Geological Summary for New Zealand Area, December 2009

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

GeoNet, the U.S. Geological Survey and GNS Science reported 29 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during December 2009.

The magnitude distributions were as follows:
M6 to 6.9 (none), M5 to 5.9 (5), M4 to 4.9 (8) M3 to 3.9 (10).
An additional 6 events in the magnitude 2 range were deemed worthy of mention.

Earthquake activity in the Kermadec Islands eased from November levels. Four quakes with magnitudes between 4.8 and 5.1 were reported near Raoul Island. In the southern Kermadecs, two quakes with magnitudes between 4.9 and 5.6 were reported near L’Esperance Rock.

Aucklanders had the unusual experience of feeling a local earthquake when a magnitude 2.5 quake struck 30 km east of the city on December 30th. The quake was centred off the coast of Waiheke Island (north of Palm Beach) and was reported felt on Waiheke.

A deep magnitude 4.7 quake which struck 20 km south-east of White Island on December 22nd was felt at several locations in the Bay of Plenty and in Gisborne.

Three earthquakes struck off the coast of Horowhenua between the 9th and 13th of December. The main event, a magnitude 5.1 earthquake centred 40 km west of Levin at a depth of 50 km was widely felt in the southern part of the North Island. The two aftershocks of magnitude 4.1 and 4.2 were also felt.

On the 23rd a magnitude 4.3 quake, also 50 km deep struck off the coast 10 km north of Porirua.

A very shallow quake struck 40 km north-east of Milford Sound on the 16th of December. The quake was felt from Glenorchy to Queenstown.

An early morning magnitude 5.0 earthquake centred 160 km west of Invercargill on the 13th was felt in Southland and on Stewart Island. Shaking was reported as strong at Te Anau.

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 December.

At the end of December 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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