Geological Summary for New Zealand Area, July 2007

Earthquake activity continued at a low level, and activity associated with the Matata earthquake swarm virtually ceased. White Island, Mt Ngauruhoe, and Mt Ruapehu remained at Alert Level 1.

Geonet, the US Geological Survey (NEIC) and GNS Science reported 36 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during July 2007. The magnitude distributions were as follows:
M6 to 6.9 (2), M5 to 5.9 (7), M4 to 4.9 (9) M3 to 3.9 (12).
An additional 6 events in the magnitude 2 range were deemed worthy of mention.

Three earthquakes with magnitudes between 4.6 and 5.0 were recorded south of L’Esperance Rock in the Kermadecs during July 2007. A pair of magnitude 4.6 quakes struck 285 km SSE and 120 SSW of the rock on the 4th, and a magnitude 5.0 quake struck 310 km south of L’Esperance Rock on the 7th. All were shallow, between 10 and 45 km in depth.

A pair of quakes with magnitudes of 5.1 and 5.0 struck 265 and 290 km NNE of Raoul Island on the 5th and 6th at depths of 35 and 25 km. A swarm of 5 quakes located between 325 and 345 km north of the island then followed. These events occurred between the 9th and 19th, and ranged in magnitude between 5.0 and 6.1 at depths between 10 and 55 km. Two more quakes of magnitude 4.7 and 4.8 nearby completed the burst of activity on July 25th.

Only two quakes in the swarm occurring near Matata were reported during the month. A magnitude 3.1 event was reported on the 8th and a 2.0 event on the 22nd.

The largest on-shore quake struck at 5:42 p.m. on July 12th. The magnitude 5.3 quake was located 10 km east of Taupo at a depth of 100 km.

A swarm of six very shallow quakes struck between 20 and 40 km south-west of Taupo between July 25th and 28th. The quakes ranged between magnitude 2.5 and magnitude 3.1.

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. Discussions with GNS Science indicate that regular reporting may resume soon, and lobbying continues.

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

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