Geological Summary for New Zealand Area, November 2009

Earthquake activity increased. White Island and Mt. Ruapehu remained at Alert Level 1.

GeoNet, the U.S. Geological Survey and GNS Science reported on 39 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during November 2009.

The magnitude distributions were as follows:
M6 to 6.9 (2), M5 to 5.9 (6), M4 to 4.9 (9) M3 to 3.9 (15).
An additional 7 events in the magnitude 2 range were deemed worthy of mention.

Earthquake activity in the Kermadec Islands increased during November, a month during which the South Pacific experienced several strong quakes. Magnitude 6.8 earthquakes struck near Fiji on November 9th and Tonga on the 25th. A magnitude 6.2 quake was recorded near Tonga on the 2nd and a 6.3 near Fiji on the 22nd of November.

Apart from a magnitude 4.9 event located 95 km south of Raoul Island on the first, most activity in the Kermadec Islands occurred during the latter stages of the month when five quakes with magnitudes between 4.5 and 6.1 struck within 200 km of the volcanic island.

Further south, three earthquakes with magnitudes between 4.9 and 6.2 were reported near L’Esperance Rock. The largest event, the magnitude 6.2 quake which struck at 11:47 a.m. on the 23rd, was felt at several locations in the Bay of Plenty and along the eastern coast of the North Island from Gisborne to Wairarapa. This earthquake was centred 160 km west of L’Esperance Rock (670 km NE of Whangarei) at a depth of 440 km.

A swarm of very shallow earthquakes struck within 5 km of Kawerau on the 27th. Three quakes with magnitudes between 2.6 and 3.0 were reported over a period of four hours.

A pair of quakes with magnitudes of 5.1 and 4.3 were recorded 10 km south of Palmerston North on the 19th of November. The 7:04 a.m. and 8:05 a.m. quakes were 40 km deep. Of the more than 1200 reports lodged with GeoNet only one reported damage, at Marton.

On the 30th of November a magnitude 5.1 quake struck 50 km south-west of Hastings (10 km west of Waipukurau) at 1:42 a.m. The 70 km-deep quake was felt throughout the southern North Island, but none of the 350 respondents who reported feeling the quake on the GeoNet website reported moderate or serious damage.

Earthquake activity in the South Island consistently mainly of individual events scattered across a wide area. Three events with magnitudes between 2.7 and 4.3 were reported near Hanmer Springs. A magnitude 4.2 quake struck near Amberley on the 20th and a magnitude 3.5 near Methven on the 24th. On the 29th a magnitude 3.5 quake struck near Springfield.

Very shallow magnitude 3.0 events were recorded near Cromwell and Greymouth on the 7th and 26th.

A magnitude 4.5, 12 km-deep earthquake located 10 km south of Haast on the 1st of November was felt from Okarito to Wanaka and Horseshoe, strongly at Haast.

Just before 1 a.m. on November 24th, a magnitude 5.3 earthquake struck offshore 190 km west of Tuatapere (240 km west of Invercargill, 200 km NW of The Snares.) The 12 km-deep quake was felt in Southland and on Stewart Island.

Regular reporting of the status of New Zealand’s volcanoes ceased at the end of June 2007, with the closure of the Hazard Watch service. GNS Science now only issues bulletins which record significant changes in volcanic behaviour.

No Alert Bulletins were issued by GNS Science during November 2009.

At the end of November 2009, New Zealand’s active volcano status can be summarised as follows:
Raoul Island (Alert Level 0).
White Island (Alert Level 1).
Mt Ngauruhoe (Alert Level 0).
Mt Ruapehu (Alert Level 1).

[Compiled from data supplied by GNS Science, US Geological Survey, GeoNet, and their contributing agencies.]

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