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Geohazards in Marlborough

During the Geohazards 2015 field trip you will be investigating geohazards in Marlborough, including earthquakes, tsunami and landslides.

Geohazards in the Marlborough Region

Geohazards are common in the Marlborough Region. The northern end of the Alpine Fault splits into several parallel faults that spread out across this region. There have been several recorded earthquakes in the region including in 1848 and 2013, and a tsunami in 1855. 

Because of its proximity to active faults Marlborough region is, not surprisingly, one of the most seismically active in New Zealand and a very good place to explore the nature of geohazards!

Cook Strait earthquakes

Seddon earthquake

In 2013 a magnitude 6.5 earthquake known as the Seddon earthquake occurred:

  • it was centred in Cook Strait, around 20 kilometres east of the town of Seddon in Marlborough
  • the earthquake struck at 5:09pm on 21 July 2013 at a depth of 17 kilometres. 
  • it followed two earlier shakes of magnitude 5.7 and 5.8

The quake caused moderate damage in the wider Marlborough area and Wellington, 55 kilometres north of the epicentre. Only minor injuries were reported. Several aftershocks occurred during 21–29 July.

The Seddon earthquake is related to a second major earthquake which occurred on 16 August known as the Lake Grassmere earthquake.

Lake Grassmere earthquake

This earthquake had a magnitude of 6.6. The epicentre was located about 10km south-east of Seddon, under Lake Grassmere, at a depth of 8km.

This earthquake caused;

  • significant land damage in the local area, with landslips
  • slips blocked roads, including the main highway between Blenheim and Christchurch
  • damage to buildings in Seddon with some having to be demolished.

The earthquake was widely felt in both the North and South Islands of New Zealand.

In Wellington, the earthquake caused minor damage to buildings, breaking some display windows and cracking plaster. 

This earthquake occurred on an adjacent fault to the July earthquake. It started its own aftershock sequence. 

Other geohazards in Marlborough

Marlborough also has hazards related to landslides, particularly in areas that have been developed for farming.

Marlborough has also been affected by tsunamis in the past. In 1855 the Wairarapa earthquake, which ruptured the Wairarapa fault east of Wellington, generated a tsunami with a wave height of 4-5 metres along the Marlborough coast.

Marlborough is a geologically active area with several active fault lines. Image: Niwa & GNS Science.

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The 2013 Seddon earthquake caused damage to some houses in the area. Can you find out how widespread this damage was? Image: Public Domain.

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There was significant land damage caused by the Lake Grassmere earthquake which was part of the Cook Strait sequence of quakes in 2013. Image: Peter Hamill.

Find out about the geohazards that exist in your own local area and compare them with Marlborough.