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1998: A summary of the earthquakes - 06/01/1999

New Zealand was fortunate to avoid a large damaging earthquake in 1998, but moderate-sized events occurred, including several in places where we usually record few earthquakes.

Seismologist Terry Webb of the Institute of Geological & Nuclear Sciences Limited said the first quake in an unusual place occurred inland from Timaru, near Danseys Pass, on February 9. It was shallow with a magnitude of 5.1, and felt from Dunedin to Christchurch. Several aftershocks occurred in the following weeks.

A magnitude 5.8 earthquake occurred 40km east of Haast on October 21. "It was large enough to trigger icefalls near Mt Cook and knock goods from shelves at Mt Cook Village, Dr Webb said. It was also felt strongly on the West Coast and as far away as Christchurch and Dunedin. This part of the central South Island does not often experience large earthquakes.

Another earthquake in an unusual location was the one that occurred near Waiheke Island, east of Auckland, on May 17. Although small magnitude 2.4 it was a useful reminder that all parts of New Zealand can experience earthquakes.

New Zealands biggest earthquake in 1998 measured 6.5 and occurred on April 21. It was centred 30km southwest of Taumarunui at a depth of 230km. It was New Zealand felt from Gisborne to Christchurch and across to Taranaki.

Swarms of earthquakes a series of jolts with no clear main shock are common in New Zealand, especially in volcanic regions. The most active swarm in 1998 started on March 25, just south of Rotorua.

Over 40 earthquakes occurred during the first swarm and the Institute recorded hundreds more over the next four weeks. The biggest jolt during the swarms was a magnitude 4.8 earthquake.

Another swarm occurred 20km south of Ohakune in February, with the largest event measuring 4.9.

There were two near misses in 1998 both were shallow offshore magnitude 5.2 earthquakes. The first, on February 25, was 30km south of Seddon, and the other was 60km west of New Plymouth.

While magnitude 5.2 earthquakes do not typically cause major damage in New Zealand, the fact that these two events were offshore meant that damage was minor.

For more information contact:
Terry Webb or Martin Reyners