Jan 5 2010 - Principal earthquakes of New Zealand in 2009

Felt earthquakes in 2009.

On 15 July the largest earthquake to occur in New Zealand since the 1931 Napier earthquake struck remote Dusky Sound in the Fiordland region. With a magnitude of 7.8, the rupturing caused by the earthquake started at a depth of about 30 km and moved upwards and to the south, directing most of the energy offshore; the resulting damage was much less than expected for an earthquake of this size. Structural damage included cracking to exterior walls and instances of pile damage in Southland, and there were reports of ground slumping in the area around Invercargill. Items fell from shelves throughout Otago and Southland and power and telephone outages occurred at several localities throughout these areas. Minor landsliding occurred in south-west Fiordland. The earthquake was felt throughout the South Island and mainly on the western side of the lower North Island, with scattered reports from as far north as Auckland, and also from Sydney, Australia. A small tsunami was detected, with a one metre wave measured on a tide gauge at Jackson Bay in south Westland. The biggest aftershock was a magnitude 6.1 that occurred 20 minutes after the main shock, and there have been thirty of magnitude 5.0 to 5.9 spread over the faulting area, with the latest a magnitude 5.0 on December 13.

A magnitude 5.4 earthquake centred 90 km south of Opunake and at a depth of 170 km occurred 16 minutes after the Fiordland earthquake, and was felt from Taranaki to the West Coast.

Two deep earthquakes of magnitude 6.1 were the other largest earthquakes of the year. The first, on 22 March at a depth of 160 km and centred 30 km north-west of Whakatane, was felt from Coromandel to Christchurch; the second, on 1 September at a depth 280 km and centred 120 km north of Whakatane, was felt from Gisborne to Nelson.

The most strongly felt earthquake in the Wellington region was a shallow magnitude 5.2 on 28 August. It was centred 20 km south of Wellington and felt from Wanganui to the top of the South Island, and there were several reports of items falling from shelves in the Wellington region. On 10 October, a magnitude 4.8 quake at a depth of 40 km and centred 20 km north-west of Wellington, was also felt strongly in the region.

On the morning of 27 June, two shallow earthquakes centred about 5 km north-west of Turangi and of magnitudes 4.3 and 4.4 were reported felt strongly in the area at the southern end of Lake Taupo. These were the biggest of a swarm of several hundred earthquakes that commenced in late May, and as a result residents of Waihi village were advised to evacuate because of a risk of landslide activity.

There were five earthquakes outside the New Zealand region that were reported felt. The most significant, on 20 March, was a shallow magnitude 7.6 quake centred in the Tonga Islands region, about 2000 km north-east of Auckland, that was felt on the eastern side of the North Island and in Nelson. Another earthquake to affect New Zealand was the magnitude 8.1 Samoa Islands quake on 30 September which, while it was not felt here, generated a tsunami for which northern coastal areas were on alert for some hours.

In 2009, a total of 42 earthquakes of magnitude 5.0 or greater occurred in New Zealand. 392 earthquakes were reported felt on the GeoNet website. All significant damage was caused by the Dusky Sound earthquake or its larger aftershocks, and was it not for this sequence, this would have been a quiet year for earthquakes in New Zealand.