Kaikoura landslide found off Hawke's Bay coast

Scientists analysing sediment cores onboard the Tangaroa. Photo Supplied

Scientists say they've found new geological evidence offshore Hawke's Bay of sediment flows produced by underwater landslides near Kaikoura, about 700km away from its source.

The underwater landslides were caused by strong ground shaking from the November 2016 Kaikoura earthquake that caused sediment to cascade down-slope off the north-east South Island.

Scientists have been aboard NIWA's research vessel Tangaroa collecting sediment cores along the Hikurangi plate boundary looking for geological evidence of past earthquakes.

"We are looking for distinctive sediment layers on the seabed known as turbidites.

"Turbidites are the deposits formed from fast-moving dense clouds of mud and sand triggered by ground shaking, transported down-slope and eventually settle on the seafloor," says Dr Alan Orpin from NIWA.

Sediment cores collected from sites more than 100km off the coast of Hawke's Bay very clearly show recently deposited turbidites.

"This new evidence demonstrates that the turbidity current triggered by the Kaikoura earthquake was approximately 200m thick, some 700km from source, making it likely the event travelled the length of the Hikurangi channel," says Dr Jamie Howarth from Victoria University of Wellington.

The sediment cores and turbidite layers have been processed aboard the R/V Tangaroa and have been measured and cut into sections to be CT-scanned, logged and packaged for further analysis when on land.

As part of the same voyage, scientists have also retrieved five seafloor pressure instruments from off the Gisborne coast that have recorded the Te Araroa earthquake and tsunami in September 2016 and the Kaikoura earthquake in November 2016.

"These seafloor pressure instruments are capable of sensing vertical movements of the seafloor as small as one centimetre, and also track the passage of tsunami waves," says Dr Laura Wallace from GNS Science.

This research helps us to better understand the behaviour of the Hikurangi plate boundary, New Zealand's largest earthquake and tsunami hazard.

The work involves scientists from various New Zealand research institutions (including GNS Science, NIWA, Victoria University of Wellington and University of Otago), in collaboration with international researchers from the USA (Colombia University) and Japan (Tohoku University and Kyoto University).

The research is part of a five-year Ministry of Business, Innovation and Employment (MBIE) Endeavour fund research programme called 'Diagnosing the peril posed by the Hikurangi subduction zone: New Zealand's largest plate boundary fault'.