'Ghost quake' reported in C.Otago

A report of a severe earthquake in Central Otago turned out to be a ``ghost quake'' which was actually centred more than 1000km away.

GeoNet initially reported a magnitude 5.3 quake had struck 30km southeast of Roxburgh, at a depth of 12km, at 9.48am.

It quickly became apparent there was no severe shaking in Central Otago, with a woman who lived near the reported epicentre saying: ``I know nothing about it.''

GeoNet later corrected the initial report saying the quake had struck west of the Macquarie Islands, which is about halfway between New Zealand and Antarctica and part of Australia.

The United States Geological Survey, which is better equipped to detect seismic activity outside New Zealand's borders, reported a 6.1 magnitude quake struck 28km of the island at a depth of 10km at 9.46am.

GNS duty seismologist Caroline Little said such ``ghost quakes'' happened every so often.

``More often we get this from earthquakes halfway up to Tonga and our system pulls them in and puts them in close to Gisborne, but this is the opposite case,'' Ms Little said.

The occasional ghost quakes happened because its system was so geared towards picking up earthquakes in New Zealand.

``With earthquakes far off the coast our [equipment] can still record all that shaking, but it's very poor at getting a location because we don't have seismographs surrounding the earthquake to confine where it is.''

The quake was reported through its new automatic location system and corrected once a seismologist looked at the data.

GNS would look at ``tweaking'' the system so such occurrences did not happen as often, but would be careful not to alter it in a way which risked it missing New Zealand earthquakes.

She would be ``surprised'' if the few people who reported feeling the quake in New Zealand actually felt it.

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