Four earthquakes rock New Zealand, aftershocks continue (Roundup)

Jul 17, 2009, 6:34 GMT

   Wellington - Four more earthquakes with a magnitude of over 5 on the Richter scale rocked New Zealand's southern Fiordland region Friday as aftershocks continued in the wake of a major shake two days earlier.

   All were in the same region as Wednesday night's quake, which New Zealand seismologists insisted was of magnitude 7.8, equal to the one that devastated the North Island city Napier in 1931, killing 256 people.

   At 7.8, it would be the biggest in the world this year.

   However, the US Geological Survey downgraded its strength to 7.6, which would equal the year's most powerful quakes recorded off the Pacific island state of Tonga in March and off Indonesia on January 3.

   Friday's quakes measured 5.3, 5.6, 5.5 and 5.2 on the Richter scale and scientists said that aftershocks would continue for some time.

   New Zealand is one of the world's most earthquake-prone countries, recording about 14,000 a year, though only 100 to 150 are big enough to be felt, according to GNS Science, the government institute of geological science and home to the country's official seismologists.

   There have now been 10 aftershocks over magnitude 5 since the big one on Wednesday. Normally fewer than 20 of that size are recorded in a year.

   The country survived Wednesday night's 7.8 rocker with no casualties and very little damage, although GNS Science principal scientist, Martin Reyners, said its size and its shallowness, only 12 kilometres deep, would normally be a dangerous combination.

   But the quake occurred in a remote location, off the south-west coast of the South Island, and in 'soft rocks' that muffled some of its power, he said.

   Civil defence officials said the quake should come as a wake-up call to New Zealanders to prepare survival kits for a similarly large shake in a major population area.