Geological Summary for New Zealand Area, March 2008

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

Geonet, the U.S. Geological Survey and GNS Science reported 24 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during March 2008.

The magnitude distributions were as follows:
M6 to 6.9 (1), M5 to 5.9 (4), M4 to 4.9 (7) M3 to 3.9 (10).
An additional 2 events in the magnitude 2 range were deemed worthy of mention.

Three earthquakes with magnitudes between 4.8 and 6.1 were reported to the north of Raoul Island during March. The magnitude 6.1 event which struck on the evening of the 18th was shallow at 28 km. Other activity in the Kermadec islands included a deep magnitude 5.6 quake on the evening of the 28th. This quake was felt at several locations in the Bay of Plenty, down through the eastern part of the North Island to Wellington.

A pair of 5th magnitude earthquakes struck 500 km north-north-east of Gisborne on the 2nd of March. The first was a deep magnitude 5.6 quake at a depth of 73 km, the second a shallower magnitude 5.4 event at a depth of 42 km which struck just after midday, an hour and 12 minutes later.

The Matata earthquake swarm activity continued at a lower level during March. The database shows about a dozen events of magnitude 3 or greater, three of which were reported on the GeoNet website. Of those reported by GeoNet, magnitudes ranged between 3.0 and 3.9, the largest of which struck just after 5 p.m. on the 25th, being felt widely in the Bay of Plenty area.

A cluster of three quakes struck the Hawke’s Bay area between the 13th and 15th. The earthquakes with magnitudes between 3.7 and 4.2 were located off-shore to the east or north-east of Napier at depths of 30 km.

A pair of quakes with magnitudes of 3.6 and 3.5 struck 30 km south of Hastings on the morning of the 16th. Both quakes were shallow at 25 and 30 km.

The strongest onshore quake during March was a deep magnitude 5.0 event located 30 km east of Stratford early on the morning of the 18th. The 220 km-deep quake woke some sleepers in the lower North Island, attracting 42 felt reports.

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 March 2008.

At the end of March, 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, and their contributing agencies.]

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