Geological Summary for New Zealand Area, June 2007

Earthquake activity continued at a low level, with swarms reported at Matata, Kawerau and Taupo. White Island, Mt Ngauruhoe, and Mt Ruapehu volcanoes remained at Alert Level 1.

Geonet, the USGS (NEIC) and GNS Science reported 48 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during June 2007. The magnitude distributions were as follows:
M6 to 6.9 (none), M5 to 5.9 (2), M4 to 4.9 (8) M3 to 3.9 (30).
An additional 8 events in the magnitude 2 range were deemed worthy of mention.

The first of a swarm of very light, shallow tremors within 10 km of Taupo was reported on June 1st 2007. The quakes ranged in magnitude between 1.7 and 2.4, and activity ceased on June 24th.

The Matata earthquake swarm continued at a slightly reduced rate during June. Fifteen quakes with magnitudes between 2.5 and 3.8 were reported within 10 km of the town at depths of 7 km or less. The number of events reported was slightly less than that reported during May, and the magnitude of the larger members of the swarm had also decreased.

A brief swarm of three earthquakes was reported within 10 km of the Bay of Plenty town of Kawerau between June 8th and 26th. The quakes ranged in magnitude between 2.7 and 3.5 at depths of 5 km or less.

A series of 3 quakes with magnitudes between 3.4 and 3.6 struck 40-50 km south of Hastings on June 5th, 6th and 13th.

Five quakes rippled through the Kermadecs during the month. The nearest was a magnitude 5.0 quake located 290 km south of L’Esperance Rock on June 2nd, the northernmost was a magnitude 4.9 event 275 km NNE of Raoul Island on the 19th.

The South Island town of Seddon hosted a series of 5 quakes with magnitudes between 3.8 and 4.1 between June 3rd and 24th. All of the events were within 10 km of the town at varying depths of 10 to 40 km.

Two earthquakes tossed objects off shelves during June 2007. The first event at 6:15 a.m. on Friday June 15th struck within 5 km of Stratford at a depth of 15 km. The magnitude 4.2 quake was followed by a magnitude 3.9 event further east (20 km north of Raetihi) at a depth of 11 km at 2:14 p.m. the same day.

Vulcanologists reported that the nation’s volcanoes were quiet during June 2007.

Seismic activity at White Island remained low throughout June 2007, and the steam plumes which had been seen over the island during May ceased. By the 22nd, the crater lake had dropped to 28 metres below overflow, and started refilling.

Mt Ruapehu was quiet until a few very small high-frequency earthquakes were recorded in the days before June 15th. No significant seismic or hydrothermal activity was reported, and the earthquake activity ceased.

During the first week of June, the small volcanic earthquakes beneath Mt. Ngauruhoe continued, but at a lower level. This activity continued until the 22nd when reporting ceased.

At the end of June 2007, 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 1).
Mt Ruapehu (Alert Level 1).

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

Leave a Reply