Disaster clusters keep scientists guessing

JACOB SAULWICK

Last updated 11:10 12/03/2011

 

http://www.stuff.co.nz/world/asia/japan-earthquake/4761548/Disaster-clusters-keep-scientists-guessing

 

Mammoth earthquakes tend to strike across the world in a cluster but scientists do not know why.

The director of the Australian Seismological Centre in Canberra, Kevin McCue, said yesterday's quake in Japan, the largest recorded there, would not have been linked to the one that struck Christchurch last month.

''This earthquake is a rupture of the plate boundary,'' Professor McCue said. ''The Christchurch earthquake was not. It was an earthquake on the conjugate fault, a fault that's at an angle to the main fault and 100 kilometres away from the plate boundary.

''It seems unbelievable but relative to this the Christchurch earthquake was small.''

However, Professor McCue said earthquakes on plate boundaries often came in quick succession.

''We had a sequence of earthquakes in 1906 where there were at least six 'grade earthquakes' around the Pacific. And now we've had Chile last year and this one,'' he said.

''It's something we observe in all extreme events - they are clustered in time. That's what we observe they do but we don't have an answer for it.''

Japan sits off the largest plate boundary in the world. The Pacific plate runs from New Zealand, around Samoa, Japan, and off the west coast of North America and South America.

The boundary can move as much as 10 centimetres a year and is moving at its fastest near Japan, increasing the risk of earthquakes.

Professor McCue said the earthquake was bigger than the magnitude 7.9 Kanto quake of 1923 that killed 147,000 people.

Yesterday's quake was said to have a magnitude of 8.9, which would make it the fifth largest earthquake in the world since 1900.

''I don't know they were anticipating one this big but [Japan was] planning for a recurrence of the great 1923 earthquake for at least as long as I have been a seismologist,'' he said.

A co-director of the Australian tsunami research centre and natural hazards research laboratory at the University of NSW, James Goff, said it would have been highly unlikely for a tsunami not to be generated by a quake of this size.

''Japan has a rigorous earthquake building code and excellent tsunami warning system and evacuation plans. This event will likely provide a severe test for all of them.''