Seddon Earthquakes of 2013


Marlborough is no stranger to earthquakes, sitting as it does on its own fault system, lying at the boundary of the Alpine Fault and the Kermadec Trench.

seddon earthquakes geonetMap showing the 21 July quakes. Source Geonet
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However, the swarm of quakes that struck in the winter of 2013 proved both shocking and destructive for residents – particularly those of the small Seddon community.

The first major quake struck on 21 July, about 20km east of Seddon, at a depth of 17kms and measuring 6.5 on the moment magnitude scale. It caused minor damage in the region, with more significant impact in Wellington, but was followed by a series of aftershocks.

Seddondamage A badly damaged house in Seddon.
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The most damaging quake was yet to come. On 16 August a second quake hit. This is now known as the Lake Grassmere Earthquake, and measured 6.6, with an epicentre only 10km south east of Seddon, 8km in depth. The earthquake caused significant land damage in the local area, with landslips blocking roads, including the main highway between Blenheim and Christchurch. Most of the buildings in Seddon were damaged in some way, with many declared uninhabitable. The quake was felt strongly in Blenheim and a number of businesses closed as damage was assessed. The quake swarm continued over several weeks, unnerving residents.

Seddon SH1Damage to SH1 between Seddon and Ward following Lake Grassmere Earthquake. Dougal Townsend GNS Science.
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The most immediate danger for Seddon was the Halden Dam, lying in the headwaters above Seddon and close to the quake’s epicentre. The dam suffered severe cracking, and houses downstream were evacuated, while the dam was drained over several days.

The community gathered around to support the residents of Seddon as people came to terms with the impact of the quakes. Affected businesses, amongst them many wineries and the Grassmere saltworks, soon reopened with minimal long term effects, however in the aftermath one third of the houses in the vicinity of Seddon were left empty, with eight uninhabitable and eleven restricted. As in Christchurch, the restoration of buildings was inevitably slow, particularly as the threat of earthquakes continued. Many families have left the area, possibly never to return.

Following the 2013 events more earthquakes have been felt in the Seddon area including:

  • 14 November 2016 - The magnitude 7.8 Kaikōura earthquake started near Culverden and set off a series of faults which shook the north eastern part of the South Island, including Seddon
  • 4 December 2016  - a 5.5 magnitude quake struck 10km east of Seddon at a depth of 12km 
  • 22 August 2019  - a 4.6 magnitude quake struck 30km away from Seddon at a depth of 12km.

Read more about these quakes in the story Life on the fault lines - Marlborough's East Coast earthquakes.

Listen to Radio New Zealand's Insight, broadcast 1 December 2013: Recovery from the Seddon Shakes. Alison Hossain returns to Seddon to find out how the area is recovering in the run up to Christmas.

2019, updated Dec 2020

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