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The biggest earthquake this year - No tsunami risk - 27/03/1998

Movement during a big earthquake near Antarctica two days ago was horizontal which meant there was little likelihood of a tsunami, a seismologist said today.

The earthquake, the biggest recorded in the world this year, measured between 7.7 and 7.9 on the Richter scale -- not 8.1 as originally estimated.

Institute of Geological & Nuclear Sciences Limited seismologist Martin Reyners said Institute scientists ''saw it come in'' on seismographs.

'' It's quite impressive when one that big comes in. It sets the whole world ringing like a bell.''

The earthquake struck at 3.11pm NZT and was centred just off the Balleny Islands, which are in New Zealand's Antarctic territory, about 2000km south of New Zealand and 700km from the Antarctic continent. Its focal depth was 30 to 40km.

Dr Reyners said large earthquakes in this region were quite rare.
The earthquake was slightly smaller that the 1858 Wairarapa jolt that caused sideways movement in the ground of 12m and an lifted an area of 12,000sq km near Wellington by 1m. This week's quake was about the same size as the magnitude 7.9 earthquake that struck Hawke's Bay in 1931 and resulted in the deaths of 256 people.

Dr Reyners said vertical movement -- which displaces water very quickly -- or a submarine landslide was needed to spark off a tsunami.

'' But if bits of rock just slide past each other, they are not displacing a lot of water and we wouldn't expect a tsunami to occur.''

Dr Reyners said a tsunami would take about four hours to reach New Zealand from the earthquake epicentre.

He added that an earthquake of magnitude 7.7 to 7.9 would cause a major disaster if it had occurred near a populated area.

The earthquake that struck the Japanese port city of Kobe in January 1995, killing about 5500 people and injuring about 35,000, was 7.2 on the Richter scale. It caused an estimated $NZ200 billion in property damage and left 300,000 people homeless. About 190,000 buildings either collapsed or were seriously damaged.

The Kobe quake was centred about 20km offshore from Kobe, although some of the faults that ruptured were directly beneath the city. The zone of greatest destruction was about 2km wide and extended roughly parallel to the coast for nearly 30km through the cities of Kobe, Ashiya, and Nishinomiya.