Geonet, the USGS (NEIC) and IGNS reported 41 earthquakes in the New Zealand area between Raoul Island in the north, and the Auckland Islands to the south during November 2005. The magnitude distributions were as follows:
M5 to 5.9 (3), M4 to 4.9 (15) M3 to 3.9 (23).
An additional 4 events in the magnitude 2 range were deemed worthy of mention.
Four earthquake swarms, one in conjunction with a cluster of earthquakes, were reported during the month. A loose cluster of 8 earthquakes which had occurred in southern Wairarapa near Eketahuna and Martinborough since August 31st came to an end on November 11th.
A swarm of 9 earthquakes centred 10 km east of Seddon started on November 1st and ended its run on the 11th. An associated cluster of 7 earthquakes in the nearby area commenced on the 3rd and was represented by a magnitude 4.2 event on the 29th. Minor damage was reported following some of these earthquakes.
A swarm of 4 earthquakes between magnitude 3.3 and 4.0 occurred 30 km South of Wanganui between November 4th and 27th. Initially the first two events appeared to be a normal earthquake and aftershock sequence, but the continuing activity disproved this. A similar swarm of 5 earthquakes with a largest magnitude of 3.9 occurred in the same area between May 20th and July 4th this year. Two weeks later a swarm of 4 earthquakes with a largest magnitude of 3.7 occurred 20 km South of Wanganui between July 20th and August 5th.
The Mahia Peninsula hosted a short swarm of 3 earthquakes within 15 minutes, with magnitudes between 3.7 and 3.9 on November 16th. This area too had earlier experienced a similar sequence of 3 reported events (magnitudes 3.5, 3.9 and 3.2) on May 6th, 8th and June 10th.
Waiheke Island residents in the Hauraki Gulf near Auckland had the novel experience of feeling and hearing earthquakes on the 29th and 30th. Initial reports mentioned 3 events with magnitudes between 2.5 and 3.3 within 12 hours of each other in this area near to the Auckland volcanic field. Geonet issued a news release on 30th November, showing 6 small earthquakes within a period of 2 days near Waiheke, and described the events as “rare, but not unexpected.” Adding, “If magma started rising from deep within the earth, we would expect it to start causing earthquakes much deeper than 8 kilometres.”
The three largest earthquakes during November were:
A magnitude 5.3 quake, 33 km deep between The Snares and the Auckland Islands on November 7th, reported by Geonet. This was felt on Stewart Island.
A magnitude 5.6 earthquake 290 km deep located 10 km east of Tauranga on November 9th, reported by Geonet. This was felt in Napier, Palmerston North, Wellington and Nelson.
A magnitude 5.1 quake, 46 km deep located 400 km SSW of Raoul Island on November 25th, reported by USGS National Earthquake Information Centre.
Vulcanologists report the nation’s volcanoes to be quiet during November, with only two at Alert Level 1 (some signs of volcano unrest). Their status can be summarised as follows:
Mt Ruapehu (Alert Level 1). Seismic activity low, crater lake temperature rose 6 degrees to 36 degrees C in the last weeks of October.
White Island (Alert Level 1). Seismic activity continues at a low level, crater lake remains at 1 metre below overflow, as it has for the past few months.
Mt Tongariro (Alert Level 0). An increase in the usual number of small volcanic earthquakes was detected early in the month. The increased incidence continues.
On a lighter note –
Against the odds, Dino the pink dinosaur who took up sentry duty in front of the crater camera at White Island in May 2004, has survived the acidic conditions at the volcano. Initially it was expected that he would go the way of his ancestors within a few months. However, though he has started to lose his brilliant pink sheen, his hide has remained intact, and he still makes his hourly appearance on the Geonet website.
Dino, who is not on the GNS payroll, has done a wonderful job as an ambassador for the work being carried out by the scientists who regularly visit the island.