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Big shake was complex and may have been two earthquakes Waves of around 30 centimetres and were detected on the East Cape and Great Barrier GNS seismologist Bill Fry explains what that means and what the risk of a tsunami is

Scientists are investigating the possibility Friday's big shake off the East Cape may have been two earthquakes The complexity made it hard to estimate how deep the quake was, and to identify whether The Ministry of Civil Defence and Emergency Management (MCDEM) sent out its first national advisory at 510am but that was only about the earthquake A potential tsunami threat notice was not issued until 533am, and a request for an emergency announcement to be broadcast was not made until 5

58am GNS Science said the maximum of the first tsunami wave was measured on an East Cape tide gauge at 458am It was about 24cm above the normal tide level GeoNet boss Ken Gledhill said everybody, including overseas agencies such as the US Geological Survey, had trouble working out the depth of the quake

"Because of the complexity of the quake, models used by some agencies to make fast tsunami warnings would have been wrong