Otago University research has recorded quakes up to 40 kilometres deep in one of country's least seismically active regions - while also uncovering evidence of a hidden fault.
Lead researcher Jack Williams says they've essentially uncovered an extra deep layer of the Earth where quakes can occur.
He says it's more likely that a six-or-seven magnitude earthquake could happen on a fault, previously not known about.
Williams says there's no evidence of anything occurring at the surface, because it's so deep in the surface.
