Geological Summary for New Zealand Area, February 2009

Earthquake activity declined further during February 2009. 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 February 2009.

The magnitude distributions were as follows:
M6 to 6.9 (2), M5 to 5.9 (4), M4 to 4.9 (10) M3 to 3.9 (12).
An additional event in the magnitude 2 range was deemed worthy of mention.

Earthquake activity during February 2009 was largely confined to the Kermadec Islands and New Zealand’s North Island.

Five earthquakes with magnitudes between 4.5 and 6.9 were reported near Raoul Island during February. Three of the events were shallow, including the magnitude 6.9 event of the morning of the 19th. Reports of shaking from this event were filed from Palmerston North, the Kapiti Coast, Wellington and as far south as Lincoln in Canterbury. Initially thought to be magnitude 7.3, the Pacific Tsunami Warning Centre issued a bulletin for the event, but considered the risk of a tsunami to be low. No significant variation in sea levels was reported by New Zealand’s Tsunami Monitoring Network. Unusually, the large quake was not followed by a significant aftershock.

Activity further south near L’Esperance Rock consisted of four quakes with magnitudes between 4.8 and 6.0. A magnitude 5.9 quake on the morning of the 13th was located 80 km east-north-east of L’Esperance Rock at a depth of only 4km. Initially though to be magnitude 6.1, the PTWC did not issue a bulletin for the event.

The largest of the four events struck on the afternoon of the 17th, 70 km north-north-east of L’Esperance Rock. This magnitude 6.0 earthquake was also very shallow, at 10km, but not felt in mainland New Zealand.

The quake was swiftly followed by an event much nearer the mainland, when a magnitude 4.2 earthquake struck 10 km east of Te Araroa at a depth of 60 km. The quake, which struck at 5:14 p.m., less than an hour after the event near L’Esperance Rock, was not widely felt with reports being filed from Opotiki and Taneatua.

The remaining earthquake activity was largely confined to the North Island, with only three events reported from the South Island. Only one event from the earthquake swarm near Matata was felt during February.

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 February.

At the end of February 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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