23 Jul 2013

Aftershocks continue after 6.5 quake

4:04 pm on 23 July 2013

Aftershocks from Sunday's 6.5 magnitude earthquake have continued, with 13 quakes since 7am on Tuesday morning.

The GeoNet website says a strong 4.7 magnitude quake was recorded at 9.24am, centered 10 kms east of Seddon, and 14 kms deep.

A moderate 3.8 magnitude earthquake was reported at 10.32am, 25 kms east of Seddon and 15 kms deep.

GNS Science seismologist John Ristau told Radio New Zealand's Morning Report programme that while the cluster of earthquakes appears to have occurred between two known active faults in Cook Strait, there is a possiblity they stem from an fault as yet to be identified.

Dr Ristau has said that if the earthquake occurred on one of the known active faults, the likelihood of having another large earthquake along that fault is is much less.

"Whereas if it occurred on an unknown fault nearby, it therefore may have actually added stress onto one of these known active faults."

Dr Ristau says GNS will on Tuesday try to narrow down where the quakes are coming from.

A Victoria University professor in earth sciences, Euan Smith, says Sunday's 6.5 earthquake was the biggest in the area since 1942 when two 7.0 earthquakes hit the central North Island.

Professor Euan Smith says the cluster of quakes that occured in the Cook Strait before the big shake at 5.09pm were slippages between the Pacific and Australian tectonic plates, while the larger quake was unusual because it was a sideways movement.