article: Jan 1 2006 - Principal earthquakes of New Zealand in 2005

It was an average year for earthquake activity in New Zealand in 2005, with two events of magnitude over 6.0, and 24 in the magnitude range 5.0 to 5.9. Of these, ten occurred at depths greater than 100 km. A total of 390 events were reported felt through the GeoNet website during this year.

Felt earthquakes in 2005. Green are likely to have been felt, yellow had the potential to cause contents damage, red had the potential to cause structural damage.

The most destructive of these occurred on the morning of January 21 and was centred just north of Upper Hutt. It had a magnitude of 5.5, was at a depth of 32 km, and was felt throughout the lower North Island and upper South Island, from New Plymouth to Christchurch. Reports were received of goods falling off shelves and furniture moving in the Wellington region. This was in a similar location to a sequence of felt events that occurred in April and May 2004.

The largest event for the year was a deep earthquake of magnitude 6.4 on March 14. This was centred 80 km south of Opunake at a depth of 154 km, and was felt from Auckland to Christchurch. GeoNet received a record 1974 felt reports for this event, with just a few reports of breakages from falling goods in the Wellington and Taranaki regions.

The largest shallow earthquake was on the west coast of the South Island, centred 10 km south of Haast. This occurred on May 3 and had a magnitude of 6.2. The depth was 13 km and it was felt from Westport to Bluff, with a few reports of ornaments and books falling over. An aftershock of magnitude 5.7 five minutes later was also felt widely.

Two earthquakes on January 18 and one on February 1 centred off the Wairarapa coast, 20 km south-east of Martinborough, about 15 km deep and of magnitudes just above 5.0, were felt widely in the lower North Island, and caused some things to fall from shelves and from cupboards that were burst open in the Wellington region. Also in the lower North Island, on February 18 there was a magnitude 5.2 event centred 20 km south of Waverley and with a depth of 28 km which was felt from Hamilton to Nelson and caused some items to fall over in the Wanganui region. On December 13, a shallow magnitude 5.0 earthquake centred 10 km west of Pongaroa was felt widely throughout the lower North Island. Fallen items were reported in Manawatu and Wairarapa.

In the South Island, a shallow magnitude 5.2 earthquake centred 60 km west of Te Anau on February 13 was felt throughout Fiordland, Southland and Otago. On April 25, an event of magnitude 5.5 and 90 km deep under Fiordland was felt widely in the lower South Island.

Three notable swarms of earthquakes occurred during this period. During the first nine days of July, a swarm of small, shallow earthquakes occurred near Te Aroha. The biggest of these had a magnitude of 3.8, and 15 were reported felt in the western Bay of Plenty region. Beginning on February 1, and still continuing, is a swarm centred close to Matata in the Bay of Plenty. Close to 100 of these events have been reported felt in the central Bay of Plenty. They all were at a depth of about 5 km and the largest was a magnitude 4.1 that occurred on June 13. The third swarm, centred near Seddon in the Marlborough region and at a depth of 5 km, started on March 2 and is also ongoing. The largest of these were two earthquakes of magnitude 4.8 in early November which were felt in the Marlborough and Wellington regions. These caused damage to walls and pipes near Seddon and there were reports of broken glass and many things off shelves in Seddon and Blenheim. About 30 others have been reported felt in this period.

A unusual cluster of six small quakes under Waiheke Island, east of Auckland, in late November startled some island residents, but there was no damage reported.