Another Strong Earthquake Near Fiji

New Zealand’s seismometers were triggered by a strong earthquake which struck 620 km south-east of Suva, Fiji at 3:08 p.m. New Zealand Daylight Time. The magnitude 6.5 earthquake was very deep at 545 km. The earthquake left traces on all of Geonet’s seismometers but was too distant to have been felt here.

The earthquake occurred in an area north of Raoul Island that is very active and hosts many deep earthquakes. Since February 20th, the USGS National Earthquake Information Centre has recorded three magnitude 4.6 earthquakes at various depths in the area near today’s earthquake.

Today’s earthquake occurred 200 km further south of the magnitude 7.1 quake that occurred at a similar depth on January 23rd (NZDT).

These earthquakes are occurring beneath the Tonga Microplate which sits at the edge of the much larger Australian tectonic plate. The activity is caused by the edge of the Pacific Plate sliding underneath the Australian Plate along the seafloor from near Samoa to just north of Cook Strait.

It is reasonable to expect that today’s earthquake has altered strain on the plate interface between Tonga and the Kermadec Islands in an indirect manner, owing to the greater depth of the earthquake. How the plate interface nearer New Zealand will react to this event, either by accepting more strain or through further slippage is less clear. This is part of a process that involves movements measured in mm per year with strain alternately building and then releasing during earthquakes.

It could equally be argued that today’s event is the result of the deep activity near the Kermadecs in recent months transferring strain to the north.

Seismologists study the inter-relationships between earthquakes over periods of years and decades in the hope of finding general trends.

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