A team of US and Kiwi scientists have left Wellington's port today to study the Hikurangi subduction zone.
It's one of three voyages this summer looking at what fluid conditions generate earthquakes.
Dr Samer Naif says they chose the fault for its accessibility and contrasting earthquake behaviour.
He says in the north of the fault there are slow slips and silent earthquakes but there're none in the south.
He says there are few places in subduction zones around the world that show a distinct black and white behaviour like that.