Earthquake series warning

History suggests Saturday's destructive 7.1 Canterbury earthquake could be a trigger for a series of major earthquakes which New Zealand must prepare for, scientists say.

Victoria University's geophysics professor Euan Smith said Saturday morning's magnitude 7.1 quake did some things "as expected" but "had some surprises as well."

He said policy regarding unreinforced masonry structures should now become "urgent" because a 1929 west Canterbury magnitude 7 earthquake turned out to be the first of a series of seven major, magnitude greater than 7, earthquakes over the next 13 years.

The series included the second and third largest earthquakes in European times - the magnitude 7.8 Buller and Hawke's Bay earthquakes.

The series ended with two magnitudes 7.2 and 7.0 earthquakes in the Wairarapa in 1942.

"It is improbable that this occurrence of such large earthquakes in rapid succession was coincidental. It is more likely that the faults which broke during the series were all stressed and ready to break, and that the occurrence of successive earthquakes helped bring forward the occurrence of the next," he said.

"There is no reason to think that such a series could not happen again."

"The first lesson, for local authorities and policy makers, concerns what happened to the unreinforced masonry structures in this earthquake.

"It is time for the rest to act. Owners of unreinforced masonry buildings, and chimneys, everywhere in New Zealand should be given a reasonable period of time - say 10 years - to demolish them or make them safe in future earthquakes."

- © Fairfax NZ News