23 Jan 2019

Two earthquakes at the same time confuse quake monitoring system

10:19 pm on 23 January 2019

Thousands of New Zealanders felt the jolt of an earthquake tonight but it wasn't where many thought it was.

Recording earthquake information

Two earthquakes at the same time have confused the quake monitoring system. Photo: 123rf

Geonet had reported a magnitude six earthquake had shaken the East Coast but it turns out two quakes that happened at the same time had confused the quake monitoring system.

The first quake was far to the north of New Zealand in the Kermadec Islands and a few minutes later, there was a quake near Whanganui.

The overlap of the shaking tricked the system into thinking a quake had happened at Ruatoria, a seismologist from GNS Science, Matthew Gerstenberger said.

"It takes a couple of minutes for the wave forms from the Kermadec earthquake to travel to the system so the shaking from the first event was occurring at the same time as the shaking of the Whanganui event," Mr Gerstenberger said.

"So in the initial eyes of the system those are happening together so that's the reason they were combined together."