Geological Summary for New Zealand Area, July 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 on 32 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during July 2008.

The magnitude distributions were as follows:
M6 to 6.9 (none), M5 to 5.9 (2), M4 to 4.9 (10) M3 to 3.9 (17).
An additional 3 events in the magnitude 2 range were deemed worthy of mention.

Earthquake activity in the Kermadec Islands was quieter than normal, with only one quake of 5th magnitude and one of 4th magnitude being reported during July.

The Matata earthquake swarm continued at a low level with only three events with magnitudes between 3.1 and 3.5 reported.

Six events with magnitudes between 3.2 and 4.5 were reported in the Hawke’s Bay region. All of the quakes were 30 to 40 km deep.

Two quakes of magnitude 4.0 and 5.9 were reported west of Te Anau during July. The larger of the two was a deep event, being 100 km deep while the magnitude 4.0 quake was at a depth of only 10 km.

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.

One Alert Bulletin was issued by GNS Science during July 2008. The bulletin, which was issued on the 21st, reported that the recent unrest at Mt. Ruapehu had declined.

The volcano’s crater lake, which had hovered at temperatures ranging between 34 ºC and 37 ºC in recent months had fallen to 23.3 ºC by July 15th. Sulphur dioxide and carbon dioxide gas levels, which had significantly increased to ten times the normal levels on June 12th, had reduced to normal background levels. In addition, the slightly increased level of volcanic tremor had declined.

At the end of July 2008, 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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