Kermadec Earthquakes

Two 5th magnitude earthquakes have struck the Kermadec Islands in recent days.

The first was a magnitude 5.2 quake which struck at 7:21 a.m. on March 26th 2007, NZ Standard Time. It was located 180 km NNE of Raoul Island at a depth of 51 km.

The second event struck last night at 8:08 p.m. on the 28th March 2007. This was a magnitude 5.7 quake located 170 km south of Raoul Island at a depth of 35 km.

These two events are the only quakes for the area appearing in the US Geological Survey (USGS) database at the time of writing, but there has clearly been much more activity in the area between the central North Island and the Kermadec Islands during the past ten days.

New Zealand seismographs recorded a burst of activity overnight on the 20th and 21st of March, when 6 distant earthquakes were recorded between 9:27 p.m. and 4:59 a.m. Traces for 4 of the events indicated they occurred about 650 km from the Matahi, Urewera seismic station. After more than a week, data for these events has not appeared in either the USGS or IRIS databases.

Following last night’s Kermadec quake, a much stronger earthquake trace appeared on the Matahi seismograph at about 11:15 p.m. indicating an earthquake event about 240 km from the station. Data for this event has yet to appear in the Geonet and USGS databases.

Data from the Kermadec seismic instruments rarely appears in the publicly searchable databases operated by Geonet. However, it is regularly sent to both the USGS and IRIS (Incorporated Research Institutions for Seismology) in the United Kingdom where it is used to refine data for earthquake actvity reported by other networks.

GNS Science is working with other organisations to improve detection of seismic activity in the South Pacific, but in the meantime a blind spot exists for the public dissemination of moderate earthquake activity occurring between the Bay of Plenty and the Kermadec Islands.

[Compiled from data supplied by the US Geological Survey, IRIS, Geonet and their contributing agencies.]

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