Geological Summary for New Zealand Area, January 2007

Earthquake activity continued at a low level. White Island, Mt Ngauruhoe, and Mt Ruapehu remained at Alert Level 1.

Geonet, the USGS (NEIC) and GNS Science reported 32 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during January 2007. The magnitude distributions were as follows:
M6 to 6.9 (1), M5 to 5.9 (2), M4 to 4.9 (13) M3 to 3.9 (9).
An additional 7 events in the magnitude 2 range were deemed worthy of mention.

Two deep magnitude 4.8 earthquakes struck during the first week of January 2007, but only one was felt. The 120 km-deep quake of January 2nd struck 30 km west of Taupo and was felt from Ohakune to Wellington. The more distant event located 420 km north-east of Rotorua at a depth of 145 km on the 6th seems to have attracted no felt reports. Later the same day, a magnitude 4.0 quake 40 km south-west of Gisborne at a depth of 32 km also seems to have escaped attention.

A swarm of 5 earthquakes centred 10 km north-east of Matata rattled various localities on the Bay of Plenty coast between January 9th and 28th. The quakes were all 5 km deep or shallower, as was the earthquake centred within 5 km of Matata on the 29th.

A 5 km deep magnitude 4.0 earthquake struck 10 km east of White Island at 9 a.m. on the 12th and was felt at Te Kaha, nearby.

A magnitude 5.3 quake which struck 10 km north of Taihape at a depth of 50 km on January 18th was the strongest on-shore quake since November 2006. It was felt from Nelson to the Bay of Plenty, and caused tall buildings in Wellington to sway slightly.

A busy swarm of shallow earthquakes commenced 30 km east of Ruatoria on the afternoon of Saturday January 20th, with a magnitude 4.2 and 4.3 quake, two minutes apart. Another pair of quakes, this time magnitude 4.1 spaced 33 seconds apart, struck the same area on the 22nd. Geonet’s database showed that 7 quakes with magnitudes between 2.8 and 4.1 struck the area within the hour. The swarm finished its run with a magnitude 4.1 and 4.0 quake on January 23rd.

Yet another quake struck near White Island toward the end of the month. This magnitude 5.0 quake struck 100 km north of the volcano at a depth of 12 km on the 27th. The shaking was reported from Whangamata and Waihi.

Rocks fell onto the track to Denham Bay on Raoul Island when a magnitude 6.5 earthquake struck 55 km south-west of the volcano on January 31st.

Vulcanologists reported the nation’s volcanoes to be quiet at the beginning of January, but this changed slightly as the month progressed.

Raoul Island volcano remained quiet throughout January 2007, with its alert level at 0 (dormant or quiescent).

White Island’s seismic activity remained low during the early part of the month but its hot crater lake continued evaporating, heating as the month progressed. The temperature rose from 60°C early in the month to 62.6°C on the 20th, at about the same time as weak volcanic tremor commenced. Dino the Internet-famous pink dinosaur was able to make his hourly appearance on the Geonet website when the crater webcam was replaced mid-month.

Mt Ngauruhoe continued to experience the volcanic earthquakes that commenced last year. The frequency of the quakes increased slightly as January progressed with about 30 to 40 volcanic quakes occurring daily by the month’s end.

Mt Ruapehu started the month exhibiting little seismic activity, but became the focus of attention as January progressed. With the tephra dam leaking, maintenance of the lahar warning equipment generated a lahar warning on January 4th, and State Highway 1 was temporarily closed by emergency services for part of the afternoon. By the middle of the month, the crater lake had warmed by 2°C to 24°C and the tephra dam leakage had increased.

At the end of January 2007, New Zealand’s volcano status was as follows:
Raoul Island (Alert Level 0).
White Island (Alert Level 1).
Mt Ngauruhoe (Alert Level 1).
Mt Ruapehu (Alert Level 1).

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

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