Schools in New Zealand are in their second and last week of holidays and then they return for the final term before Christmas.
Last night we felt two earthquakes here in Dunedin. At 6:24 on the evening of Sunday September 30th, a magnitude 7.3 earthquake struck the Puysegur Trench at a location 200 km north-west of the Auckland Islands. The quake occurred near the interface between the Australian and Pacific tectonic plates, in an area where the Australian Plate is sliding under the Pacific Plate at a rate of approximately 32 mm per year. The motion is not smooth and, while averaged out at 32 mm per year, actually occurs through spasmodic events such as earthquakes which account for months or years of accumulated strain. The quake was located 475 km south-west of Invercargill and the shockwave of the earthquake registered on seismographs located in Otago and Southland at about 6:25 p.m. Residents of Southland, Otago, Fiordland and South Canterbury felt the shaking.
At 10:48 p.m. another large earthquake struck the Puysegur Trench area. This quake was measured at Magnitude 6.8 and located at a depth of 10-12 km about 35 km away from the first event, being at 235 km west-north-west of Auckland Island.
The shaking from this event 505 km south-west of Invercargill reached the seismograph at Wanaka less than a minute later and the tremor was felt in Southland, Otago, Fiordland, South Canterbury and Christchurch city. By this time many people were aware of the earlier earthquake, and hence more alert to any sign of another event. Since last night, the area has been relatively quiet.