Eight minutes is not a long time, but it was enough on Sunday to confuse thousands of Kiwis on tenterhooks after a tsunami alert.
At 11.37am, the Ministry of Civil Defence and Emergency Management (MCDEM) tweeted it had “issued a beach and marine tsunami warning following the M7.4 Kermadec Islands region earthquake”.
After eight anxious minutes, many turned to social media to ask for urgent clarification about which beaches, whether the warning included river mouths and the possible timing, the ministry tweeted again.
This time it said there was “no tsunami threat to New Zealand” after the revised magnitude 7.0 Kermadec quake.
“Based on current information, the initial assessment is that the earthquake is unlikely to have caused a tsunami that will pose a threat to NZ,” MCDEM said in that second message.
So why did the message change so quickly?
GNS Science duty seismologist Sam Taylor-Offord told Stuff the organisation’s tsunami experts panel had a phone conference about 11.30am to discuss the threat.
It appeared the ministry had put out its warning message based on information from the Pacific Tsunami Warning Centre while that phone meeting was still taking place, he said.
“My understanding is they wanted to get something preliminary out while we were finalising things. And we want to make sure what we tell the ministry is reliable and we can stand behind it.
“It was just coincidence that, around the time we were telling them of our thoughts, they were sending out their preliminary thoughts.
“We don’t want to advise them and then redact that. We want to say ‘yes’ or ‘no’.
“We were looking at about 90 minutes from the earthquake to the arrival of any tsunami here. The time pressure is still on, but we did have time to get this right and still give a good hour [for people] to react,” Taylor-Offord said.
Through GNS Science, the ministry pointed Stuff to a document developed with GNS Science about the tsunami warning process and the ministry’s messaging guidelines.
GNS Science’s 24-hour a day national geohazards monitoring centre opened last December.
After the magnitude 7.8 November 2016 Kaikōura earthquake, there were calls for full-time monitoring which annoyed the then acting Civil Defence minister Gerry Brownlee.
That came after muddled tsunami warnings following a magnitude 7.1 quake off East Cape on September 2, 2016.