Huge fault rupture stretches 34km offshore from Kaikoura
The Kekerengu Fault ruptured for 36km on land and a further 34km in its offshore continuation the Needles Fault.
22 November, 2016
Scientists have found a huge fault rupture stretching 34km offshore from Kaikoura following last week's magnitude-7.8 earthquake.
Surveying the seabed from Niwa's research ship Tangaroa, they found the rupture in the offshore continuation of the Kekerengu Fault, known as the Needles Fault.
Voyage leader and Niwa marine geologist Dr Philip Barnes said the length of the Kekerengu-Needles fault rupture may extend for about 70km – 36km on land and 34km under the sea.
Mapping and profiling confirmed the Needles Fault had ruptured, forming newly discovered scarps - where one side of the fault moves vertically relative to the other side - on the seafloor along the Marlborough coast south of Cape Campbell.
Where it was measured under the sea, the scarps were 1-2 metres high, which was consistent with the uplift being seen onshore, Barnes said.
Scientists collected 61 sediment cores, each about 5.5m long from sites on the continental margin between the Kaikoura coast and Poverty Bay that will provide evidence of submarine landslides.
The cores revealed the earthquake generated a huge turbidity current in the Hikurangi Trough, offshore from Marlborough and Wairarapa. A turbidity current is a rapidly moving underwater current comprising mud, sand, gravel and water. It eventually results in layers of sediment being deposited across the sea floor. These are known as turbidite.
"We detected a very recent turbidite about 10-20cm thick over a very large region, extending at least 300km from Kaikoura. It is still settling on the seabed from the water column and may not complete this process for some time," Barnes said.
The precise location of the underwater landslides that generated the turbidity current was not studied.
Tangaroa was doing seismological research on the Hikurangi subduction zone, off the North Island's East Coast, before it was diverted to study the Kaikoura earthquake. The Hikurangi research is part of a five-year programme to fill in gaps in understanding about the earthquake potential of the one.
This is coming....
Urgent warning to stay away from the Conway River over "imminent" danger of dam collapse
22 November, 2016
A 40-metre high landslide dam is in "imminent danger of over-topping".
Canterbury Civil Defence issued an urgent warning for Towy River, a tributary of Conway River in north Canterbury, shortly after 5pm.
"People are urged to stay out of the river bed and well away from the Conway River," the warning said.
"There are serious concerns for safety and nobody should be in or near the river."
Over-topping could result in a rapid water level and debris downstream on the Conway River.
The dam was caused after a huge landslide blocked the Towy River following Monday's earthquake.
Initial estimates put the dam at 40 metres high, and on Monday the water level was 15 metres below the top of the dam.
At the time, Civil Defence said "once water crests the top of the dam the possibility of rapid failure significantly increases".
An even larger dam was created over the Hapuku River, where a 150-metre high dam could also "rapidly fail", spilling water from a new lake into the river.
Due to the earthquake sequence, there was a risk of landslides and slips into the majority of rivers in North Canterbury and Kaikoura.
"As a precaution it is strongly advised to keep away from all riverbeds in case there are any sudden releases of water," Canterbury Civil Defence said.
This report is from 17 November
Landslide creates dangerous dam on Hapuku River, New Zealand
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