been rocked by 20 aftershocks since the 6.3 quake and University of Melbourne seismologist Gary Gibson said they were likely to continue for weeks, gradually lessening in intensity over time.

"(They) may cause further damage in weakened buildings and will be very distressing for residents," he said.

Gibson said Christchurch lies on a secondary fault line, away from the main boundary between the Pacific and Australian tectonic plates, meaning quakes in the area are destructive because they are close to the surface.

"All earthquakes in the Christchurch region will be shallow, so the effect of a given earthquake will be worse than from a deeper plate boundary earthquake of the same magnitude," he said.

Australian Seismological Centre director Kevin McCue said the tremor could increase pressure on plate boundaries across New Zealand, increasing the likelihood of a tremor elsewhere, particularly in the capital Wellington.

"If you have one (quake) it ups the hazard," he told the New Zealand Herald.

"This quake has the potential to load up the plate boundary, increasing the likelihood of a quake at Wellington."

"Wellington has always been considered much more at risk because it straddles the plate boundary. New Zealand has been relatively quiet since the 1930s -- maybe (it's) about to catch up."

New Zealand sits on the "Pacific Ring of Fire", a vast zone of seismic and volcanic activity stretching from Chile on one side to Japan and Indonesia on the other.

Tuesday's quake is the most deadly to hit New Zealand since a 7.8-magnitude tremor killed 256 people in the Hawke's Bay region in 1931.

del.icio.us	Digg	Reddit
YahooMyWeb	Google	Facebook

Memory Foam Mattress Review

SPACE MEDIA NETWORK PROMOTIONS Solar Energy Solutions Tempur-Pedic Mattress Comparison ... Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

Lake-Effect Theory Sinks, But Quake Timing Questions Go
Eugene OR (SPX) Feb 14, 2011
A chronology of 1,000 years of earthquakes at the southern end of the San Andreas Fault nixes the idea that lake changes in the now-dry region caused past quakes. However, researchers say, the timeline pulled from sediment in three deep trenches confirms that this portion of the fault is long past the expected time for a major temblor that would strongly shake the Los Angeles Basin. The ne ... read more