New Zealand's most active fault line could cause a major earthquake and tsunami affecting Whanganui at any time.

The Hikurangi subduction zone is a fault line that runs offshore along the East Coast from Gisborne to the top of the South Island.

It's caused by the Pacific tectonic plate sliding under the Australian one.

A public lecture is being held tonight with a group of scientists and emergency managers discussing the risk the fault poses to Whanganui.

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Scientists researching it in a $6 million, five-year Endeavour Fund project have found it has ruptured in large earthquakes at least 10 times in the last 7500 years. Its full length may have ruptured about 840 years ago, causing an earthquake of at least 8.5 magnitude.

The fault's movement can also be gradual, in slow slip events.

What is certain is that the plates' movement will continue. An earthquake as big as the disastrous magnitude 9 quake and tsunami that hit Japan in 2011 is possible in the region.

The quake could be long and strong, and cause landslides and liquefaction, as well as a tsunami for both coasts of the lower North Island.

To prepare for this, Civil Defence managers from across the lower North Island are working together.

Kate Boersen, from the East Coast LAB (Life at the Boundary) programme, says this region needs to be ready.

"It's really important that people make an emergency plan, practise their drop, cover, hold and their tsunami hīkoi."

Horizons Regional Council emergency manager and Manawatū Whanganui Civil Defence and Emergency Management Group leader Ian Lowe said the talk will tell people about the diverse scientific research projects under way to understand the subduction zone.

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"Scientists have been researching the Hikurangi subduction zone to seek patterns, movements and possible clues from the past, to hopefully get a clearer picture of what is happening out there, and what that might mean for New Zealand. These talks will give people a chance to hear about it first hand from the experts."

The talk will be from two GNS scientists involved in the research - Dr Laura Wallace and Dr Kate Clark.

Whanganui Science Forum talk is free - though koha is appreciated - at 7.30pm in the Davis Lecture Theatre.