Geological Summary for New Zealand Area, January 2010

Earthquake activity increased. White Island and Mt. Ruapehu remained at Alert Level 1. No tsunami alerts were raised.

GeoNet, the U.S. Geological Survey and GNS Science reported 35 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during January 2010.

The magnitude distributions were as follows:
M6 to 6.9 (1), M5 to 5.9 (8), M4 to 4.9 (10) M3 to 3.9 (14).
An additional two events in the magnitude 2 range were deemed worthy of mention.

On the 4th of January, two earthquakes with magnitudes of 7.2 and 6.5 struck the New Georgia Islands in the western Solomon Islands. The larger quake caused sea disturbances locally and a wave of 6 cm was measured at Honiara. The islands of Rendova and Tetepare experienced significant landslides and waves thought to be up to two metres in height.

A magnitude 6.9 quake in the same area on January 6th generated a wave measured at 3 cm at Honiara with larger waves being reported near the epicentre. Neither tsunami event generated a wave of significance to New Zealand shores.

Four earthquakes with magnitudes between 4.7 and 5.1 were reported near Raoul Island during January. The quakes were at various depths ranging from 35 to 500 km. In the southern part of the Kermadec chain, another four events with magnitudes between 5.0 and 5.4 were reported near L’Esperance Rock. All of the southern quakes were shallow, at depths of 35 km or less.

Two very deep earthquakes with magnitudes of 5.7 and 5.4 struck near White Island on the 19th and 24th. The quakes were centred 80 and 70 km north of the Bay of Plenty volcano at depths of 230 and 240 km respectively.

Two quakes of magnitude 2.7 and 3.3 were reported near Matata on the 12th and 19th but this did not mark a re-activation of the swarm activity that has plagued the coastal township in recent years.

A slow-slip event commenced near Tolaga Bay on the eastern coast of the North Island mid-January. Also known as a slow earthquake, the slow-slip occurs when the plate boundaries begin to slowly and smoothly slip past each other over a period of days or weeks instead of suddenly lurching and causing the more familiar earthquakes. Associated with the slow-slip were three typical earthquakes with magnitudes between 2.9 and 3.5 at a location 10 km north-west of Tolaga Bay.

Three earthquakes struck the Wanganui Bight during January. Two of the quakes, with magnitudes of 3.5 and 3.9 were located off-shore 20 km from Wanganui. The largest quake was magnitude 4.4 and located 70 km north-east of French Pass.

Residents of Kapiti and Wellington’s northern suburbs felt earthquakes on the 9th and 11th of January. The shallow magnitude 3.8 and 3.0 quakes were located near Porirua and Paraparaumu.

Three earthquakes with magnitudes between 3.7 and 4.6 struck 70 km north-east of Milford Sound during January. The quakes were all very shallow, at depths of three to five km.

Two quakes of magnitude 4.7 and 4.1 struck two minutes apart 70-80 km west of Te Anau on the 23rd of January. The quakes were both 12 km deep.

A magnitude 6.0 earthquake struck the Southern Ocean 460 km south-west of Invercargill late in the evening of the 6th of January. The quake was shallow at 12 km, and centred 200 km north-west of the Auckland Islands. The quake was felt in Fiordland, Southland, Otago and on Stewart Island but did not cause serious damage.

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 January.

At the end of January 2010, 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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