Geological Summary for New Zealand Area, August 2008

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

GeoNet, the U.S. Geological Survey and GNS Science reported 34 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during August 2008.

The magnitude distributions were as follows:
M6 to 6.9 (none), M5 to 5.9 (4), M4 to 4.9 (6) M3 to 3.9 (18).
An additional 6 events in the magnitude 2 range were deemed worthy of mention.

Earthquake activity in the Kermadec Islands increased during August 2008, with 7 events being reported by the U.S. Geological Survey. Four events near Raoul Island ranged in magnitude between 4.7 and 5.2 at depths of 30 to 300 km. Further south, three events reported near L’Esperance Rock had magnitudes between 4.7 and 5.3 and were at depths of 8 to 425 km.

The Matata earthquake swarm was relatively quiet during August, with only two quakes of magnitude 3.8 and 3.9 being reported by GeoNet.

A cluster of shallow earthquakes within 20 km of the town of Taupo was reported during August. Six quakes, some beneath the lake, with magnitudes between 2.3 and 3.6 were felt between the 7th and 27th. All of the quakes were at a depth of 5 km or shallower.

A swarm of three shallow quakes struck south of Wanganui between the 2nd and 23rd. The quakes ranged between 3.3 and 3.6 in magnitude and 10 and 20 km in depth.

After a rattling time during July when six earthquakes with magnitudes between 3.2 and 4.5 were reported in the Hawke’s Bay region, things appeared to quieten down. A magnitude 3.4 quake located 20 km south-east of Hastings on the 13th of August could well have been the foreshock of something much larger.

A magnitude 5.9 quake then struck 10 km south-west of Hastings just before midnight on August 25th. The 11:25 p.m. quake was only 30 km deep and was quickly followed by a magnitude 3.5 aftershock 10 minutes later.

Damage was reported from several locations in Hawke’s Bay where residents reported items thrown from shelves and cupboards, pictures off walls and broken glassware. Electricity supplies, which were tripped in some areas, were quickly restored. Claims for earthquake-related damage were filed from throughout the Hawke’s Bay area, with just over two-thirds of the $4.8 million claimed to date going to Hastings and Napier.

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 August 2008.

At the end of August, 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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