A bogus report of a large earthquake near Auckland this morning was caused by a glitch in GNS Science's new automated alerts system.
GNS issued an preliminary report of a magnitude 5.6 earthquake west of Auckland shortly after 9.36am. Half an hour later, it reported a magnitude 6.4 quake west of Opunake.
The reports were issued within minutes of the quakes being detected - but the problem was, neither quake actually happened.
GNS Science duty seismologist Martin Reyners said the false reports were due to teething problems with the new automated system, which had been on trial for several weeks.
"Previously, we didn't release any information until someone had actually looked at the earthquakes and sometimes, depending on whether people were in the office or not, that might take half an hour.
"But some of our stakeholders want a more immediate response, so what we do now is send out emails when the automatic system first tweaks that there has been an earthquake, based on usually very limited data."
Dr Reyners said as more data came in from other seismic stations, the location of a quake could be narrowed down within minutes.
The problem today was that two small quakes happened at the same time - one in Canterbury and the other near the Kermadec Islands - which caused the automated system to pinpoint its location halfway between in Auckland.
"That location obviously was wrong, but within a few minutes it had honed in on the correct location," Dr Reyners said.
"The system gets confused if there are two earthquakes happening at the same time, initially, and as more data comes in it's able to separate out those two earthquakes.
"It's just a quirk of the system that some of the initial locations may be bogus ... These are teething problems that we're going to try to obviously work through and improve."
Dr Reyners said the email alerts made it clear the results were preliminary.
He said a magnitude 6.4 quake could occur near Opunake as often as every few years - but a magnitude 5.6 west of Auckland was more unlikely.
GNS has apologised for any alarm caused by the new system.
It suggested people look at its website and check the "quake history".
Those marked "caution" have only had a few observations, while those marked "good" and "best" are more reliable.
"We're trying to balance getting quick notifications out rather than wait minutes before letting you know."
- Additional reporting nzherald.co.nz
