article: Jan 3 2004 - Principal Earthquakes of New Zealand in 2003

The largest earthquake to occur in New Zealand since the Inangahua event in 1968 occurred near Secretary Island, Fiordland, early on the morning of August 22, 2003.

Felt earthquakes in 2003. Green are likely to have been felt, yellow had the potential to cause contents damage, red had the potential to cause structural damage.

Thanks to its relatively remote location, there were no casualties and no major damage in residential areas, although damage to the landscape in the epicentral region was considerable, with many landslides and rockfalls reported. It was felt from Auckland to Stewart Island, and also across the Tasman, in some high-rise buildings in Sydney. While structural damage caused by these earthquakes has not been major, it has been widespread, and close to 4,000 claims for related damage have resulted.

Aftershocks to this event and related seismic activity in the region still continues, though at a much reduced level, and so far there have been three events of magnitude around 6.0 and 24 of magnitude between 5.0 and 5.9. About 60 of these have been reported felt, although the actual number felt may be considerably higher, as many people may have become inured to the phenomena with time and omitted to report them.

The Fiordland activity aside, 2003 was an average year seismically, with a total of about 20 events of magnitude 5.0 or greater. On January 26, an event of magnitude 5.5 centred 20 km east of Woodville caused minor damage in the region and was felt throughout the lower North Island. On June 30, an event of magnitude 5.0 centred 10 km south-east of Seddon was felt widely in the Marlborough and Wellington regions, with minor damage resulting near the epicentre.

The most significant earthquake in the North Island in 2003 was on the night of August 3, a magnitude 5.4 event centred 10 km east of Pahiatua that was felt from the Bay of Plenty to Canterbury. Damage was reported from Ohakune to Lower Hutt, with over 300 claims, mostly for minor damage, being lodged.

On September 30, a magnitude 4.9 earthquake centred 40 km north-east of Christchurch was felt throughout Canterbury, and because of its proximity to a major centre, was the second most destructive earthquake in 2003, resulting in about 720 damage reports.

Two other smaller events were centred about 10 km south of Porangahau, the first a magnitude 4.7 on February 18, followed by a magnitude 4.9 the following day. These were felt widely in the central North Island, with some minor damage reported.

As usual, there were a number of sizable deep earthquakes throughout the year, with 12 events of magnitude 5.0 or greater at depths of greater than 100 km. The one of most interest is possibly the event on August 8, centred 115 km under Rotorua with a magnitude of 5.3. This was felt from Bay of Plenty to Wellington, with two reports of minor damage.