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4/7/2018 — Education, Science and Technology
More scientists put Kaikoura under the microscope

GNS Science staff are major contributors to a landmark collection of research papers on the geoscience nitty-gritty of the November 14 2016 magnitude 7.8 Kaikōura earthquake, which has been published this week.

The special Kaikōura Earthquake issue of the Bulletin of the Seismological Society of America contains 21 detailed articles written by expert teams over the past 18 months. The 21 papers join at least 60 others already published on the earthquake and its impacts.

A number of the papers in the bulletin are large collaborative efforts, with one having 47 co-authors. It involved analysis of all of the surface faulting and was led by earthquake geologist Nicola Litchfield of GNS Science.

It showed about two-thirds of the earthquake’s energy was released on the 24 surface-rupturing faults, with the remaining third occurring on the underlying Hikurangi subduction interface - the boundary where the Pacific and Australian tectonic plates meet.

The paper also noted that the rupture intervals of the two dozen faults involved in the earthquake range from 300 to 10,000 years. But scientists estimate the occasion when the all the intervals coincide, as happened in November 2016, is between 5,000 and 10,000 years. GNS Science said this underlines that the Kaikōura earthquake was a rare event.

The Bulletin of the Seismological Society of America has its origins in the 1906 San Francisco earthquake and is regarded as one of the world’s top earthquake science journals. Every so often, the Society publishes a ‘special issue’ in addition to its regular two-monthly edition. There have been eight special issues on different themes in the past 10 years.

The Kaikōura earthquake caused extensive surface deformation as it ruptured 24-plus faults with the largest horizontal displacement of 12metres on the Kēkerengū Fault and vertical displacement of 9m on the Papatea Fault. Along 110 kilometres of coastline, vertical movement ranged from subsidence of 2.5m to uplift of 6.5m.

There was also a small tsunami and tens of thousands of landslides over an area of about 10,000 square kilometres.

The rupture began near Waiau in North Canterbury and travelled north-east at about 2 km-a-second and ended up off Cape Campbell in Marlborough. It covered 174 km in about 74 seconds. The direction of rupture – south-west to north-east – strongly focused seismic energy toward the north.

An unusual feature were fault step-overs of up to 22 km, where the rupture jumped between faults. This length of step-over had not previously been seen anywhere in the world.

For scientists, the quake provided a rare opportunity to study the surface expression and impacts of a major fault rupture. Among the research themes in this publication were the complex distribution of surface ruptures and displacements, the subsequent slow-slip episode in the Hikurangi subduction zone, and how stress is transferred among tectonic regimes.

Earthquake-induced landslides also feature in the publication. A paper led by engineering geologist Chris Massey of GNS Science with a large international team characterises the number of landslides associated with the earthquake.

It identifies distance from fault rupture as a better predictor of landslide density than maps of peak ground acceleration or peak ground velocity. Scientists also found coastal slopes more vulnerable to landslides than inland slopes in similar materials, likely because of many decades of being exposed to energetic coastal processes.

GNS Science staff were lead authors on three of the 21 papers and co-authors on a further seven. In total, 32 GNS Science staff contributed as either authors or co-authors.

The volume was coordinated by an editorial team comprising scientists Kelvin Berryman, Anna Kaiser and Ian Hamling from GNS Science and Tim Stahl from Canterbury University. The publication is the culmination of about eight months of work by this team.

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Geologists map one of the man surface ruptures from the 2016 Kaikoura earthquake. Photo: GNS Science.
Damage to State Highway 1 near Kaikoura from the magnitude 7.8 quake in November 2018. Photo: Will Reis, GNS Science.